Microstructure of surface layers in Cu(In,Ga)Se2 thin films

In most Cu(In,Ga)Se-2 thin films used for solar cells, there usually exist interfaces lying about 0.1 to 0.2 mum below surfaces. We report on convergent-beam electron diffraction and energy-dispersive x-ray spectroscopy study of the microstructure and chemical composition of the surface region in Cu(In,Ga)Se-2 thin films. We find that the surface region and the bulk are structurally similar, with no ordered defect chalcopyrite structure observed. However, their composition is slightly different, indicating that they can have different point defect physics. Our results suggest that the subinterfaces and the bulk absorber may form homojunctions. (C) 2002 American Institute of Physics.