Multi-reflection structure and photo-electric device

This application claims the priority benefit of Taiwan application serial no. 100122891, filed on Jun. 29, 2011. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification.

1. Field of the Application

The present application relates to a multi-reflection structure and a photo-electric device. More particularly, the present application relates to a multi-reflection structure that reduces surface reflection and a photo-electric device having the same.

2. Description of Related Art

Recently, photo-electric industries (display industry, solid-state illumination device industry, solar cell industry, and so on) grow rapidly and continuously change living habits of human beings. However, during research and development of the aforesaid photo-electric industries, surface reflection issue resulted from difference of refractive indices is inevitable. In displays, overall brightness thereof is reduced by surface reflection. In solid-state illumination devices (e.g. light-emitting diodes or organic electro-luminescent devices), illumination performance thereof is reduced by surface reflection. According to some researches, in organic electro-luminescent devices, about 70% to 80% optical loss is resulted from surface reflection.

Similarly, in the solar cells, photoelectric conversion efficiency thereof is reduced by surface reflection also. Specifically, solar cells are kinds of photo-electric devices that convert light into electric power. The photoelectric conversion efficiency of solar cells is related to photo current and voltage generated therefrom. In order to increase photo current of solar cells, light absorption of solar cells is required to be increased. Since the conventional mono-crystalline silicon solar cells have sufficient thickness, light absorption of mono-crystalline silicon solar cells is not a problem. Accordingly, it is imperative to reduce optical loss resulted from surface reflection of mono-crystalline silicon solar cells.

According to the Fresnel's Law, when light propagates through an interface of two mediums having different refractive indices, reflectivity of the propagated light is proportional to difference of refractive indices. Specifically, the smaller the difference of the refractive indices of the two mediums is, the lower the reflectivity of the propagated light can be obtained. On the contrary, the greater the difference of the refractive indices of the two mediums is, the higher the reflectivity of the propagated light can be obtained. Take silicon substrates that are often used in semiconductor devices as an example, refractive index thereof is about 3 to 4. When light propagates the interface of air and the silicon substrate having a flat surface, reflectivity of the propagated light is considerably high (e.g. reflectivity is about 36%).

In the conventional solar cells, a hydrogen containing amorphous silicon nitride serving as an anti-reflection coating is suggested to be formed on the solar cells to reduce surface reflection issue and enhance photoelectric conversion efficiency of solar cells. However, the anti-reflection coating cannot significantly enhance photoelectric conversion efficiency of solar cells. According, some prior arts (e.g. U.S. Pat. No. 5,081,049, U.S. Pat. No. 5,080,725, US 2009/071536, TWM 354858, U.S. Pat. No. 7,368,655) have proposed. In the aforesaid prior arts, Optical micro-structures are suggested to be formed on a light-incident surface of solar cells, such that light incident from the light-incident surface of solar cells can be reflected twice and optical loss resulted from surface reflection can be reduced. However, in the aforesaid prior arts (e.g. U.S. Pat. No. 5,081,049, U.S. Pat. No. 5,080,725, US 2009/071536, TWM 354858, U.S. Pat. No. 7,368,655), since almost light is reflected by the optical micro-structures twice, optical loss resulted from surface reflection cannot be reduced significantly.

As such, it is imperative to further reduce optical loss resulted from surface reflection.

The present application provides a multi-reflection structure and a photo-electric device having favorable optical performance.

The present application provides a multi-reflection structure comprising a substrate and a pyramid. The substrate comprises an inversed pyramid shaped recess having at least three first reflection sidewalls. The pyramid is disposed on the substrate and is located in the inversed pyramid shaped recess. The pyramid has at least three second reflection sidewalls, wherein a normal of each of the second reflection sidewalls and a normal of each of the first reflection sidewalls are not located in the same plane.

The present application provides a multi-reflection structure comprising a substrate at least one first pyramid and at least one second pyramid. The first pyramid is disposed on the substrate and has at least three first reflection sidewalls. The second pyramid is disposed on the substrate and has at least three second reflection sidewalls, wherein a normal of each of the second reflection sidewalls and a normal of each of the first reflection sidewalls are not located in the same plane.

The present application provides a photo-electric device comprising a photoelectric conversion layer and a plurality of electrodes. The photoelectric conversion layer comprises a plurality of inversed pyramid shaped recesses and a plurality of a pyramids, wherein each of the inversed pyramid shaped recesses has at least three first reflection sidewalls, each of the pyramids is located in one of the inversed pyramid shaped recesses respectively, each of the pyramids has at least three second reflection sidewalls, and a normal of each of the second reflection sidewalls and a normal of each of the first reflection sidewalls are not located in the same plane. Furthermore, the electrodes are electrically connected to the photoelectric conversion layer.

In order to the make the aforementioned and other objects, features and advantages of the present application comprehensible, several embodiments accompanied with figures are described in detail below.

The accompanying drawings constituting a part of this specification are incorporated herein to provide a further understanding of the invention. Here, the drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

FIG. 1A is a perspective view of a multiple-reflection structure according to the first embodiment of the present application.

FIG. 1B is a top view of the multiple-reflection structure according to the first embodiment of the present application.

FIG. 1C is a cross-sectional view of a multiple-reflection structure according to the first embodiment of the present application.

FIG. 2A through FIG. 2E are top views and cross-sectional views of different multiple-reflection structures according to the first embodiment of the present application.

FIG. 3A and FIG. 3B are schematic views of a multiple-reflection structure according to the second embodiment of the present application.

FIG. 4 is a schematic view of a photo-electric device according to the third embodiment of the present invention.

FIG. 5 is a SEM view of the multiple-reflection structure as depicted in FIG. 1A .

FIG. 6 is a simulation result regarding to reflectivity of the multiple-reflection structure according to the first embodiment of the present application.

First Embodiment

FIG. 1A is a perspective view of a multiple-reflection structure according to the first embodiment of the present application. FIG. 1B is a top view of the multiple-reflection structure according to the first embodiment of the present application. FIG. 1C is a cross-sectional view of a multiple-reflection structure according to the first embodiment of the present application. Referring to FIG. 1A through FIG. 1 C, the multi-reflection structure 100 of the present embodiment includes a substrate 110 and at least one pyramid 120 . The substrate 110 includes an inversed pyramid shaped recess 112 having at least three first reflection sidewalls 112 a . The pyramid 120 is disposed on the substrate 110 and is located in the inversed pyramid shaped recess 112 . The pyramid 120 has at least three second reflection sidewalls 120 a , wherein a normal NL 2 of each of the second reflection sidewalls 120 a and a normal NL 1 of each of the first reflection sidewalls 112 a are not located in the same plane. In this embodiment, the quantity of the inversed pyramid shaped recess 112 may be plural, the quantity of the pyramid 120 may be plural, and the quantity of the inversed pyramid shaped recess 112 is the same as the quantity of the pyramid 120 . For example, the plurality of inversed pyramid shaped recesses 112 are arranged in array on a light-incident surface 110 a of the substrate 110 .

In this embodiment, the substrate 110 is, for example, a silicon substrate, a plastic substrate, a glass substrate, a quartz substrate or a metal substrate. The substrate 110 and the pyramid 120 are of the same material. Take the silicon substrate as an example, the inversed pyramid shaped recess 112 and the pyramid 120 are formed by an anisotropic etching process. The etchant used in the anisotropic etching process is, for example, a water solution of KOH or a water solution of tetra methyl ammonium hydroxide (TMAH). The composition of etchant, the concentration of etchant and the process time of the anisotropic etching process can be properly modified by one ordinary skilled in the art. Accordingly, the composition of etchant, the concentration of etchant and the process time of the anisotropic etching process are not limited in the present application. Further, the inversed pyramid shaped recess 112 and the pyramid 120 on the silicon substrate can also be fabricated by thermo-compression or UV curing. Take the plastic substrate as an example, the inversed pyramid shaped recess 112 and the pyramid 120 thereon can be fabricated by molding process or stamping process. Take the glass, quartz or metal substrate as an example, the inversed pyramid shaped recess 112 and the pyramid 120 thereon can be fabricated by etching process or stamping process.

As shown in FIG. 1A through FIG. 1C , the quantity of the first reflection sidewalls 112 a is 4, the quantity of the second reflection sidewalls 120 a is 8, wherein each of the first reflection sidewalls 112 a is a flat surface, and each of the second reflection sidewalls 120 a is a flat surface. It is noted that the quantity of the first reflection sidewalls 112 a and the quantity of the second reflection sidewalls 120 a are not limited in the application. In other words, the quantity of the first reflection sidewalls 112 a is N 1 (N 1 is an integral greater than or equal to 3), and the quantity of the second reflection sidewalls 120 a is N 2 (N 2 is an integral greater than or equal to 3). The relationship of N 1 and N 2 is not limited in this embodiment. Base on actual requirements, N 1 may be smaller than N 2 . In another embodiment of the present application, N 1 may be equal to or greater than N 2 .

In this embodiment, each one of the four first reflection sidewalls 112 a has substantially the same area, and each one of the eight second reflection sidewalls 120 a has substantially the same area. In other words, the pyramid 120 has regular polygonal bottom surface. It is noted that the area of each first reflection sidewalls 112 a does not required to be the same as the area of each second reflection sidewalls 120 a.

For example, when the quantity of the first reflection sidewalls 112 a is 4, the quantity of the second reflection sidewalls 120 a may be 4, 6, 8, 16 or 32, as shown in FIG. 2A through FIG. 2E . When the quantity of the first reflection sidewalls 112 a and the quantity of the second reflection sidewalls 120 a are the same (i.e. N 1 =N 2 ), adjoining lines L 1 between any two adjacent first reflection sidewalls 112 a are not aligned with the crest lines L 2 between any two adjacent second reflection sidewalls 120 a , as shown in FIG. 2A . When N 1 <N 2 and N 2 is not an integral multiple of N 2 , each of the adjoining lines L 1 is not aligned with any one of the crest lines L 2 , as shown in FIG. 2B . When N 1 <N 2 and N 2 is an integral multiple of N 2 , parts of the adjoining lines L 1 are aligned with the crest lines L 2 , and the rest of the adjoining lines L 1 are not aligned with the crest lines L 2 , as shown in FIG. 2C through FIG. 2E .

In this embodiment, with respect to the light-incident surface 110 a , each of the first reflection sidewalls 112 a has an inclined angle θ 1 , and 45°<θ 1 ≦90°. For example, the aforesaid inclined angle θ 1 is about 54.7°. In addition, with respect to the light-incident surface 110 a , each of the second reflection sidewalls 120 a has an inclined angle θ 1 , and 45°<θ 2 ≦90°. For example, the aforesaid inclined angle θ 2 is about 71.4°. It is noted that the inclined angle θ 1 is not required to be identical with the inclined angle θ 2 . One ordinary skilled in the art may modify the inclined angle θ 1 and the inclined angle θ 2 according to the incident angle of light.

Please refer to FIG. 1C , the height H of the pyramid 120 this embodiment may be smaller than or substantially equal to the depth D of the inversed pyramid shaped recess 112 . For example, the height H of the pyramid 120 ranges from 0.05 micrometer to 500 micrometers, and the depth D of the inversed pyramid shaped recess 112 ranges from 0.05 micrometer to 500 micrometers. Further, the maximum width W of the inversed pyramid shaped recess 112 ranges from 0.1 micrometer to 1000 micrometers.

When the quantity of the first reflection sidewalls 112 a is 4, the quantity of the second reflection sidewalls 120 a is 8, the inclined angle θ 1 is about 54.7°, and the inclined angle θ 2 is about 71.4°, approximately 44% of light is twice reflected, approximately 47% of light is reflected three times, and approximately 9% of light is reflected four times. Accordingly, an overall reflectivity of the multi-reflection structure 100 of this embodiment can be reduced to about 5%. Compared with reflectivity (about 10%) of the prior art (U.S. Pat. No. 7,368,655), the multi-reflection structure 100 of this embodiment can effectively lower surface reflection issue.

Second Embodiment

FIG. 3A and FIG. 3B are schematic views of a multiple-reflection structure according to the second embodiment of the present application. Referring to FIG. 3A through FIG. 3B , the multi-reflection structure 200 of this embodiment includes a substrate 210 , at least one first pyramid 220 and at least one second pyramid 230 . The first pyramid 220 is disposed on the substrate 210 and has at least three first reflection sidewalls 222 . The second pyramid 230 is disposed on the substrate 210 and has at least three second reflection sidewalls 232 , wherein a normal NL 2 of each of the second reflection sidewalls 323 and a normal NL 1 of each of the first reflection sidewalls 222 are not located in the same plane.

In this embodiment, the substrate 210 is, for example, a silicon substrate, a plastic substrate, a glass substrate, a quartz substrate or a metal substrate. The substrate 210 , the first pyramid 220 and the second pyramid 230 are of the same material. Take the silicon substrate as an example, the first pyramid 220 and the second pyramid 230 are formed by an anisotropic etching process. The etchant used in the anisotropic etching process is, for example, a water solution of KOH or a water solution of tetra methyl ammonium hydroxide (TMAH). The composition of etchant, the concentration of etchant and the process time of the anisotropic etching process can be properly modified by one ordinary skilled in the art. Accordingly, the composition of etchant, the concentration of etchant and the process time of the anisotropic etching process are not limited in the present application. Further, the first pyramid 220 and the second pyramid 230 on the silicon substrate can also be fabricated by thermo-compression or UV curing. Take the plastic substrate as an example, the first pyramid 220 and the second pyramid 230 thereon can be fabricated by molding process or stamping process. Take the glass, quartz or metal substrate as an example, the first pyramid 220 and the second pyramid 230 thereon can be fabricated by etching process or stamping process.

As shown in FIG. 3A , the quantity of the first reflection sidewalls 222 is 4, the quantity of the second reflection sidewalls 232 is 4, wherein each border of the bottom surface the first pyramid 220 is not parallel with any one border of the bottom surface the second pyramid 230 . In addition, each of the first reflection sidewalls 222 is a flat surface, and each of the second reflection sidewalls 232 is a flat surface.

As shown in FIG. 3B , the quantity of the first reflection sidewalls 222 is 4, the quantity of the second reflection sidewalls 232 is 3, wherein each of the first reflection sidewalls 222 is a flat surface, and each of the second reflection sidewalls 232 is a flat surface. It is noted that the quantity of the first reflection sidewalls 222 and the quantity of the second reflection sidewalls 232 are not limited in the application. In other words, the quantity of the first reflection sidewalls 222 is N 1 (N 1 is an integral greater than or equal to 3), and the quantity of the second reflection sidewalls 232 is N 2 (N 2 is an integral greater than or equal to 3). The relationship of N 1 and N 2 is not limited in this embodiment. Base on actual requirements, N 1 may be smaller than, equal to or greater than N 2 .

In this embodiment, each one of the four first reflection sidewalls 222 has substantially the same area, and each one of the second reflection sidewalls 232 has substantially the same area. In other words, the first pyramid 220 has regular polygonal bottom surface, and the second pyramid 230 has regular polygonal bottom surface. It is noted that the area of each first reflection sidewalls 222 does not required to be the same as the area of each second reflection sidewalls 232 .

In this embodiment, with respect to the substrate 210 , each of the first reflection sidewalls 222 has an inclined angle θ 1 , and 45°<θ 1 ≦90°. For example, the aforesaid inclined angle θ 1 is about 54.7°. In addition, with respect to the substrate 210 , each of the second reflection sidewalls 232 has an inclined angle θ 1 , and 45°<θ 2 ≦90°. For example, the aforesaid inclined angle θ 2 is about 54.7°. It is noted that the inclined angle θ 1 is not required to be identical with the inclined angle θ 2 . One ordinary skilled in the art may modify the inclined angle θ 1 and the inclined angle θ 2 according to the incident angle of light.

In the present embodiment, the height H 1 of the first pyramid 220 may be substantially equal to height H 2 of the second pyramid 230 . For example, the height H 1 of the first pyramid 220 ranges from 0.05 micrometer to 500 micrometers, and the height H 2 of the second pyramid 230 ranges from 0.05 micrometer to 500 micrometers.

The Third Embodiment

FIG. 4 is a schematic view of a photo-electric device according to the third embodiment of the present invention. Referring to FIG. 4 , the photo-electric device 300 of this embodiment includes a photoelectric conversion layer 310 and a plurality of electrodes 320 a , 320 b . The photoelectric conversion layer 310 includes a plurality of inversed pyramid shaped recesses 312 and a plurality of a pyramids 314 , wherein each of the inversed pyramid shaped recesses 312 has at least three first reflection sidewalls 312 a , each of the pyramids 314 is located in one of the inversed pyramid shaped recesses 312 respectively, each of the pyramids 314 has at least three second reflection sidewalls 314 a , and a normal NL 2 of each of the second reflection sidewalls 314 a and a normal NL 1 of each of the first reflection sidewalls 312 a are not located in the same plane. Furthermore, the electrodes 320 a and 320 b are electrically connected to the photoelectric conversion layer 310 .

Since the inversed pyramid shaped recesses 312 and the pyramids 314 of this embodiment are the same as the inversed pyramid shaped recesses 112 and the pyramids 120 , description regarding to the inversed pyramid shaped recesses 312 and the pyramids 314 is omitted.

For example, the material of the photoelectric conversion layer 310 is mono-crystalline silicon, poly-crystalline silicon, amorphous silicon, CdTe, CIS, CIGS, Ge, AlInGaAs or active materials of the polymer solar cell.

In this embodiment, the photoelectric conversion layer 310 includes a p-type doped silicon substrate 310 a , a n-type lightly doped region 310 b , a plurality of n-type heavily doped region 310 c electrically connected to the electrode 320 a , and a plurality of p-type heavily doped region 310 c electrically connected to the electrode 320 b . The photoelectric conversion layer 310 is capable of converting light into electric power. In other words, the photo-electric device 300 of this embodiment is a solar cell. Though the photoelectric conversion layer 310 shown in FIG. 4 is illustrated here, the photoelectric conversion layer 310 can be modified by one ordinary skilled in the art. In other words, different types of photoelectric conversion layers can be used in the present application.

As shown in FIG. 4 , the photo-electric device 300 of this embodiment may further include an anti-reflection coating 330 that covers the inversed pyramid shaped recesses 312 and the pyramids 314 . For example, the material of the anti-reflection coating 330 is silicon nitride (SiNx), silicon oxide (SiO 2 ), ZnS, TiO 2 , ZnO, SnO 2 , MgF 2 , CaF 2 , Al 2 O 3 , LiF, NaF, mesoporous silicon, mesoporous silica. Of course, the anti-reflection coating 330 may be formed by stacking the above-mentioned materials.

Experimental Example

FIG. 5 is a SEM view of the multiple-reflection structure as depicted in FIG. 1A . Referring to FIG. 5 and FIG. 1A , in this embodiment, the inversed pyramid shaped recess 112 has four first reflection sidewalls 112 a , the pyramid 120 has eight second reflection sidewalls 120 a , the inclined angle θ 1 is about 54.7° (as shown in FIG. 1C ), and the inclined angle θ 2 is about 71.4° (as shown in FIG. 1C ).

Referring to FIG. 6 , curve A represents simulated reflectivity of a substrate having a flat surface, curve B represents simulated reflectivity of a substrate having inversed pyramid shaped recesses, and curve C represents simulated reflectivity of a substrate having inversed pyramid shaped recesses and pyramids. As shown in FIG. 6 , the simulated reflectivity of the first embodiment (curve C) is lower than the other two (curves A and B). Accordingly, surface reflection can be reduced by this application.

This application can be applied to displays, solid-state illumination devices, solar cells, optical films, and so on. Accordingly, surface reflection can be reduced and photoelectric conversion efficiency of the photo-electric devices.

Although the present invention has been disclosed above by the embodiments, they are not intended to limit the present invention. Anybody skilled in the art can make some modifications and alteration without departing from the spirit and scope of the present invention. Therefore, the protecting range of the present invention falls in the appended claims.