Perovskite-organic tandem solar cells with a photo-transformable stabilizer.

Wide-bandgap (WBG) mixed-halide perovskites with high Br content, which are employed as the front cell material in perovskite-organic tandem solar cells (TSCs), often suffer from initial halide-mixing inhomogeneity and light-induced halide segregation 1-3 , limiting the performance of perovskite-organic TSCs. Here, we introduced a photo-transformable additive 4-[3-(trifluoromethyl)-3H-diazirin-3-yl]benzylamine (TDB) into the WBG perovskite precursor solution to establish a two-stage strategy for stabilizing the mixed-halide phase. During crystallization, TDB improves the initial halide homogeneity by suppressing the rapid precipitation of the Br-rich phase and accelerating halide mixing upon annealing. During operational illumination, TDB undergoes transformation to form a new species with stronger adsorption on the perovskite grain-boundary surfaces, which inhibits the formation of iodide-related defects, suppresses defect-assisted carrier trapping and ion migration, thereby mitigating light-induced halide segregation 4-6 . The representative WBG perovskite (E g = 1.88 eV) solar cell achieved a power conversion efficiency (PCE) of 20.01%, with an open-circuit voltage of 1.42 V, a fill factor of 85.13% and improved stability under illumination. By integrating the WBG perovskite solar cell into a monolithic perovskite-organic TSC, we achieved a PCE of 28.80% with a certified steady-state PCE of 28.04%. The perovskite-organic TSC retained 90% of its initial PCE after 625 h of operation under the ISOS-L-1 protocol.