Synergistic Surface Copassivation of PbS Colloidal Quantum Dot Films for Efficient Inverted Solar Cells

Inverted p-i-n structure lead sulfide colloidal quantum dots (PbS CQDs) solar cells are more process compatible and flexible in interface engineering, but their efficiency is still behind that of n-i-p conventional structures. Their performance is restricted by surface defects and interfacial recombination losses because of their high surface-to-volume ratio. To address these restrictions, here, we report a synergistic surface copassivation strategy that combines in situ mercaptopropionic acid (MPA) passivation during PbS CQD synthesis and postdeposition 2-phenylethylammonium iodide (PEAI) treatment to passivate residual surface and interfacial defects. Spectroscopic analysis, electrical characterization, and density functional theory (DFT) calculations collectively suggest that this copassivation strategy enhances surface coordination and interface passivation effects. Consequently, the optimized inverted PbS CQD solar cells have a champion power conversion efficiency (PCE) of 11.15% compared to control devices 10.41% with simultaneous enhancements in open-circuit voltage and fill factor. This work demonstrates that complementary surface copassivation provides an effective way to suppress defect-induced losses and advance the performance of inverted PbS CQD solar cells through a simplified processing route.