Tailoring residual stress of flexible Cu2ZnSn(S,Se)4 solar cells by Ga doping for high mechanical endurance

Tremendous Voc deficit and residual stress are the main bottlenecks for efficient and flexible CZTSSe thin film solar cells. For the sake of promoting the mechanical endurance of flexible devices, a convenient and effective strategy for Ga doping is proposed, which can synchronously suppress the defects and tailor the residual stress of CZTSSe. The formed CZTGSSe with a doping concentration of 0.28 mol L−1 presents an optimized heterojunction characteristic with a CBO of −0.30 eV and a released residual stress of −1.87 GPa. Benefitting from the optimum Ga doping concentration with the reduced electrostatic potential fluctuation of 81.18 meV, the ultimately structured device with a PCE of 5.37% is achieved, which can maintain 80% of its original PCE after suffering in a harsh bending environment. The proposed Ga doping strategy may pave a promising way for congener flexible and portable solar cells.