Study Of Key Materials For Cu（In, Ga）Se₂-based Thin Film Solar Cells

Energy is the material resources in nature to provide a particular form of energy for human, which is the material basis of all human activities and the driving force behind the entire development of human society. With the further development of human civilization, a global energy shortage is increasingly plagued human society. So seeking a green alternative energy and achieve sustainable development, has become the subject of facing all countries in the world. The solar energy, as a clean and cheap renewable energy, is more and more concerned by people. So far among many kinds of solar cells, the Cu(In, Ga)Se2 (CIGS) thin film solar cell is regarded as a promising future generation of solar cells due to its high conversion efficiency, low cost and prominent stability. In order to establish the foundation for green, high-performance and low-cost CIGS solar cells, the absorption layer, CdS buffer layer and ZnSe buffer layer have been research in our thesis. Therefore, the thesis structure is also divided into three main parts, as follows:The first part mainly includes studying the performance of CIS and CIGS thin films by vacuum sputtering precursor and selenization process. First, the CuInSe2 thin films are prepared by magnetron sputtering and selenization. CuIn metal prefabricated layer was prepared by direct sputtering CuIn alloy target and co-sputtering of CuIn alloy target and pure In target, the selenium to replace the highly toxic H2Se and "three-step heating selenization" is used to selenide the CuIn metal prefabricated layer, and prepared the copper-rich CIS thin films. The CuInSe2 thin films were characterized by SEM、EDS and XRD. Focus on the influence of prefabricated layer preparation process and follow selenization process on the quality of CuInSe2 thin films. Then, the preparation techniques of Cu(In, Ga)Se2 thin films were further studies. In order to prepared the CIGS absorber layer with gradient band gap in the thickness direction, the laminated CuInGa prefabricated layer with "sandwich" structure were prepared by alternately sputtering the CuIn target and CuGa target. The results show that:with the In content of CuIn prefabricated layer increasing, Cu atom ratio of CIS thin films decreased gradually and In atom ratio increased, the Se/(Cu+In) atom ratio of CIS films also increased accordingly. CuIn prefabricated layer with various Cu/In atom ratio after selenized annealing can generate CuInSe2 thin films which have chalcopyrite structure and (112) crystal plane preferred orientation. The CIGS thin films with chalcopyrite structure were obtained by selenized in 450-550℃ and the grain size increased gradually with the selenide temperature increasing. Cu, In, Ga and Se atomic ratio of CIGS thin films selenized in 550℃ was 1.15:0.72:0.28:1.46, and the films show the P-type conduction properties.The second part is the preparation of CdS buffer layer. CdS thin films were deposited on ordinary glass substrates by chemical bath deposition (CBD) technique using the precursors of CdCl2, NH4Cl, NH3·H2O and SC(NH2)2. Examine the impact of ammonia concentration, thiourea concentration, ammonium chloride concentration and deposition temperature for CdS thin film morphology, structure and optical properties. At last, we explored the optimal parameters of preparation CdS thin films by chemical bath deposition: 0.005 M Cadmium chloride,0.03 M ammonium chloride,0.4 M ammonia and 0.025 M thiourea, the deposition temperature is 60℃ and deposition time is 60 min. Good dense and smooth, high crystallinity and good optical performance, high-quality CdS thin films were obtained.The last part is the preparation of non-toxic environmentally friendly buffer layer of ZnSe thin films. First, we prepared the selenomethionine sodium sulfate (Na2SeSO3) to replace the expensive selenium urea as a source of selenium. ZnSe thin films were deposited on ordinary glass substrates by chemical bath deposition (CBD) technique using the precursors of ZnS04, H4N2H2O, NH3·H2O and Na2SeSO3. Examine the impact of deposition time, ammonia concentration, hydrazine hydrate concentration, zinc sulfate concentration and deposition temperature for CdS thin film morphology, structure and optical properties. At last, we explored the optimal parameters of preparation ZnSe thin films by chemical bath deposition:0.05 M zinc sulfate,2.14 M hydrazine hydrate,0.7 M ammonia,0.025 M sodium selenosulfate, the deposition temperature is 80℃ and deposition time is 60min. Higher quality of ZnSe thin films than the CdS thin films were obtained under this process. Moreover, ZnSe thin films are expected to replace CdS as buffer layer for high efficiency CIGS thin film solar cells.