Comparative Study on the Photoanode Nanoarchitectures for Photovoltaic Application

Vertically-aligned TiO₂ nanotube (NT) arrays prepared by electrochemical anodization are considered promising alternatives to the conventional nanoparticle (NP)-based electrodes for photovoltaic devices. Recently, such NT arrays have been employed in dye-sensitized solar cells (DSSCs) by transferring them onto NP-based electrodes, to obtain multi-layered nanoelectrodes. Here, we comparatively evaluate the photovoltaic and photoelectrochemical properties of TiO₂ NP-only electrodes and multi-layered electrodes comprising NP and NT arrays at the same thickness of 15 μm. Although the multi-layered electrodes have a smaller surface area compared to the NP-only electrodes, they show much higher transmittance. In addition, impedance studies reveal that the multi-layered electrodes have lower charge recombination with the electrolyte as well as enhanced electrolyte diffusion when applied as a photoanode in DSSCs. As a result, the multi-layered electrodes exhibit a photovoltaic conversion efficiency (η = 5.37%) comparable to that of the NP-only electrodes (η = 5.80%), despite 36.6% lower dye loading.