Solvent Engineering in PbS Colloidal Quantum Dot Inks: Enabling Colloidal Stability, Ligand Versatility, Large-Area Film Fabrication, and Multilayer Processing.

PbS colloidal quantum dots (CQDs) have attracted considerable attention for photovoltaics and infrared (IR) optoelectronics because their bandgap can be tuned across the near-infrared (NIR) and short-wavelength infrared (SWIR) regions. This review highlights solvent engineering as a central strategy for fabricating high-performance PbS CQD inks, rather than treating it simply as a dispersion step. We first discuss the key parameters governing CQD surface chemistry throughout the dispersion and film-formation processes. We then compare the conventional butylamine (BTA)-based system with emerging alternatives, including BTA-based co-solvents and BTA-free weakly polar solvents such as γ-butyrolactone (GBL) and 2,6-difluoropyridine (DFP) used with lead halide ligands. In addition, we summarize solvent platforms developed for other ligand systems, including 3-mercaptopropionic acid (MPA), aromatic ligands dispersible in weakly polar solvents for orthogonal hole-transport layer (HTL), self-assembled monolayer (SAM)-functionalized CQDs, and thiolate-capped CQDs processed in fluorinated alcohols. Overall, this review highlights how solvent engineering governs not only ink stability, but also interfacial compatibility, multilayer integration, large-area coating, and device performance. Finally, we emphasize the key directions that require further development and investigation to establish more sophisticated solvent-engineering strategies.