Room temperature non-vacuum preparation of nanocrystalline CuInSe2 employing aqueous solvents

A new room-temperature, aqueous solution-based preparation method for chalcopyrite CuInSe₂ has been developed. Using 10% aqueous ethylenediamine as a solvent, the slow addition of Cu(NO₃)₂ to a mixture of indium(III) acetate, elemental Se, and sodium thioglycolate results in the formation of CuInSe₂ as characterized by Raman spectroscopy. During this reaction, a kinetically-stable Cu_2-xSe(s) intermediate initially forms followed by slow conversion to CuInSe₂ that likely involves a direct Cu_2-xSe + In₂Se₃ solid-state reaction. The ethylenediamine in the reaction mixture acts as a complexing agent, establishing equilibria that can be in competition with Cu_2-xSe(s) formation, limiting particle size and accelerating rates of reaction with In. Over several hours, the CuInSe₂ material undergoes a phase decomposition that can be reversed by annealing at 550 °C. Attempts to prepare CuIn_1-xGa_xSe₂ and CuGaSe₂ via this method result primarily in CuInSe₂ and Cu_2-xSe products, respectively, with nearly all gallium staying in the solution phase.