Enhanced mobility of Cu4SnS4 films prepared by annealing SnS-CuS stacks in a graphite box

High-quality Cu4SnS4 thin films are prepared by annealing chemical bath-deposited SnS-CuS stacks in a graphite box. The effects of annealing temperature on the grain growth and morphology of these films are investigated in this study. Results showed that the films prepared at 500-580 °C yielded an orthorhombic crystal structure with lattice parameters a = 1.371 nm, b = 0.766 nm and c = 0.643 nm, a crystallite size of 260 nm, an increased grain size from 2 μm to greater than 6 μm, a direct optical band gap of 1.0 eV, and p-type electrical conductivity. The films prepared at 550 °C and 580 °C exhibited a relatively high hole mobility of 150 cm2V−1s−1. These properties suggest that the films developed in this study can yield reasonable device efficiency when used as solar cell absorber layers.