Synthesis And Characterization Of Chalcogenide Photoelectrical Materials

Because of growing concerns about environmental problem and energy exhaustion, a cheap and clean source of renewable energy is essential for mankind. Among a wide variety of renewable energy sources, solar energy is the best alternative. Chalcogenide photoelectrical materials(CuxS, CuInSe2, CuInS2, CuFeS2, Cu2ZnSnS4) have attracted considerable attention due to their wide application in photoelectric transition, luminescence, piezoelectricity, gas sensor and thermoelectricity, etc.CuInSe2 and CuInS2 are promising absorber layer materials for thin film solar cells. In particular, a CuInxGa1-xSe2(CIGS) thin film solar cell doped by gallium to CuInSe2 has achieved the highest efficiency of 19.9%. Since CuInS2 does not include a toxic element, CuInS2 is more environment-friendly than the selenium-contained material. Furthermore, because the band gap of CuInS2 is the most suitable for solar cell application, there is no need to add other elements to optimize the band gap. The highest reported efficiency of CuInS2 based thin film solar cell is close to 13%.Thin film solar cells based on CulnGaSe2/CdS have developed greatly. However, due to the limited supply and increasing price of rare metals, such as tellurium, indium and gallium, there is a great need to find alternative materials with high abundance and low cost. CuFeS2 and Cu2ZnSnS4 are the most promising materials for the absorber layer of thin-film solar cells of low-priced thin film solar cells, which do not contain any toxic or low abundance elements.In this paper, chalcogenide photoelectrical materials were chosen as the research subiect, and were prepared by a relative facile chemical method based on the review of the current research status.X-ray diffraction (XRD) and scanning electron microscope (SEM) were used to characterize the performance of samples. Several important results were summarized as follows:Firstly, CuInSe2 thin films were prepared by chemical co-reduction. It is analyzed that the effect on surface morpholopy and structure of thin films with different solvents, heat-treatment temperatures and reaction times. The major experimental results were as follows:(1) From the XRD analysis, it can be seen that CuInSe2 thin film with H2O and NH3·H2O as solvent has the better continuous surface,denser, higher degree of crystallization, less impure peaks than ethanol and ethylene glycol.(2) CuInSe2 thin films were prepared at different heat-treatment temperatures(120,160,180, 200 and 220℃)by chemical co-reduction. Results showed that, the degree of crystallization of CuInSe2 thin films are improved with heat-treatment temperature increasing. The optimal heat-treatment temperatures are 160℃and 200℃.(3) With the reaction time's increasing, the surface morphology of CuInSe2 which prepared at 160℃, with NH3H2O as solvent, become rougher and the degree of crystallization increase, with the reaction time's increasing, the surface morphology of CuInSe2 which prepared at 200℃, with H2O as solvent and with chalcopyrite structure with preferred (112) orientation,compactness decreased.Secondly, CuInS2 thin films were prepared by chemical co-reduction. The results show that:(1) With thiourea as sulfur source, the CuInS2 thin films prepared by chemical co-reduction with deionized water as solvent at 200℃for 20h, which shows the chalcopyrite structure with preferred (112) orientation. From the SEM images, the surface morpholopy of CuInS2 thin films was improved by adding NH3 H2O, EDTA and C2H7NO solvents.(2) With thiourea as sulfur source. CuInS2 thin films prepared by two-step method have the lower degree crystallization than CuInS2 thin films prepared by chemical co-reduction.Thirdly, nostoichiometric CuS thin films were prepared by chemical reduction sulfurization method using CuCl·2H2O and S powders as reactant, N2H4·H2O as reducing agent at diferent reaction temperatures. In particular, the XRD shows that, it can obtain different orientation of CuS thin films at 150℃,180℃and 200℃for 20h, respectively. This is a promising approach for fabricating CuS thin film at low cost.Lastly, the ternary and quaternary sulfides nanoparticles CuFeS2 and Cu2ZnSnS4 were synthesized using hydrothermal co-reduction method at 200℃for 20h. The starting reagents were inorganic chloride and thiourea. The phase structure and crystallinity of nanoparticles were investigated using X-ray diffraction and scanning electron microscopy. The results show that, the particle average size is 300nm; inadequate dispersion degree of reactants is the main reason of unequal morphology of the nanoparticles.