Trifunctional TiO2 Nanoparticles with Exposed {001} Facets as Additives in Cobalt-Based Porphyrin-Sensitized Solar Cells

In this study, highly mesoporous TiO2 composite photoanodes composed of functional {001}‐faceted TiO2 nanoparticles (NPs) and commercially available 20 nm TiO2 NPs are employed in efficient porphyrin‐sensitized solar cells together with cobalt polypyridyl‐based mediators. Large TiO2 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 TiO2 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 TiO2 films. Electrochemical impedance spectroscopy confirms that the FMAH TiO2 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 TiO2 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. A cost‐efficient TiO2 composite photoanode for YD2‐oC8 dye‐sensitized cells (DSCs) with a Co(polypyridyl) mediator is fabricated by blending exposed {001}‐faceted TiO2 nanoparticles (approximately 50 nm) with commercial 20 nm TiO2. This photoanode simultaneously overcomes sensitizer aggregation, interfacial recombination, and ionic diffusion in cobalt‐mediated, porphyrin‐sensitized DSCs.