Selenization of Cu and In thin films for the preparation of selenide photo-absorber layers in solar cells using Se vapour source

Gas phase selenization of vacuum deposited Cu and In thin films employing an elemental Se vapour source is demonstrated as an essential first step in the search for optimized process parameters for the formation of single phase CuInSe₂ materials suitable for solar cell applications. The selenization was accomplished in Se vapour, derived from an elemental Se source, held at 240–260°C. This source was placed in a flow of nitrogen gas at 500 Torr to transport the Se vapour to the metal films. The selenization reaction readily occurs at Cu and In films kept at 340–400°C. Lower selenization temperatures invariably lead to the formation of Cu and In selenides with well defined crystalline microstructures. Hexagonal CuSe with an excess of Se in the matrix is the equilibrium growth phase, while the cubic Cu_2−xSe phase evolves under conditions of excess Se flux. Selenization of the In films consistently led to the formation of the β-form of hexagonal In₂Se₃. At high selenization temperatures (400°C), while the β-form still emerges as the major component, traces of the α-form of In₂Se₃ are also detected. Detailed X-ray diffraction, electron probe analysis and microstructure data are presented.