Characterization of solution-grown and sputtered In_x(O,S)_y buffer layers in Cu(In,Ga)Se_2 solar cells by analytical TEM

摘要

Cu(In,Ga)Se-2 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)Se-2 absorber and In-x(O,S)(y) layer as well as of the buffer itself. In general, the solutiongrown 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.