Grain boundaries in polycrystalline Cu(In,Ga)Se2 thin films exhibited only slightly enhanced recombination, as compared with the grain interiors, allowing for very high power-conversion efficiencies of more than 20% in the corresponding solar-cell devices. This work highlights the specific compositional and electrical properties of Cu(In,Ga)Se2 grain boundaries by application of appropriate sub-nanometer characterisation techniques: inline electron holography, electron energy-loss spectroscopy, and atom-probe tomography. It was found that changes of composition at the grain boundaries were confined to regions of only about 1nm in width. Therefore, these compositional changes were not due to secondary phases but atomic or ionic redistribution within the atomic planes close to the grain boundaries. For different grain boundaries in the Cu(In,Ga)Se2 thin film investigated, different atomic or ionic redistributions were also found. This chemical flexibility made polycrystalline Cu(In,Ga)Se2 thin films particularly suitable for photovoltaic applications.

Confined and Chemically Flexible Grain Boundaries in Polycrystalline Compound Semiconductors. D.Abou-Ras, S.S.Schmidt, R.Caballero, T.Unold, H.W.Schock, C.T.Koch, B.Schaffer, M.Schaffer, P.P.Choi, O.Cojocaru-Mirédin: Advanced Energy Materials, 2012, 2[8], 992-8