Influence of window and absorber layer processing on device operation in superstrate thin film CdTe solar cells

Processing strategies are presented for controlling junction quality as both window and absorber layer thickness are reduced in polycrystalline superstrate CdS/CdTe thin-film solar cells. High resistance In₂O₃ and SnO₂ oxide buffer layers improve coverage of chemical bath deposited CdS and device performance with PVD CdTe, resulting in efficiencies >13.5%. A new method of CdS and Cd_1-xZn_xS chemical bath deposition for high Cd utilization and growth rate and low occurrence of adherent particulates is presented. Alloying the CdS film with ZnS can reduce the window thickness tolerance needed to obtain high photocurrent and good junction properties with no oxide buffer layer. CdS diffusion is reduced by annealing in air at 450°C or in argon at 580°C prior to CdCl₂ treatment and by reducing the CdCl₂ and O₂ partial pressures during treatment. Promising device results are presented for CdTe/CdS cells with 1 micron thick CdTe deposited at T<400°C