Constructing CsPbBr3 Cluster Passivated‐Triple Cation Perovskite for Highly Efficient and Operationally Stable Solar Cells

Ion migration and phase segregation, in mixed‐cation/anion perovskite materials, raises a bottleneck for its stability improvement in solar cells operation. Here, the synergetic effect of electric field and illumination on the phase segregation of Cs_0.05FA_0.80MA_0.15Pb(I_0.85Br_0.15)₃ (CsFAMA) perovskite is demonstrated. CsFAMA perovskite with a CsPbBr₃‐clusters passivated structure is realized, in which CsPbBr₃‐clusters are located at the surface/interface of CsFAMA grains. This structure is realized by introducing a CsPbBr₃ colloidal solution into the CsFAMA precursor. It is found that CsPbBr₃ passivation greatly suppresses phase segregation in CsFAMA perovskite. The resultant passivated CsFAMA also exhibits a longer photoluminescence lifetime due to reduced defect state densities, produces highly efficient TiO₂‐based planar solar cells with 20.6% power conversion efficiency and 1.195 V open‐circuit voltage. The optimized devices do not suffer from a fast burn‐in degradation and retain 90% of their initial performance at maximum power under one‐sun illumination at 25 °C (65 °C) exceeding 500 h (100 h) of continuous operation. This result represents the most stable output among CsFAMA solar cells in a planar structure with Spiro‐OMeTAD.