Inhibiting defect passivation failure in perovskite for perovskite/Cu(In,Ga)Se₂ monolithic tandem solar cells with certified efficiency 27.35%

Thin-film tandem solar cells with wide-bandgap perovskites and Cu(In,Ga)Se₂ hold promise for cost-effective lightweight photovoltaics. However, the power conversion efficiency and stability of perovskite/Cu(In,Ga)Se₂ tandem solar cells are not yet comparable to single-junction counterparts due to recombination losses and photothermal-induced degradation in wide-bandgap perovskites. In this study, we show that common strategies for perovskite passivation often fail under combined thermal and illumination stresses due to the passivator desorption. We demonstrate a robust passivator with deliberately designed functional groups that inhibits passivator desorption regardless of perovskite surface termination, enhances resistance to photothermal stresses and substantially suppresses phase segregation. The wide-bandgap perovskite solar cells achieved a champion power conversion efficiency of 23.5% with negligible degradation after 1,000 hours of continuous operation under 1-sun illumination at approximately 50 °C. When integrated into perovskite/Cu(In,Ga)Se₂ tandem cells, they achieved the steady state power conversion efficiency of 27.93% (certified 27.35%), with stable operation for over 420 hours at ~38 °C in ambient air.