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

Tremendous V-oc 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.