Cesium Lead Mixed-Halide Perovskites for Low-Energy Loss Solar Cells with Efficiency Beyond 17%

In spite of rapid progress in cesium lead halide (CsPbX 3 ) perovskites solar cells (PSCs), their power conversion efficiencies (PCEs) achieved to date leave much space for further improvement, principally as a result of their large energy losses ( E loss ). Herein, after incorporating 5% of Br ions into the CsPbI 3 film as the mixed-halide CsPbI 2.85 Br 0.15 -absorber layer, the optimized PSCs obtain a record reverse scan PCE of 17.17% and stabilized PCE of 16.83% with lower E loss of 0.58 eV. A record PCE of 12.28 and 13.14% are also achieved for large areas (1 cm 2 ) and flexible substrates, respectively. More importantly, the optimized devices exhibit excellent thermal and compositional stability. Further characterizations have proved the much enhanced PCE and stability original from the Br induced suppressing bulk trap-assisted nonradiative recombination and lattice strain relaxation.