Characterization of solution-grown and sputtered in x (O,S) y buffer layers in Cu(In,Ga)Se2 solar cells by analytical TEM

Abstract

Cu(In,Ga)Se2 thin-film solar cells were fabricated with In x (O,S) y as buffer material, where the buffer was deposited by either solution growth or radio-frequency sputtering. To elucidate the influence of the particular deposition technique on the properties of the In x (O,S) y layers, their structural peculiarities were characterized by high-resolution transmission electron microscopy (TEM) and nanobeam electron diffraction. Energy-dispersive x-ray spectroscopy in combination with scanning TEM was used for chemical analysis of the interfacial regions between Cu(In,Ga)Se2 absorber and In x (O,S) y layer as well as of the buffer itself. In general, the solution-grown and sputtered In x (O,S) y layers show a nanocrystalline structure. In both types of In x (O,S) y buffer layers, crystalline phases of tetragonal In2S3 and cubic In2O3 were detected. In addition, there are hints for the formation of a Cu-containing phase, e.g. hexagonal CuS in the sputtered In x (O,S) y layer. Moreover, there are also distinct differences in the chemical composition of the two analyzed In x (O,S) y layers, namely in the solution-grown In x (O,S) y buffer layer the oxygen content is considerably higher than in the sputtered In x (O,S) y layer.