Precrystallization of the Cs₂PbI₂Cl₂ Intermediate Phase for MA- and Br-Free Wide Bandgap Perovskite Solar Cells

A wide bandgap perovskite has broad application prospects in perovskite-based tandem solar cells. However, the I/Br mixed wide bandgap perovskite suffers from inevitable photoinduced halide segregation, while the pure iodine wide bandgap perovskite FA 1– x Cs x PbI 3 ( x > 0.3) typically has high defect densities due to its high annealing temperatures. To address these issues, we reported a Cs 2 PbI 2 Cl 2 intermediate method to lower the preparation temperature and prepare high-quality FA 0.5 Cs 0.5 PbI 3 perovskite films. The precrystallization of the Cs 2 PbI 2 Cl 2 intermediate phase demonstrated effective control over Cs-rich intermediate phases in the raw films, resulting in accelerated ion exchange, lowered activation energy of the solid reaction, and reduced defect density. Consequently, the champion device reaches a power conversion efficiency (PCE) of 22.67%, with only 3% degradation after 500 h of continuous operation. Importantly, the champion mini-module (active area of 14 cm 2 ) reached a PCE of 18.46% which is one of the highest perovskite solar modules based on wide bandgap perovskites.