Stabilizing wide-bandgap halide perovskites through hydrogen bonding

Wide-bandgap (WBG) perovskites have emerged as promising materials for the construction of perovskite/silicon tandem solar cells. However, poor long-term operational stability due to the notorious photo-induced halide segregation is commonly observed. Here, we report the synthesis of stable ∼1.73 eV MA-based mixed I/Br WBG perovskites by ionic liquid solvent, methylammonium acetate (MAAc). The special internal hydrogen bond (N—H⋯I and N—H⋯Br) environment in the ionic liquid MAAc solvent over traditional N,N-dimethylformamide/dimethyl sulfoxide solvent stabilizes the diffusion of halide ions. This allows the suppression of the halide segregation in the mixed I/Br WBG perovskite film, which is previously suggested to be difficult. The hydrogen bonds also enable excellent decoupling of the crystal nucleation and growth process. Finally, a champion device efficiency of 20.59% is achieved, which is one of the highest reports, with improved ambient air, heat, and light stability.