Precrystallized‐Heterojunction Strategy on Precursor Solution Enables High‐Performance Semitransparent Perovskite Solar Cells

Abstract For semitransparent perovskite solar cells (ST‐PSCs), decreasing the thickness of perovskite film is one of the most feasible approaches to increase the average photopic transmittance (APT). However, ultrathin perovskite film always suffers poor crystalline quality with pinhole and uniformity. Here, a precrystallized‐heterojunction strategy (PHS) is developed to fabricate high‐quality heterostructured perovskite films based on the mixture solution of 2D (3‐TMA)₂PbCl₄ (3‐TMA = 3‐thiophenemethylammonium) and 3D formamidinium‐cesium‐alloyed crystals. In the PHS, the 3D crystals with precise stoichiometry control ensure reproducibility, while the 2D crystals act as nuclei for the templated growth of large‐grain 3D perovskite with reduced defects. As a result, this strategy with excellent thickness‐independent tunability enables the champion opaque devices and ST‐PSCs to achieve a power conversion efficiency of 22.7% and 14.1% (APT of 22.1%), respectively. This deep understanding of precursor materials opens new vistas to regulate nucleation/crystallization kinetics precisely for boosting the commercial feasibility of ST‐PSC applications.