Sol-Gel Processed TiO 2 Nanotube Photoelectrodes for Dye-Sensitized Solar Cells with Enhanced Photovoltaic Performance.

The performance of dye-sensitized solar cells (DSCs) critically depends on the efficiency of electron transport within the TiO ₂ -dye-electrolyte interface. To improve the efficiency of the electron transfer the conventional structure of the working electrode (WE) based on TiO ₂ nanoparticles (NPs) was replaced with TiO ₂ nanotubes (NTs). Sol-gel method was used to prepare undoped and Nb-doped TiO ₂ NPs and TiO ₂ NTs. The crystallinity and morphology of the WEs were characterized using XRD, SEM and TEM techniques. XPS and PL measurements revealed a higher concentration of oxygen-related defects at the surface of NPs-based electrodes compared to that based on NTs. Replacement of the conventional NPs-based TiO ₂ WE with alternative led to a 15% increase in power conversion efficiency (PCE) of the DSCs. The effect is attributed to the more efficient transfer of charge carriers in the NTs-based electrodes due to lower defect concentration. The suggestion was confirmed experimentally by electrical impedance spectroscopy measurements when we observed the higher recombination resistance at the TiO ₂ NTs-electrolyte interface compared to that at the TiO ₂ NPs-electrolyte interface. Moreover, Nb-doping of the TiO ₂ structures yields an additional 14% PCE increase. The application of Nb-doped TiO ₂ NTs as photo-electrode enables the fabrication of a DSC with an efficiency of 8.1%, which is 35% higher than that of a cell using a TiO ₂ NPs. Finally, NTs-based DSCs have demonstrated a 65% increase in the PCE value, when light intensity was decreased from 1000 to 10 W/m ² making such kind device be promising alternative indoor PV applications when the intensity of incident light is low.
Competing Interests: The authors declare no conflict of interest