The influence of metastabilities on the luminescence in the Cu(In,Ga)Se2 solar cells

Photoluminescence and electroluminescence spectra of the absorber layer in ZnO/CdS/Cu(In,Ga)Se-2 solar cells were measured. Their dependence on temperature, excitation intensity and applied voltage were studied. Electroluminescence measurements were used to investigate light- and bias-induced metastabilities in the absorber of the cells. We showed that metastable changes of defect distributions, which produce an effect on the electrical characteristics of ZnO/CdS/Cu(In,Ga)Se2 material, affect also the luminescence yield. The dependence of the intensity and shape of the electroluminescence spectra on the state of the sample is observed. These results fit well into the theoretical calculations of Lany and Zunger model showing that divacancy complex (V-Sc-V-Cu) is responsible for metastable changes observed in ZnO/CdS/Cu (In, Ga) Se-2-based solar cells. We conclude that during light soaking or/and forward bias the probability of nonradiative recombination is decreased.