Influence of annealing conditions on the performance of sputtered grown CZTS thin film solar cells

Abstract

Kesterite Cu2ZnSnS4 (CZTS), with direct and tunable bandgap, high absorption coefficient, low-cost processing, earth-abundance, and non-toxicity, has become a promising absorber material for emerging thin film solar cells. The film growth, phase formation, and stoichiometry, as well as the electrical and optical properties of the sputtered grown CZTS thin films, are greatly influenced by the annealing temperature and pressure. In this work, we use a series of material characterization techniques followed by numerical simulations to determine how the annealing conditions affect the properties of CZTS thin films and the photovoltaic performance of the corresponding thin film solar cells. Sputtered grown CZTS samples were annealed at different temperatures (470 and 560 °C) and pressures (250 and 350 Torr). UV-visible spectroscopy was used to determine the optical bandgap and the absorption spectra. The experimentally determined values are then used as input parameters in the Solar Cell Capacitance Simulator-1 Dimension (SCAPS-1D) simulator tool to determine the solar cell performance. Simulation results show a maximum theoretical power conversion efficiency for the CZTS sample annealed at 560 °C and 350 Torr pressure. The results can lead to the optimization of sputtering conditions for obtaining high quality CZTS films that can yield excellent solar cell performance.