Electron‐Bridge Effect of Inorganic SnO ₂ ‐GQDs Electron Transport Layer for Sn–Pb Perovskite Solar Cells and Tandems

Solution‐processed SnO 2 nanoparticles are promising nonfullerene electron transport materials, yet their performance in low‐bandgap (LBG) tin‐lead perovskite solar cells (Sn‐Pb PSCs) is hindered by inadequate charge transport and interface energy misalignment. To address these issues, we developed a SnO 2 ‐graphene quantum dot (GQD) electron transport layer (ETL) by functionalizing solution‐processed SnO 2 with GQDs. Both theory calculations and experiments indicate the electron‐bridging role of GQDs in perovskite/GQD‐SnO 2 heterojunction, greatly facilitating directional charge transfer. Moreover, GQDs play a dual role by passivating defects on both SnO 2 and perovskite surfaces, while optimizing the energy level alignment at this critical interface. Consequently, the optimized LBG Sn‐Pb PSCs exhibit significantly enhanced voltage and fill factor, achieving a champion efficiency of 23.38% with robust stability under ISOS‐L‐1 and ISOS‐D‐2 protocols. When integrated into all‐perovskite tandem solar cells, the optimized device delivers a promising efficiency of 29.40%. This work enables the first viable inorganic ETL for realizing high‐performance Sn‐Pb PSC and its tandem applications.