Synthesis And Characterization Of CuInS₂Thin Film At Low Temperature

In the context of the rapid development of global economy and the decline of environment quality aswell as frequently in an emergency of the traditional energy, people has recently been groping for a newkind of green, undefiled and rich energy to replace the traditional energy. In the past unceasing research,CIS-type thin film solar cells have attracted attention for their unique material superiority and advantages.For example, CIS-type thin film solar cell has a high conversion efficiency and an optimum optical bandgap which can absorb most wave length of sunlight. No noxious element such as Se was doped during thepreparation of CIS-type thin film solar cell. These characteristics make CIS-type thin film solar cell becomeone of the most promise new energys. However，the application of CIS-type thin film solar cell on a largescale has not been achieved. The main reason includ the complex technologies, expensive equipments inthe preparation, the vacuum-based preparation process, and the difficulty in controlling the quality of thefilm accurately and obtaining large area thin film. Therefore, exploring a low-cost and green preparation isone of the key problems to develop CIS solar cells. In addition, structural propertie of CIS-type materialplays a vital role on their performances. Exporement of Effective regulate by a simple method in CIS thinfilm structure was basilica for the use of CIS materials. It has a very important significance for theapplication of these materials to achieve effective control of CIS thin-film structure by a simple way.Materials prepared by biomimetic mineralization method have a series of features, such as, low energyconsumption （mild conditions such as temperature and pressure）, high crystallinity, controled morphologyand structure, etc. Biomimetic mineralization method is introduced into the CIS preparation could achievemorphology and structural controllable adjustment, thereby improving the performance of CuInS₂thin film. It will not only expand the application scope of biomimetic mineralization, but also promote theimprovement of solar cell performance. In addition, the mixed phase of Cu₂S and In₂S₃are always obtainedsince the inconsistent reaction rate of Cu, In and S, in previous attempts of one-step synthesis of CuInS₂thin film at room-temperature. The process is complicated and cumbersome using complexing agents toadjust the reaction rate of Cu, In and S. Complexing agents in product are difficult to remove. Thereactiong rate of Cu in reaction system can be reduced while Cu sheets are introduced into as copper source,achieving the reaction rates consistent of Cu, In and S. The wet chemical method using copper sheets ascopper source is a simple and practical method for the preparation of CuInS₂films under ambientconditions. Preparing CuInS₂films by this method does not require expensive equipments, no vacuumcondition and toxic elements introduced. The wet chemical process using Cu sheet as cooper sourceprovides a new ideas for the preparation of CuInS₂thin films.Based on the above thought, firstly, In₂S₃thin films were prepared by the wet chemical methods atroom temperature, and Cu₂（OH）₃（NO₃） thin films were prepared by the biomimetic mineralization methodin this thesis. Then Cu₂（OH）₃（NO₃） thin film materials were prepared through biomimetic mineralizationmethod on In₂S₃thin film substrates. The In₂S₃/Cu₂（OH）₃（NO₃） composite thin films transformed intoCuInS₂after sulfidizing at500℃for30min. The influence of the In/S ratio and the reaction time on theIn₂S₃substrate films was studied, and the optical absorption characteristics of CuInS₂thin films wasstudied as well. However, the connection between thin films synthetized by this method and substrate wasunstable. In order to explore a simple method for preparing high-quality CuInS₂thin films, we introducedthe Cu sheets as copper source, to the wet chemical process. Compact large area CuIn₅S₈and CuInS₂thinfilm materials were prepared successfully by one step. The results show that, using copper as coppersource could effectively reduce the reaction rate of the copper in the reaction system to achieve the consistency of the reaction rates of Cu, In and S, resulting the the synthesis oflarge-scale, continuous,dense CuInS₂thin films at room temperature. Overall, the reseach provids a new way for the preparationsof CuInS₂thin films. They may be a new method in low-cost preparation of CIS thin film materials.The research is composed of the following parts:1. Fabrication of CuInS₂thin film via two-step deposition sulfide methodUniform and compact monolayer In₂S₃thin films were deposited on glass substrates by the wetchemical methods, dense and close-packed Cu₂（OH）₃（NO₃） thin films were prepared by the biomimeticmineralization method, respectively. Then Cu₂（OH）₃（NO₃） thin films prepared by biomimeticmineralization method were transferred onto the In₂S₃thin film substrates by vertical lift method, achievingthe uniform and compact In₂S₃/Cu₂（OH）₃（NO₃） compound films. The composite thin films as a precursortransformed into polycrystalline CuInS₂thin films after the vulcanization process at500℃for30min. Theinfluence of the In/S ratio and the reaction time on the In₂S₃substrate films was studied in detail, and theoptical absorption characteristics of CuInS₂thin films was studied as well. It turned out that thecompactness and continuity of the In₂S₃thin films were good at the ratio of In/S of1:5and the reactiontime of72hours, and the films obtained at this condition are formed by closely packed In₂S₃single-layer.The CuInS₂thin films presented good crystalline properties and absorption characteristics. The optimumoptical band gap of CuInS₂thin films was1.45eV.2. The synthetize and growth process research of CuIn₅S₈and CuInS₂thin films by wet chemicalmethodCompact large area CuIn₅S₈and CuInS₂thin films were synthetized via wet chemical method with Cusheets as copper source. The structure properties of CuIn₅S₈and CuInS₂thin films were characterized. Theanalysis result indicated that the reaction rate of Cu in reaction system could be reduced effectively by using Cu sheet as copper source, achieving the reaction rate consistency of Cu, In and S. In the reactionsystem, the balance of reaction rates of Cu and In is the key facror of the CuInS₂thin film synthesis, andthe amount of Cu in the reaction system also played a crucial role in the transform from CuIn₅S₈to CuInS₂.Using copper sheets as copper source, compared with copper compounds, such as copper nitrate and copperacetate, etc, cuold effectively reduce the release rates of the copper in the reaction system. The decrease inthe reaction rates of Cu achieves by some complicated reaction process, for example, Cu dissolves first, andthen transforms into copper ions. By these complex transformation processes, the reaction rate consistencyof Cu, In and S have been achieved, and CuInS₂thin films have been successfully prepared. This method issimple and low-cost. Thin films prepared by this method were excellent in compactness and continuity. Itprovides a good idea for the preparation of CuInS₂thin films.