Heterogeneous 2D/3D Tin‐Halides Perovskite Solar Cells with Certified Conversion Efficiency Breaking 14%

As the most promising lead‐free one, tin‐halides based perovskite solar cells still suffer from the severe bulk‐defect due to the easy oxidation of tin from divalent to tetravalent. Here, a general and effective strategy is delivered to modulate the microstructure of 2D/3D heterogeneous tin‐perovskite absorber films by substituting FAI with FPEABr in FASnI 3 . The introduction of 2D phase can induce highly oriented growth of 3D FASnI 3 and it is revealed in the optimal 2D/3D film that 2D phase embraces 3D grains and locates at the surfaces and grain boundaries. The FPEA + based 2D tin‐perovskite capping layer can offer a reducing atmosphere for vulnerable 3D FASnI 3 grains. The unique microstructure effectively suppresses the well‐known oxidation from Sn 2+ to Sn 4+ , as well as decreasing defect density, which leads to a remarkable enhanced device performance from 9.38% to 14.81% in conversion efficiency. The certified conversion efficiency of 14.03% announces a new record and moves a remarkable step from the last one (12.4%). Besides of this breakthrough, this work definitely paves a new way to fabricate high‐quality tin‐perovskite absorber film by constructing effective 2D/3D microstructures.