Flexible CdTe Prototype Modules
Xunlight 26 is currently scaling up the fabrication of flexible, thin-film cadmium telluride solar cells from the research lab scale of square centimeters to a proof of commercial viability with a scale of several square feet. The photo illustrates a polyimide sheet coated with all the semiconductor layers needed for a solar module. (Transparent conducting oxide / cadmium sulfide / cadmium telluride (TCO/CdS/CdTe)). These layers were deposited by magnetron sputtering in a large-area sputtering system.
Figure: 1' x 3' deposition of PV structure on polyimide
Xunlight 26 has a second large-area sputter deposition system for back-contact metallization used to complete the fabrication of cells and modules from large sheets.
The square-foot or larger sheets are fabricated into monolithically integrated submodules using laser scribing. The cell integration into a high voltage module is sketched in Figure 2. The monolithically interconnected module voltage is the sum of the voltages of individual cells and the current is the same as the individual cells.
Figure: Monolithic interconnect schematic
Xunlight 26 Solarís scale up of deposition size, its demonstration of monolithic interconnection, and other aspects of module fabrication are being supported with seed funding from investors and grants from the Advanced Energy Program and the Research Commercialization Program of the Ohio Department of Developmentís Third Frontier Program.
Transparent Thin-film CdTe Modules
Xunlight 26 Solar and UT have recently demonstrated that magnetron sputtering is particularly well suited for the deposition of ultra-thin absorber layers of CdTe that are thin enough to be intrinsically transparent.
Development of semitransparent CdTe modules suitable for tinted windows is a second thrust area of X26. X26 and UT have collaborated to fabricate a solar cell with 10% efficiency using 500 nm of CdTe. In addition, X26 and UT have developed solar cells that transmit 3-5% of the incident light and have an aperture-area module efficiency of about 9%. This breakthrough opens up very large potential for development of power-producing PV windows and skylights that are truly building-integrated and uniformly transparent without the need to do selective removal of areas of an opaque coating in order to achieve some degree of light transmission.
An example of this semitransparent PV is given in the figure.
Figure: Image showing semitransparent PV structure