Research On Preparation Of CuInS₂ And In₂S₃ Thin Films For Solar Cells By Wet Chemical Method

With the shortage of and serious environmental pollution problems caused by the use of conventional energy, the renewable energy, especially the research and industrialization of solar cells, has developed rapidly in recent years. Crystal silicon solar cells currently occupy 90 percent of the solar cells market and the leading position in solar industry, but crystal silicon solar cells' further promotion and application are limited because of the high cost of silicon raw materials and its high production costs. In recent years, thin films solar cells with its low cost, low production costs and high performance stability have drawn lots of attention. I-III-VI2 family compound thin film such as CuInS2, with its high theoretical conversion efficiency, high absorption, well match with the solar radiation and good thermal stability, and other advantages, is regarded as a very promising candidate of the next generation thin films solar cells, and it currently is an international research hot topic.In this thesis, ultrasonic spray pyrolysis and electro deposition were used to fabricate CuInS₂ and In₂S₃ thin films based on the review of the current research status. After the preparation of the thin films, a systematic analysis and characterization was applied. The wet chemical methods don't need high vacuum, so it doesn't request expensive equipments, which is critical to achieve industrialization. Besides, the wet chemical methods have many advantages such as easy control of film thickness, good uniformity and density of the films, and so on. The research results are as follows:1. Homogenous and compact CuInS₂ thin films were prepared by ultrasonic spray pysolysis, and its thickness is 2～3μm and it is an n-type semiconductor. First, based on referring to other researches on ultrasonic spray pysolysis and our needs, the ultrasonic spray pysolysis equipment was designed. Second, the influences of different size and placed way of the substrate, different Cu/In ratio, different alcohol concentrations of precursor solutions and post anneal treatment on the fabrication of CuInS₂ was studied. It was found that better thin films were obtained when the molar ratio of Cu/In was 1.2:1, the volume alcohol was 10 %, and substrate with small size was placed under the spray nozzle orderly. Besides, it was also found that post anneal treatment could decrease thin films' absorption to visible light.2. Uniform and compact In₂S₃ thin films were successfully fabricated by ultrasonic spray pysolysis with a post rapid thermal process (RTP). It was found that thin films with better crystallinity were obtained as the RTP treatment temperature increased. After the characterization of optical properties, the thin films, with the Eg of 2.25～2.38 eV, had excellent transmittance to visible light, and it could be expected to be the buffer layer in the thin films solar cells.3. At the part of eletrodeposition CuInS₂ thin films, the influence of different Cu/In ratio, pH value and concentration of complex agent in the eletrodeposition solution to the fabrication had been studied, and it was found that when Cu/In ratio was 1:1, pH was 4, and 20 ml 0.025 mol/L citrate were added to the electrodeposition solution can get a better CuInS₂ thin films. Then, the influence of different post anneal temperature to the quality of CuInS₂ also was studied, and it was found that thin films with better crystallinity but worser absorption of solar radiation were obtained as the post anneal treatment temperature increased, and the E_g of CuInS₂ thin films found to be 1.44 eV, which indicate that the thin films are adapt to be thin films solar cells absorber layer.