Synthesis and characterization of ZnO/TiO2 composite core/shell nanorod arrays by sol–gel method for organic solar cell applications

ZnO/TiO2 core/shell nanorod arrays were deposited on indium tin oxide (ITO) substrate via a facile sol–gel dip-coating process. Effects of solution pH for ZnO, annealing temperature, growth time and temperature on the physical properties of nanorods have been investigated. X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM) were employed to characterize the structural and morphological properties of the prepared composite nanorods. XRD result revealed wurtzite structure of ZnO with a mixed anatase and rutile structure phase for TiO2. Energy-dispersive X-ray (EDX) and UV–vis spectroscopy were used to study the chemical composition and optical properties of the films, respectively. Electrical resistivity of the films was also investigated. The optical and electrical properties of the bare TiO2 thin film and core/shell composite were compared together. The results showed that owing to smaller band gap and lower resistivity, the core/shell structure as an electron transport layer for inverted photovoltaic devices is more suitable than bare TiO2 thin film.