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.