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NANO EXPRESS

Open Access

Growth and optical properties of ZnO nanorod arrays on Al-doped ZnO transparent conductive film Suanzhi Lin1, Hailong Hu2, Weifeng Zheng1, Yan Qu1 and Fachun Lai1*

Abstract ZnO nanorod arrays (NRAs) on transparent conductive oxide (TCO) films have been grown by a solution-free, catalyst-free, vapor-phase synthesis method at 600°C. TCO films, Al-doped ZnO films, were deposited on quartz substrates by magnetron sputtering. In order to study the effect of the growth duration on the morphological and optical properties of NRAs, the growth duration was changed from 3 to 12 min. The results show that the electrical performance of the TCO films does not degrade after the growth of NRAs and the nanorods are highly crystalline. As the growth duration increases from 3 to 8 min, the diffuse transmittance of the samples decreases, while the total transmittance and UV emission enhance. Two possible nanorod self-attraction models were proposed to interpret the phenomena in the sample with 9-min growth duration. The sample with 8-min growth duration has the highest total transmittance of 87.0%, proper density about 75 μm−2, diameter about 26 nm, and length about 500 nm, indicating that it can be used in hybrid solar cells. Keywords: ZnO nanorod, Al-doped ZnO films, Catalyst-free growth, Optical properties PACS: 81.07.-b, 61.46.Km, 78.67.-n

Background ZnO, one of the most important metal oxides, has a wide bandgap of 3.37 eV and a high exciton binding energy of 60 meV at room temperature. One-dimensional nanostructures have a high aspect ratio and surface area, and can provide a direct conduction path for electrons. Accordingly, a wide range of ZnO nanostructures [1] such as nanowires (NWs), nanorods (NRs), and nanonails are extensively studied for their applications in various optoelectronic devices, e.g., gas sensors [2], UV photodetectors [3,4], lasers [5,6], electron field emitters [7], solar cells [8-12], and nanogenerators [13]. For most photovoltaic devices, the light is coupled in devices through transparent conductive oxide (TCO) substrate, so tailored well-aligned ZnO nanorod arrays (NRAs) grown on TCO substrate are of particular interest because they can improve the device performance [14]. Previously, ZnO NRAs and NWs on different TCO * Correspondence: [email protected] 1 College of Physics and Energy, Fujian Normal University, Fuzhou 350108, People’s Republic of China Full list of author information is available at the end of the article

substrates have been synthesized by various growth methods including chemical bath deposition [8,10,11], electrochemical deposition [9,12,14], and thermal vaporphase deposition [15,16]. Among these methods, the vapor-phase growth method has many advantages such as excellent crystalline quality of the nanostructures [15], low cost, and simplicity [17]. Generally, ZnO NRs in dyesensitized solar cells or hybrid solar cells are used to extract the carriers from an organic material and transfer the carriers toward the electrode [15]. Moreover, the density, dia