Halide-mixing braking strategy for 1.95 eV wide-bandgap perovskites enabling high-efficiency triple-junction tandems

Abstract

Wide-bandgap perovskites are widely used in tandem solar cells due to their tunable bandgaps (1.5–2.3 eV) enabled by mixed halide compositions. However, significant open-circuit voltage losses persist, especially when the bandgap is increased to ∼1.95 eV with high bromine (Br) content. High Br incorporation often leads to heterogeneous halide distributions within the bulk, resulting in severe phase segregation and enhanced carrier recombination. To address these issues, a halide-mixing braking strategy is employed by introducing potassium cyanate as a halide-mixing “brake”. This approach effectively slows the halide exchange rate during annealing, promoting homogeneous halide distribution throughout the films. Additionally, it improves perovskite film quality by reducing defect densities, thereby suppressing non-radiative recombination losses. As a result, single-junction 1.95 eV-bandgap perovskite solar cells achieved a power conversion efficiency of 15.93%, with a high open-circuit voltage of 1.40 V and a fill factor of 0.83. Furthermore, mechanically stacked triple-junction all-perovskite tandem solar cells employing 1.95, 1.60, and 1.25 eV perovskite light absorbers achieved efficiencies exceeding 30%. Therefore, this work provides a simple and effective strategy for optimizing high-Br-content perovskites, enabling the development of high-efficiency wide-bandgap perovskite and multi-junction tandem solar cells.