Solution-Processed, Antimony-Doped Tin Oxide Colloid Films Enable High-Performance TiO₂ Photoanodes for Water Splitting

Photoelectrochemical (PEC) water splitting and solar fuels hold great promise for harvesting solar energy. TiO₂-based photoelectrodes for water splitting have been intensively investigated since 1972. However, solar-to-fuel conversion efficiencies of TiO₂ photoelectrodes are still far lower than theoretical values. This is partially due to the dilemma of a short minority carrier diffusion length, and long optical penetration depth, as well as inefficient electron collection. We report here the synthesis of TiO₂ PEC electrodes by coating solution-processed antimony-doped tin oxide nanoparticle films (nanoATO) on FTO glass with TiO₂ through atomic layer deposition. The conductive, porous nanoATO film-supported TiO₂ electrodes, yielded a highest photocurrent density of 0.58 mA/cm² under AM 1.5G simulated sunlight of 100 mW/cm². This is approximately 3× the maximum photocurrent density of planar TiO₂ PEC electrodes on FTO glass. The enhancement is ascribed to the conductive interconnected porous nanoATO film, which decouples the dimensions for light absorption and charge carrier diffusion while maintaining efficient electron collection. Transient photocurrent measurements showed that nanoATO films reduce charge recombination by accelerating transport of photoelectrons through the less defined conductive porous nanoATO network. Owing to the large band gap, scalable solution processed porous nanoATO films are promising as a framework to replace other conductive scaffolds for PEC electrodes