• • SCT annealing at 85°C for 5 h yields a power conversion efficiency of 13.07% in flexible CZTSSe solar cells, compared to 12.1% for reference devices, representing a relative improvement of 8.0%.
• • The SCT process reduces open-circuit voltage loss by passivating interface defects and suppressing CuZn defects, leading to a V_OC of 474.9 mV and a fill factor improvement from 68.2% to 71.5%.
• • Gradient Cd2+ diffusion into the absorber optimizes band alignment, reducing interface recombination and enhancing carrier collection, as evidenced by increased short-circuit current density from 36.06 to 37.2 mA/cm2.
• • SCT annealing alleviates residual stress from thermal expansion mismatch, improving mechanical flexibility; bending tests show the device retains 90% of initial efficiency after 1000 cycles at a radius of 5 mm.