Electron-Bridge Effect of Inorganic SnO2-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.