Preparation of In2Se3 Thin Films by MOCVD with a New In-Se Single Source Precursor

Abstract

In2Se3 is a binary compound, which is attracting wide attention because it can be used as an important material for polycrystalline thin film solar cell. It has various structural modifications of α, β, and γ-phase, and they have quite different electronic properties; α-phase of In2Se3 has low band gap, 1.2-1.3 eV at the temperature below 200 C. As temperature goes up to above 200 C, it is transformed to βphase with a band gap of 1.4 eV. In addition, when temperature goes to higher temperature, 350 C, it is converted to γIn2Se3 with a band gap of 1.8 eV. Particularly, γ-In2Se3 is interesting since it can be adopted as a suitable absorber layer in CdS/In2Se3 or In2S3/In2Se3 photovoltaic cells because of its high absorption coefficient and the band gap which is in an optimum range for solar energy conversion. Moreover, it can be used as a starting material to obtain CuInSe2 or Cu(InGa)Se2 thin films. The In2Se3 thin films can be prepared through various methods such as thermal evaporation, spray pyrolysis, metal organic chemical vapor deposition (MOCVD), electrochemical atomic layer epitaxy, electrodeposition, and many other methods. Among them, MOCVD method has many practical benefits than any other methods; especially, the composition, structure, and morphology of the In2Se3 thin films can be properly controlled. Furthermore, its process is rather simple and less expensive if a suitable single source precursor is available. In this research, two single source precursors, containing indium and selenium atoms: tris(N,N-ethylbutyldiselenocarbamato)indium(III) and tris(2-ethylpiperidinediselenocarbamato)indium(III), designated as In(ebdsc)3 and In(epdsc)3, respectively, were synthesized with high purity, and using them, γ-In2Se3 thin films were prepared by MOCVD.