Long-term efficiency gain of Cu(In, Ga)Se2 solar cell

The electrical performance of Cu(In, Ga)Se₂ solar cells were measured repeatedly over several months period. The efficiency was found to continue to improve with aging time due to substantially increased doping density in the space charge region. The long-term aging effect was found to be irreversible and to disappear by thermal annealing. The increase of doping density was probably originated from Cu migration taking place under the influence of electric field existing in the space charge region.