Comparative study of ZnO nanorod array and nanoparticle film in photoelectric response and charge storage

The sol-gel method and the aqueous solution method were employed to synthesize the ZnO nanoparticle film (NPs) and the nanorod array film (NRs). The photoelectric responses of the NPs and the NRs were investigated. Compared to the ZnO NPs film, the as-grown ZnO NRs array was composed of hexagonal wurtzite nanorods which grew in preferential c-axis [0001] direction. The band gap of the ZnO NRs decreased, and its absorption edge exhibited the red shift. X-ray photoelectron spectroscopy confirmed that the ZnO NRs array film contained more oxygen vacancy defects and chemisorbed oxygen. After removing the UV illumination excitation source, the photoconductivity of the ZnO NPs film rapidly degraded. However the ZnO NRs film exhibited a special charge storage property. The photoconductivity of the ZnO NRs performed a long time degradation process that indicated the photogenerated carriers in the NRs had the longer lifetime and the lower recombination rate. The special photoelectric response and the charge storage of the ZnO NRs were attributed to the carrier transport mechanism which was different from the one of the NPs, as well as the different charge state oxygen vacancies distributed in the different regions of the ZnO NRs. (C) 2013 Elsevier B.V. All rights reserved.