Two-step growth of a hierarchical ZnO nanostructure by aqueous thermal decomposition in a neutral solution and its photovoltaic property

A two-step aqueous thermal decomposition method was used to synthesize a hierarchical ZnO nanostructure on indium–tin-oxide (ITO) glass in a neutral solution. As revealed by scanning electron microscopy and transmission electron microscopy, the product consists of a layered structure of ZnO nanorods at the bottom and nanowire atop. The ZnO nanowires were grown along the [0 0 0 1] direction with 20 nm in diameter and exceeded 10 μm in length. The growth mechanism of the hierarchical ZnO nanostructure is discussed. Our results indicate that neutral solution and low Zn concentration are the keys for growing long and thin ZnO nanowires in large scale. Hierarchical ZnO nanostructure has applications in solar cell device as the electrode can largely improve the incident photon to current conversion efficiency (IPCE) and photovoltaic conversion efficiency (PCE) values due to the high aspect ratio. Nanowire ZnO on the top layer can absorb significant amount of quantum dots and the photoexcited electrons can efficiently get transferred into the FTO surface though nanorod array.