Study On Preparation Of TiO₂ Hierarchical Structures And Its Application In Ti Foil-based Quais-Solid State Dye-sensitized Solar Cells

Dye-sensitized solar cells?DSSCs?as a photovoltaic device instead of silicon-based one have attracted much attention.However,the rigid and heavy conductive glass substrates used in DSSCs limit the DSSCs mass production and application range.Therefore,the development of flexible DSSCs has become one of the key strategies in the field of DSSCs.In addition,the traditional liquid electrolytes in the flexible DSSCs has defects of leakage,low transparency,solvent evaporation,dye decomposition and corrosion of Pt electrode,resulting in the decreases of conversion efficiency and lifetime of DSSCs.Herein,an iodine-free ionic liquid?IL?gel electrolyte and various anatase and rutile hierarchical structures were developed and the photovoltaic performance of Ti-foil based quasi-solid-state DSSCs with prepared electrolytes and hierarchical structured TiO₂ photoanodes were studied.The main experimental contents and conclusions are as follows:1.Iodine-free ionic-liquid gel electrolytes were prepared by using polyethylene oxide?PEO,MW = 300000?and polyethylene glycol?PEG,MW=10000?as a gelling agent,and using 1,2-dimethyl-3-propylimidazolium iodide?DMPII?as charge transport medium and iodine source.In this kind of IL gel electrolytes,a higher PEG/PEO mass ratio can improve the transmittance,conductivity and permeability in the TiO₂ porous films of the electrolytes,which is beneficial to the light absorption and Js,value of DSSCs,and a lower PEG/PEO mass ratio is beneficial to reduce the charge recombination and dark current,which can improve the Voc and fill factor of the Ti foil-based quasi-solid-state DSSCs.As a result of the above mentioned effects,the best conversion efficiency?6.44%?was obtained from the Ti foil-based quasi-solid-state DSSCs fabricated with the electrolyte B with PEG/PEO mass ratio of 1/3.This IL-gel electrolyte can avoid the problems of liquid electrolyte containing I3-/I-redox couple,such as strong visible light absorption,solvent evaporation and corrosion of Pt counter electrode.This new type electrolyte is efficient and stable,and have a good potential application prospects for the Ti foil-based flexible DSSCs.2.Anatase TiO₂ microspheres?AMS?with hierarchical structure were synthesized via an alkali-assisted hydrothermal process and post-treatment of commercial nanosized TiO₂?P25?.The obtained AMS microspheres have an average diameter of 5?m,and the porous 3D network structure is formed by the accumulation and winding of fibrous TiO₂ nanotubes with diameter<10 nm.The specific surface area is as large as 160 m2 g-1.The hierarchical structure and high specific surface area of AMS microspheres can not only provide sufficient dye loading area,but also can provide the larger pore size of the TiO₂ film,which is favor in the penetration of IL gel electrolyte with high viscosity.The fibrous nanotubes provide a good path for electron transport and reduce charge recombination within the photoanode.The efficiency of the Ti foil-based quasi-solid-state DSSCs fabricated with AMS was 7.16%,higher than that?5.34%?of the P25-based one,and thus showing a good application prospect.3.A two-step hydrothermal method was used to synthesize rutile sea urchin micro-spheres?RMS?with an anatase nanotubes?ANT?with a diameter of 10 nm and a wall thickness of about 2-3 um,The specific surface area of RMS/ANTx was up to 106.9 m2 g-1.The newly formed anatase nanotubes?ANT?thin layers self-organized on the surface of the Ti foil-based RMS film not only provide a greater surface area and pore volume for dye loading,but also improve the electrical contact between Ti foil and the RMS film,which overcome the defects of small surface area and low electrical conductivity of the single RMS film,and thus effectively improve the efficiency of DSSCs.Among them,the efficiency of Ti foil-based quasi-solid-state DSSCs fabricated with RMS/ANT3 film electrode was 5.42%,much higher than that?0.73%?of the pure RMS-based one.The present study broadens the range of photoanode materials suitable for the Ti foil-based quasi-solid-state DSSCs,and provides a new idea for the future research on DSSCs' key materials and its preparation technology.4.The RMS/sTPP3/bTPP3 film electrode was prepared by spin-coating a diluted TPP3 slurry?sTPP3?,and than scraping the TPP3 slurry?bTPP3?on the Ti foil-based RMS film,in which the Ti foil-based RMS film was used as light-scattering layer.It was found that the light-scattering ability of the RMS film in the visible region?400-800 nm?was better than that of the Ti substrate,and the efficiency of the Ti foil-based quasi-solid-state DSSCs fabricated with the RMS/sTPP3/bTPP3 film electrode was 7.27%,increased by 22%compared with the single TPP3 film-based one.The spin-coating of TPP3 slurry?sTPP3?on the RMS film is beneficial to improve the photovoltaic performance of the DSSCs.Its main role is to fill the large gaps among nanorods in the RMS film.This structure can improve the electrical contact between bTPP3 and RMS films,reduce the electrode resistance and charge recombination,and thus promote the electrons transfer from bTPP3 film to tlhe Ti substrate.The present results have some theoretical significance in exploring the new and efficient light-scattering layer materials and the optimization strategy of photoanodes' structures.