Fabrication Of Titania Photoanodes With High Scattering Capability And Study On Related Photoelectrochemical Performance

Solar cells,as the photovoltaic converting devices,have been one of the most promising strategies to solve energy crisis.Dye sensitized solar cells?DSSCs?have great potential of development due to the advantages of colorful and tunable dye molecules,simple fabrication process,low cost,environmental-benignity,high efficiency and high stability.Photoanode acts as an essential component of DSSCs,where the most reactions are occurred.There are serval problems existing in traditional photoanodes based on TiO₂ nanoparticles:large numbers of grain boundaries result in limited electron transfer and increased charge recombination;high transparency for the small-size particles leads to low light harvesting and utilization efficiency;and low energy facet reduces electron injection efficiency.To solve these problems,multifunctional TiO₂ hierarchical structures including hollow box with highly exposed?001?surface?BTiO₂?,peanut-like TiO₂ microarchitecture with highly exposed?001?surface?PN TiO₂?and microsphere constructed with one-dimensional nanorod unit?MS TiO₂?were synthesized and introduced into photoanodes as the scattering centers/scattering layer.Meanwhile,a simple mild photoanode treatment based on surface plasmonic resonase was presented and applied in DSSCs with enhanced photovoltaic performance.Hollow TiO₂ box with highly exposed?001?surface was synthesized by a two-step method with processor of TiOF₂.BTiO₂ was embedded into photoanodes with various mixing ratio.According to the UV-vis diffused reflectance spectra of photoanodes,diffuse reflectance in the spectral range from 400 nm to 800 nm increased with the mixing ratio due to hollow structure and size effect.The electrolyte diffusion can be promoted due to the hollow structure,leading to increased open circuit voltage with mixing ratio of BTiO₂.Electrochemical impedance spectroscopy analysis evidenced that enhanced electron transfer and reduced charge recombination were achieved with BTiO₂ embedded into photoanode,along with improved charge collection efficiency and electron diffusion length.An optimal efficiency of 6.1%was obtained at the content of 20 wt%,with charge collection efficiency up to 0.91.Peanut-like anatase TiO₂ microarchitecture constructed with ultrathin nanosheets with highly exposed?001?facet was successfully synthesized by a two-phase hydrothermal method.Doubled photoanodes were fabricated with additional PN TiO₂scattering layer.The as-prepared DSSCs exhibited a photovoltaic conversion efficiency up to 9.14%with 34%enhancement compared to similar-thickness P25photoanode.Ultrathin nanosheets provide large specific surface area up to 180.8 m²/g for PN TiO₂,which guarantees sufficient dye loading amount.Size effect and surface light-trapping structure enhance the light scattering capability.Existence of Ti³⁺can narrow TiO₂ bandgap and make the flat-band potential positively shift,leading to improved electron injection efficiency.Self-assembly size-controllable hierarchical rutile TiO₂ microspheres constructed with nanorod were synthesized by solvothermal method.MS TiO₂ was embedded into photoanode acting as scattering centers with various mixing ratio.An optimal conversion efficiency up to 9.3%was achieved at the mixing ratio of 10 wt%,with corresponding short-circuit current density and open-circuit voltage of 15.6 mA/cm²and 0.79 V,respectively.One-dimensional nanorods provide fast electron transfer paths,promoting charge separation and electron transport and reducing electron recombination.Size effect combined nanorods and microsphere enhance light scattering capability,thus improving photon utilization efficiency.The voids between nanorods can benefit electrolyte diffusion,indeed increasing open-circuit voltage.Plasmonic photoanode treatment induced by gold nanoparticles was presented.The optimal photovoltaic conversion efficiency up to 9.47%was obtained with the temperature at 30?,UV illumination time of 60 min and 2.5×10^-6 mol HAuCl₄ as gold source.After plasmonic photoanode treatment,photoanodes exhibited light absorption in visible-light region for plasmonic effect.Local electronic field enhances light absorption of dye molecules,result in improved light harvesting efficiency and short-circuit current density.Gold nanoparticles were coated with TiO₂ film after TiCl₄ treatment,thus local electron storage effect was generated with positive shift of Fermi level and enhanced open-circuit voltage.The decoration of gold nanoparticles improves conductivity of photoanodes for the reduced series resistance.Enhanced local electric field can reduce the electron recombination,leading to the improved charge collection efficiency.