Mutual stabilization of hybrid and inorganic perovskites for photovoltaics

Stabilizing black-phase formamidinium lead triiodide (FAPbI 3 ) is critical for high-performance perovskite solar cells (PSCs). We present a stabilization strategy utilizing co-evaporated cesium lead iodide (CsPbI 3 ) capping layers. Enabled by favorable crystal lattice matching, cubic-phase CsPbI 3 spontaneously forms on FAPbI 3 surfaces, establishing mutual phase stabilization with the underlying black-phase FAPbI 3 . When combined with ammonium salt interface modification, the CsPbI 3 interlayer effectively suppresses the ion (FA + and F-PEA + ) diffusion between the stacked perovskite layers. The FAPbI 3 /CsPbI 3 bilayer structured devices exhibited a certified record reverse-scanning power-conversion efficiency of 27.17% and maintained a stabilized power output efficiency of 26.62%. Remarkably, the cells retain 93.5% of the initial efficiency after 1500 h damp-heat test, and retaining over 94.2% of its maximum PCE after about 1185 h with a linear extrapolation to a T 90 of 2352 h operation under continuous illumination at maximum power point tracking at 85 °C. • Cubic CsPbI 3 capping stabilizes black-phase FAPbI 3 via mutual lattice matching. • Ion diffusion between perovskite layers is suppressed by the CsPbI 3 interlayer. • Achieved certified PCE of 27.17% and 24.88% for small and large area PSCs. • Stable operation with 94.2% PCE retention after 1185 h at 85 °C under 1-sun MPP. • Bilayer 3D/3D perovskite design enables universal efficiency boost across bandgaps.