Micro-Raman/PL and Micro-LBIC studies of CZTSe materials and PV devices

Micro-Raman/PL/LBIC (Laser Beam Induced Current) was applied to investigate the homogeneity of polycrystalline Cu₂ZnSnSe₄ (CZTSe) thin-films from both front surface and cleaved edge with sub-micron spatial resolution. By comparing the materials before and after CdS coating, we have investigated the effect of non-uniformity of CdS layer on the spatial variation of the photo-response, correlating to the μ-Raman/PL probes. The CdS induced spatial variation is found to be a source of inhomogeneity in addition to that of the absorber layer itself. The devices investigated typically have > 8.5% efficiency. The contrast of the LBIC signal adjacent to the CdS rich area is found to depend on excitation laser power, indicating a potential for further efficiency improvement. Cleaved edge Raman probe has revealed possible variation in the compositions along the growth direction.