Study On Synthesis Methodology Of Metal Selenide Semiconductor Nanomaterials Based On The Acitivation Of Elemental Selenium

CuInSe2(CIS), one of the most promising light-absorbing semiconductor materials, is widely used in solar cells, photoelectric sensor, light-emitting diode, optoelectronic storage devices and so on because of its high absorption coefficients(α≈5×105 cm-1), desirable band gap through doping(1.02~1.67 eV), high theoretical cell efficiency and good thermal stability. The preparation methods of CIS can be divided into two categories: physical methods and chemical methods. Physical methods include evaporating, sputtering, molecular beam epitaxy, liquid-phase epitaxy and halogen vapor deposition. However,high demanding of the experiment equipments and capital investment hinder large scale production for industrialization. On the contrary, chemical methods represented by solvothermal synthesis are suitable methods for easy operation, with low capital investment and in favor of large-scale production. Moreover, it is also simple to adjust the ratios of different elements by using chemical methods. But the synthesis of the ternary compounds through solvothermal method has the problem of low reaction efficiency. The diversity of the intermediate products leading to the complication of the reaction pathways is the essential reason. This thesis describes our investigation regarding the reaction process of CIS ternary compounds by using solvothermal method. The two-step approach is used to investigate the different reaction pathways and their influence on the chemical reaction kinetics. The main achievements are concluded as follows:(1) Different stoichiometric ratios of Cu-Se and In-Se binary compounds are first produced by solvothermal method at 200 °С. Through comparing the different products obtained at different reaction time and element ratios, we find that the reaction between Cu and Se precursor produce Cu2-xSe after heating 4 h at 200 °С regardless using sufficient Se or difficient Se. Unidentified In-Se impurity phase are produced in Se-rich condition after heating 12 h. In comparison, In(OH)3 is produced through hydrolysis with Se-poor condition. More important, the experimental results of the experiment imply that Cu precursor reacts more quickly with Se than In precursor and the competition between Cu and In precursor with Se, which probably results in the global kinetics decreasing when synthesizing CIS ternary compounds.(2) Using general sovothermal method, Cu, In and Se sources are added in the solvent ethelydiamine at the same time and react for different time at the temperature of 200 °С. The results imply that the synthesis of the CIS is not from the direct reaction among three sources but results from competition between Cu and In precursor to react with Se. The reaction process results in a set of Cu-Se, In-Se binary compounds and In(OH)3 intermediate products. Through analyzing different products obtained at different reaction time, two possible reaction pathway can be described as:CuSe2 + In(OH)3 â†' CuInSe2 and CuSe + In(OH)3 + Se â†' CuInSe2.(3) Two-step method is first used to prepare CIS material. Certain ratio of In precursor and Se react prior the addition of Cu precursor. The final products are synthesized with the subsepuent addition of Cu. Compared with general solvothermal method, two step method can produce pure phase CIS and the reaction time is reduced from 16 h to 8 h. Meanwhile, the morphology and size of the particles are obviously improved. The reason can be attributed to the competition between Cu and In precursor to react with Se, which leads the reaction pathway in favor of synthesizing CIS particles. Through analyzing different products obtained at different reaction time, two possible reaction pathways can be described as follows: CuSe + 1/2In2Se3- 1/2Se â†' CuInSe2 and CuSe + InSe â†' CuInSe2.(4) Related precursors are chose to synthesize the CIS material based on the different reaction pathway referred above. The different reaction pathways are verified at the same time.(5) We use the lattice matching principle to conduct the crystal analysis for the related compounds observed in the different reaction such as InSe, In2Se3, CuSe, CuSe2, Cu2-xSe, In(OH)3, CuInSe2 and we explain possible reaction pathway and the efficiency of the reaction by comparing the lattice parameter of different precursors.