Characterization of ZnIn_xSe_y Thin Films as a Buffer Layer for High Efficiency Cu(InGa)Se₂ Thin-Film Solar Cells

The structural, optical and electrical properties of ZnIn_xSe_y (ZIS) thin films on Cu(InGa)Se₂ (CIGS) thin films and glass substrates were characterized. Polycrystalline ZIS thin films were grown by the coevaporation method using three constituent elements. We confirmed the formation of ZnIn₂Se₄ from the X-ray diffraction patterns of the ZIS thin films on glass substrates. From the transmittance and reflectance measurements of these films, the bandgap of ZIS is estimated at around 2.0 eV in this study. In addition, the ZIS films on glass substrates show low dark conductivity and high photosensitivity, which are suitable for the buffer layer in CIGS thin-film solar cells. We also fabricated the CIGS thin-film solar cells with a ZnO/ZIS/CIGS structure, and investigated the relationship between the cell performance and the beam intensity ratio of zinc to indium.