Abstract: Methods of forming copper indium gallium diselenide (CIGS) layers for photovoltaic devices are disclosed. In one aspect, a solution based selenization method in the formation of CIGS is provided. In some embodiments a substrate containing elemental copper (Cu), indium (In) and gallium (Ga) is coated with a solution comprising a source of selenium (Se) dissolved in a solvent. After coating with the selenium based solution, the substrate is heated to form the CIGS layer. Coating of the substrate with the selenium based solution may be carried out by dip coating, slit casting, gap coating, ink-jet type coating, among other techniques. The solution based selenization method disclosed herein provides high material utilization and low cost, unlike vacuum based processes.