The development of high-performance, stable quantum dot (QD) inks is critical yet challenging for advancing the efficiency and scalability of next-generation solution-processed optoelectronic devices. Inorganic lead iodide ligands passivated lead sulfide QDs (PbS-PbI₂) have been attractive for their superior surface passivation and strong inter-dot coupling. However, the state-of-the-art inks typically require strongly coordinating alkylamine solvents to dissociate and solvate the PbI₂ ligand, yet these solvents can continuously etch the QDs, leading to rapid ink degradation within a few hours. Herein, an amine-vapor pre-solvation strategy is proposed using a facile butylamine (BA) vapor (<10 min) pretreatment of QDs, enabling stable dispersion of QDs in BA-free solvents (e.g., N-methyl-2-pyrrolidone (NMP) and propylene carbonate). The resulting QD inks remain stable for >60 days with no variation in QD size, while QD films exhibit reduced trap-related losses. Solar cells processed from 60-day-aged NMP inks retain 90% of their initial power conversion efficiency (12.1%), whereas BA-based inks degrade within hours, reducing their device efficiency from 11% to 0.3% after only 4 hours of aging. The shelf-stable NMP ink further enables large-area blade-coating of uniform PbS-PbI₂ films, manifesting the potential in scalable manufacturing of high-performance QD optoelectronic devices.

Lead sulfide quantum dots (PbS QDs) are promising for near-infrared photovoltaics due to their large exciton Bohr radius and size-tunable bandgap. However, extending absorption into the near-infrared (bandgap < 1.13 eV) necessitates larger QDs, which weakens quantum confinement and lowers the conduction band (CB) energy towards bulk-like levels. This CB shift induces severe energy-level misalignment at the ZnO/QDs heterojunction interface, impeding charge extraction efficiency. Conventional dipole-based energy-level tuning strategies rely on ligands coordinated to Pb sites. However, large PbS QDs expose more non-polar (100) facets with a stoichiometric 1:1 Pb:S ratio, where traditional ligands fail to bind S sites, presenting a fundamental barrier to precise energy-level control. To address this issue, we introduce a novel approach: modulating PbS QD energy levels by inducing interfacial dipoles through direct metal cation coordination to the S sites. Systematic screening of metal salts revealed that Zn²⁺ coordination induces the most prominent dipole effect, reducing the work function (WF) of PbS QDs from 4.38 to 4.28 eV. This optimization aligns the band arrangement at the ZnO/QDs interface and facilitates efficient extraction of photogenerated electrons from the PbS absorber layer to the ZnO electron transport layer (ETL). Solar cell devices fabricated using this strategy achieved a power conversion efficiency (PCE) of 11.0%, representing a 12% relative enhancement over the control group (9.8%).