Interfacial Bridging Enables High Performance Perovskite Solar Cells with Fill Factor Over 85%

Abstract The power conversion efficiency (PCE) of perovskite solar cells (PSCs) is approaching their Shockley‐Queisser (S‐Q) limit through numerous efforts in key parameters improvement. To further approaching the limit, it is important to facilitate the fill factor (FF), a parameter closely related to carrier transport and nonradiative recombination. Herein, an interfacial bridging strategy is proposed to improve FF, which utilizes functional graphene quantum dots at the tin oxide (SnO 2 )/perovskite buried interface. As a result, synergistic effects of enhanced conductivity of SnO 2 , preferable energy alignment at the buried interface and improved perovskite crystal orientation are realized. The champion FF reaches 85.24% in formamidinium lead iodide (FAPbI 3 ) based PSCs, which ranks among the highest in the n‐i‐p structure. Such strategy is also proven successful in other perovskite systems, where the champion PCE reaches 24.86% in the formamidinium‐cesium (FACs)‐based devices and 24.44% in the flexible devices. Therefore, this work provides a practical design rule for pursuing high FF of PSCs with carbon materials.