Atmospheric Pressure Synthesis of In2Se3, Cu2Se, and CuInSe2 without External Selenization from Solution Precursors

In ₂Se ₃, Cu ₂Se, 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-In _xSe _y phase at processing temperatures between 300 and 400 °C and (ii) the γ-In ₂Se ₃ phase for films annealed above 450 °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 CuSe ₂, CuSe, and Cu ₂Se, can be produced and stabilized. The ternary Cu-In-Se precursor can be used to produce relatively dense CuInSe ₂ films at temperatures between 300 and 500 °C. Layering the binary precursors together has provided an approach to producing CuInSe ₂ 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 μm) CuInSe ₂ thin films. This method has significant potential as a manufacturable route to CIGS-based solar cells.