CuSbS2 thin films by heat treatment of thermally evaporated Sb2S3/CuS stack: Effect of [Cu]/[Sb] ratio on the physical properties of the films

Abstract

We report the experimental development and theoretical evaluation of single-phase CuSbS2 thin films with the purpose of studying a material with potential applications in photovoltaics. Optimal control of [Cu]/[Sb] ratio in the evaporated Sb2S3/CuS stack allowed to tune the stoichiometry, electron affinity, and bandgap of the processed CuSbS2 thin films. The CuSbS2 film developed with [Cu]/[Sb] ratio 0.96 is phase-pure with a band gap of 1.55 eV and exhibited higher photosensitivity. The film is p-type with carrier concentration ∼8.5 x 1017 cm−3. Device simulations were performed to estimate the attainable efficiency with an ideal absorber film and compared with the experimentally determined material parameters of the film developed in this work. Our device model assumes carrier recombination via defects at both CuSbS2/CdS interface and in the CuSbS2 bulk, suggesting that the experimentally reported low values of Voc can be attributed to two factors: (i) the defects at the absorber/buffer interface, and (ii) doping concentration in the CuSbS2 layer. In particular, the concentration of shallow acceptors (NA) in CuSbS2 bulk has a crucial effect on the power conversion efficiency (PCE). The results of this study offers new insight into pathways for increasing the Voc and PCE of CuSbS2 based devices.