Studies On Nano-crystalline ZnO Porous Films Prepared By Wet-chemical Method

ZnO is n-type wide band-gap semiconductor materials. Because of its highabsorption for light and good electron transportation, ZnO is used asphoto-electrodes of nanocrystalline solar cell which should have porousstructure and larger surface area. The key that synthesizes good property,nanocrstalline and porous ZnO films is the preparing method.Porous ZnO films were synthesized respectively by using inorganicchelating sol-gel method, electrochemical deposition and PEG-assisted sol-gelmethod. The effects of processing conditions on the microstructure andproperties of the ZnO films were studied and the pore forming mechanism ofeach method was discussed fundamentally.The stable chelate complex of citric acid and Zn²⁺ was synthesized byinorganic chelating sol-gel method. The surface of ZnO films was porous andthe pore distribution was mainly in the range of 2.02～4.97nm. The surface areaof the ZnO film was 27.6m²/g. The transmittance was above 90% in visibleregion and the band gap was 3.25eV.The ZnO film deposited from 0.02M aqueous solution of Zn(NO₃)₂·6H2Omixed with 5wt%SDS was composed of lamellar crystalline and porousstructure, which indicated that the anionic headgroups of SDS cooperativelyinteract with Zn²⁺ under our deposition condition on the electrode. Thetransmittance was above 75% in visible region and the band gap was 3.6eV.The ZnO film deposited from 0.02M aqueous solution of Zn(NO₃)₂·6H₂Omixed with 1wt%CTAB was composed of curl flake crystalline and porous,which result from the sorption of CTAB on the electrode. The transmittance ofZnO films decreased with reducing wavelength, and the more the depositionvoltage was, the less the transmittance was.The ZnO films synthesized by PEG-assisted sol-gel method were porous andthe PEG-O-Zn complex was formed between PEG and sol particle. The solbathed at 70℃ was propitious to the formation of big pores and the pore sizewas about 200-400nm, which result from phase separation in this system.However, the less pore could be formed without sol bath and the pore size wasabout 40-100nm, which resulted from the linking and wrapping colloid action ofPEG..