چكيده به لاتين
This work is a contribution to the obtain of CuInS2 stable colloidal which is applied in the deposition of CuInS2 compound by electrostatic spray method as a absorbance films to chalcopyrite thin film solar cells. Furthermore, the effect of different synthesis conditions on the crystalline structure and optical properties of the synthesized particles has been studied. The effects of process parameters on the crystalline structure and optical absorption spectra were investigated by X-ray diffraction (XRD) and ultraviolet and visible spectroscopy (UV-VIS), respectively. Moreover, to investigate the mechanism of intermediate compounds complex formation, Fourier transform infrared (FT-IR) in order to determine bands formed between organic and inorganic materials were used. A versatile method for a relatively low temperature synthesis of metastable CuInS2 nanocrystals using copper chloride salt, indium sulfate and thiourea in a solvent containing diethylene glycol and ethylenediamine with polyvinylpyrrolidone as a surfactant has been developed. The complex formed at 80°C and it decomposes at 240°C then particles form and after one hour the combination of solid solution changes to monophasic CuInS2 particles with a chalcopyrite and wurtzite structure (polytypism) with an average particle size 40nm. By the presence of peaks such as polyvinylpyrrolidone, diethylene glycol, ethylenediamine and thiourea on the surface of the nanoparticles in the analysis of FT-IR, these factors as a surfactant increase the stability of colloidal particles. Synthesized nanoparticles under the mentioned conditions, showed the absorption in visible areas and near IR at 820nm and 730nm which are related to chalcopyrite and wurtzite phases, respectively. The band gap of 1.45eV was obtained for the synthesized nanoparticles under the mentioned conditions which were in good agreement with the theoretical value and is suitable for making solar cell absorber layer. A stable colloid with 1 wt. % of these particles which dispersed in ethanol by applying ultrasonication was ready to film deposition. This colloid deposited on FTO glass by electrostatic spray deposition method by applying the voltages of 24, 26 and 28 kV, flow rates of 1, 2 and 3μl/min and the distance between nozzle to substrate of 60, 80 and 100 mm. After deposition process, heat treatment at 500°C was applied on deposited layers to enhance crystallinity and adhesion. The heat treating was carried out in the presence of sulfur powder to create a positive vapor pressure of sulfur and prevent sulfur leaving from composition of solid solution. After studying the microstructure using an optical microscope (OM), scanning electron microscope (SEM) and scanning electron field emission microscope (FE-SEM) images, it was identified that the suitable conditions to form a uniform layer with 1μm thickness are voltage of 26kV, flow rate of 2μl/min and nozzle to substrate distance of 80mm. The CuInS2 layer showed a high optical absorption in the visible wavelength range at 760nm and the band gap of 1.5 eV was obtained for this layer.
Keywords: CuInS2 particles, thermolysis, polytypism (chalcopyrite and wurtzite), electrospray, colloid.
