Current promoted micro-annealing in anodic TiO2tube arrays and its application in sensitized solar cells

Abstract

Crystallization in nanostructured materials is an important basis of solar cells and other nanoscience fields. For instance, crystalline TiO₂ for photovoltaic and photocatalysis applications is normally formed by high-temperature annealing above 450 °C for a long period of time (normally more than one hour). In this work, we have established a method to artificially induce crystallization in ordered anodic TiO₂ tube arrays at around room temperature for the first time. Assisted by the existence of an electric field in the reaction system, crystallization could take place at a much lower temperature than isothermal annealing. Aided by the low thermal conductivity of TiO₂, the sample surface temperature could be limited to an even lower value (below 130 °C). The as-fabricated samples could show significant efficiencies of up to 2.05% after being installed into back-side illuminated dye sensitized solar cells. Furthermore, a nearly monocrystalline-like structure could be formed through some simple physical and chemical manipulation. As a result, an efficiency of 3.51% could be achieved, together with V_OC = 0.63 V, J_SC = 13.03 mA cm⁻², and FF = 0.47. This method can easily realize high quality crystallization in nanostructures like TiO₂ tube arrays of a particular size. It can be helpful for the development of new solar cells and other opto-electronic devices, and hopefully for mechanistic studies of other materials as well.