Cadmium Telluride Solar Cells on Ultrathin Glass for Space Applications

This paper details the preliminary findings of a study to achieve a durable thin-film CdTe photovoltaic (PV) device structure on ultrathin space-qualified cover glass. An aluminum-doped zinc oxide (AZO) transparent conducting oxide was deposited directly onto the cover glass using metalorganic chemical vapor deposition (MOCVD). The AZO demonstrated low sheet resistance of 10 Ω/□ and high optical transparency of 85% as well as excellent adherence and environmental stability. Preliminary deposition of PV layers onto the AZO on cover glass, by MOCVD, showed the possibility of such a structure, yielding a device conversion efficiency of 7.2%. High series resistance (10 Ω cm2) and low Voc (586 mV) were identified as the limiting factors when compared with the authors’ platform process on indium tin oxide-coated aluminosilicate. The coverage of the Cd1−xZnxS window layer along with the front contacting of the device were shown to be the major causes of the low efficiency. Further deposition of AZO/CdTe employing an oxygen plasma cleaning step to the cover glass and evaporated gold front contacts significantly improved the device performance. With a highest conversion efficiency of 10.2%, series resistance improved to 4.4 Ω cm2, open-circuit voltage (Voc) up to 667 mV, and good adhesion, this represents the first demonstration of direct deposition of CdTe solar cells onto 100-μm-thick space-qualified cover glass.