Electrophoretically self-assembled mixed metal oxide-TiO2 nano-composite film structures for photoelectrochemical energy conversion: Probing of charge recombination and electron transport resistances

Abstract

Nanotitania/metal oxide composite films are prepared via the coupling of low DC voltage Electrophoretic Deposition (EPD) of P25 TiO2 nanoparticles with simultaneous electrolytic deposition of hydrous metal oxides, namely ZnO, MgO and Al2O3. The nanocomposite films are built into dye-sensitized solar cell photoanodes and their interfacial charge recombination and electronic resistances are investigated. The nano hydrous oxides were found to co-deposit (1–3 wt%) uniformly within the TiO2 film (forming island-like nanodeposits) significantly increasing film adhesion. Analysis via Electrochemical Impedance Spectroscopy and Open Circuit Voltage Decay techniques found, among the three composite films, the TiO2–Al2O3 electrode to exhibit the highest charge recombination resistance at the TiO2/electrolyte interface (Rrec) and as consequence an increase in Voc. However, its conversion efficiency (4.14%) was the lowest because it suffered from very high electron transport resistance (Rt) in the TiO2 network. By comparison, the TiO2–MgO film resulted in 5.40% efficiency and the TiO2–ZnO film in 5.85% efficiency-both exhibiting significantly lower Rt resistance. The obtained results point to the need for simultaneous optimization of the nanocomposite TiO2/metal oxide film structure in terms of high interfacial charge recombination resistance and low overall electron transport resistance.