Transparent organic light emitting display device and method for manufacturing the same

This application claims priority under 35 U.S.C. §119 to Korean Patent Application No. 10-2012-0155590 filed on Dec. 27, 2012, the disclosure of which is hereby incorporated by reference in its entirety.

1. Field of Technology

Embodiments of the inventive concept relate to a transparent organic light emitting display device (OLED) and a method for manufacturing the same, and more particularly, to a transparent organic light emitting display device which improves transmittance and minimizes degradation in luminance and a method for manufacturing the same.

2. Description of Related Art

Organic light emitting display devices are self-emissive display devices, and may be manufactured to be lightweight and thin without a separate light source unlike liquid crystal display devices (LCDs). Further, the organic light emitting display devices are advantageous in terms of power consumption due to low-power driving, have good color realization, response speed, a view angle, and a contrast ratio, and have been researched as next-generation displays.

Attempts to manufacture the organic light emitting display devices as transparent display devices have been made. The transparent organic light emitting display devices are organic light emitting display devices which can observe objects located at the rear thereof, and include a pixel region which displays an image through emission of organic light emitting elements, and a transmissive region which transmits external light.

In an aspect, there is provided a transparent organic light emitting display device with improved configurations for increased light transmittance through the transmissive area of each sub pixel. In one embodiment, the transparent organic light emitting display device includes a first substrate with a plurality of sub pixel regions. Each of the sub pixel regions contains an emissive area and a transmissive area. The transparent organic light emitting display device further includes a thin film transistor (TFT) in the emissive area of the sub-pixel and an organic light emitting element electrically connected to the TFT. Also included in the transparent organic light emitting display device is a plurality of insulating layers disposed in the emissive area of the sub pixel region. Here, at least one of the insulating layers is configured such that it is extended from the emissive area into the transmissive area of the sub pixel region. The insulating layer, which is being extended into the transmissive area, has at least some part that has the same refractive index as the first substrate. The same refractive indices between the first substrate and the insulating layer being extended into the transmissive area reduces the total internal reflection at the interface their interface, thereby allowing more external light to pass through the transmissive area.

In some embodiments, the insulating layer that is extended into the transmissive area has a multilayered structure. Not all layers included in the multilayered structure are extended into the transmissive area of the sub pixel region. Instead, at least one layer of the multilayered structure is contained within the emissive area without being extended into the transmissive area while at least one layer of the multilayered structure disposed in the emissive area is extended into the transmissive area.

In some embodiments, the insulating layer that is in both the emissive area as well as the transmissive area is an insulating layer interposed between the TFT and the first substrate. In one embodiment, the insulating layer interposed between the TFT and the first substrate has the multilayered structure, and the TFT has a coplanar structure with an oxide semiconductor layer disposed on the multilayered structure. In this case, the layer of the multilayered structure contacting the oxide semiconductor layer is extended into the transmissive area and does not include silicon nitride. Also, in one embodiment, the TFT with an oxide semiconductor layer disposed on the gate electrode. In this case, the insulating layer that is in both the emissive area as well as the transmissive area is interposed between the gate electrode and the oxide semiconductor of the TFT. The insulating layer interposed between the gate electrode and the oxide semiconductor has a multilayered structure, and the layer in the multilayered structure contacting the oxide semiconductor does not include silicon nitride.

In some embodiments, the transparent organic light emitting display device includes a second substrate opposing the first substrate. The TFT, the organic light emitting element, the plurality of insulating layers and the encapsulating layer are interposed between the first and second substrates. In the transparent organic light emitting display device, the first substrate, the insulating layer being extended into the transmissive area and the second substrate all have substantially the same refractive index with respect to each other. That is, the first and second substrates have substantially the same refractive index as the insulating layer being extended into the transmissive area and the opposing substrate. Likewise, the insulating layer being extended into the transmissive area has substantially the same refractive index as the first and second substrates.

In one aspect, there is provided a transparent organic light emitting display device configured for increased overall light transmittance through the display device.

In one embodiment, the organic light emitting display device includes a substrate having a plurality of sub pixels. Each of the sub pixels has an emissive area for emitting light and a transmissive area for allowing the external light to pass through. The organic light emitting display device also includes one or more thin film transistors, which are formed with a gate electrode, an active layer and source/drain electrodes, operatively coupled to one or more organic light emitting elements. An encapsulation layer is included in the organic light emitting display device to protect the organic light emitting elements and/or the TFT from the permeation of moisture and air. Also included in the organic light emitting display device is a plurality of insulating layers, including a first, a second and a third insulating layers. The first insulating layer is interposed between the substrate and the TFT; the second insulating layer is interposed between the gate electrode and the active layer of the TFT; and the third insulating layer is disposed on the TFT. Among the first, second and third insulating layers, at least one insulating layer has a refractive index that is different from the refractive index of the substrate by more than a predetermined value.

In some embodiments, at least one insulating layer among the first, second and the third insulating layers has substantially the same refractive index as the substrate. Also in some embodiments, at least one of the first, second and the third insulating layers has a multilayered structure including at least one layer that has substantially the same refractive index as the substrate and at least one layer with a refractive index differing from the substrate by more than the predetermined threshold value. In such embodiments, the layer of the multilayered structure having the refractive index different from that of the substrate is contained within the emissive area of the sub pixel.

In yet another aspect of the present disclosure is related to a method of manufacturing a transparent organic light emitting display device that includes a plurality of sub pixels, each sub-pixel including an emissive area and a transmissive area. In an embodiment, the method includes forming a buffer layer on a first substrate; forming an active layer on the buffer layer; forming a gate insulating layer on the active layer; forming a plurality of electrodes on the active layer, the plurality of electrodes including a source electrode, a drain electrode, and a gate electrode electrically insulated from each other by an interlayer insulating layer; forming an overcoating layer over the emissive area and the transmissive area of the transparent organic light emitting display device; and forming an organic light emitting element on the overcoating layer in the emissive area.

In some embodiments, the buffer layer is formed as a multilayered structure including a first buffer layer and a second buffer layer. The first buffer layer, which includes of silicon nitride, is formed in the emissive area without being extended into the transmissive area. In contrast, the second buffer layer, which includes of silicon oxide, is formed to contact the active layer, and extended into the transmissive area.

The above and other objects, features and advantages of the present invention will become more apparent to those of ordinary skill in the art by describing in detail exemplary embodiments thereof with reference to the accompanying drawings, in which:

FIGS. 1A to 1D are cross-sectional views illustrating transparent organic light emitting display devices in accordance with various embodiments of the inventive concept;

FIG. 2A is a cross-sectional view illustrating a transparent organic light emitting display device in accordance with another embodiment of the inventive concept;

FIG. 2B is a conceptual diagram illustrating a transparent organic light emitting display device in accordance with another embodiment of the inventive concept;

FIGS. 2C to 2F are cross-sectional views illustrating transparent organic light emitting display devices in accordance with various embodiments of the inventive concept;

FIGS. 3A to 3C are conceptual diagrams illustrating transparent organic light emitting display devices in accordance with various embodiments of the inventive concept;

FIG. 4 is a flowchart illustrating a method for manufacturing a transparent organic light emitting display device in accordance with an embodiment of the inventive concept; and

FIGS. 5A to 5D are processional cross-sectional views illustrating a method for manufacturing a transparent organic light emitting display device in accordance with an embodiment of the inventive concept.

Exemplary embodiments of the present invention will be described in detail below with reference to the accompanying drawings. While the present invention is shown and described in connection with exemplary embodiments thereof, it will be apparent to those skilled in the art that various modifications can be made without departing from the scope of the invention.

An element or layer formed “on” another element or layer includes all a case in which an element is directly formed on another element, and a case in which an element is formed on another element with an additional element or layer formed therebetween.

Although the terms first, second, etc. may be used to describe various elements, it should be understood that these elements are not limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of exemplary embodiments.

In this specification, like numbers refer to like elements throughout the description of the drawings.

Sizes and thicknesses of respective elements shown in the drawings are shown for the sake of convenience of description only and are not intended to limit the scope of the present invention.

In this specification, an organic light emitting display device with a top emission mode refers to an organic light emitting display device, wherein light emitted from the organic light emitting diode radiates from an upper portion of the organic light emitting display device. That is, the organic light emitting display device with a top emission mode refers to an organic light emitting display device, wherein light emitted from the organic light emitting diode radiates in a direction of a top surface of a substrate having a thin film transistor formed therein for driving the organic light emitting display device. In this specification, an organic light emitting display device with a bottom emission mode refers to an organic light emitting display device, wherein light emitted from the organic light emitting diode radiates from a lower portion of the organic light emitting display device. That is, the organic light emitting display device with a bottom emission mode refers to an organic light emitting display device, wherein light emitted from the organic light emitting diode radiates in a direction of a bottom surface of a substrate having a thin film transistor formed therein for driving the organic light emitting display device. In this specification, an organic light emitting display device with a dual emission mode refers to an organic light emitting display device, wherein light emitted from the organic light emitting diode radiates from upper and lower portions of the organic light emitting display device. In this specification, in the organic light emitting display devices with top, bottom, and dual emission modes, a thin film transistor, an anode, and a cathode are disposed to optimize a configuration of each emission mode, thereby optimally disposing the thin film transistor without interfering with an emission direction of a light emitting element.

In this specification, a flexible display device refers to a display device endowed with flexibility, and may be used to have the same meaning as a bendable display device, a rollable display device, an unbreakable display device, or a foldable display device. In this specification, a flexible organic light emitting display device is one example of various flexible display devices.

In this specification, a transparent display device refers to a transparent display device that is at least a part of a screen of a display device viewed by a user. In this specification, transparency of the transparent display device refers to a degree of transparency at which a user at least recognizes an object behind a display device. In this specification, the transparent display device includes a display area and a non-display area. The display area is an area on which an image is displayed, and the non-display area is an area on which no image is displayed, such as a bezel area. To maximize transmittance of the display area, the transparent display device is configured to dispose opaque components, such as a battery, a printed circuit board (PCB), and a metal frame, under the non-display area rather than the display area.

In this specification, front and rear surfaces of the transparent display device are defined based on light emitted from the transparent display device. In this specification, the front surface of the transparent display device means a surface on which light from the transparent display device is emitted, and the rear surface of the transparent display device means a surface opposite to the surface on which the light from the transparent display device is emitted.

The features of various exemplary embodiments of the present invention may be partially or entirely bound or combined with each other, and be technically engaged and driven using various methods as apparent to those skilled in the art, and the exemplary embodiments may be independently practiced alone or in combination.

Hereinafter, various exemplary embodiments of the present invention will be described in further detail with reference to the accompanying drawings.

FIG. 1A is a cross-sectional view illustrating a transparent organic light emitting display device in accordance with an embodiment of the inventive concept. Referring to FIG. 1A , a transparent organic light emitting display device 100 A includes a first substrate 110 A, a thin film transistor (TFT) 130 A, a gate insulating layer 132 A, an interlayer insulating layer 133 A, an overcoating layer 134 A, an organic light emitting element 140 A, and a bank layer 135 A.

The first substrate 110 A is substrates configured to support and protect various elements of the transparent organic light emitting display device 100 A. Accordingly, the first substrate 110 A is illustrated as being disposed at the bottom of the transparent organic light emitting display device 100 A, and may be referred to as a lower substrate, a supporting substrate, a thin film transistor substrate, a lower supporting member, and the likes. The first substrate 110 A is made of a transparent insulating material, for example, glass, plastic, and the likes. For purposes of explanations, is the first substrate 110 A is described as being a glass substrate in the present disclosure with a refractive index of 1.5. However, it should be appreciated that the first substrate 110 A can be made of various other materials having different refractive indexes

When the transparent organic light emitting display device 100 A is a flexible transparent organic light emitting display device, the first substrate 110 A may be formed of a flexible transparent insulating layer. The available flexible transparent insulating material may include polyetherimide (PEI), polyethyelene terephthalate (PET), polycarbonate (PC), polymethylmethacrylate (PMMA), polystyrene (PS), styrene acrylonitrile copolymer (SAN), silicon acryl resin, and the like in addition to polyimide (PI).

The transparent organic light emitting display device 100 A may include a plurality of pixel regions. Each of the plurality of pixel regions includes a plurality of sub pixel regions including a red (R) sub pixel region, a green (G) sub pixel region, and a blue (B) sub pixel region. In some embodiments, the pixel region further includes a white (W) sub pixel region to reduce the power consumption and improve the luminance of the transparent organic light emitting display device. Herein, the pixel region may be referred to as a pixel, and a sub pixel region may be referred to as a sub pixel.

The first substrate 110 A may include a pixel region including an R sub pixel region, a G sub pixel region, and a B sub pixel region, and may further include a W sub pixel region. The first substrate 110 A may include a plurality of pixel region. When the first substrate 110 A includes the plurality of pixel regions, the first substrate 110 A may include a plurality of R sub pixel regions, a plurality of G sub pixel regions, and a plurality of B sub pixel regions, and may further include a plurality of W sub pixel regions. When the first substrate 110 A includes the plurality of pixel regions, the plurality of pixel regions may be arranged in a matrix form. For convenience of description, FIG. 1A illustrates one sub pixel region, and the illustrated one sub pixel region may be one of the R sub pixel region, the G sub pixel region, the B sub pixel region, and the W sub pixel regions.

The one sub pixel region of the transparent organic light emitting display device 100 A includes an emissive area EA and a transmissive area TA. The emissive area EA may be defined as a region in which light is emitted to so that lights from the plurality of emissive areas collectively form an image content. The transmissive area TA is an area where the external light can pass through. Because the external light can pass through the transmissive area TA, objects behind the display through the transmissive area TA. Accordingly, a viewer can simultaneously see the image content displayed by the transparent organic light emitting display device 100 A and the background through the transmissive area TA. An area ratio between the emissive area EA and the transmissive area TA in the sub pixel region may vary depending on the image visibility and transparency of the transparent organic light emitting display device.

As shown in FIG. 1A , a thin film transistor (TFT) is formed on the first substrate 110 A within the emissive area EA. The TFT includes an active layer 121 A, a gate electrode 122 A, a source electrode 123 A, and a drain electrode 124 A. One or more insulating layers may be formed between these electrodes such as a gate insulating layer 132 A and/or an interlayer insulating layer 133 A. The TFT may be formed in every pixel region and/or in every sub pixel region on the first substrate 110 A so that each pixel or each sub pixel can be driven independent of the other pixels or sub pixels. The configuration of a TFT is not limited to the above-described example, and may be variously modified without departing from the spirit of the present invention.

The TFT described in the present disclosure can be operatively connected to an organic light emitting layer 144 A to emit light. In a conventional organic light emitting device, a switching TFT and a driving TFT are used to control the organic light emitting layer 144 A to emit light according to appropriate signals (e.g., data signal, scan signal). The switching TFT operates to transfer data signal from a data line to a gate electrode of the driving TFT when the scan signal is applied from a gate line. Upon receiving the date signal, the driving TFT operates to transfer current from a power line to an anode, thereby controlling the emission of the organic light emitting layer of the corresponding pixel or sub pixel. The transparent organic light emitting display device 100 A may include additional TFTs, such as a TFT for a compensation circuit designed to prevent abnormal driving of the transparent organic light emitting display device 100 A.

It should be noted that the TFT being illustrated in the drawings and described in the embodiments of the present disclosure may be a switching TFT, a driving TFT or any other TFT that may be included in a transparent organic light emitting display device 100 A.

Also, the TFT may have an inverted-staggered structure or a coplanar structure. The inverted-staggered thin film transistor may be defined as a thin film transistor having a structure in which the gate electrode is positioned on one side of the active layer and the source/drain electrodes are positioned on the opposite side of the active layer, and may also be referred to as the bottom gate TFT. The coplanar TFT may be defined as a TFT having a structure in which the gate electrode and the source/drain electrodes are positioned on the same side of the active layer. The TFT shown in FIG. 1A has the coplanar structure, but it should be noted that an inverted staggered TFT may be employed. A transparent organic light emitting display device employing an inverted staggered TFT will be described in further detail below with reference to FIG. 1D .

The active layer 121 A is formed on the first substrate 110 A. The active layer 121 A may include a channel region, in which a channel is formed, and a source region and a drain region in contact with a source electrode 123 A and a drain electrode 124 A. In the present disclosure, the active layer 121 A is described as being formed of an oxide semiconductor. For example, the active layer 121 A can include an indium oxide (InO)-based material, a tin oxide (SnO)-based material, a zinc oxide (ZnO)-based material, and the likes. The active layer 121 A can be formed of a quaternary metal oxide composite material such as indium tin gallium zinc oxide (InSnGaZnO)-based material. The active layer 121 A can also be formed of a ternary composite material including, but not limited to, an indium gallium zinc oxide (InGaZnO)-based material, an indium tin zinc oxide (InSnZnO)-based materials, an indium aluminum zinc oxide (InAlZnO)-based material, a tin gallium zinc oxide (SnGaZnO)-based material, an aluminum gallium zinc oxide (AlGaZnO)-based material and a tin aluminum zinc oxide (SnAlZnO)-based material. Further, the active layer 121 A can also be a binary composite material including, but not limited to, an indium zinc oxide (InZnO)-based material, a tin zinc oxide (SnZnO)-based material, an aluminum zinc oxide (AlZnO)-based material, a zinc magnesium oxide (ZnMgO)-based material, a tin magnesium oxide (SnMgO)-based material, an indium magnesium oxide (InMgO)-based material and an indium gallium oxide (InGaO)-based material. Composition ratios of the elements contained the oxide semiconductors can vary depending on the desired performance and reliability of the TFT 130 A.

The gate insulating layer 132 A is formed on the active layer 121 A to insulate the active layer 121 A from the gate electrode 122 A. The gate insulating layer 132 A may be formed of a single layer or a plurality of layers. Also, the length of the gate insulating layer 132 A may vary based on the design of the TFT 130 A. In FIG. 1A , the gate insulating layer 132 A is illustrated as having a length that is substantially equal to the length of the gate electrode 122 A. In some other embodiments, however, the gate insulating layer 132 A can be formed over the entire emissive area EA of the first substrate 110 A and may even extend over to the transmissive area TA of the first substrate 110 A.

The materials for forming the gate insulating layer 132 A as well as its stack configuration may vary depending on the size and/or the location of the gate insulating layer 132 A. When the gate insulating layer 132 A is formed only within the emissive area EA, the gate insulating layer 132 A does not affect the transmissivity of the display device 100 A transmissive area TA. Therefore, the gate insulating layer 132 A can be formed of any material that is capable of electrically insulating the active layer 121 A and the gate electrode 122 A. When the gate insulating layer 132 A extends further into the transmissive area TA of the first substrate 110 A, however, the gate insulating layer 132 A may affect the transmissivity of the display device 100 A at the transmissive area TA depending on the composition and/or the stack formation of the gate insulating layer 132 A. For instance, the difference of refractive indices between the first substrate 110 A and the gate insulation layer 132 A can cause total reflection at their interface, and distort the light passing through the transmissive area TA. Accordingly, it is preferred that the gate insulating layer 132 A is formed of a material having the same or substantially the same refractive index as the first substrate 110 A if the gate insulating layer 132 A is to be extended into the transmissive area TA.

In cases where the gate insulating layer 132 A is formed of multiple layers of different refractive indices. The layer with substantially the same refractive index as the first substrate 110 A may be extended further into the transmissive area TA while the insulation layer with a refractive index that differs from the first substrate 110 A is contained within the emissive area EA.

In the present disclosure, two layers or materials are said to have substantially the same refractive indices when the difference of their refractive indices is equal to or less than 0.1. Accordingly, the gate insulating layer 132 A that extends into the transmissive area TA may be formed of, for example, a silicon oxide film having a refractive index of 1.45, assuming the first substrate 110 A is a glass substrate having a refractive index of 1.5. In the example of multi-layered gate insulating layer 132 A, the layer(s) that extends into the transmissive area TA can be formed of, for example, a silicon oxide film. The layer(s) that is limited within the emissive area EA can be formed of, for example, a silicon nitride film having a refractive index of 1.88. It should be understood that the materials for forming the gate insulating layer 132 A and the first substrate 110 A described above are only exemplary. The first substrate 110 A can be formed of various other materials with a variety of different refractive indices, and thus the gate insulating layer 132 A can also be formed with various other materials by considering the difference of the refractive indices between the materials of the gate insulating layer 132 A and the materials of the first substrate 110 A.

The gate electrode 122 A is formed on the gate insulating layer 132 A. The gate electrode 122 A at least partially overlaps the active layer 121 A, and specifically overlaps the channel region of the active layer 121 A. Exemplary materials for forming the gate electrode 122 A includes, but are not limited to, molybdenum (Mo), aluminum (Al), chromium (Cr), gold (Au), titanium (Ti), nickel (Ni), neodymium (Nd), copper (Cu), and an alloy thereof. Multi-layered stacks of these materials can also be employed as the gate electrode 122 A. The interlayer insulating layer 133 A is formed on the first substrate 110 A to electrically insulate the gate electrode 122 A from the source electrode 123 A and the drain electrode 124 A. Contact holes extending from the active layer 121 A to the source electrode 123 A and to the drain electrode 124 A are formed through the interlayer insulating layer 133 A so that the source electrode 123 A and the drain electrode 124 A contact the respective ends of the active layer 121 A. The interlayer insulating layer 133 A may be formed of the same material as the gate insulating layer 132 A. For example, the material for forming the interlayer insulating layer 133 A may include, but are not limited to, a silicon oxide, a silicon nitride or a combination thereof. Also, multi-layered stacks of these materials can be employed as the interlayer insulating layer 133 A. In the example illustrated in FIG. 1A , the interlayer insulating layer 133 A is formed only within the emissive area EA. In other embodiments, however, the interlayer insulating layer 133 A may be formed over the entire emissive area EA and transmissive area TA of the first substrate 110 A.

Similar to the gate insulating layer 132 A, the materials and the stack configurations of the interlayer insulating layer 133 A can change according to the location in which the interlayer insulating layer 133 A is formed. When the interlayer insulating layer 133 A is formed only within the emissive area EA of the first substrate 110 A, the materials and the stack configuration of the interlayer insulating layer 133 A do not affect the external light passing through the transmissive area TA. Therefore, the interlayer insulating layer 133 A may be formed of, for instance, silicon oxide or a silicon nitride, or a combination thereof. Multilayered stacks or multilayered structure of such materials can be employed as the interlayer insulating layer 133 A within the emissive area EA.

When the interlayer insulating layer 133 A is formed to in both the emissive area EA and the transmissive TA of the first substrate 110 A, the materials and the stack configuration of the interlayer insulating layer 133 A can have detrimental effect on the transmissivity of the display device 100 A at the transmissive area TA. The greater the difference of refractive indices between the interlayer insulating layer 133 A and the first substrate 110 A, the greater the distortion of light caused by the total reflection. Therefore, when the interlayer insulating layer 133 A is formed in both the emissive area EA and the transmissive area TA of the first substrate 110 A, only the layer(s) formed of a material having substantially the same refractive index as the first substrate 110 A extends into the transmissive area TA. The layer(s) employed within the interlayer insulating layer 133 A formed of a material with a refractive index that differs over a predetermined limit (e.g., the difference of refractive indices greater than 0.1) is formed only within the emissive area EA.

For example, an interlayer insulating layer 133 A having a single-layered configuration, which covers both the emissive area EA and the transmissive area TA, may be formed of a material such as a silicon oxide with a refractive index of 1.45. An interlayer insulating layer 133 A having a multi-layered configuration can be formed a plurality of layers formed of silicon oxide and silicon nitride that are alternately stacked, in which only the silicon oxide layer(s) is extended into the transmissive area TA.

The source electrode 123 A and the drain electrode 124 A are formed on the interlayer insulating layer 133 A. The source electrode 123 A and the drain electrode 124 A may be electrically connected to the source region and the drain region of the active layer 121 A through the contact holes formed in the interlayer insulating layer 133 A and/or the gate insulating layer 132 A, respectively. The source electrode 123 A and the drain electrode 124 A may include any one among Mo, Al, Cr, Au, Ti, Ni, Nd, and Cu or an alloy thereof. However, the source electrode 123 A and the drain electrode 124 A are not limited thereto, and may be formed of various materials. Further, the source electrode 123 A and the drain electrode 124 A may include multiple layers including any one selected from the group consisting of Mo, Al, Cr, Au, Ti, Ni, Nd, and Cu or an alloy thereof.

A passivation layer may be formed over the TFT disposed in the emissive area EA. The passivation layer is a protection layer, which provides electrical stability by isolating the transistor surface from electrical and chemical conditions in the environment. The passivation layer may be formed of the same material as the interlayer insulating layer 133 A and/or the gate insulating layer 132 A such as a single layer of silicon oxide or silicon nitride or multiple layers thereof. However, the passivation layer is not limited thereto, and may be formed of various materials. When the passivation layer is formed in both the emissive area EA and the transmissive area TA, the passivation layer may be formed in the similar stack configuration as the gate insulating layer 132 A and/or the interlayer insulating layer 133 A.

As depicted in FIG. 1A , the overcoating layer 134 A is formed on the first substrate 110 A to provide a planar surface from the emission area EA to the transmissive area TA. In other words, the overcoating layer 134 A planarizes a top of the first substrate 110 A. As such, the overcoating layer 134 A may be referred to as a planarization layer. In embodiments employing a passivation layer as described above, the overcoating layer 134 A may be formed on the passivation layer. Further, the overcoating layer 134 A may be provided with a contact hole that exposes the source electrode 123 A and/or the drain electrode 124 A, which may be electrically connected to other electrodes of the organic light emitting device 100 A.

As illustrated in FIG. 1A , the overcoating layer 134 A may compensate for the height difference between the emissive area EA and the transmissive area TA, which is caused by formation of various elements in the emissive area EA, thereby planarizing the surface over the emissive area EA and the transmissive area TA. In the exemplary embodiments shown in FIG. 1A , the overcoating layer 134 A is formed on the TFT (e.g., the active layer 121 A, the gate electrode 122 A, the source electrode 123 A, the drain electrode 124 A) and other insulating layers (e.g., the gate insulating layer 132 A, the interlayer insulating layer 133 A, the passivation layer) disposed in the emissive area EA of the first substrate 110 A, and extended further into the transmissive area TA of the first substrate 110 A. Since there is no other elements formed in the transmissive area TA of the first substrate 110 A, the overcoating layer 134 A is disposed on the upper surface of first substrate 110 A in the transmissive area TA, and fills the space caused by the missing elements (e.g., the gate insulating layer 132 A, the interlayer insulating layer 133 A, the TFT, etc.) in the transmissive area TA of the first substrate 110 A.

The overcoating layer 134 A is made of a material that has the same refractive index as that of the first substrate 110 A. As described above, distortion of light such as total reflection of the light is caused in the interface between the first substrate 110 A and the overcoating layer 134 A if their refractive indices do not match, or otherwise differ more than the predetermined threshold value (e.g., 0.1). Therefore, in the transparent organic light emitting display device 100 A of an embodiment, the refractive index of the overcoating layer 134 A is the same, or substantially the same, as that of the first substrate 110 A. In the present disclosure, elements or materials are described as having “substantially the same refractive index” even if their refractive indices are not exactly the same so long as the difference is small enough (e.g., equal to or less than 0.1) to minimize the total reflection of light at the interfacing surface of the elements. The material for forming the overcoating layer 134 A may include, but are not limited to, polyaluminum chloride (PAC) which is a resinous material having a refractive index of 1.5 or silicon oxide (SiO x ). Hereinafter, for convenience of description, it is described that the overcoating layer 134 A is formed of PAC.

The organic light emitting element 140 A including an anode 141 A, the organic light emitting layer 144 A, and a cathode 145 A is formed on the overcoating layer 134 A. The organic light emitting element 140 A is driven by the emission principle through recombination of holes provided from the anode 141 A and electrons provided from the cathode 145 A in the organic light emitting layer 144 A to form an image.

The transparent organic light emitting display device 100 A is an independent driving type display device, and is driven in sub pixel region units. Therefore, the above-described TFT and organic light emitting element 140 A are disposed in each of the sub pixel regions so that the TFT disposed in each of the sub pixel region independently drives the organic light emitting element 140 A.

As depicted in FIG. 1A , the anode 141 is formed on the overcoating layer 134 A. The anode 141 A may be referred to a positive electrode, a pixel electrode, or a first electrode. The anode 141 may be connected to the source electrode 123 A of the TFT through the contact hole formed in the overcoating layer 134 A. However, the connection of the anode is not limited thereto, and the anode may be connected to the drain electrode 124 A according to a type of the thin film transistor.

The anode 141 A may be formed of a conductive material having a high work function to provide holes. The transparent conductive layer 143 A may be formed of a material having a high work function, for example, a transparent conductive oxide (TCO). Materials for forming the transparent conductive layer 143 A may include, but are not limited to, indium tin oxide (ITO), indium zinc oxide (IZO), Indium tin zinc oxide (ITZo), zinc oxide (ZO), tin oxide (TO), or a combination thereof.

In FIG. 1A , the transparent organic light emitting display device 100 A is a top-emission type organic light emitting display device. Generally, the organic light emitting layer 144 A emits light in all directions. Although the emitted light may be reflected off by some of the elements disposed under the transparent conductive layer 143 A and exit towards the top of the organic light emitting element 140 A, a significant portion of the light may still exits through the first substrate 110 A, leading to poor luminance efficiency. As such, when the organic light emitting display device is configured as a top-emission type, the anode 141 A can be formed of stacked layers of a reflection layer 142 A and a transparent conductive layer 143 A, in which the reflection layer 142 A is formed below the transparent conductive layer 143 A.

The reflection layer 142 A may be formed of a material having low electrical resistance property and good light reflectivity, for example, silver (Ag), Ni, Au, platinum (Pt), Al, Cu, molybdenum/aluminum neodymium (Mo/AlNd), or a combination thereof. Herein, the anode 141 A is defined to include the transparent conductive layer 143 A and the reflection layer 142 A, but the anode 141 A may be defined to include only transparent conductive layer 143 A, and the reflection layer 142 A may be defined as a separation configuration. Further, herein, it has been described that the anode includes a transparent conductive material having high work function and a reflection metal layer, however, the anode 141 A in itself may be formed of a conductive material having high work function and good reflectance.

Since the anode 141 A primarily serves to provide holes to the organic light emitting layer 144 A, the anode 141 A only needs to be formed in the emissive area EA. Accordingly, the anode 141 A is formed in the emissive area (EA) in each of the pixel/sub pixel regions of the first substrate 110 A so that each of the pixel/sub pixel regions can be driven individually. As for the transparent conductive layer 143 A, external light can still pass through the transmissive area TA even if the transparent conductive layer 143 A is extended further into the transmissive area TA, albeit at decreased clarity. The reflection layer 142 A, however, may significantly or wholly block the external light if it is extended into the transmissive area TA. Therefore, the reflection layer 142 A should not be extended into the transmissive area TA.

Any one or both of the transparent conductive layer 143 A and the reflection layer 142 A that constitute the anode 141 A may be electrically connected to the source electrode 123 A. In FIG. 1A , the electrical connection between the source electrode 123 A and the anode 141 A is made by connecting the transparent conductive layer 143 A to the source electrode 123 A via a contact hole formed through the overcoating layer 134 A and the reflection layer 142 A. In some other embodiments, however, such electrical connection between the source electrode 123 A (or the drain electrode 124 A) and the anode 141 A can be made by connecting the reflection layer 142 A to the source electrode 123 A via a contact hole through the overcoating layer 134 A.

The bank layer 135 A is formed on the overcoating layer 134 A. The bank layer 135 A serves to divide adjacent sub pixel regions, and additionally serves to divide the emissive area EA and the transmissive area TA in one sub pixel region. The bank layer 135 A may be formed to open a portion of the anode 141 A. The bank layer 135 A can be formed of an organic insulating material, for example, any one of polyimide, photoacryl, and benzocyclobutene (BCB). The bank layer 135 A may be formed in a tapered shape. When the bank layer 135 A is formed in a tapered shape, the bank layer 135 A may be formed using a positive photoresist.

In some embodiments, the transparent organic light emitting display device 100 A may employ direct emission organic light emitting elements (referred hereinafter as “RGB type”). The RGB type organic light emitting element generally uses three sub pixels that each emits a designated color (red, green or blue) to create a full-color pixel without filtering the light from the sub pixels. In some other embodiments, the transparent organic light emitting display device 100 A may employ white organic light emitting elements in conjunction with color filters (referred hereinafter as “RGBW type”). The white organic light emitting element is configured to emit white light, and the white light is passed through a color filter to form a specific color (red, green, blue) at each of the sub pixels. The white organic light emitting element may have additional sub pixel, which emits white light without being filtered to increase the overall luminance of each pixel of the display device 100 A.

As described above, each sub pixel region has an emissive area EA and a transmissive area TA, and the anode 141 A is formed in the emissive area EA in each of the sub pixel regions. The red sub pixel region, the green sub pixel region and the blue sub pixel region can be defined by openings in the bank layer 135 A. When the transparent organic light emitting display device 100 A employs the RGB type organic light emitting elements 140 A, the organic light emitting layer 144 A that emits one of red, green or blue light is formed on the anode 141 A so that each sub pixel directly emits a corresponding colored light without a color filter. When the transparent organic light emitting display device 100 A employs the RGBW type organic light emitting elements 140 A, a white organic light emitting layer 144 A may be formed over the substantially the entirety of the first substrate 110 A. Alternatively, the white organic light emitting layer 144 A may be discretely formed in the emissive area of the red, green and blue sub pixel regions to be separated from each other.

In FIG. 1A , for convenience of description, the organic light emitting element 140 A is illustrated as the RGBW type and that the organic light emitting layer 144 A formed in the emissive area EA is a white organic light emitting layer. The arrangement of the color filters will be described in further detail below with reference to FIG. 1C .

The cathode 145 A is formed on the organic light emitting layer 144 A. The cathode 145 A may be referred to as a negative electrode, a common electrode, or a second electrode. The cathode 145 A is connected to a separate voltage line, and may apply the same voltage to all the sub pixel regions.

The cathode 145 is formed of a material having high electrical conductivity and a low work function, that is, a cathode material to provide electrodes. The specific material constituting the cathode 145 A may be different according to an emission type of the flexible organic light emitting display device. In a top-emission type organic light emitting display device as shown in FIG. 1A , the cathode 145 A may be formed of a very thin layer of a metal material having a low work function. Materials for forming the cathode 145 A may include, but are not limited to, Ag, Ti, Al, Mo, or an alloy of Ag and Mg. In the top-emission type, the cathode 145 A should have a thickness of several hundreds of A or less, for example, 200 Å or less. At this range, the cathode 145 A is substantially a transparent. Even if metal layer having high light reflectivity is used, sufficient transparency can be obtained if the cathode 145 A is formed in a thickness equal to or less than a predetermined thickness (for example, 200 Å). As such, the cathode 145 A may be substantially referred to as a transparent cathode. The cathode 145 A can also be formed with a material including carbon nano tube and/or graphene, which is known to be highly conductive and transparent.

The cathode 145 A is formed in the emissive area EA of each of the sub pixel regions of the first substrate 110 A. As described above, the emissive area EA is a region that emits light to collectively display the actual image and the transmissive area TA is a region in which external light is passed through, and thus the cathode 145 A needs to be formed in the emissive area EA. In FIG. 1A , the cathode 145 A is illustrated as being formed only on the emissive area EA. However, the cathode 145 A can be substantially transparent when its thickness is sufficiently thin, or otherwise has a thickness below a predetermined threshold value (e.g., 200 Å or less). As such, in some embodiments, the cathode 145 A may be formed in the emissive area EA and the transmissive area TA.

To improve transmittance and minimize degradation in luminance, it is important to improve the transmittance of the external light through the transparent organic light emitting display device 100 A, especially the light entering from the first substrate 110 A and exiting to the top of the device 100 A. Referring to FIG. 1A , in the transparent organic light emitting display device 100 A according to an embodiment, the organic light emitting element 140 A is not formed on the overcoating layer 134 A formed in the transmissive area TA of the first substrate 110 A. Instead, only the first substrate 110 A and the overcoating layer 134 A are formed in the transmissive area TA of the first substrate 110 A, in which the first substrate 110 A and the overcoating layer 134 A have substantially the same the refractive index. Therefore, distortion such as total reflection of light in the interface between the first substrate 110 A and the overcoating layer 134 A is minimized, or eliminated, to improve the transmittance at the transmission area(s) TAs of the transparent organic light emitting display device 100 A.

FIG. 1B is a cross-sectional view illustrating an exemplary transparent organic light emitting display device 100 B according to an embodiment of the present invention. In should be noted that the same elements are denoted with the same numerals in the drawings of the present disclosure. As such, the element illustrated in FIG. 1A and FIG. 1B that are denoted with the same numeral should be understood as the same element, and thus repeated description thereof will be omitted.

As shown in FIG. 1B , a buffer layer 131 B is formed on a first substrate 110 B to reduce permeation of moisture or other impurities through the first substrate 110 B, and to planarize the surface of the first substrate 110 B. The inclusion of the buffer layer 131 B in the organic light emitting display device is optional, and may or may not be employed in the organic light emitting display device based on the materials of the first substrate 110 B and/or the TFT.

The buffer layer 131 B can formed of a single layer or multiple layers. When the buffer layer 131 B is formed of multiple layers, a layer of silicon oxide and a layer of silicon nitride may be alternately stacked. Specific order of the layers within the buffer layer 131 B can be configured by considering the interface characteristic between the buffer layer 131 B and the TFT. More specifically, the material for forming the buffer layer 131 B may be selected according to the interface characteristic with the active layer 121 B depending on the structure of the thin film transistor. For example, the buffer layer and the semiconductor layer may be in direct contact in a coplanar TFT. In this case, a layer containing hydrogen atoms may react with the oxide semiconductor and form moisture within the TFT, thereby negatively affecting the performance of the TFT. For this reason, in a coplanar TFT using an oxide semiconductor, the layer of the buffer layer 131 B contacting the oxide semiconductor should not contain hydrogen. For example, the buffer layer 131 B may be formed of a stack of silicon oxide layer and a silicon nitride layer, and the layer contacting the oxide semiconductor can be a silicon oxide layer rather than the silicon nitride layer.

When the buffer layer 131 B is formed in a multi-layered stack of a silicon oxide layer and a silicon nitride layer, the refractive index of the silicon oxide (1.45) is substantially the same as the refractive indexes of the first substrate 110 B (assuming the first substrate 110 B is made of glass: refractive index of 1.5) and the overcoating layer 134 B. However, the refractive index of the silicon nitride layer (i.e., 1.88) is greater than the refractive indices of the first substrate 110 B and the overcoating layer 134 B by more than the threshold value (e.g., 0.1). Such difference in the refractive indices causes distortion of light such as total reflection of light at their interface. Therefore, as illustrated in FIG. 1B , only the layer(s) among the multi-layered buffer layer 131 B that has the same or substantially the same refractive index as the first substrate 110 B and the overcoating layer 134 B (e.g., silicon oxide layer) may be extended out to the transmissive area TA while other layer(s) (e.g., silicon nitride layer) are contained within the emissive area EA.

FIG. 1C is a cross-sectional view illustrating an exemplary transparent organic light emitting display device 100 C according to an embodiment of the present invention. In should be noted that the same elements are denoted with the same numerals in the drawings of the present disclosure. As such, the element illustrated in FIG. 1A and FIG. 1C that are denoted with the same numeral should be understood as the same element, and thus repeated description thereof will be omitted.

The second substrate 115 C is a substrate configured to support and protect various elements of a transparent organic light emitting display device 100 C, and disposed to face the first substrate 110 C. The second substrate 115 C is a supporting plate located in a top of the transparent organic light emitting display device 100 C, and may be referred to as an upper substrate, a protection substrate, a color filter substrate, a cover, a cover substrate, and an upper supporting member, or the like. The second substrate 115 C may include a transparent insulating material, and the second substrate 115 C may be formed of substantially the same material as the first substrate 110 C. Therefore, the second substrate 115 C may have substantially the same refractive index as the first substrate 110 C.

A black matrix may be formed on the second substrate 115 C. The black matrix may be formed in a boundary between the sub pixel regions. The black matrix may be formed of chromium (Cr) or another opaque metal, or formed of a resin. The black matrix may separate sub pixel regions and color filters 170 C formed in the sub pixel regions.

When the transparent organic light emitting display device 100 C employs RGBW type organic light emitting element, a color filter 170 C is formed on the second substrate 115 C. The color filter 170 C may be formed in each of the sub pixel regions on the second substrate 115 C. When the color filter 170 C is formed in the red sub pixel region, the color filter 170 C may be a red color filter. When the color filter 170 C is formed in the green sub pixel region, the color filter 170 C may be a green color filter. When the color filter 170 C is formed in the blue sub pixel region, the color filter 170 C may be a blue color filter. As described above, the organic light emitting layer 144 C is configured to emit white light, and filtered by the color filter 170 C. For example, the white light emitted by the organic light emitting layer 144 C is filtered by the red color filter to be transformed into red light, filtered by the green color filter to be transformed into green light, and filtered by the blue color filter to be transformed into blue light. As illustrated in FIG. 1C , when the transparent organic light emitting display device 100 C is a top-emission type organic light emitting display device, the color filter 170 C is disposed at the upper side the organic light emitting layer 144 C.

The color filter 170 C is formed in a region corresponding to an emissive area EA of the second substrate 115 C. As illustrated in FIG. 1C , when the transparent organic light emitting display device 100 C is a top-emission type organic light emitting display device, and the organic light emitting layer 144 C emits white light, the white light emitted by the organic light emitting layer 144 C is passed through the color filter 170 C to be transformed into light of a specific color. However, since a transmissive area TA is not a region emitting light of a specific color but a region transmitting external light of the transparent organic light emitting display device 100 C, when the color filter 170 C is disposed in the transmissive area TA, a color of the external light is color-shifted to the color represented by the color filter 170 C. Therefore, the color filter 170 C is not formed in the transmissive area TA, but formed only in the emissive area EA.

Although now shown in FIG. 1C , in some embodiments, a polarizing film may be disposed on the second substrate 115 C. Specifically, the polarizing film may be disposed on a surface of the second substrate 115 C opposite to the surface on which the color filter 170 C is formed. The polarizing film may improve linearity of the light emitted from the organic light emitting layer 144 C to prevent scattering or interference and improve color sense. Further, the polarizing film may selectively transmit the external light, and reduce the reflection of external light to improve visibility of the organic light emitting display device.

In the exemplary embodiment shown in FIG. 1C , an encapsulating layer 160 C is formed between the first substrate 110 C and the second substrate 115 C. More specifically, the encapsulating layer 160 C is formed between the organic light emitting element 140 C and the color filter 170 C within the emissive area EA. Also, in the transmissive area TA, the encapsulating layer 160 C is formed between the overcoating layer 134 C and the second substrate 115 C. The encapsulating layer 160 C may protect internal elements of the transparent organic light emitting display device 100 C such as the TFT and the organic light emitting element 140 C from moisture, air, and shock from the external environment. The encapsulating layer 160 C may be referred to as an encapsulating layer, an encapsulating member, a sealing layer, or a sealing member. For example, as the encapsulating layer 160 C, a face seal may be used.

A refractive index of the encapsulating layer 160 C is substantially the same as that of the overcoating layer 134 C. Therefore, the refractive indices of the first substrate 110 C, the overcoating layer 134 C, the encapsulating layer 160 C, and the second substrate 115 C may substantially the same in the region corresponding to the transmissive region TA. A material of the encapsulating layer 160 C for matching of a refractive index may include, but are not limited to, glycerol, 1,2-propanediol, glycerin, trimethylopropane, triethanolamine, ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,8-octanediol, 1,2-butanediol, 2,3-butanediol, 1,2-pentanediol, etohexadiol, p-Methane-3,8-diol, and 1-Methyl-2,4-pentanediol. The material of the encapsulating layer is not limited thereto, and another adhesive material substantially having the same refractive index as that of the first substrate 110 C may be used.

In the transparent organic light emitting display device 100 C, refractive indices of insulating materials constituting the overcoating layer 134 C and the encapsulating layer 160 C disposed in the transmissive area TA of the first substrate 110 C and the second substrate 115 C are substantially the same as those of the first substrate 110 C and the second substrate 115 C. Therefore, distortion such as total reflection of the light in the region corresponding to the transmissive area TA of the transparent organic light emitting display device 100 C may be minimized.

In some embodiments, a transparent resin layer may be formed in a region of the second substrate 115 C in which the color filter 170 C is not formed, that is, in a region of the second substrate 115 C corresponding to the transmissive area TA of the first substrate 110 C. As described above, it is preferable that the external light passes through the transmissive area TA of the transparent organic light emitting display device 100 C with minimum distortion. Therefore, the transparent resin layer may be formed in the second substrate 115 C corresponding to the transmissive region TA, and the transparent resin layer may be formed to the same thickness as that of the color filter 170 C. The transparent resin layer may be formed of a material having substantially the same refractive index as those of the second substrate 115 C and the encapsulating layer 160 C.

FIG. 1D is a cross-sectional view illustrating a transparent organic light emitting display device according to an embodiment of the present invention. Referring to FIG. 1D , the first substrate 110 D, the overcoating layer 134 D, the organic light emitting element 140 D, the bank layer 135 D, the encapsulating layer 160 D, the color filter 170 D, and the second substrate 115 D are substantially the same as the respective elements depicted in FIG. 1C , and thus repeated description will be omitted.

In the embodiment shown in FIG. 1D , an inverted-staggered TFT is used as opposed to the coplanar TFT used in the embodiment shown in FIG. 1C . A buffer layer 131 D is formed on the first substrate 110 D. As described above, the buffer layer 131 D is an optional element, and its inclusion in the display device may depends on the type of the first substrate 110 D and/or the type of TFT used in display device 100 D.

When an inverted-staggered TFT is employed in the display device, a silicon nitride based buffer layer is more advantageous than the silicon oxide based buffer layer for the transistor efficiency due to the interface characteristic with the active layer 121 D. The buffer layer 131 D formed of silicon nitride, however, may distort the external light passing through the display device 100 D due to the relatively large refractive index difference with respect to the other elements (e.g., first and second—assuming glass—substrates, overcoating layer, interlayer insulating layer, encapsulating layer). Accordingly, the buffer layer 131 D is formed only within the emissive area EA to improve transmittance in the transmission area TA and minimize degradation in luminance of the display device 100 D.

As previously described, the buffer layer 131 D may be formed with multiple layers, which may include one or more layers of silicon oxide and one or more layers of silicon nitride. Since the silicon nitride based buffer layer is likely to improve the TFT efficiency (inverted-staggered TFT), the upper most layer of the multi-layered buffer layer may be formed of silicon nitride. The location for disposing the multi-layered buffer layer in the display device, however, remains the same as the embodiments employing the coplanar TFT. That is, since the refractive index of the silicon oxide film is 1.45 and the refractive index of the silicon nitride film is 1.88, the distortion of light such as total reflection of light is caused when both the silicon oxide film and the silicon nitride film of the buffer layer 131 D are formed in the transmissive area TA. Therefore, as illustrated in FIG. 1D , the buffer layer 131 D may be formed only in the emissive area EA, or alternatively, only the layer(s) of the multi-layered buffer layer that has the same refractive index as the other elements disposed in the transmissive area TA extends further into the transmissive area TA.

The gate electrode 122 D may be formed on the first substrate 110 D or on the buffer layer 131 D as depicted in FIG. 1D . Other than a formation location of the gate electrode 122 D formed on the first substrate 110 D according to the structure of the thin film transistor, that is, the inverted-staggered thin film transistor, the gate electrode 122 D is substantially the same as that of FIG. 1A , and thus repeated description will be omitted.

The gate insulating layer 132 D is formed on the gate electrode 122 D. The gate insulating layer 132 D insulates the active layer 121 D from the gate electrode 122 D. Other than being formed on the gate electrode 122 D and below the active layer 121 D, other aspects of the gate insulating layer 132 D is substantially the same as that of FIG. 1A .

The active layer 121 D is formed on the gate insulating layer 132 D. The active layer 121 D may be formed on the gate electrode 122 D and the gate insulating layer 132 D to be in contact with a partial region of the gate electrode 122 D. Other than being formed on the gate insulating layer 132 D, other aspects of the active layer 121 D is substantially the same as that of FIG. 1A .

The source electrode 123 D and the drain electrode 124 D are formed on the gate insulating layer 132 D. The source electrode 123 D is formed to be in contact with a partial region of the gate insulating layer 132 D and a partial region of the active layer 121 D formed on the gate insulating layer 132 D. The drain electrode 124 D is formed to be in contact with the other partial region of the gate insulating layer 132 D and the other partial region of the active layer 121 D formed on the gate insulating layer 132 D. Other than the formation location of the source electrode 123 D and the drain electrode 124 D, other aspects of the source electrode 123 D and the drain electrode 124 D are substantially the same as those of FIG. 1A . Although not shown in FIG. 1D , a separate resistance reduction member may be disposed between the active layer 121 D and the source electrode 123 D and between the active layer 121 D and the drain electrode 124 D to reduce the contact resistance between the active layer 121 D and the source electrode 123 D and between the active layer 121 D and the drain electrode 124 D.

FIG. 2A is a cross-sectional view illustrating a transparent organic light emitting display device according to an embodiment of the present invention. Referring to FIG. 2A , a transparent organic light emitting display device 200 A includes a first substrate 210 A, a thin film transistor, a gate insulating layer 232 A, an interlayer insulating layer 233 A, an overcoating layer 234 A, an organic light emitting element 240 A, and a bank layer 235 A. The first substrate 210 A, the thin film transistor, the gate insulating layer 232 A, the interlayer insulating layer 233 A, an overcoating layer 234 A, the organic light emitting element 240 A, and the bank layer 235 D are substantially the same as those of FIG. 1C , and thus repeated description will be omitted.

The transparent organic light emitting display device 200 A includes a first insulating layer and a second insulating layer formed between the first substrate 210 A and the second substrate 215 A. Among the first and second insulating layers, the insulating layers having substantially the same refractive index as the first substrate 210 A are disposed in both the emissive area EA and the transmissive area TA, while the insulating layers having refractive index that differs from the refractive index of the first substrate 210 A by more than certain value are disposed only within the emissive area EA. For convenience of description, the first insulating layer refers to the insulating layer with a refractive index that differs from the refractive index of the first substrate 210 A by more than certain value. Also, the second insulating layer refers to the insulating layer having the same or substantially the same refractive index as the first substrate 210 A. More detailed description for the first insulating layer and second insulating layer will be made with reference to FIG. 2B .

Reference is now made to FIG. 2B , which is a pictorial representation of how light propagates through multiple optical mediums. FIG. 2B (a) illustrates refraction of light when the light travels through a medium having a refractive index n 1 to a medium having a refractive index n 2 , in which the refractive index n 1 is larger than the refractive index n 2 . FIG. 2B (b) illustrates refraction of light when the light travels through a medium having a refractive index n 3 to a medium having a refractive index n 4 , in which the refractive index n 3 substantially the same as the refractive index n 4 . In FIGS. 2B (a) and 2 B(b), it is assumed that an incident angle (θ) of incident light is larger than the critical angle.

Referring to FIG. 2B (a), when the light travels from a medium having a high refractive index to a medium having low refractive index, the light projected an incident angle greater than the critical angle reflected off at the interface between the two medium. Therefore, when the light travels from the medium having the refractive index n 1 to the medium having the refractive index n 2 , the light does not pass through the boundary between the medium having the refractive index n 1 and the medium having the refractive index n 2 , and is totally-reflected back toward the medium having the refractive index n 1 . For example, the medium having the refractive index n 1 may be the buffer layer including a silicon nitride film, and the interlayer insulating layer, and the likes, and the medium having the refractive index n 2 may be the buffer layer including a silicon oxide film, the interlayer insulating layer, the first substrate, the overcoating layer, and the encapsulating layer.

However, as illustrated in FIG. 2B (b), when light travels to the media having the refractive index, which substantially the same, the light is not reflected, and crosses the interface between the two mediums, then eventually passes through them. For example, the media having refractive indexes n 3 and n 4 may be the buffer layer including a silicon oxide film, the first substrate, the overcoating layer, and the encapsulating layer. Therefore, it is preferred to match the refractive indices of the medium disposed along the path of the light to minimize such total reflection.

Referring back to FIG. 2A , the second insulating layer may be the overcoating layer 234 A substantially having the same refractive index as that of the first substrate 210 A and formed in the transmissive area TA. The first insulating layer may be the gate insulating layer 232 A or the interlayer insulating layer 233 A having a refractive index which is not substantially the same as the first substrate 210 A being formed only in the emissive area EA. Accordingly, in the transparent organic light emitting display device 200 A, all of the insulating layers, which are formed to be extended from the emissive area EA to the transmissive area TA, are formed with a material having the same or at least substantially the same refractive index as the first substrate 210 A. In this way, the light transmittance at the transmissive area TA and the luminance of the display device 200 A can be improved.

FIGS. 2C and 2E are cross-sectional views, each illustrating a transparent organic light emitting display device according to an embodiment of the present invention. A buffer layer ( 231 C, 231 E) formed on the first substrate ( 210 C, 210 E) for reducing permeation of moisture or other impurities through the first substrate ( 210 C, 210 E). The buffer layer ( 231 C, 231 E) may be formed of materials selected based on the type of the TFT employed in the display device, particularly based on the interface characteristic of the active layer ( 221 C, 221 E). For a coplanar TFT as shown in FIG. 2C , which has its active layer 221 C in contact with the buffer layer 231 C, the buffer layer formed of a silicon oxide film provides better transistor efficiency due to the interface characteristic with the active layer 221 C. On the other hand, for an inverted-staggered TFT as shown in FIG. 2E , the buffer layer 232 E formed of a silicon nitride film provides better transistor efficiency due to the interface characteristic with the active layer 221 E.

Assuming the first substrate is formed of glass, the buffer layer 231 C formed of the silicon oxide film is considered to have substantially the same refractive index of the first substrate 210 C. (e.g., 1.5 and 1.45) Further, the buffer layer 231 C has substantially the same refractive index as the overcoating layer 234 C that has the same or substantially the same refractive index as the first substrate 210 C. Since the refractive index of these layers substantially match with respect to each other, total reflection of the light at the interface of these layers can be minimized. While the buffer layer 231 C can be formed only in the emissive area EA as illustrated in FIG. 2C , the buffer layer 231 C formed in the emissive area EA may be extended further to the transmissive area TA for various reasons, such as for improved durability, prevention of moisture/impurity prevention as well as ease of fabrication.

Referring to FIG. 2D , the buffer layer 231 E can be formed in stacks of layers (e.g., first buffer layer 236 D and second buffer layer 237 D). Each layer may be formed of one or more of different materials. For instance, the first buffer layer 236 D can be formed of silicon nitride and the second buffer layer 237 D can be formed of silicon oxide. The order of layers being stacked in forming the buffer layer 231 D can still be based on the type of the TFT employed in the display device 200 D. Since a layer formed of Silicon oxide is more advantageous for coplanar TFT in terms of transistor efficiency; the second buffer layer 237 D formed of silicon oxide is used as the upper most layer of the buffer layer 231 E. In contrast, since a layer formed of silicon nitride is more advantageous for inverted-staggered TFT, a layer formed of silicon nitride should be the layer of the buffer layer being in contact with the active layer of the TFT.

It should be reminded that refractive index of Silicon nitride layer (i.e., 1.88) is much higher than the silicon oxide layer. Therefore, the layer formed of silicon nitride and the layer formed of silicon oxide should not be formed in the transmissive area TA of the display device. For instance, any layers including silicon nitride should not be extended further into the transmissive area TA if the first substrate is formed of glass (or other material having refractive index that differs by more than 0.1).

FIG. 2F is a cross-sectional view illustrating a transparent organic light emitting display device according to another embodiment of the inventive concept. A first substrate 210 F, a thin film transistor, a buffer layer 231 E, a gate insulating layer 232 F, an interlayer insulating layer 233 F, an overcoating layer 234 F, an organic light emitting element 240 F, a bank layer 235 F, a color filter 270 F, and a second substrate 215 F illustrated in FIG. 2F are substantially the same as those of FIG. 2D , and thus repeated description will be omitted

In a transmissive area TA of the second substrate 215 F, the color filter 270 F is not formed, but a transparent resin layer 275 F may be formed. The transparent resin layer 275 F is formed to the same thickness as the color filter 270 F to remove a step on the second substrate 215 F.

An encapsulating layer 260 F is formed between the first substrate 110 F and the second substrate 115 F. The encapsulating layer 260 F may protect internal elements of the transparent organic light emitting display device 200 F such as a thin film transistor and an organic light emitting element 240 F from moisture, air, and a shock from the outside. The encapsulating layer 260 F may be referred to as an encapsulant, an encapsulating member, a sealing layer, or a sealing member. Specifically, the encapsulating layer 260 F may be formed between the organic light emitting element 240 F and the overcoating layer 234 F formed in the first substrate 210 F and the transparent resin layer 275 E and the color filter 270 F formed in the second substrate 215 F. As the encapsulating layer 260 F, a thin film encapsulation may be used.

FIG. 3A is a cross-sectional view illustrating a transparent organic light emitting display device according to another embodiment of the inventive concept. Referring to FIG. 3A , a transparent organic light emitting display device 300 A includes a first substrate 310 A, a buffer layer 331 A, a thin film transistor 320 A, an overcoating layer 334 A, an organic light emitting element 340 A, a color filter 370 A, and a second substrate 315 A. The first substrate 310 A, the buffer layer 331 A, an overcoating layer 334 A, the color filter 370 A, and the second substrate 315 A are substantially the same as those of FIG. 1C , and thus repeated description will be omitted. Although the thin film transistor 320 A and the organic light emitting element 340 A has been conceptually illustrated in FIG. 3A , the thin film transistor 320 A and the organic light emitting element 340 A are substantially the same as those of FIG. 1C , and thus repeated description thereof will be omitted.

A plurality of insulating layers may be formed between the transmissive TA of the first substrate 310 A and the second substrate 315 A, and the plurality of insulating layers may include at least two among the buffer layer, the gate insulating layer, the interlayer insulating layer, the overcoating layer, and a passivation layer. Referring to FIG. 3A , the plurality of insulating layers include the buffer layer 331 A and the overcoating layer 334 A.

The buffer layer 331 A and the overcoating layer 334 A included in the plurality of insulating layers may have substantially the same refractive indexes. Specifically, when the first substrate 310 A includes glass, a refractive index of the first substrate 310 A is 1.5. When the buffer layer 331 A includes a silicon oxide film, a refractive index of the buffer layer 331 A is 1.45. When the overcoating layer 334 A may be formed of PAC, a refractive index of the overcoating layer 334 A is 1.5. Therefore, since the refractive indexes of the buffer layer 331 A and the overcoating layer 334 A substantially coincide with the first substrate 310 A, distortion such as total reflection of light in the interfaces between the first substrate 310 A and the overcoating layer 334 A and between the buffer layer 331 A and the overcoating layer 334 A may be minimized in the transmission area TA of the transparent organic light emitting display device 300 A.

FIG. 3B is a cross-sectional view illustrating a transparent organic light emitting display device according to another embodiment of the inventive concept. Elements illustrated in FIGS. 3A and 3B are substantially the same when numbers are the same in the reference numeral other than alphabet, and thus repeated description thereof will be omitted.

A plurality of insulating layers may be formed between the transmissive TA of the first substrate 310 B and the second substrate 315 B, and the plurality of insulating layers may include at least two among a buffer layer, a gate insulating layer, an interlayer insulating layer, an overcoating layer, and a passivation layer. Referring to FIG. 3B , the plurality of insulating layers include an interlayer insulating layer 333 B and the overcoating layer 334 B.

The interlayer insulating layer 333 B and the overcoating layer 334 B included in the plurality of insulating layers may have the refractive indexes which substantially coincide with the first substrate 310 B. Specifically, when the first substrate 310 B includes glass, a refractive index of the first substrate 310 B is 1.5. When the interlayer insulating layer 333 B includes a silicon oxide film, a refractive index of the interlayer insulating layer 333 B is 1.45. When the overcoating layer 334 A may be formed of PAC, a refractive index of the overcoating layer 334 A is 1.5. Therefore, since the refractive indexes of the interlayer insulating layer 333 B and the overcoating layer 334 A substantially coincide with that of the first substrate 310 B, distortion such as total reflection of light in the interfaces between the first substrate 310 B and the overcoating layer 134 B and between the interlayer insulating layer 333 B and the overcoating layer 331 B may be minimized in the transmission area TA of the transparent organic light emitting display device 300 B.

FIG. 3C is a cross-sectional view illustrating a transparent organic light emitting display device according to another embodiment of the inventive concept. Elements illustrated in FIGS. 3A, 3B, and 3C are substantially the same when numbers are the same in the reference numeral other than alphabet, and thus repeated description thereof will be omitted.

A plurality of insulating layers may be formed between the transmissive TA of the first substrate 310 C and the second substrate 315 C, and the plurality of insulating layers may include at least two among a buffer layer, a gate insulating layer, an interlayer insulating layer, an overcoating layer, and a passivation layer. Referring to FIG. 3C , the plurality of insulating layers include, a buffer layer 331 C, an interlayer insulating layer 333 C and an overcoating layer 334 C.

The buffer layer 331 C, the interlayer insulating layer 333 C, and the overcoating layer 334 C included in the plurality of insulating layers may have the refractive indexes which substantially coincide with that of the first substrate 310 C. Specifically, when the first substrate 310 C includes glass, a refractive index of the first substrate 310 C is 1.5. When the buffer layer 331 C includes a silicon oxide film, a refractive index of the buffer layer 331 C is 1.45. When the interlayer insulating layer 333 C includes a silicon oxide film, a refractive index of the interlayer insulating layer 333 C is 1.45. When the overcoating layer 334 C may be formed of PAC, a refractive index of the overcoating layer 334 C is 1.5. Therefore, since the refractive indexes of the buffer layer 331 C, the interlayer insulating layer 333 C and the overcoating layer 334 C substantially coincide with that of the first substrate 310 C, distortion such as total reflection of light in the interfaces among the first substrate 310 C, the buffer layer 331 , the interlayer insulating layer 333 C, and the overcoating layer 334 C may be minimized in the transmission area TA of the transparent organic light emitting display device 300 C.

FIG. 4 is a flowchart illustrating a method for manufacturing a transparent organic light emitting display device according to an embodiment of the inventive concept. FIGS. 5A to 5D are cross-sectional views illustrating respective parts of an exemplary embodiment of transparent organic light emitting display device during each step of exemplary method for manufacturing the exemplary transparent light emitting display device.

First, a supporting substrate including a sub pixel region having a first region and a second region is provided (S 40 ), and a thin film transistor including a first insulating layer is formed (S 41 ). The preparing of the supporting substrate and the forming of the thin film transistor including the first insulating layer will be described in detail with reference to FIGS. 5A and 5B .

Referring to FIG. 5A , a supporting substrate 510 having a first area EA as an emissive area EA and a second area TA as a transmissive area TA is provided as the supporting substrate 510 , and a material 538 for a buffer layer is formed on the first substrate 510 . The material 538 for a buffer layer may be formed both in the first area EA and in the second area TA. After the material 538 for a buffer layer, an active layer 521 , a gate insulating layer 532 , and a gate electrode 522 are sequentially formed in the first area EA, and then a material 539 for an interlayer insulating layer is formed on the gate electrode 522 .

Referring to FIG. 5B , the material 538 for a buffer layer and the material 539 for an interlayer insulating layer formed in the second area TA are patterned to remove the material 538 for a buffer layer and the material 539 for an interlayer insulating layer formed in the second area TA, and to form an insulating layer including a buffer layer 531 and an interlayer insulating layer 533 formed in the first area EA. A first insulating layer included in the thin film transistor may be the buffer layer 531 and the interlayer insulating layer 533 . The removing of the material 538 for a buffer layer and the material 539 for an interlayer insulating layer formed in the second area TA may include dry etching the material 538 for a buffer layer and the material 539 for an interlayer insulating layer formed in the second area TA. The removing of the material 538 for a buffer layer and the material 539 for an interlayer insulating layer formed in the second area TA may include forming an opening in the material 538 for a buffer layer and the material 539 for an interlayer insulating layer formed in the second area TA. After the material 538 for a buffer layer and the material 539 for an interlayer insulating layer formed in the second area TA are removed, a source electrode 523 and a drain electrode 524 electrically connected to an active layer 521 may be formed. The supporting substrate 510 , a thin film transistor, the buffer layer 531 , and the interlayer insulating layer 533 are substantially the same as those in FIG. 1C , and thus repeated description thereof may be omitted.

Subsequently, a second insulating layer is formed on the first area and the second area (S 42 ). The forming of the second insulating layer will be described in detail with reference to FIG. 5C .

Referring to FIG. 5C , an overcoating layer 534 as the second insulating layer is formed on an entire surface of the supporting substrate 510 including the source electrode 523 and the drain electrode 524 . The forming of the overcoating layer 534 may include forming the overcoating layer 534 on the insulating layer in the first area EA, and forming the overcoating layer 534 to be in contact with the supporting substrate 510 in the second area TA. Herein, the forming of the overcoating layer 534 in the second area TA includes forming the overcoating layer 534 to fill the opening formed in the material 538 for a buffer layer and the material 539 . The overcoating layer 534 is substantially the same as that illustrated in FIG. 1C , and thus repeated description thereof may be omitted.

Subsequently, an organic light-emitting element is formed on the overcoating layer (S 43 ). The forming of the organic light-emitting element will be described in detail with reference to FIG. 5D .

Referring to FIG. 5D , the forming of the organic light emitting element 540 includes forming a contact hole connecting an anode 541 and the source electrode 523 in the overcoating layer 534 , and sequentially forming the anode 541 including a reflection layer 542 and a transparent conductive layer 543 , an organic light emitting layer 544 , and a cathode 545 on the overcoating layer 534 of the first area EA. The organic light emitting element 540 is substantially the same as that illustrated in FIG. 1C , and thus repeated description thereof may be omitted.

Subsequently, a second substrate 515 is formed to face the first substrate 510 , and a color filter 570 is formed on a region of the second substrate 515 corresponding to the first area EA.

While the present disclosure has been particularly shown and described with respect to preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in forms and details may be made without departing from the spirit and scope of the present disclosure. It is therefore intended that the present disclosure not be limited to the exact forms and details described and illustrated, but fall within the scope of the appended claims.