Growth of copper indium sulphide films by thermal evaporation of mixtures of copper sulphide and indium sulphide powders

摘要

The physical evaporation of a 1:1 mixture of copper sulphide (CuS) and indium sulphide (In_2S_3) powders by resistive heating followed by the vacuum annealing of the resulting films at 723 K produces copper indium sulphide (CuInS_2) films with about 95% phase purity. Composed of sub-micron sized grains, the films bear stoichiometric or Cu-rich composition and are endowed with p-type conductivity, a band gap of about 1.5 eV and an absorption coefficient of about 4 × 10~4 cm~-1 in visible region. Mechanistically, the formation of CulnS_2 films takes place as a result of solid state reaction among Cu_7S_4, InS and In_2S_3 in the condensed phase. These intermediate species are produced from the decomposition of CuInS_2 formed in the evaporating mixture due to the reaction between CuS and In_2S_3, and excess CuS. Process simplicity and the absence of a sulphurisation step make this approach attractive for synthesising CulnS_2 absorber layers for photovoltaic applications.