Toward α-phase stabilization of formamidinium lead iodide perovskites with dual-trivalent metal regulation

Perovskite solar cells have garnered significant attentions due to their rapidly increased power conversion efficiency and cost-effective manufacturing processes. Methylammonium (MA)-free formamidinium (FA)-dominated Cs_xFA_1−xPbI₃-based perovskite solar cells have immense potential but encounter challenges in α-phase deactivation derived from lattice distortion and ion migration, which dramatically hindered their reliability in real use. To enhance the α-phase Cs_0.03FA_0.97PbI₃ stability, we propose a strategy of dual trivalent metal doping with Cr³⁺ and Er³⁺ to simultaneously promote δ- to α- phase transition, release residual strain, and mitigate the migration of the unbonded halides, thus markedly enhancing α-phase Cs_0.03FA_0.97PbI₃ phase stability and the overall performance of solar cells. The best solar cell delivers a champion efficiency of 24.88 % and 82 % efficiency retention after 1069 h of maximum power point tracking under continuous illumination at 45 °C.