Cadmium Zinc Telluride Films for Wide Band Gap Solar Cells

摘要

The CdTe-ZnTe alloy system is evaluated for application in high efficiency polycrystalline thin-film multijunction solar cells. Single phase Cd{sub}(1-x)Zn{sub}xTe alloy films 3-4 mm thick, with x from 0 to 1 and band gap from 1.5 to 2.25 eV, were deposited by co-evaporation from binary CdTe and ZnTe sources. Film composition, x in Cd{sub}(1-x)Zn{sub}xTe varied linearly with source effusion rate ratio. Lattice parameter varied linearly with composition, while optical band gap exhibited a bowing parameter, b = 0.3. Sub-band gap transmission, T/(1-R), is ～80%. Post-deposition treatment in argon at 400°C to 600°C does not measurably alter the alloy composition. Treatment in CdCl{sub}2:O{sub}2:Ar vapor at 400°C preferentially removes Zn from the Cd{sub}(1-x)Zn{sub}xTe alloy. Treatment in ZnCl{sub}2:O{sub}2:Ar vapor at ～400°C results in slight compositional change due to formation of ZnO and Te at the surface. The photovoltaic operation of Cd{sub}(1-x)Zn{sub}xTe/CdS devices is presented.