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

Abstract 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 0.05 FA 0.80 MA 0.15 Pb(I 0.85 Br 0.15 ) 3 (CsFAMA) perovskite is demonstrated. CsFAMA perovskite with a CsPbBr 3 ‐clusters passivated structure is realized, in which CsPbBr 3 ‐clusters are located at the surface/interface of CsFAMA grains. This structure is realized by introducing a CsPbBr 3 colloidal solution into the CsFAMA precursor. It is found that CsPbBr 3 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 TiO 2 ‐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.