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

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 (SnO₂)/perovskite buried interface. As a result, synergistic effects of enhanced conductivity of SnO₂, preferable energy alignment at the buried interface and improved perovskite crystal orientation are realized. The champion FF reaches 85.24% in formamidinium lead iodide (FAPbI₃) 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.