Solution-processing of semiconductor materials is an emerging strategy that can potentially reduce the cost of thin-film photovoltaic devices. The fundamental challenge accompanying this effort lies in processing of nanoparticles inks into high-performance solids that show high crystallinity and low defect density. This task becomes exceedingly difficult with a decreasing nanoparticle size. Here, we develop the ionic intercalation strategy by which nanostructured films are being forced to undergo an inter-particle ion exchange towards reducing the inter-surface tension (improves crystallinity) and achieving overall charge neutrality at boundaries (reduces defects). Such non-thermal interparticle fusion has been enabled by raising the ion solubility in deposited nanoparticles through establishing the lattice-solvent equilibrium regime. The degree of inter-particle intercalation has been varied towards achieving either a complete sintering of the film or a partial fusion that preserves the quantum confinement of individual dots. Thus, the ionic intercalation approach improves electrical characteristics of nanoparticle solids and provides a reliable starting platform for developing photovoltaic and other photoconducting solids.