Colloidal copper indium gallium selenide (and sulfide) (CIGS) nanocrystals approximately 10 nm in diameter or less were synthesized by high temperature arrested precipitation. The ligand chemistry turns out to be extremely important for the synthesis of these CIGS nanocrystals, and many common ligands used for arrested precipitation of metal and semiconductor nanocrystals do not work because they negatively impact the reaction chemistry and yield primarily stable molecular byproducts. Deposition strategies were then developed to achieve uniform, thick (~1 micrometer) CIGS nanocrystal films largely free of cracks. The as-deposited films are relatively resistive and prototype photovoltaic (PV) devices constructed from these films show only a weak PV response. Further processing steps were developed to greatly improve the properties of the nanoparticle films, resulting in decreased resistance, better photoresponse and higher PV efficiencies from devices constructed with these nanoparticle-based absorber layers.