Crystallographic and optical properties of wide bandgap photovoltaic semiconductor system, Cu(Al,In)Se 2 .

We characterized the optical and electronic properties of chalcopyrite-type Cu(Al,In)Se₂, which is a candidate for wide-bandgap solar cell materials. The bandgap energy was determined from diffuse reflectance spectra. The bandgap energy increased from 1.00 eV for CuInSe₂ to 2.61 eV for CuAlSe₂ with an increase in the Al content. The ionization energy corresponding to the energy levels of the valence band maximum (VBM) was determined using photoemission yield spectroscopy. The VBM level of the Cu(Al,In)Se₂ system stayed relatively constant, but the conduction band minimum level increased with increasing Al content. To analyze the local structures of Cu and In atoms in Cu(Al,In)Se₂, Cu and In K-edge X-ray absorption fine structure (XAFS) spectra were measured at SPring-8. We discuss the crystallographic characteristics of Cu(Al,In)Se₂ based on the results of the XAFS analyses and a comparison of the phase diagrams of the Cu₂Se–Al₂Se₃, Cu₂Se–In₂Se_3, and Cu₂Se–Ga₂Se₃ systems. [ABSTRACT FROM AUTHOR]