Atmospheric degradation of unencapsulated CdS‐CdTe solar cells was modeled by assuming that the initial CdTe/electrode interface becomes a metal/insulator/semiconductor junction as oxygen diffuses through the metal to form a CdTeO3insulating layer. The doping concentration, barrier height, and oxide thickness were varied and the numerical calculations were compared with the experimental data on cells aged in a humidity chamber. The degradation was most severe when the cells were exposed to high humidity and high temperature. This degradation could be modeled in terms of the growth of the insulating CdTeO3layer from 20 A˚ to 80 A˚. ©1995 American Institute of Physics.