Surface Reconstructionof Epitaxial CIS Thin Films and Device Performance

The mechanism of preferential orientation and surfacereconstruction of CIS thin films was systematically investigated. Epitaxial CISthin films with orientations of (220/204), (001) and (112) were deposited onGaAs(110), (001), (111)A and (111)B substrates, respectively, by using ametal―sputtering and Se―evaporation hybrid technique. The main epitaxialrelationship was found to be GaAs(110) /÷CIS(220), GaAs(001) /÷CIS(001), and GaAs(111) /÷CIS(112), respectively. The morphological and structuralproperties of CIS thin films were determined by scanning electron microscope,atomic force microscope and X―ray diffraction. The (220/204) and (001) surfacesof CIS thin films were found to be unstable under the growth conditions. The depositedsurfaces were mainly covered by the lowest specific surface―energy (112) facetregardless of its orientation. Sequence of the specific surface―energy for CISfacets was deduced, based on the geometrical analysis of the defects. Solarcells with preferential oriented CIS thin films as absorber layers werefabricated. The (220/204)―oriented film is characterized to have the best photovoltaicperformance, which is consistent with the charge transportation and separationpreferring along [220] direction. It indicates that higher efficiency of CIS thinfilm solar cells can be expected by enhancing (220/204) orientation through processoptimization.