SBIR Phase I: High Quality, Low Cost, Polycrystalline CdS/CdTe Photovoltaic Cells.

This Small Business Innovation Research (SBIR) Phase 1 will develop new processes for producing lower cost and higher quality thin films from the compound semiconductors CdS and CdTe. These will be used to more inexpensively produce high performance photovoltaic modules that generate electricity from sunlight. Thin film CdTe-based photovoltaics currently require a post-deposition CdCl2 treatment and anneal to achieve reasonable performance. This anneal is known to increase the grain size in some films and increase the minority carrier lifetime in all CdTe films. The minority carrier lifetime is generally correlated with device efficiency in photovoltaic cells. However, the CdCl2 anneal cannot be optimized to maximize the minority carrier lifetime because attempts to do so have caused film delamination. Film delamination occurs due to strain induced during the anneal at the interface between the film and the glass substrate. This proposal seeks to develop a film deposition process that simultaneously avoids this problem and makes better quality films. This process will foster large grain growth, defect passivation, and grain boundary passivation while eliminating the need for a post-deposition CdCl2 treatment and anneal. This will result in higher efficiency solar cells and a streamlined production process. Commercially, solar photovoltaic modules are a silent, pollution free means to generate electricity from sunlight. Once the capital investment is made to install a photovoltaic electricity system, its operating cost is essentially zero because its "fuel", sunlight, is free. Photovoltaic electricity provides a means for homes to generate as much energy as they use over the course of a year. The production of photovoltaic modules has been increasing 20-30% annually for the past decade due to increases in efficiency and reductions in cost. However, for photovoltaics to achieve significant market penetration into mainstream electricity generation, this growth rate must be continued. This requires further increases in module efficiency and reductions in module cost. This research proposal addresses both of these issues. Successful development of this technology will ensure the marketplace success of CdTe photovoltaic modules, and pave the way for widespread stable-priced, sustainable, pollution-free electricity generation.