Characterization of the structural and optical properties of CuIn1−xGaxSe2 QJ;thin films by X-ray diffraction

The structural and optical properties of Cu-poor CuIn1−xGaxSe2 thin films with different gallium contents grown using the co-evaporated technique were studied. Measurements of X-ray diffraction (XRD), temperature-dependent photoluminescence (PL), and photoreflectance (PR) were performed on the samples. The emission peaks in the PL spectra and PR spectra observed around 1.0-1.2 eV are attributed to donor-acceptor pairs and defect-related luminescence. With increasing gallium content, the linewidths of the luminescence spectra for the samples become wider, which we attribute to greater statistical disordering between indium and gallium. The structural properties of the CuIn1−xGaxSe2 thin films are further characterized by simulation of the XRD spectra with a theoretical model. It is found that the sample with higher gallium content exhibits less uniformity of microstructure size. The X-ray diffraction line profile analysis also shows a stronger internal strain in the sample with the higher gallium content, which is consistent with its broader microstructure size distribution. The conversion efficiency of the CuIn1−xGaxSe2-based solar cells is also obtained and investigated through theoretical analysis. The experimental results coincide with the inferences given by the X-ray diffraction line profile analysis.