Stress-redistributing Ag2Se quantum dots as universal nanomodifiers for efficient and stable perovskite photovoltaics

The electron transport layer (ETL) is widely recognized as a critical component in perovskite solar cells (PSCs), as it modulates the efficiency of charge extraction and transport processes, which largely dictates the overall device performance.In this study, we incorporated cysteine-functionalized silver selenide quantum dots (Cys-Ag₂Se QDs) into the SnO₂ ETL to establish efficient electron transport pathways. The introduction of Cys-Ag₂Se QDs effectively modulated the optoelectronic properties of SnO₂, including carrier mobility, conductivity, and energy level alignment. Furthermore, the Cys-Ag₂Se QD-modified SnO₂ ETL regulated perovskite crystallization dynamics, yielding perovskite film with enlarged grain sizes and improved quality. Notably, the Cys-Ag₂Se QDs exhibited remarkable stress-relieving properties at the buried interface due to their nanoscale curvature and ligand interactions, mitigating residual lattice strain and enhancing interfacial integrity and long-term stability. Additionally, the Cys-Ag₂Se QDs passivated uncoordinated Sn⁴⁺ and Pb²⁺ defects at the SnO₂/perovskite interface, reducing trap-state density and suppressing non-radiative recombination. The optimized device (0.03 mg/mL Cys-Ag₂Se QDs) achieved a champion power conversion efficiency (PCE) of 23.42%, with enhanced short-circuit current density (J sc ) and fill factor (FF). After 1000 h of continuous heating at 60°C under nitrogen, the Cys-Ag₂Se incorporated PSCs retained 90.54% of their initial efficiency. This work presents a facile fabrication strategy and a novel QD-based additive system for high-performance SnO₂ ETLs in PSCs. • Ag 2 Se QDs are introduced as universal stress-redistributing nanomodifiers. • Ag 2 Se QDs release lattice strain and suppress ion migration in perovskites. • The modified devices achieve a champion PCE of 23.42%. • The modified devices show enhanced operational and humid stability. • This work provides a nanoscale stress-management strategy for perovskites.