Preparation And Investigation Of ZnO Film Deposited By LPCVD Technology

Zinc oxide（ZnO） is the main transparent conductive oxide（TCO） materials applied as front electrodes in silicon thin film solar cells and CIGS thin film solar cells owing to its high electrical conductivity and optical transparency. The study of preparation and properties of ZnO films is a hot research topic in photoelectric field. ZnO films were grown by low pressure chemical vapor deposition（LPCVD） technique in this paper. The influence of deposition parameters on the properties of ZnO films was systematically investigated.Meanwhile, the stability of Zn O films was studied by damp heat（DH） treatment and annealing treatment. Ar plasma dry-etching technique could be used to modify the surface texture of ZnO films and therefore enhance the efficiency of applied silicon thin film solar cells. Detailed works of the thesis is included as follows.Firstly, the influences of deposition parameters such as deposition time, substrate temperature, gas flow rate and etc. on the properties of ZnO films were systematically investigated. It is found that deposition rate of ZnO films prepared by LPCVD technology is relatively high. The Crystal structure, surface texture, electrical and optical properties of ZnO films strongly depend on the deposition parameters. Under the optimized deposition conditions i.e. substrate temperature of 155 o C, working pressure of 50 Pa, DEZ flow rate of 5sccm and H₂O flow rate of 20 sccm. The pyramid-shape rough Zn O films are obtained with high deposition rate of 210nm/min and good electrical and optical properties（Resistivity of1.05×10-3 Ω·cm, mobility up to 39.9 cm2/Vs）. Optimized ZnO films were applied in CIGS solar cells as window layer（front TCO electrode） and the cell efficiency of 10.06% was obtained.Secondly, ZnO films were put into the environmental chamber for damp heat（DH）exposure treatment under a temperature of 85 o C and a relative humidity of 85 % to study the stability of ZnO films. It was proved that the surface structure and optical properties didn’t change through the DH exposure here. The electrical properties of Zn O films have greatly degraded after the DH exposure treatment since H₂O and O₂ might migrate into the films toreside in the grain boundaries. By annealing treatment the properties of ZnO films could be partly recovered.Thirdly, a dry-etching treatment with Ar plasma was carried out on LPCVD ZnO films to modify their surface textures. It was proved that the pyramids gradually disappeared and the surface texture turn to U-shape morphology with the increasing treatment time. Such a technology could effectively improve the growth of silicon thin films and thus enhance open circuit voltage and fill factor of solar cells when the modified ZnO films were applied as front contact in the silicon thin film solar cells.