Defect related negative temperature coefficiency of short circuit current of Cu(In, Ga)Se2 solar cells

The negative temperature coefficient of the short circuit current of Cu(In, Ga)Se₂ solar cells, contrary to the positive one of Si cells, may cause more degradation of power conversion efficiency at high temperature than Si solar cells due to defects. Photoluminescence spectra show both donor-acceptor transition and band-impurity transition. At higher temperature, more unoccupied states of donors and acceptors yield relatively low luminescence intensity from the donor-acceptor-pair transition, and become efficient traps to capture photo-generated carriers. This reflects that both the short circuit current and the external quantum efficiency degrade at high temperature due to the donor and acceptor states.