Synthesis and Physicochemical Investigation of CuInS2 Quantum Dots based Photo Anode for Photovoltaic Devices /

Abstract

The importance of energy is apparent in human life, especially in the modern time when almost every aspect in our daily life is related to energy consumption. However, with the explosion of the world’s population and the depletion of fossil fuels, energy crisis is threatening the whole world now. Uninterrupted clean energy supply is a vital issue for all countries today. Solar energy is a promising solution to the problems of the energy crisis and environmental pollution, since solar energy is highly abundant, renewable and clean. Quantum dot (QDs) based solar cells have gained substantial attention due to their prominent factors such as tunable band gap, quantum confinement effects that enhances their efficiency due to multiple excitons generation. Group I-III-IV are emerging material for solar cells due to their high absorption coefficient in visible light range, direct band gap, and low toxicity. Copper Indium Sulphide (CuInS2) QDs are chosen in this work for use in solar cells as a photo anode material because of their relatively low toxicity compared to other QDs materials such as Cd, Pb etc. This thesis is focused on the fabrication of CuInS2 QDs based photo anode by simplest, safest and cheapest approach. The concerns about the synthesis of photo anode materials is also important. In this thesis, firstly nanostructured wide band gap oxide (TiO2) material is synthesized by sol gel approach and then copper indium sulfide quantum dots (QDs) are synthesized by simple co-precipitation method. After synthesis procedure the CuInS2 QDs are annealed at different temperature to examine the effect on the crystalline structure and the sizes of the QDs. Electrophoretic deposition (EPD) is the simplest and low-cost approach used to deposit the nanostructured TiO2 and CuInS2 QDs. After the synthesis of photo anode materials the TiO2 and CuInS2 QDs films are fabricated on conducting FTO glass as an absorber layer for solar cells. As the quality and the thickness of the film play important role on the performance of the advanced nanostructured materials so different electrophoretic deposition parameters are investigated to achieve the required film because it is great challenge in EPD to create the stable and uniformly thick film. The effect of the EPD for CuInS2 at different voltages over the smoothness and the thickness of the film was also studied in this thesis. v After the fabrication of photo anode the characterization (XRD, SEM/EDS, and UV-Vis spectroscopy) is performed to identify the crystallite size, phase, surface morphology, elemental composition and to figure out the size of the CuInS2 QDs based on their band gap calculated by its optical properties. The XRD patterns indicates the chalcopyrite structure of CuInS2 QDs. The SEM images shows that smooth film is obtained at low applied voltage (90V). The purity of the sample detected by EDS spectra. The calculated molar ratio for Cu:In:S are 1.03:1:1.65, which is closely matched with the nominal stoichiometry of CuInS2 materials (1:1:2). Based on the UV-Vis spectral data the estimated band gap and particle size of the CuInS2 are 2.33eV and 8.4nm respectively which confirmed the formation of QDs. Quantum mechanical simulation based on DFT methods using Gaussian 09 software is carried out to compare with the part of our experimental results.