On the assessment of incorporation of CNT–TiO2 core–shell structures into nanoparticle TiO2 photoanodes in dye-sensitized solar cells
Herein, we report dye-sensitized solar cells (DSCs) based on conventional nanocrystalline TiO2 photoanodes decorated with one-dimensional (1D) CNT–TiO2 core–shell structures (CTH). The core–shell nanotubes are synthesized by a simple sol–gel template-assisted method via in situ deposition of TiO2 on the surface of non-covalently functionalized CNTs. The core–shell nanotubes are well characterized by various techniques. Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) images show that formation of the TiO2 shell on the surface of the CNT core follows a layer or Frank–van der Merwe growth mode, resulting in a highly uniform interface with excellent charge transfer from the TiO2 conduction band into the CNTs. The thickness and crystal structure of the TiO2 shell can be tailored by controlling the processing parameters. X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy verify that CNTs have no surface defects and are well preserved using the employed method and the subsequent heat treatment in air, respectively. UV-vis spectroscopy and photoluminescence spectroscopy reveal an extension to visible regions with an increase in overall intensity and a significant reduction in charge recombination due to a shift of the Fermi level toward positive potentials. We find an increase by up to 37% in the DSC device's power conversion efficiency by incorporating the CNT–TiO2 core–shell nanotubes into the nanoparticle TiO2 photoanode due to the charge recombination reduction and electron injection enhancement.