The growth and characterization of Cu(ln,Oa)Se, polycrystalline thin films under the presence of thin-MF (M=Na, K, Cs) precursor layers is presented. Some electrical, structural, and electronic absorber properties due to the presence of such Group la impurities are quantified along with their influence in device performance. We present a growth model for the role of Na in Cu(ln,Ga)Se, that attributes the enhancemeiits in electrical conductivity and photovoltaic device performance to the extinction of a finite number of donor states (i.e., I n , ) at the bulk and grain-boundary regions.
In most Cu(In,Ga)Se2 thin films used for solar cells, there usually exist interfaces lying about 0.1 to 0.2 μm 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)Se2 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.
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