Electrical contact technique for electrochromic windows

The subject matter disclosed herein relates to dynamic windows, such as smart windows. More particularly, the subject matter disclosed herein relates to a technique for making electrical contact to a dynamic window, such as a dynamic Insulated Glass Unit (IGU) window assembly.

For a conventional dynamic IGU, the transparent conducting layer of an electrochromic pane is semi-hermetically sealed within the IGU and electrical contact must be made between the transparent conducting layer and the exterior of the sealed IGU. Conventional techniques for making the electrical contact involve using a fired, silk screened or soldered bus bar. FIG. 1 depicts a conventional dynamic IGU 100 in which a bus bar 101 runs underneath a seal 102 in order to provide an electrical connection to an Electrochromic (EC) coating layer 103 . Bus bar 101 creates an electrical contact path to a top conducting layer (not indicated) formed on EC coating layer 103 . The electrical path is completed through the stack of the electrochromic device to a bottom conductive layer 104 and then to a second bus bar 105 that is outside seal 102 . Second bus bar 105 is connected back to a voltage source 106 . Bus bar 101 allows an electrical contact to be made to the top of EC coating layer 103 from outside the sealed volume of IGU 100 . EC coating layer 103 is too delicate for seal 102 to be attached directly to EC coating layer 103 so EC coating layer 103 cannot extend underneath and be available for electrical contact.

The breaching of seal 102 by bus bar 101 reduces the reliability of seal 102 . FIG. 2 is a Pareto chart depicting a typical EC Absorptive Window Failure Mode Effects Analysis (FEMA) in a finished IGU product. FIG. 2 shows that failure of the primary seal at the bus bar is one of the highest risk reliability failure modes in a finished IGU product. Accordingly, if the breaching of the seal by the bus bar could be eliminated, one of the highest risk reliability failure modes in a finished IGU product could be eliminated.

The subject matter disclosed herein is illustrated by way of example and not by limitation in the accompanying figures in which like reference numerals indicate similar elements and in which:

FIG. 1 depicts a conventional dynamic IGU in which a bus bar breaches a seal in order to provide an electrical connection to an Electrochromic (EC) coating layer;

FIG. 2 is a Pareto chart depicting a typical EC Absorptive Window Failure Mode Effects Analysis (FEMA) in a finished IGU product; and

FIGS. 3A-3E depict a sequence of a technique for producing a dynamic IGU comprising a bus bar that provides an electrical connection to an Electrochromic (EC) coating layer without breaching the seal of the IGU according to the subject matter disclosed herein.

As used herein, the word “exemplary” means “serving as an example, instance, or illustration.” Any embodiment described herein as “exemplary” is not to be construed as necessarily preferred or advantageous over other embodiments.

The subject matter disclosed eliminates a bus bar from running underneath the seal which, in turn, eliminates one of the highest risk reliability failure modes in a finished IGU product by utilizing a conducting substrate as a contact path for control signals in place of a conventional bus bar. Another benefit of the subject matter disclosed herein is that bus bars can take up shapes on more of the perimeter of the coating inside the volume which enhances performance of the electrical operation of the electrochromic (EC) stack.

FIGS. 3A-3E depict a sequence of a technique for producing a dynamic IGU comprising a bus bar that provides an electrical connection to an Electrochromic (EC) stack without breaching the seal of the IGU according to the subject matter disclosed herein. FIG. 3A depicts a transparent substrate that has been coated in a well-known manner with a transparent conductive material layer 301 . Suitable materials for conductive material layer 301 include, for example, fluorine-doped tin oxide (SnO 2 :F, also abbreviated as FTO), Indium Tin Oxide (ITO), 80-90% indium oxide with a minor amount of ITO, and aluminum doped ZnO (ZnO:Al), sometimes abbreviated as AZO. The transparent substrate has not been indicated for clarity. It should be understood that the transparent substrate could be glass, acrylic or polycarbonate. Transparent conductive material layer 301 is formed into two electrically isolated zones, zones 301 a and 301 b , using a well-known technique, such as laser ablation to scribe an isolation line 302 . Both conductive zones 301 a and 301 b on the substrate will act as a bus bar that passes beneath the primary seal thereby keeping the primary seal intact and eliminating one of the highest risk reliability failure modes in a finished conventional IGU product.

In FIG. 3B , an electrochromic stack is formed in a well-known manner on conductive material layer 301 in zone 301 b so that stack 303 overlaps isolation line 302 . A second transparent conductive material layer 303 is formed in a well-known manner on the electrochromic stack so that the second transparent conductive layer 303 overlaps isolation line 302 . (The electrochromic stack is not shown in FIGS. 3B-3E for clarity, but it should be understood that the electrochromic stack is underneath second transparent conductive layer 303 , as viewed in FIGS. 3B-3E .) Suitable materials for second conductive material layer 303 include, for example, FTO, ITO and AZO. In one exemplary embodiment shown in FIGS. 3B-3E , electrochromic stack comprises a counter electrode (CE) layer formed in a well-known manner on conductive material layer 301 , an ion conductor (IC) layer formed in a well-known manner on the CE layer, and an electrochromic (EC) layer formed on the IC layer. In another exemplary embodiment, electrochromic stack comprises an electrochromic (EC) layer formed in a well-known manner on conductive material layer 301 , an ion conductor (IC) layer formed in a well-known manner on the EC layer, and a counter electrode (CE) layer formed on the IC layer. Both exemplary embodiments of electrochromic stack 303 can be formed from well-known materials that are used for forming electrochromic stacks.

In FIG. 3C , a bus bar 304 is formed in a well-known manner, such as by ultrasonic soldering, so that it overlaps the edge of transparent coating 301 of zone 301 a and to overlap edges of second transparent conductive layer 303 that overlaps zone 301 a . Bus bar 304 is formed so that it will be within the sealed volume of the resulting IGU. Bus bar 304 , when formed, shorts through the electrochromic stack, thereby creating a conductive path between first conductive material layer 301 and second conductive material layer 304 . The short created when bus 304 is formed is in zone 301 a so that the short is isolated from the operational portion of the electrochromic stack in zone 301 b . A terminal contact 305 is formed in a well-known manner on transparent coating 301 in zone 301 a in a place that will be outside of the sealed volume of the resulting IGU. The position, size and shape of terminal contact 305 is selected so that terminal contact 305 does not come into contact with and/or compromise the integrity of the seal (seal 307 in FIG. 3D ) of the IGU. A bus bar 306 is formed in a well-known manner on transparent coating 301 in zone 301 b in a place that will be outside of the sealed volume of the resulting IGU. Suitable materials for bus bars 304 and 306 include, for example, silver frit/fired paste and ultrasonic solder of various types.

In FIG. 3D , a primary seal 307 is formed in a well-known manner on zones 301 a and 301 b so that bus bar 304 is entirely within the sealed volume and bus bar 306 is outside the sealed volume. A suitable material for primary seal 307 is poly-isobutylene. In FIG. 3E , the IGU is finalized by trimming the substrate in a well-known manner. A voltage source 308 is connected to terminal contacts 305 and bus bar 306 to control in a well-known manner the transparency/reflectivity of the dynamic IGU.

While the exemplary embodiments disclosed herein are formed with two electrically isolated zones, it should be understood that more than two electrically isolated zones could be formed for a multi-zone dynamic IGU. Additionally, while the exemplary embodiments disclosed herein are formed so that the two conductive material layers cover substantially the same area as the electrochromic stack, it should be understood that at least one conductive material layer could be formed to cover an area that is substantially different from the area of the electrochromic stack. Further, an alternative exemplary embodiment provides that the electrochromic stack is formed so that it does not overlap the isolation line. For this alternative exemplary embodiment, an additional masking step is required to keep the electrochromic stack from overlapping the isolation line, while the second (or top) transparent conductive layer overlaps the isolation line. Yet another exemplary embodiment provides that the electrochromic stack overlaps one or more selected portions of the isolation line.

Although the foregoing disclosed subject matter has been described in some detail for purposes of clarity of understanding, it will be apparent that certain changes and modifications may be practiced that are within the scope of the appended claims. Accordingly, the present embodiments are to be considered as illustrative and not restrictive, and the subject matter disclosed herein is not to be limited to the details given herein, but may be modified within the scope and equivalents of the appended claims.