Improved performance of dye-sensitized solar cells using TiO₂ nanotubes infiltrated by TiO₂ nanoparticles using a dipping-rinsing-hydrolysis process

An efficient back-illuminated dye-sensitized solar cell (DSSC) is made with a flexible Ti-foil based photoanode composed of a composite TiO₂ film with TiO₂ nanotubes (TNT) and TiO₂ nanoparticles (TNP). The composite TiO₂ film is fabricated through a novel dipping-rinsing-hydrolysis (DRH) process by inserting TiO₂ into TNT and sintering the product to form TNP inside TNT. By directly placing TiO ₂ nanoparticles into TNT, the former grow internally from the base of TNT to occupy it completely. This solves previous problems of incomplete filling of TNP into TNT, which used partial penetration of TiCl₄ reactant from the top of the TNT. In the present case, the TNP are grown from the base of TNT. A DSSC containing TNT and TNP prepared in this way shows a photoelectric efficiency of 6.45%, which is much higher than that (4.21%) of a DSSC with untreated TNT. The films are characterized by using scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. The improvement in the photoelectric efficiency is explained by using electrochemical impedance spectroscopy (EIS), incident photon-to-current conversion efficiency (IPCE) analysis, and UV-absorption spectra analysis.