Preparation of In2S3Thin Films by MOCVD Using Single Source Precursors: Tris(N,N-ethylbutyldithiocarbamato)indium(III) and Tris(2-ethylpiperidinedithiocarbamato)indium(III)

Abstract

The ternary chalcopyrite semiconductor CuInSe2 (CIS) or related Cu(In,Ga)Se2 (CIGS) are well known materials for high efficiency thin film solar cells. In case of CIGS absorber film prepared through chemical bath deposition method, photovoltaic conversion efficiency was reported to be higher than 19%. Such high efficiency has been reached with a CdS buffer layer processed in a wet chemical bath and the CdS has been found to be best suited as a buffer layer material. However, cadmium is toxic and has a negative effect on environment. Therefore, there have been many studies to find replacement materials for cadmium sulfide. The possible candidates for the cadmium free solar cells are ZnS, In2S3, ZnSe, InxSey. Among these materials, In2S3 is nontoxic and exhibits optical and electrical properties similar to those of CdS. Also, In2S3 thin film deposited by ALCVD using In(acac)3 and H2S was reported to be an n-type semiconductor and was found to properly function as a buffer layer for the heterojunction solar cells. For the preparation of In2S3 thin films without using toxic H2S gas, various single source precursors suitable to the MOCVD process are possible. Among them, the precursors containing dialkyldithiocarbamate ligands with non-symmetrical structure are interesting since they were found to have better thermal properties compared to symmetrical ones. In this work, two single source precursors, tris(N,Nethylbutyldithiocarbamato)indium(III) and tris(2-ethylpiperidinedithiocarbamato)indium(III) (designated as In(ebdtc)3 and In(epdtc)3, respectively) were synthesized with high purity and yield. Using them, In2S3 thin films were successfully grown on various substrates, such as glass, ITO glass, and CIGS film through MOCVD process. Experimental Details