Fabrication of CuInSe2 and Cu2ZnSnSe4 films from metal-oxide precursors and SeO2 using supercritical ethanol

•Conversion of Cu–In/Cu–Zn–Sn oxide films to CuInSe2/Cu2ZnSnSe4 films using SeO2.•Supercritical ethanol was employed as the reaction medium for selenization process.•Supercritical ethanol assists the reduction of oxide precursor films and SeO2.•High solubility of supercritical ethanol enables high concentration of Se species.•Prepared metal-selenide films showed ideal band gap.

In this study, we achieved the conversions of Cu–In and Cu–Zn–Sn oxide precursor films to CuInSe2 and Cu2ZnSnSe4 films, respectively, using SeO2 as a selenium source in supercritical ethanol (EtOH). EtOH enables sufficient supply of SeO2 to reaction field due to its high solubility. Moreover, EtOH in high temperature condition reacts with SeO2 to form diethylselenide, Et2Se, and elemental selenium, and shows self-oxidation to release hydrogen. These features of EtOH will contribute to the selenization for the fabrication of the metal-selenide film facilitates the fabrication of metal-selenide film with ideal band gap, even when both precursor film and selenium source are oxides. Supercritical-alcohol-assisted selenization will contribute to the development of the cost-effective non-vacuum fabrication process for metal-selenide in optical devices, such as solar cells.

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