Surface-deprotonated ultra-small SnO2 quantum dots for high-performance perovskite solar cells

SnO2 electron transport layers (ETLs) have significantly boosted the recent record efficiencies in perovskite solar cells (PSCs). However, solution-processed SnO2 ETLs often suffer from surface protonation with interface/surface defects, leading to substantial energy loss and interface instability. Herein, we investigated the surface properties of SnO2 quantum dots (QDs) on device performance and then developed surface-deprotonated ultra-small SnO2 QD ETLs. Our findings revealed that traditional SnO2 QDs with thiourea doping introduced surface positive-charge protonation to recombine transferred electrons and lengthen their migration path, thereby reducing the electron-transfer efficiency and increasing the surface photocatalytic activity. In contrast, our surface-deprotonated ultra-small SnO2 QDs (2.5 nm average size) exhibited effective coordination between PbI2 and SnO2, lowering the interface barrier and suppressing carrier accumulation for rapid electron transfer and extraction. Consequently, PSCs with non-protonated SnO2 QDs as ETLs achieved a significantly improved champion PCE of 25.55% and enhanced stability, outperforming those with the protonated SnO2 QD ETLs. The corresponding X-ray detector devices also demonstrate broad applicability for superior detection performance.