The influence of processing conditions on the performance of polycrystalline thin-film CdTe-based solar cells and the relationship to device stability are addressed. Specifically, processing conditions with respect to the window layer, post-CdTe deposition treatments, and contacting treatments are examined. The use of high resistivity interlayers between the transparent conductive oxide and the CdS allows open circuit voltage to be maintained as the CdS thickness is reduced. CdS-CdTe interdiffusion is reduced by either use of a short 600&hthinsp;°C anneal prior toCdCl2vapor treatment or by use ofCdTe1−xSxalloy absorber layers. Finally, the effects ofCdTe1−xSxsurface modification and Cu reaction on device current-voltage behavior are presented. ©1999 American Institute of Physics.