Stable high-efficiency monolithic all-perovskite tandem solar cells enabled by a natural reactive oxygen species scavenger

Monolithic tandem solar cells (TSCs) based on metal halide perovskite semiconductors are the prime candidate for the next generation of photovoltaic technologies. Here, we introduce 4-ethenyl-2,6-dimethoxyphenol (canolol, CNL), a natural reactive oxygen species scavenger, to process narrow bandgap perovskite (NBG) subcells with enhanced efficiency and stability. A proton coupled electron transfer reaction between CNL and Sn4+ is discovered and Sn4+ is reduced to Sn2+. The interaction between CNL and inorganic cations facilitates film crystallization and effective defect passivation in NBG perovskite films. These significantly enhance perovskite oxidation resistance during various stages, including precursor solution preparation, film annealing, and device operation. The resulting single-junction NBG devices achieve a champion power conversion efficiency (PCE) of 23.7% with enhanced stability. Moreover, the resulting all-perovskite tandem solar cells achieved an efficiency of 28.48%, which is certified by a public test center. The encapsulated tandem device retains >90% of its initial efficiency after 750 hours of maximum power point tracking (MPPT) under simulated AM 1.5G illumination.