By analyzing CdTe/CdS devices fabricated by vacuum evaporation, a self consistent picture of the effects of processing on the evolution of CdTe cells is developed which can be applied to other fabrication methods. In fabricating CdTe/CdS solar cells by evaporation, a 400°C CdCI2heat treatment is used which recrystallizes the CdTe and interdiffuses the CdS and CdTe layers. The interdiffuson can change the bandgap of both the CdTe and CdS which modifies the spectral response of the solar cell. After this heat treatment a contacting/doping procedure is used which converts the CdTe conductivity to p-type by diffusion from Cu from the contact. Finally, the cell is treated with Br2CH3,OH which improves both Voc and FF. Analogous process steps are used in most fabrication processes for CdTe/CdS solar cells.