In solid-state ligand exchange, a film of quantum dots capped with native long-chain organic ligands is first deposited onto a substrate, typically via spin-coating. A treatment solution containing short-chain ligands or inorganic ions is then dispensed directly onto the pre-formed nanocrystal film. As the solution interacts with the solid layer, the incoming short ligands diffuse into the matrix and displace the original bulky molecules. Excess unbound reagents and displaced ligands are subsequently rinsed or spun off, resulting in a densely packed, highly conductive quantum dot solid film with significantly reduced interparticle spacing and improved charge transport characteristics. 

In liquid-state ligand exchange, the replacement of native organic ligands occurs directly within the colloidal solution phase prior to any film deposition. As-synthesized quantum dots dispersed in a non-polar solvent are mixed with a solution containing new, shorter ligands, often facilitating a phase transfer where the nanocrystals migrate between immiscible solvent layers. This approach allows for a uniform and thorough ligand exchange across the entire surface of every individual quantum dot. By performing the exchange in solution, researchers can avoid the mechanical stress, cracking, or incomplete reactions often associated with solid-state treatments, yielding highly stable and processable nanoparticle inks for subsequent device fabrication.