Fabrication of Cu$_2$ZnSnSe$_4$ thin films by selenising Cu$_{1.8}$Se, SnSe, and ZnSe precursor layers: effects of the sequence of layers

Thin films of Cu$_2$ZnSnSe$_4$ (CZTSe) with a deficiency of Cu and Zn excess are fabricated by a selenisation of precursors composed of several layers of the selenides Cu$_{1.8}$Se, SnSe, and ZnSe (with different sequences of the layers), deposited on glass substrates from water-based solutions. The elemental composition of the films is examined by electron dispersive analysis and X-ray photoelectron spectroscopy whereas the structure is analysed by X-ray diffraction. Films fabricated from precursors with the selenide layer sequence Cu$_{1.8}$Se|SnSe|ZnSe|SnSe demonstrate the CZTSe kesterite structure, whereas those produced from precursors with other sequences of the selenides are mixtures of binary phases.