Two-stage co-evaporated CuSbS₂ thin films for solar cells

CuSbS₂ is a promising absorber for thin film solar cells because of its suitable band gap, high absorption coefficient, low cost and nontoxic characteristics. Here we report CuSbS₂ thin films fabricated from three-source co-evaporation for the first time. We used two-stage co-evaporation process in which Sb-rich precursor was first deposited by Cu, Sb and S co-evaporation at a lower substrate temperature (typically ∼ 230 °C) followed by Sb and S co-evaporation at a relatively elevated temperature (typically ∼ 370-390 °C). This process leads to an improved crystallinity and phase purity of CuSbS₂. The phases of the deposited films are extremely sensitive to the substrate temperature and film composition. Excess of copper resulted in a separation of Cu₁₂Sb₄S₁₃ secondary phase from CuSbS₂, while excess of antimony resulted in a separation of Sb₂S₃. CuSbS₂ films with good crystallinity and improved phase purity can be obtained at second stage substrate temperature of 370 °C. Finally a thin film solar cell was fabricated using stoichiometric CuSbS₂ absorber with Mo/CuSbS₂/CdS/ZnO/ZnO:Al/Ag structure, achieving an encouraging 1.9% power conversion efficiency with one of the highest open-circuit voltage of 526 mV for CuSbS₂ solar cells.