Preparations And Optical Properties Of ZnO/Cu₂ZnSnS₄P-N Junction And ZnS Buffer Layer

(CZTS) thin film solar cells have become a research hotspot recently. ZnO/CZTS P-N junction is the core of the thin film solar cells. Buffer layer introduced between CZTS and ZnO can reduce their lattice mismatch and improve the quality of P-N junction. In this thesis, the laser molecular beam epitaxy method was adopted to prepare ZnO/CZTS P-N junction on the high quality CZTS thin film, which was early prepared on ITO glass substrate by our research group, and ZnS buffer layers were prepared directly on the ITO glass. The effects of process parameters on the microstructure and optical properties of ZnO and ZnS thin films were systematically analyzed in this thesis, and the main research results are as follows:1) All ZnO thin films deposited on CZTS films exhibit the wurzite hexagonal structure with preferred orientation along (002) plane, and their surfaces are uniform and densely packed with island grains. The film shows the best crystallization quality at the pulsed laser energy of180mJ·P-1, oxygen partial pressure of0.8Pa, and substrate temperature of200℃. However, large mismatch-stress exists in the ZnO thin films for their large lattice mismatch without any buffer layer. 2) When ZnS thin films were directly deposited on the ITO substrates by the laser molecular beam epitaxy technique, all the films show the cubic sphalerite structure with a preferred orientation along the (111) plane. The crystallization quality of ZnS thin films improves with the increasing of substrate temperature, and it firstly improves then deteriorates with the increasing of pulsed laser energy. At the substrate temperature of500℃and pulsed laser energy of180mJ·P-1, the ZnS thin film shows the good crystallization quality and smooth surface.3) ZnS thin films deposited under different process parameters exhibit high transmission in the visible region, about75%. Their absorption curves show a strong absorption edge in the wavelength region of325～365nm. Based on the transmittance spectra, the calculated bandgap energys of ZnS thin films lies in3.492～3.594eV, which is slightly less than the standard value of3.6eV for the lack of sulfur element.