Interfacial Rivet to Fill Structural Defects: A Spacer Engineering Gift for 3D Solar Cells

Abstract The combination of 2D and 3D perovskites to passivate surfaces or interfaces with a high concentration of defects shows great promise for improving the efficiency of perovskite solar cells (PSCs). Constructing high‐quality perovskite film systems by precisely modulating 2D perovskites with good morphologies and growth sites on 3D perovskite films remains a formidable challenge due to the complexity of spacer‐engineered surface reactions. In this study, phase‐pure 2D (HA) 2 (MA) n−1 Pb n I 3n+1 perovskites with a controlled number of layers (n) are separated on a large scale and exploited as interface rivets to optimize 3D perovskite films, resulting in tunable film structural defects and grain boundaries. The optimized PSCs system benefits from a reduction in non‐radiative recombination, resulting in improved optical performance, higher mobility, and lower trap density. The corresponding device achieves a champion power conversion efficiency (PCE) of more than 25%, especially for voltage (V OC ) and fill factor (FF). The quality and uniformity of the perovskite films are further confirmed using large‐area devices with an active area of 14 cm 2 , which exhibits a PCE of more than 21.24%. The high‐quality thin‐film system based on the 2D perovskites presented herein provides a new perspective for improving the efficiency and stability of PSCs.