Optical Properties of Thin Film Sb2Se3 and Identification of its Electronic Losses in Photovoltaic Devices

Antimony selenide (Sb2Se3) is a highly promising solar cell absorber material with excellent optoelectronic properties including high absorption coefficient in the visible energy range. Here, we investigate the optical and electronic properties of thin film polycrystalline Sb2Se3 deposited on glass. The indirect bandgap of 1.117 ± 0.001 eV, direct optical gap of 1.175 ± 0.002 eV, and Urbach energy of 21.1 ± 0.6 meV are determined from the absorption coefficient spectra obtained from photothermal deflection spectroscopy. Complex dielectric function (ε = ε1 + iε2) spectra are determined using through-the-glass spectroscopic ellipsometry measurements in 0.75 – 4 eV spectral range due to the roughness of the Sb2Se3 film. These spectra in ε along with the solar cell component layer thicknesses are used as input parameters for external quantum efficiency (EQE) simulation to investigate electronic losses in substrate type Sb2Se3 based solar cells. The difference between simulated EQE for Sb2Se3 based PV assuming complete carrier collection in absorber layer Sb2Se3 and measured EQE are evaluated to obtain 97.0 ± 0.2% carrier collection probability in Sb2Se3 at the heterojunction interface and a 400 nm carrier collection length throughout the Sb2Se3 absorber layer. The difference between measured short circuit current density and that simulated assuming no electronic losses shows that 5.4 mA/cm ² is lost due to incomplete carrier collection.