Electrical conduction channel along the grain boundaries of Cu(In,Ga)Se2 thin films

We report on a direct nm-resolution resistance mapping on the Cu(In,Ga)Se2 photovoltaic thin films, using scanning spreading resistance microcopy. We found a conductance channel along the grain boundaries (GBs) of the polycrystalline materials, which is consistent with the argument that carrier polarity of the GB and the space charge region around it is inverted. To minimize the probe/film contact resistance, so that the local spreading resistance beneath the probe is measured, the probe must be adequately indented to the film and a bias voltage larger than the onset value of the probe/film barrier should be applied.