Study On The Synthesis And Characterization Of Copper Indium Sulfide Materials Under Room Temperature

Among all kinds of solar cells, CIS thin film solar cells have been attracting more and more attentiondue to its chacteristics of high energy conversion efficiency, stable performance under outdoor conditionsand insensitivity to the change of temperature. CIS materials are usually prepared in harsh conditions (highvacuum, high temperature, other expensive devices and so on). So there is no large-scale industrializationof CIS-based solar cells. It is important to explore a low-cost synthesis method of CIS. The Cu/In ratio andstructural features play an important role on their performance. By studying the reaction process andreaction mechanism, we can synthesize CuInS2which can better conform to our requirements. In particular,the preparation of CIS materials at room temperature and the research of its reaction mechanism canpromote the application of CIS.We have synthesized CuInS2at room temperature with Cu foil as copper source in our early study. Thepreparation method does not need expensive devices and high vacuum. No toxic materials are included inthe method. This method also avoids the segregation of copper ions and indium ions in aqueous phasewhich contains sulfide ions. But the products have weak crystallinity. At the same time, copper reacts withsulfur ions faster than indium ions, indium ions can react with sulfur ions to generate well crystalline In2S3.How the copper foil reacts with sulfur and incorporates with indium to generate CuInS2is the the topic westudy. The reaction process and reaction mechanism are not clear.Based on the discussions above, we first synthesized large area of CuInS2and CuIn5S8films with theuse of copper foil, secondly with the addition of BSA, changed the morphology of products. Finally wepreliminary studied the reaction mechanism by analyzing more intense intermediate products.The concrete work is listed below.1. Fabrication of CuInS2and CuIn5S8at room temperatureWith the addition of copper foil, we synthesized CuIn5S8with a wet chemical method. With theincreasing of copper foil, the products phase changes from CuIn5S8to CuInS2. But we did’t get the singlephase CuInS2. Then we decreased the concentration of In2(SO4)3and TAA. We got single phase CuInS2.During the changing process, the crystallinity of the products becomes weaker. 2. Research on the reaction mechanism of synthesis of CuInS2and CuIn5S8thin filmsBased on the results listed above, we preliminary studied the change of the composition and structureof the material during the reaction process. Then with the introduction of BSA, We changed themorphology of CuInS2. We investigated the effect of the different dosage of BSA on the products. Themore BSA resulted in more monodisperse products. To better understand the formation mechanism of thematerials, we carried out a more detailed TEM study to determine the formation and shape evolution of thenanocrystals as a function of reaction time. On the basis of results above, a reaction mechanism wasproposed. At first, the In3+reacted with S2-to generate In2S3. Then the Cu was reducted by TAA into Cu+,with time passing by, the products transformed into CuIn5S8, finally transformed into CuInS2.