The influence of different film textures on the electronic properties of polycrystalline Cu(In,Ga)Se2 absorbers was studied by measuring the laterally resolved opto-electronic properties of differently textured Cu(In,Ga)Se2 films with Kelvin probe force microscopy and cathodoluminescence. The grain boundaries in (112)- and (220/204)-textured films behave differently. The work-function profile measured with the Kelvin probe across a grain boundary in (112)-textured films showed a dip indicating positive charges at the grain boundaries. In panchromatic cathodoluminescence mappings in a transmission electron microscope, such grain boundaries appear dark, i.e. the strongly reduced luminescence indicated that the grain boundaries represent strong non-radiative recombination centres. In contrast, grain boundaries in (220/204)-textured films gave rise to a dip or a step in the work function indicating slightly negative charge or neutrality. Cathodoluminescence was reduced at such grain boundaries, but less dramatically than in the (112)-textured case. However, when Na was present in the (220/204)-textured films, the grain boundaries were almost invisible in cathodoluminescence mappings. This strong passivating action of Na occurred only in the (220/204)-textured films, due to a particular grain-boundary population. In (112)-textured films and films without pronounced texture, this passivation effect was much less noticeable.

Texture and Electronic Activity of Grain Boundaries in Cu(In,Ga)Se2 Thin Films. G.Hanna, T.Glatzel, S.Sadewasser, N.Ott, H.P.Strunk, U.Rau, J.H.Werner: Applied Physics A, 2006, 82[1], 1-7