Study On The Controllable Growth Of ZnO Transparent Conducting Nanowire Arrays

Transparent conductive oxide（TCO） thin film is a kind of functional material with two distinctive and outstanding properties: the visible-light transmission and electrical conductivity. Generally, the un-doped metal oxides show semiconductor nature and they need doping or other defective chemical methods to enhance their electrical conductivity.One-dimensional ZnO nanowire arrays exhibit light-trapping effect because the nanowire size is very close to the visible-light wave length and have potential applications in the transparent electrodes of thin film solar cells. However, the doping of single crystal ZnO nanowire is a great chanllenge. In this paper, the electrodeposition method was employed to prepare Al-doped ZnO transparent conducting nanowire arrays on TCO glass subtrates at low cost and large-area scale. The surface microstructure, phase composition and morphology of the samples were characterized by using scanning electron microscope, X-ray diffraction, energy diffraction spectrum, etc. and the growth mechanism was analyzed combined with the cyclic voltaammogram spectrum. The electrochemical reaction process of optimized Zn2+ and Al3+ion concentration, the applied potential, the distance between plates, temperature and other experimental conditions were determined, so as to realize the controllable growth of Al-doped ZnO nanowire arrays. The following main conclusions were obtained:（1） It was found that the crystallographic morphology of ZnO grown by electrodeposition was determined by the processes of electrochemical reaction, precipitation-dissolution and nucleation-growth. The appropriate conditions for ZnO nanowire array growth were follows:the Zn2+ concentration 0.003 M, the temperature 70⁸0 ℃, the distance between electroplates2 cm and the cathodic potential-1.6^-1.4V. The Al-doping could affect the preferential growth orientation, morphology and performance of ZnO nanowire arrays.（2） It was also confirmed that there existed great difference for electrodepositing ZnO from Zn（NO₃）₂-Al（NO₃）₃ and Zn（NO₃）₂-In（NO₃）₃ aqueous solutions, respectively. As for the former system, Al-doped ZnO nanowire arrays could be co-deposited, while as for the latter,only ZnO or In2O3 could be deposited separately, which might be attributed to the large difference between the solubility products of Zn（OH）2 and In（OH）3.（3） We have got the processing conditions that realizing the controllable growth ofAl-doped transparent conducting ZnO nanowire arrays. The structure and performance of Al-doped ZnO transparent conducting nanowire arrays were desired when the Al/Zn ratio was1 at.%, electrodeposition time was 60 min and cathodic reduction potential was-1.5V.（4） The synthesizing process of TiO₂ thin films by sol-gel method using titanium tetrachloride and tetrabutyl titanate as the precursors, respectively, was compared. The obtained films through the latter route were more uniform and compact, which was not easy to crack, and the electrical conductivity was better. It might be attributed to the reason that the continuous network chain of [-Ti-O-]n was easily formed for the latter. Therefore, the latter is more suitable for decorating fine-particle TiO₂ thin film on the surface of Al-doped transparent conducting nanowire arrays.