Environmentally friendly Cu2SnS3 absorber with titanium (IV) cation regulation enabling power conversion efficiency over 6 % in photovoltaic applications

The development of low-cost and environmentally friendly light-absorbing materials has emerged as important direction in photovoltaic (PV) technologies. Among these candidates, Cu 2 SnS 3 (CTS) material has attracted considerable interest due to the favorable band gap, strong absorption coefficient, and non-toxic elemental composition. However, the efficiency of CTS devices remains hindered by cation disorder, deep-level defects and poor film quality, indicating the need for green and controllable approaches capable of preparing high-performance CTS films. Based on this, this work developed a green mechanochemical wet ball milling strategy. By milling Cu 2 O and SnO in a deionized water/isopropanol (IPA) medium, a uniform precursor dispersion was obtained, enabling the formation of dense CTS absorber layers through spin coating followed by sulfurization. To further tune the local chemical environment, a small amount of TiO 2 was incorporated to partially replace SnO. Benefiting from the similar ionic radii and valence states of Ti 4 + and Sn 4+ , the isovalent substitution effectively adjusted the local coordination structure and reduced Sn-related deep-level defects. The optimized device delivered a marked improvement in photoelectric conversion efficiency (PCE), increasing from 4.68 % to 6.29 %, along with an open-circuit voltage ( V OC ) of 0.47 V that ranked among the highest values reported for CTS-based solar cells. This work demonstrated the effectiveness of mechanochemical methods combined with cation regulation in improving the quality and performance of CTS films, providing an effective pathway for developing green and sustainable thin-film solar cells.