Rutile TiO2 nanowire array infiltrated with anatase nanoparticles as photoanode for dye-sensitized solar cells: enhanced cell performance via the rutile–anatase heterojunction

The structural and interfacial design of TiO2 photoanodes plays an important role in improving the solar energy conversion performance of dye-sensitized solar cells (DSSCs). Herein, we report that a rutile nanowire (NW) array infiltrated with anatase nanoparticles (NPs) can combine the advantages of the one dimensional electron transportation and light scattering of a NW array and the large dye-loading capacity of NPs, due to the presence of a rutile–anatase heterojunction. The dye-sensitized NW–NP composite film (1.4 μm thick) with a roughness factor of ∼114.7 displays a significantly improved light harvesting ability than a NW array (roughness factor ∼28.2), as manifested by diffuse transmittance and reflection spectra, and even higher light harvesting than a NP film (1.5 μm thick) with a roughness of ∼414.7. Moreover, the dye-sensitized NW–NP composite film shows slower charge recombination kinetics than both the NW array and NP film, as measured by open-circuit photovoltage decay and transient absorption spectroscopy. As a result, the dye-sensitized TiO2 NW–NP composite photoanode exhibits 2.2 times and 1.5 times higher overall efficiency than NW array and NP film photoanodes, respectively, under AM 1.5G simulated solar irradiation, demonstrating the synergistic effect of rutile NW and anatase NP for photoelectrochemical solar energy conversion.