Study Of Cu（In,Ga）Se₂Absorbers And Al:ZnO Window Layers Fabricated By Magnetron Sputtering

The significant amount consumption and demand of fossil energy such as coal and oil has resulted in serious environmental and social problems. People have been looking forward to some new clean renewable energy urgently in the purpose of sus-tainable development of resources, environment and society. Solar energy is one of the most promising source for future energy demanding and to convert the solar ener-gy into electricity via photovoltaic effect of solar cells is the most effective method. Recent decade copper indium gallium selenide (CIGS) thin film solar cells have caused more and more attention, giving their outstanding energy conversion efficien-cy, excellent stability and low manufacture cost.In the CIGS thin film solar cells, the quality of the functional layers has major influence on the performance of solar cells. The window layer of the solar cells not only has great impact on the quantum efficiency of the solar cells in the near ultravio-let and the infrared band of the solar spectra, but also on the series resistance of the solar cells thus affecting the short-circuit of the solar cell; while the absorber of the solar cells affects the characteristic of the p-n junction in the solar cells thereby affect-ing the open circuit voltage. In the production of the solar cell module, the cells are usually connected in series and/or in parallel to obtain a larger output power, so the differences in the performance of the solar cells will cause the deterioration of the module performance. Usually the solar cells are fabricated by scribing the deposited large-area laminated films and then cells are assembled in series and/or parallel, thus the homogeneity of the deposited films is critical for fabricating both cells and mod-ules. Furthermore, since the rare element indium and gallium are used in fabricating CIGS thin films, it limits the development of CIGS thin film solar cells. Meanwhile, the Cu2ZnSnS4(CZTS) is known for its abundant element in the earth crust and non-toxicity together with its excellent optical and electrical characteristics, and becomes an attracting alternative materials.The CIGS absorbers and ZnO window layers in CIGS thin film solar cells have been fabricated and studied for further fabrication of high quality, homogeneous films. Also the fabrication of CZTS thin films had been attempted and studied. This disserta-tion could be divided into three major sections.In the first section, CIS/CIGS thin films fabricated by selenization of co- sputtered metallic precursor were studied. The sputtering parameters during the de-posited of the metallic precursors were systematically studied and analyzed focusing on their influence on thephase component and elementary composition, in order to obtain precursors with controllable component and composition. The temperature dis-tribution near/above the precursor surface during the selenization was obtained by an-alog calculation, displaying a significant dependence on the material thermal conduc-tivity of the selenization container. The reaction mechanism during the selenization was studied and the migration of indium in the precursors was noticed and ascribed to the difference between Gu11In9and CuIn2and the difference between copper and indi-um. Also the phaseseparation during selenization of sputtered Cu-In-Ga precursors was investigated. By introducing a ultra-thin layer of Na contaminant onto the surface of the precursors, the phase separation of fabricated CIGS thin films was significantly improved. The introduced Na also lowered the selenization temperature.The second section was focused on deposition of high quality, high transparent homogeneous ZnO and aluminum doped ZnO window layers with magnetron sputter-ing. Both deposited films were (002) preferred-oriented with average transmittance above85%in the range of visible spectrum. An (103) textile was found on the depos-ited films through GIXRD test. With the help of XPS measurements the variation of oxygen vacancy concentration of annealed films was noticed and furthermore con-tributed to the understanding of lattice reducing caused by oxygen vacancies in the ZnO lattice. The aluminum doped ZnO presented inhomogeneity in composition, op-tical and electrical properties. Further investigation suggested that such inhomogenei-ty was caused by the Al/(Zn+Al) at.%variation in the films and finally ascribed to the different sputtering yield of zinc and aluminum atoms or particles in deposition space during sputtering. Therefore an off-axis magnetron sputtering technique was suggest-ed to deposited less inhomogeneous window layers.The third section contained some basic research on fabricating CZTS thin films by sulfuration of co-sputtered metallic precursors instead of co-sputtered sulfuret pre-cursors in order to avoiding the contaminating the sputtering chamber. Sulfuration parameters such as sulfuration route, sulfuration temperature and time and H2S con-centration during sulfuration were carefully studied. After etching the fabricated CZTS thin film surface with KCN solution and HCl solution sequentially, the contam-inated sulfuret phase as Cu2-xS, SnS, ZnS,Cu2SnS3were basically supposed removed by the measurement of XRD, Raman Scattering and spectrophotometer. The band-gap of fabricated and etched film was about1.48eV.