Single-step electrodeposition of a microcrystalline Cu2ZnSnSe4 thin film with a kesterite structure

Abstract

Single-step electrodeposition synthesis of a Cu2ZnSnSe4 (CZTSe) film on a Mo-coated glass substrate from an acidic electrolyte containing Cu(II), Zn(II), Sn(IV), and Se(IV) species was investigated. The desired CZTSe film as the main phase was obtained at some selected applied potential ranges through reaction among binary selenides, Cu2Se, ZnSe and SnSe2, which were continuously formed in the present electrolyte containing all of the elements. Sulfurization of the as-deposited film at several temperatures under H2S gas flow resulted in the formation of corresponding mixed compounds of CZTSe and Cu2ZnSnS4 (CZTS), i.e., Cu2ZnSn(S,Se)4 (CZTSSe): specifically, sulfurization at temperatures higher than 500°C resulted in the formation of single-phase CZTSSe with S-rich compositions. By analyzing linear sweep voltammograms (LSVs) of sulfurized films under chopped irradiation, the films were confirmed to have p-type photoresponses; the film obtained by 500°C sulfurization showed the largest photoresponse because of its sufficiently large grain size and less voids, whereas the presence of an anodic spike in the LSV curve as well as the observation of a broad external quantum efficiency (EQE) spectrum suggested the requirement of further improvement in film quality for photovoltaic application.