Strain Regulation of Mixed-Halide Perovskites Enables High-Performance Wide-Bandgap Photovoltaics

Wide-bandgap mixed-halogen perovskite materials are widely used as top cells in tandem solar cells. However, serious open-circuit voltage (Voc) loss restricts the power conversion efficiency (PCE) of wide-bandgap perovskite solar cells (PSCs). Herein, it is shown that the resulting methylammonium vacancies induce lattice distortion in methylammonium chloride-assisted perovskite film, resulting in an inhomogeneous halogen distribution and low Voc. Thus, a lattice strain regulation strategy is reported to fabricate high-performance wide-bandgap PSCs. Rubidium (Rb) cations are introduced to fill the A-site vacancy caused by the methylammonium volatilization, which alleviates shrinkage strain of the perovskite crystal. The reduced lattice distortion and increased halide ion migration barrier result in a homogeneous mixed-halide perovskite film. Due to improved carrier transport and suppressed nonradiative recombination, the Rb-treated wide-bandgap PSC (1.68 eV) achieves an excellent PCE of 21.72%, accompanied by a high Voc of 1.22 V. The resulting device maintains more than 90% of its initial PCE after 1500 h under 1-sun illumination conditions. The Rb+ fills the A-site vacancy caused by the MA volatilization, relieving shrinkage strain of perovskite crystal. The reduced lattice distortion increases the halide migration barrier, resulting a homogeneous mixed-halide perovskite phase, and suppressing nonradiative recombination. As a result, the Rb-treated wide-bandgap perovskite solar cell exhibits an improved power conversion efficiency and stability. image