Ionic‐Rich Vermiculite Tailoring Dynamic Bottom‐Up Gradient for High‐Efficiency Perovskite Solar Cells

Abstract Mixed‐halide perovskites are emerging as excellent photovoltaic candidates because of their tunable bandgaps for semitransparent and tandem perovskite solar cells. However, the notorious film quality originated from the rapidly downward crystallization process susceptibly propagates enormous detrimental defects, which deteriorate the photovoltaic performance and accelerate halide segregation. To address this issue, herein, a multilayer alkalis‐intercalated‐vermiculite is employed as pre‐buried interface modifier to regulate the perovskite lattice property. The matchable lattice structure between perovskite and vermiculite by forming Pb─O bond not only releases the interfacial strain during the film growth but also the embedded alkalis ions can gradually diffuse into perovskite lattice to form a favorable vertical gradient owing to the weak interlamellar van der Waals interaction, playing bis‐roles of atomical lubricant and ion‐reservoir to eliminate detrimental defects. As a result, the film quality and lattice stability is significantly improved with suppressed phase segregation for mixed‐halide perovskites, accompanying a champion efficiency of 11.42% for carbon‐based CsPbIBr 2 device, 15.25% for carbon‐based CsPbI 2 Br device and 23.17% for p‐i‐n inverted (Cs 0.05 MA 0.05 FA 0.9 )Pb(I 0.93 Br 0.07 ) 3 cell. This work provides a new strategy on buried interface engineering for making high‐efficiency and stable perovskite platforms.