Microscopic characterization of individual grain boundaries in Cu-III–VI2 chalcopyrites

The role of grain boundaries in polycrystalline Cu-III–VI2 absorber material for thin film photovoltaics has not been fully understood and is currently under discussion. Recently, intensive efforts have been devoted to the characterization of the properties of individual grain boundaries using microscopic techniques, including Kelvin probe force microscopy (KPFM). KPFM provides local electronic information by measuring the surface potential in addition to the topography. We introduce the KPFM method and present simulations assessing the technique's limitations with respect to spatial resolution regarding the measurement of grain boundary properties. KPFM studies of individual GBs in the Cu(In,Ga)Se2 materials system are reviewed and critically discussed, considering also results from other microscopic characterization techniques.