CuSb: The dominant defect in Cu-rich CuSbS2 solar cells fabricated by sulfurizing co-sputtered Cu–Sb precursor

Understanding the elemental composition and point defect properties is crucial for improving device performance in Chalcogenide thin film solar cells. The correlation between composition and defect characteristics of CuSbS2 thin film sulfurized from metallic precursors was systematically investigated. Interestingly, it was found that CuSbS2 polycrystalline thin film maintains an overall Cu-rich composition with a Cu/Sb ratio greater than 1, regardless of the initial precursor compositions. Besides, no obvious difference in the performance of integrated devices is observed, due to the similar Cu/Sb atomic ratios and electronic properties (carrier concentration and mobility) in these CuSbS2 thin films. By conducting admittance spectroscopy analysis on CuSbS2 devices, identical defect energy was obtained at 280 meV above the valence band maximum, which can be ascribed to CuSb. This could be mainly explained by the Cu-rich composition induced low formation energy of CuSb. Therefore, further defects engineering focusing on CuSb is required to boost the device efficiency of CuSbS2 solar cells.