Unraveling the Crystallization Kinetics of 2D Perovskites with Sandwich‐Type Structure for High‐Performance Photovoltaics

Abstract 2D perovskite solar cells with high stability and high efficiency have attracted significant attention. A systematical static and dynamic structure investigation is carried out to show the details of 2D morphology evolution. A dual additive approach is used, where the synergy between an alkali metal cation and a polar solvent leads to high‐quality 2D perovskite films with sandwich‐type structures and vertical phase segregation. Such novel structure can induce high‐quality 2D slab growth and reduce internal and surface defects, resulting in a high device efficiency of 16.48% with enhanced continuous illumination stability and improved moisture (55–60%) and thermal (85 °C) tolerances. Transient absorption spectra reveal the carrier migration from low n to high n species with different kinetics. An [PbI₆]⁴⁻ octagon coalescence transformation mechanism coupled with metal and organic cations wrapped is proposed. By solvent vapor annealing, a recrystallization and reorientation of the 2D perovskite slabs occurs to form an ideal structure with improved device performance and stability.