Atmospheric pressure synthesis of In2Se3, Cu2Se, and CuInSe2 without external selenization from solution precursors

In2Se3, Cu2Se, and CuInSe2 thin films have been successfully fabricated using novel metal organic decomposition (MOD) precursors and atmospheric pressure-based deposition and processing. The phase evolution of the binary (In-Se and Cu-Se) and ternary (Cu-In-Se) MOD precursor films was examined during processing to evaluate the nature of the phase and composition changes. The In-Se binary precursor exhibits two specific phase regimes: (i) a cubic-InxSey phase at processing temperatures between 300 and 400 degrees C and (ii) the gamma-In2Se3 phase for films annealed above 450 degrees C. Both phases exhibit a composition of 40 at.% indium and 60 at.% selenium. The binary Cu-Se precursor films show more diverse phase behavior, and within a narrow temperature processing range a number of Cu-Se phases, including CuSe2, CuSe, and Cu2Se, can be produced and stabilized. The ternary Cu-In-Se precursor can be used to produce relatively dense CuInSe2 films at temperatures between 300 and 500 degrees C. Layering the binary precursors together has provided an approach to producing CuInSe2 thin films; however, the morphology of the layered binary structure exhibits a significant degree of porosity. An alternative method of layering was explored where the Cu-Se binary was layered on top of an existing indium-gallium-selenide layer and processed. This method produced highly dense and large-grained (> 3 mu m) CuInSe2 thin films. This method has significant potential as a manufacturable route to CIGS-based solar cells.