Characterization of solution-grown and sputtered in $_{x}$ (O,S) $_{y}$ buffer layers in Cu(In,Ga)Se$_{2}$ solar cells by analytical TEM

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 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 In$_{2}$S$_{3}$ and cubic In$_{2}$O$_{3}$ 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.