Preparation And Properties Of Electrode Materials For Dye-sensitized Solar Cells Via Electrospinning

Dye-sensitized solar cells (DSSCs) show enormous potential for future applications and have attracted much attention due to its low-cost, simple fabrication with non-toxic and pollution-free, long life. However, most DSSCs are based on glass substrate, and the rigidity and weight of glass substrates make the continuous manufacture of DSSCs a complicated and costly procedure thus limiting its applications. Therefore, it has important significance to investigate lightweight and flexible dye sensitized solar cells with high conversion efficiency and to promote its practical application. In addition, the research and development of photovoltaic textile based on solar cells is a very important content of the development of the smart textiles. Now, for most flexible dye sensitized solar cells, the large deformation of the DSSCs cause the failure. If the flexible dye sensitized solar cells with high flexibility can be fabricated, making that the deformability of the DSSCs with good stability can match that of flexible fabric,it will expand the application of the DSSCs and promote its development,which provide a important basis of the development of the photovoltaic textile based on the DSSCs. Hence, the research of the flexible dye sensitized solar cells with high flexibility and high efficiency is very meaningful, is also necessary and urgent.In order to fabricate the flexible dye sensitized solar cells with high flexiblility and high effienciy, the key issue is the flexible desigh and fabrication of the DSSCs, and the emphasis is on the desigh and fabrication of the photoanodes based on the flexible substrates and the flexibile fabrication of the counter electrode.(1) To prepare photoanodic materials with excellent property and obtain the photoanodic film firmly combined with the plastic substrate, the TiO2 nanorods (NRs) are prepared by electrospinning followed by post-treatment, and then made into photoanodic film on the ITO/PET substrate through electrospray deposition and hot-compression. The flexible DSSCs based on the TiO2 NRs shows a conversion efficiency of 1.73%. After that, Mg2+ions doping, coating with ZnO, and incorporation of CNTs into TiO2 nanorods can be easily achieved by electrospinning. The effects of the Mg2+ ions doping,coating with ZnO, and incorporation of CNTs on the properties of DSSCs are investigated. The conduction band energy (Eeb) and Fermi energy (EF) of the TiO2 shift negatively by Mg2+ ions doping,leading to the increase of VOC- And the Mg2+ ions doping may low the densith of empty trap states and improve the electron transport. With this Mg2+ ions doping, the conversion efficiency of DSSCs is 2.21%. The TiO2 coated by ZnO results in the formation of an energy barrier between the photoanode and electrolyte, hindering the electron recombination. Hence the conversion efficiency of DSSCs is enhanced to 2.28%. The incorporated CNTs accelerate the electron transport, the positive shift of the Ecb of the CNTs/TiO2 leads to the expanding of the energetic discrepancy. Therefore,the conversion efficiency of DSSCs is increased to 2.34%.(2) In order to improve light-scattering ability, the dye loading, and electron transport of the photoanodic film simultaneously, the light scattering layer composing of 1D nanostructures with different morphologies are introducted in photoanode. The Mg2+ doped TiO2 NRs with larger diameters are fabricated. The open-ended branched TiO2 nanotubes (NTs) with different morphologies are synthesized by a combined method of electrospinning,hydrothermal treatment, calcination, and ultrasonic treatment. The larger diameter Mg2+doped TiO2 NRs, the open-ended branched rutile TiO2 NTs, and the open-ended branched anatase TiO2 NTs serve as the light-scattering overlayers, respectively, and the CNTs/TiO2 nanorods with smaller diameters act as an underlayer. With addition of the Mg2+ doped TiO2 nanorods, the light harvesting efficiency as well as electron transport of photoanode is enhanced due to the improved light-scattering and two-level energy steps,resulting in the conversion efficiency being up to 3.9%. The open-ended branched TiO2 nanotubes with larger BET, lead to the great improvement of the light-scattering and the increase of the dye loading and electron collection, simultaneously. Among the numerous open-ended branched Ti02 nanotubes, the optimized anatase branched TiO2 nanotubes (In alkaline condition at 150? for 9 h) with largest BET (148.5 m2/g) make the conversion efficiency of DSSCs increase from 2.34% to 4.70%.(3) To obtain the high flexible and low-cost counter electrode, the TiO2/C nanofibers (NFs)flexible film is fabricated via electrospinning followed by calcination (stabilization in air and carbonization in N2) with the polyvinyl pyrrolidone (PVP) and polyacrylonitrile (PAN)as carbon matrix precursor, and titanium isopropoxide (TiP) as TiO2 precursor. The PVP can affect the dimeters of the TiO2/C NFs and the distribution of TiO2 NPs in the NFs. The dispersive distritbution of TiO2 NPs in CNFs greatly improve the flexibility of the Ti02/C NFs film. When the mass ratio of PVP and PAN is 50:50, and the content of TiP is 0.7 g in precusor, the elongation at break of the TiO2/C nanofibrous film reaches a largest value of 2.94% and the elastic modulus of bending reaches a lowest value of 7.74 cN/cm2, which indicates that the TiO2/C NFs film exhibits excellent flexibility.(4) A new kind of flexible DSSCs without counter electrode substrate is assembled by the TiO2/C NFs flexible film. The properties of the DSSCs based on the TiO2/C NFs films and the effects of the bending deformation on the properties of the TiO2/C NFs films are investigated in details. With increase of the mass ratio of PVP:PAN and the content of TiP in precursor, the conversion efficiency of DSSCs decreases basically. After the TiO2/C NFs film under different degree bending, the conversion efficiency of DSSCs remains conspicuously intact using the films with the mass ratio PVP:PAN of 50:50 and the content of TiP of 0.7 g in precursor. The conversion efficiency of DSSCs is about 2.40%. The methods to improve the properties of TiO2/C NFs flexible film are proposed.(5) In order to improve the electrochemical properties of TiO2/C NFs flexible film without affecting its mechanical properties, the CNTs are incorporated into TiO2/C NFs by electrospinning. With the incorporation of proper contents of CNTs,there are no obvious differences in mechanical properties, while the conductivity and electrocatalytic activity of TiO2/C nanofibrous film improves. With the increase of CNTs, the conductivity and electrocatalytic activity of TiO2/C nanofibrous film increase, reach the best values with the content of CNTs of 2.0%, and afterward deceased. Accordingly, the conversion efficiency of DSSCs increases with the increase of CNTs, reaches the largest values of 3.38%, and then decreases. The conversion efficiency of DSSCs is essentially unchanged with the increase of bending deformation after the CNTs/TiO2/C NFs film under different degree bending.