Manufacturing costs for thin film cadmium telluride-based (CdTe) photovoltaic (PV) modules are currently below $1 per watt, which is less than 50% the cost of crystalline silicon PV. Consequently, CdTe-based PV systems have reached grid parity in many locations. However, in order for this cost-effective PV technology to become a significant producer of electricity for the future, the solar energy conversion efficiency of the device must be advanced beyond the current level of 16%. Furthermore, material utilization must be improved in order to reduce tellurium loading, which is a limited resource. This research will focus on improving the fundamental understanding of polycrystalline CdTe thin films as the basis to improve the efficiency of CdTe solar cells.
Historically, CdTe thin film solar cells have been fabricated using empirical optimization of simple deposition technologies and heat treatments. A key device characteristic, the doping level in the absorber material, has never been intentionally controlled or tuned. Doping levels in CdTe solar cells are the result of several impurities introduced at various processing steps during the solar cell fabrication process. This research will focus on the deposition of polycrystalline CdTe films by an atmospheric pressure vapor transport process that allows for control of the deposition conditions. This process will controllably dope the thin films, and therefore provides a means to determine the p-type doping levels required to advance the PV efficiency towards the practical limit of 20%.
The proposed research is innovative because it will use a vapor elemental deposition technique to control the doping and defect formation process. The research is potentially transformative because it identifies the fundamental breakthroughs needed to make CdTe solar cells with efficiency superior to silicon PV but with lower cost.
Broader Impact
Improving the efficiencies of CdTe solar cells will lead to lower manufacturing costs and allow cleanly-generated power to penetrate electricity markets around the world, including many poor and underdeveloped nations.
The proposed education activities will train students at both the undergraduate and graduate levels in the fast growing field of photovoltaics, which currently has a significant shortage of engineers. Existing REU programs will be used to drive the education and outreach activities. Specifically, all REU students, in addition to their research activities, will also serve as Ambassadors for Solar PV, where they will conduct an annual Solar Energy Workshop which hosts local elementary school students for a half day and gets them involved in hands-on solar energy activities. The REU students will also assist with the development of a series of modules that will be used in the Electronic Materials and Semiconductor Device courses. These modules will serve as the lab component for these courses, and are intended to expose all undergraduate students in electrical engineering at University of South Florida to photovoltaics concepts. Research on II-VI compound semiconductor PV devices will be integrated into required courses of the electrical engineering curriculum that will reach 150 students per year.
