Aging Effect on the Efficiency of Cu(In,Ga)Se2/CdS Solar Cells

The electrical performance of two different types of Cu(Jn,Ga)Se-2/CdS solar cells were measured repeatedly over a period of several months. One of the solar cells initially showed cross-over in its current-voltage curve, whereas the other showed normal p-n diode operation. The efficiencies of both devices were found to improve with aging due to the significantly increased doping density in the space charge region. The long-term aging effect was found to be irreversible and disappeared after thermal annealing of the device at relatively low temperature. The increase in doping density was attributed to Cu electromigration under the influence of a built-in electric field existing in the space charge region of the absorbers.