Process development of CdTe solar cells grown at high temperatures on engineered glass

NREL and Corning Incorporated have collaborated on a project to investigate the effect of increasing CdTe deposition temperature on device performance. CdTe deposition temperatures are generally limited by the thermal properties of the glass superstrate. Soda-lime glass is frequently used in commercial production of CdTe, but the low strain point (~515°C) requires deposition temperatures of 550°C or below. While the CdTe industry has enjoyed great success with material grown at these relatively low temperatures, there may be significant benefits to higher deposition temperatures enabled by a high strain point glass. To demonstrate the efficiency benefits of a CdTe cell fabricated at higher deposition temperatures, it is necessary to re-optimize the device fabrication process steps for devices made with CdTe films at each deposition temperature. Using Corning, Inc.'s new engineered high-strain-point glass superstrate, we developed a fabrication process optimized for CdTe films deposited at 550° and 600°C. Here, we report details of the fabrication processes that resulted in an absolute efficiency gain of 1.2% for devices fabricated with 600°C CdTe deposition temperature versus 550°C.