ZnO-Coated TiO2 Nanotube Arrays for a Photoelectrode in Dye-Sensitized Solar Cells

In dye-sensitized solar cells, highly ordered TiO2 nanotube arrays as a photoelectrode have higher charge collection efficiencies than a nanoparticle-based structure due to their faster charge percolation and slower recombination of electrons. Highly ordered TiO2 nanotube arrays were grown by anodic oxidation of 0.5-mm-thick titanium foil. To increase the conversion efficiency of dye-sensitized solar cells with TiO2 nanotube arrays, the surface of the TiO2 nanotube arrays was modified by zinc oxide thin films. The ZnO thin film was formed by atomic layer deposition. The thin film was conformal on the inner and outer walls of TiO2 nanotube arrays. ZnO thin film improved the short circuit current (J (sc)) and open circuit voltage (V (oc)) due to increasing specific surface area from particulates of ZnO thin film and increasing the surface charge induced from the isoelectric point. The power conversion efficiency of dye-sensitized solar cells with ZnO thin film on 4.5-mu m-thick TiO2 nanotube arrays was 1.43%. Microstructure and phase were observed by scanning electron microscopy, x-ray diffractometry, and transmission electron microscopy.This research was financially supported by the Ministry of Education, Science Technology (MEST) and National Research Foundation of Korea (NRF) through the Human Resource Training Project for Regional Innovation (Grant No. 2012H1B8A202 6009)