Trifunctional TiO 2 Nanoparticles with Exposed {001} Facets as Additives in Cobalt‐Based Porphyrin‐Sensitized Solar Cells

In this study, highly mesoporous TiO 2 composite photoanodes composed of functional {001}‐faceted TiO 2 nanoparticles (NPs) and commercially available 20 nm TiO 2 NPs are employed in efficient porphyrin‐sensitized solar cells together with cobalt polypyridyl‐based mediators. Large TiO 2 NPs (approximately 50 nm) with exposed {001} facets are prepared using a fast microwave‐assisted hydrothermal (FMAH) method. These unique composite photoanodes favorably mitigate the aggregation of porphyrin on the surface of TiO 2 NPs and strongly facilitate the mass transport of cobalt‐polypyridyl‐based electrolytes in the mesoporous structure. Linear sweep voltammetry reveals that the transportation of Co(polypyridyl) redox is a diffusion‐controlled process, which is highly dependent on the porosity of TiO 2 films. Electrochemical impedance spectroscopy confirms that the FMAH TiO 2 NPs effectively suppress the interfacial charge recombination toward [Co(bpy) 3 ] 3+ because of their oxidative {001} facets. In an optimal condition of 40 wt% addition of FMAH TiO 2 NPs in the final formula, the power conversion efficiency of the dye‐sensitized cells improves from 8.28% to 9.53% under AM1.5 (1 sun) conditions.