Solvent-free synthesis of oxides for CuInSe2 thin films fabrication

► Synthesis of monodisperse oxides by solvent-free solid state reaction for CuInSe2 thin films has been described. ► Fixing Cu:In ratio molecularly by concentrating Cu-In solution into eutectoid salt before solid state reaction. ► Three categories of mixed salt-type were used to fabricate oxides with different mixing degree. ► The results also show that near stoichiometric CIS films with micron-sized dense grains are obtained in our work.