چكيده به لاتين
While conventional fossil fuels are fast vacating, the worldwide energy demand is increasing due to fast growth of industrialization and population. During the recent years, photovoltaics have promised to emerge as a viable energy technology and environmentally benignant. The ternary I-III-VI2 semiconductors, particularly CuInX2 (X= S, Se) have several favorable properties as absorber layer in thin film solar cells. CuInS2 (CIS) due to its direct band gap (≈ 1.50 eV), high absorption coefficient (α ≈ 105) and radiation stability is one of these promising materials for solar cell applications.
Vacuum based procedure is currently used for fabricating highly efficient thin film solar cells because of its advantages like high quality films and high power conversion efficiencies. But some disadvantages such as highly cost productions, high temperature process under vacuum, high material waste and using toxic elements make researchers to develop alternative low cost and solution based techniques.
Recently, many researchers have investigated non-vacuum approaches like evaporation, sputtering, spray pyrolysis, chemical method and etc. Among the main vacuum-free approaches, low temperature solution-based processes is one of the best techniques that doesn’t need any complicated instruments. This approach is based on the printing from precursor solution ink. The most important part of this method is synthesis of suitable particles and their stable colloidal ink.
CIS nano objects with different morphologies such as nanorods, nanoparticles, nanowires and so on have been reported that prepared by using different methods included hot injection, microwave and solvothermal.
Among of different methods Solvothermal is a simple and impressive method to controlled synthesis of diverse particles. The benefits of solvothermal method can be categorized in two main aspects: one; facility, high purity of products, low cost equipment and crystalline nature of products in this method. Two; flexibility of this method in synthesis of specific and controlled morphologies and facility in products separation while predominant morphology in other methods such as sol-gel, microwave, sonochemical, etc. is nanoparticles.
But the required organic solvent such as ethylenediamine in solvothermal method is counted as drawback of this method as they are not environmentally friendly. Such organic solvents are also costly and easily evaporated. To avoid this problem, using deionized water as a more environmental friendly solvent rather than ethylenediamine and hydrothermal process is the better approach.
In this research, effect of time and temperature and sonication on phase, morphology and optical properties of Copper Indium Disulfur (CuInS2, CIS) synthesized by hydrothermal method have been investigated. Chloride salts of copper (II) (Cucl2.2H2O) and indium (III) (InCl3.xH2O) and thiourea (CS(NH2)2) have been used as starting precursors and deionized water ,an environmentally friendly solvent, is used as solvent. Samples have been characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and diffuse reflection spectroscopy (DRS). According to XRD results pure chalcopyrite CuInS2 phase successfully synthesized at 180°C and 20 hours with respect to XRD accuracy while impurity phases such as Covellite (Cu6S6) and Digenite (Cu5S9) have been disappeared. Flower-shape CIS particles with the average diameter of 5-6 μm and average petal width of 35-45 nm have been revealed by FESEM analysis and optical band gap calculated by DRS was in the range of 1.5 eV that is suitable for absorption material is thin film solar cell applications.
