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

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.