An Inverse electrolysis method to Synthesize Surface Nano-roughened ZnO Contact Electrode
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1201-H05-51
An Inverse electrolysis method to Synthesize Surface Nano-roughened ZnO Contact Electrode
Yu-Hao Liao, Yi-Hao Pai, and Gong-Ru Lin Graduated Institute of Electro-Optical Engineering and Department of Electrical Engineering, National Taiwan University, No.1, Roosevelt Road Sec. 4, Taipei 10617, Taiwan R.O.C.
ABSTRACT The fabrication of surface nano-roughened zinc oxide (ZnO) is demonstrated by using a zinc/air fuel cell based chemical reactor. The chemical reaction creates the hydroxyl near the Zn and randomizes the pores with accumulated hydroxyls, which causes Zn to be oxidized to form thick and nano-roughened ZnO upon Zn anode or to be transformed into a soluble complex zincate ion in the excess electrolyte. Furthermore, controlling the quantity of (Zn(OH)2) and [Zn(OH)4]2− can significantly decrease the defect-related emission and blue-shift PL spectra to the UV range.
INTRODUCTION Zinc oxide (ZnO) is a wide direct bandgap semiconductor with Eg of 3.36 eV and has a large free exciton binding energy of 60 meV leading to efficient excitonic emission even at room temperature. In particular, it also has good chemical, mechanical, and thermal stability. These properties make ZnO a promising material for fabrication of optical devices [1]. The preparation of surface-roughened ZnO nanostructure is an important issue especially for efficient contact in solar cells. Most of the ZnO nano-structures have been prepared by vapor-based methods. However, these techniques are normally high-cost and need special equipments as well as need to be performed in strict condition, for example high-vacuum. To solve these problems, some techniques have been developed such as wet chemical method [2], aqueous solution route and rapid thermal processing [3], and solution growth method [4]. Nevertheless, weak crystalline and defect properties are normal questions for the material prepared by these techniques. In this work, we demonstrate a novel technique for preparation of nano-roughened ZnO by zinc/air fuel cell based chemical reactor at room temperature. The crystalline characterization, defect and surface morphology analyses of ZnO and growth mechanism will be discussed.
EXPERIMENT The zinc/air fuel cell based chemical reactor is shown in Figure 1. The zinc plate is used as the anode in a zinc/air cell employing 7M KOH as electrolytes. The ZnO samples with area of 10 cm2 are prepared at room temperature with a constant reactive time of 100 min by zinc/air fuel cell based chemical reactor discharging at resistance of 100, 25, and 1.6 Ω for sample A, B, and C, respectively. The room temperature photoluminescence (PL) measurements with excitation at 325 nm of He–Cd laser are performed in order to investigate defects of the nano-roughened ZnO structure.
Furthermore, the XRD measurements are applied to analyze formation of ZnO
crystals under different preparation condition.
Load Zn Plate
Air Electrode
Figure 1 the zinc/air fuel cell based chemical reactor.
RESULTS AND DISCUSSION The morphology of ZnO prepared in differ
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