Synergistic Light–Heat–Bias Activation for 21%-Efficient CdSeTe Thin-Film Solar Cells

Metastable responses to illumination, temperature, electrical bias, and exposure history complicate the performance assessment and reliability in CdTe thin-film photovoltaics. Here, we demonstrate a synergistic light–heat–bias (L–H–B) activation that reproducibly boosts the performance of graded CdSeTe devices. L–H–B suppresses nonradiative recombination at the illuminated front interface and within the absorber, coincident with deactivation of dominant shallow traps near EV + 0.35 eV and reduced occupancy of midgap states around EV + 0.76–0.79 eV. These changes mitigate defect-mediated Shockley–Read–Hall losses and increase open-circuit voltage and fill factor, yielding a champion efficiency of 21.02%─among the highest reported for CdSeTe thin-film solar cells. Specifically, the response is reversible after dark storage, recoverable upon reactivation, and not Cu-specific, generalizing to group-V-doped devices. The protocol provides an operational, standardizable preconditioning route for performance activation and reliable benchmarking.