Bilayer TiO2 photoanode consisting of a nanowire–nanoparticle bottom layer and a spherical voids scattering layer for dye-sensitized solar cells

Abstract

The structural design of TiO₂ photoanodes has proved to be a useful approach in improving the energy conversion efficiency of dye-sensitized solar cells (DSSCs). Herein, a bilayer TiO₂ photoanode consisting of rutile nanowires (NWs) infiltrated with anatase nanoparticles (NPs) as a bottom layer and spherical voids (450 nm) in a NP film as the top layer is prepared via a simple one-time spray technique on a 1D TiO₂ NW array. The bilayer structure exhibits an excellent dye-loading property and efficient light scattering ability, as confirmed by dye-desorption, diffuse transmittance and reflectance spectra, and incident-photon-to-current conversion efficiency (IPCE) results. As a result, the DSSC based on the bilayer photoanode ((1.6 + 2.6) μm) exhibits remarkably higher photocurrent output and overall energy conversion efficiency (3.2 times and 3.5 times higher, respectively) than a 1D TiO₂ NW device (1.6 μm) under AM 1.5G simulated solar irradiation. The enhanced device performance can be ascribed to the synergistic effect of a large surface area for sufficient dye-loading, efficient light scattering for sufficient light harvesting, fast charge transport for efficient charge collection and a highly porous structure of the top spherical voids layer for fast diffusion of the I⁻/I₃⁻ electrolyte in the bilayer TiO₂ photoanode. This study provides a facile route towards improving the photovoltaic performance of 1D TiO₂ NW array solar cells based on constructing bilayer structures via a simple one-time spray technique.