Photoluminescence properties of polycrystalline ZnO/CdS/CuInGaSe2 solar cells at a low temperature

Emission properties of highly efficient polycrystalline solar cells based on ZnO/CdS/CuInGaSe2 thin films were studied at T=20 K. The edge photoluminescence band was observed for the reference device at a photon energy of 1.191 eV. This band vanishes after treating the unincapsulated device in a humid atmosphere (relative humidity of 85%) at an elevated temperature (85°C). Long-wavelength bands at 1.13 and 1.07 eV, which are associated with optical transitions via defect levels in the absorber film, preserve the intensity and spectral position. A decrease in the conversion efficiency of the solar cell after treatment is caused by the degradation of upper wide-gap films and a CdS-CuInGaSe2 heterointerface.