CuInSe₂ Thin Films Synthesized By Sol-Gel Based On Nitrates As Precursors

Copper indium diselenide(CuInSe₂) semiconductor compounds has became wide research concerns in thin film solar cells field for its high absorption coefficient, low-cost and long-term stability. The best conversion efficiency of copper indium gallium diselenide solar cells has reached 19.9%, which is prepared by co-evaporation. In order to develop large-scale commercial application of CuInSe₂ thin film solar cells, mainly from the points of low-cost and environmentally friendly, the non-vacuum preparation methods of CuInSe₂ aborption layer and ZnO window layer have been researched. The thesis mainly includes two parts, as follows:The first part mainly includes the synthesis of high quality chalcopyrite CuInSe₂ films by a non-vacuum solution method using nitrates as sources. The precursor film based on sol was firstly prepared by spin-coating process and then sequential reduction and selenization treatments were performed in hydrogen and Se vapor, respectively. Through X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscope (SEM) and Raman scatting measurements, it was found that uniform, high crystalline and crack-free films were obtained by this simple method. Also, the films exhibited Cu_2-xSe secondary phase free property, indicating the excellent quality of the synthesized CuInSe₂ thin films. Moreover, the phenomenon and mechanism of the two-layered structure formation of the synthesized CuInSe₂ thin film were proposed. The synthesized film with direct sequential reduction and selenization treatments was divided into two layers: the upper layer was the CuInSe₂ while the bottom layer included carbon except for the small grains CuInSe₂. The residual triethanolamine (TEA) in the film because of less volatility, which decomposes into carbon at high temperature, is the main cause of the double-layers phenomenon. The residual carbon could not only induce the separated layers of the film, but also restricts the growth of the CuInSe₂ grains. After oxidation in air at particular temperature, such stratified phenomenon can vanish as a result of the removing of residual carbon, but induces worsening the compactness and flatness of the film, which would affect the quality of the film and next solar cells preparation.The second part is the nanostructure ZnO film synthesized by non-vacuum method. Firstly, the precursor film was prepared on glass substrate by sol-gel and then deposited in chemical bath. It was found that the different conditions had a great effect on the final film morphologies. With and without addition of 1,3?diaminopropane, the tapered ZnO nanostructure and rodlike ZnO nanostructure could be synthesized, respectively. Also, the temperature played an important role and much too higher temperature would be detrimental to the formation of tapered ZnO nanostructure. The mechanism of the tapered ZnO nanostructure formation is proposed based on the phenomena observed in the experiments. Moreover, the optical transmittances of these tapered ZnO nanostructure films for different growth time were investigated. It was found that such a tapered nanostructure could increase the transmittance and the maximum enhancement of global transmittance in range of 400-1000 nm wavelength we had achieved was about 1.6% when the growth time was 2 hours. The enhancement of transmittance allows more incident light to reach the absorber layer and could improve the conversion efficiency of the solar cells.