CTS And CZTS Based Thin Films And Solar Cells Fabricated By A CBD Method

Recently, in order to meet the aspirations of the energy, new energy resources have been widely concerned, especially the photovoltaic power generation technology. Semiconducting compounds thin film solar cells, including copper indium gallium selenide (CIGS) thin film solar cells and copper zinc tin sulfur (CZTS) thin film solar cells, have been widely researched. Over 21% and 12.6% of photoelectric conversion efficiency of CIGS and CZTS thin film solar cells have already been obtained respectively. However, the difficult preparation of complicated compounds and expensive production equipments for this kind of solar cell directly restrict the marketization process. The main position in the market is still occupied with silicon-based solar cells. In order to prepare low cost, high efficiency Cu-based thin film solar cells, in this paper, a non-vacuum and low temperature method of Chemical Bath Deposition (CBD) was introduced and studied in preparation of CTS and CZTS thin film solar cells.In the first chapter, we have detailed reviewed the principle, history, current situation of solar cells, especially the CTS and CZTS thin film solar cells. Finally, the research topic and the main research content of this paper were taken out.In the second chapter, the principle, history, and mechanism of film-forming of CBD method were introduced in detail firstly; secondly, the deposition of ZnS thin film was introduced to describe the effects on the preparation of thin films during CBD process. In the last section, a new concept, we called it ARR(Assistant Reduction Reaction), was introduced to deposit metallic Cu thin films. The successful preparation of Cu metallic thin films means the broken of original category of CBD method which has been defined as preparation of non-metallic compound films, such as metallic oxide and sulfide.In the third chapter, we have successfully prepared CTS thin films and CTS based thin film solar cells by CBD method with stack structure Mo/SnS/Cu. Not only the structural, morphological, compositional and optical properties of CTS thin films but also preliminary solar cells based on CTS thin films with stacked layer Mo/SnS/Cu by CBD-annealing route have been studied. A slightly increasing linear relationship about Jsc in a reasonable range of temperature is obtained by studied the influence of annealing temperature, and the best performance of the final devices with PEC of nearly 1%is obtained under 600 ℃ forlOmin with the ratio of Cu/Sn about 1.68.In the fourth chapter, there are two parts of work in this section:(1) CZTSSe thin films and CZTSSe based solar cells were successfully fabricated by the CBD-annealing method with the optimal order SnS/Cu/ZnS. The efficiency of the best performance CZTSSe and CZTS-based thin film solar cells under AM1.5 illumination(100mW·cm-2,25℃) fabricated by the CBD-annealing method was 3.0%and 2.2%, respectively. The photoelectric efficiency of CZTSSe thin-film solar cells was reached to 4.5%after the improvement of chemical composition and morphology of precursor films. In addition, we have attempt to preparaed large area CZTSSe based thin film solar cells. The total active area is 3.238 cm2 and the average photoelectric efficiency is 4.378%, the highest photoelectric efficiency is nearly 5.6%; (2) A comparative study was taken out on the performance of CZTS thin films and devices by introducing Cu thin films instead of CuS in stack layers SnS/Cu(S)/ZnS by CBD-annealing route. Craks and an unexpected secondary SnS2 which inevitably affect the performance of final solar devices were demonstrated in the stack SnS/CuS/ZnS. Supplementary Sn powder would equilibrate the reaction in stack SnS/CuS/ZnS and the best CZTS solar cell obtained with stack SnS/CuS/ZnS annealed with S and Sn powder at the same time achieved a conversion efficiency of 3.09%.In the fifth chapter, we extend this CBD method to prepare Cu2MSnS4 (M:Cd,Mn)thin films with stacked layer SnS/Cu/(CdS, MnS) and compare with Cu2MSnS4(M:Zn) thin films on morphology, chemical composition, structure and bandgaps. The results suggest that the high quality Cu2MSnS4(M:Zn,Cd,Mn) thin films can be obtained by this CBD-annealing route. If the present technique was properly extended, it would be also possible for the low cost and large-scale preparation of other multi-elements thin films with stacked layers for practical application.