Investigation of Cu2ZnSnS4 solar cell buffer layer fabricated via spray pyrolysis

Copper zinc tin sulfide solar cells were fabricated by using spray pyrolysis from a window layer to an absorber layer. ZnS and In₂S₃ buffer layers were deposited on the TiO₂ layer, and the photovoltaic characteristics were investigated. The ZnS buffer demonstrated a poor photovoltaic performance because of its poor surface coverage and micro-cracks at fluorine-doped tin oxide/TiO₂ layers. The In₂S₃ buffer layer sprayed at low temperature (<360 °C) showed a large difference between photo and dark currents beyond the open-circuit voltage (V_OC). When the spraying temperature exceeded 390 °C, the devices showed high dark leakage currents at reverse biases because of the high conductivity of the buffer layer, resulting in decreased V_OC and short-circuit current density (J_SC). The optimum temperature for spraying In₂S₃ is 360 °C, and the best performing device showed 410 mV, 30.4 mA/cm², 35.3%, and 4.4% of V_OC, J_SC, fill factor, and efficiency, respectively.