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

Wide-bandgap (WBG) mixed-halide perovskites with high bromine (Br) content, which are used as the front-cell material in perovskite-organic tandem solar cells (TSCs), often exhibit initial halide-mixing inhomogeneity and light-induced halide segregation^1-3, limiting the performance of perovskite-organic TSCs. Here we introduce a photo-transformable additive, 4-[3-(trifluoromethyl)-3H-diazirin-3-yl]benzylammonium salt (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 and suppresses defect-assisted carrier trapping and ion migration, thereby mitigating light-induced halide segregation^4-6. The representative WBG perovskite (bandgap energy (E_g) = 1.88 eV) solar cell had 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.