The chemical composition of Cu(In, Ga)Se2 (CIGS) thin film was monitored in real time during the physical vapor deposition. The temperature of growing CIGS film was found to depend on the composition ratio of Cu/(In+Ga) when the film was deposited under constant heating power. The composition monitoring system can be easily applied to a 3-stage deposition process of the CIGS films. The solar cells (active area: 1 cm2) fabricated by using the obtained CIGS absorber layer showed an efficiency of 15.4% under standard AM 1.5 illumination.
Polycrystalline Cu(In1−xGax)3Se5 thin films were prepared by four source evaporation with controlling and shielding of the molecular beams from elemental sources. Ga content x, can be controlled by deposition times of CuIn3Se5 and CuGa3Se5 layers, which form Cu(In1−xGax)3Se5 films through the interdiffusion. X-ray diffraction analyses showed that the films with x≲0.5 have an ordered vacancy chalcopyrite and the films with x≳0.5 have a zinc blende structure. The optical band gap of the films linearly increased from 1.23 eV (x=0) to 1.85 eV (x=1) with increasing Ga content. The conductivity of the films was about 10−6/Ω cm and about 10−7/Ω cm under and above x=0.3, respectively.
MoSe2 layers formed at the interface between Cu-In-Ga-Se and Mo layers were studied by X-ray diffraction and high resolution transmission electron microscopy. Various composition Cu-In-Ga-Se films such as Se, Cu-Se, In-Ga-Se and Cu-rich Cu-In-Ga-Se were deposited on Mo coated glass substrates by physical vapor deposition. For the case of the Se/Mo interface, a MoSe2 layer of about 100 Å thickness was observed. The c-axis of the MoSe2 grains were found to be oriented normal to the surface of Mo layer. For the Cu-Se/Mo and Cu-rich Cu-In-Ga-Se/Mo structures, the thickness of the MoSe2 layers found at the interface was thin. For the case of the In-Ga-Se/Mo structure, a 0.1 µm thick interfacial MoSe2 layer was observed whose c-axis was oriented parallel to the Mo surface. The microstructure of the In-Ga-Se/Mo film was similar to that of the device quality CIGS/Mo structure deposited by the “3-stage” process. A formation mechanism for the MoSe2 layers occurring during the “3-stage” process is proposed.
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