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

Abstract

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.