The Modification Of Titanium Dioxide Photoanode Membrane And Its Apphcation In Dye-sensitized Solar Cells

One-dimensional materials have good properties of high specific surface area, large aspectratio, a good quantum confinement effect and surface effect, making great prospects in electronic,optical, magnetic, and Biomedical fields. Compared to the TiO2nanoparticles, One-dimensionalTiO2nanofibers with fewer grain boundaries can provide direct way for electron transfer, havingimportant applications in photocatalyst and Dye-sensitized Solar Cells. The complex traditionalfabrication methods of one-dimensional material, limit its development. Electrospinning canfabricate one-dimensional nanofibers in quantity and continuously. It is simple,low-cost and hasgreat perspects, getting more and more attention from the researchers. Two-dimensional carbonnanomaterials graphene can accelerate electron transport, reducing the charge transfer resistance.It has excellent properties in flexibility, stability, lightweight, excellent light transmittance,thermal conductivity and high electrical conductivity, getting widely used in materials andenergy fields. The simple method hydrothermal synthesis can prepare highly crystallinenanostructures, and is often combined with electrospinning to get more unique properties.The Graphene-doped TiO2nanofibers were fabricated through electrospinning method. TGA,FT-IR, FESEM, TEM and Raman spectroscopy were taken to characterize the structures andmorphologies. It showed that nanofibers diameter were85nm in average, with smooth surface.After530℃calcination，the fibers turned curved and rough，packed with large amounts of littlegrains. The graphene uniformly distributed within the nanofibers, and still exsisted aftercalcination. DSSCs results showed that the0.7wt%graphene doped TiO2nanofibers havemaximum energy conversion efficiency(η=1.2%), which almost two times of the undopedDSSCs. Graphene promoted the electrons transfer, and inhibited the electron-hole recombinationThen, a hydrothermal method was taken to post-treat0.7wt%Graphene/TiO2nanofibers andthe structures dependent on time and temperature were ovserved. It showed that thenanostructures on the surface were pure rutile crystal nanorods. The nanorods growth processstarted on nucleation, and on consumption of nanofibers. The absorbance meaned the branchedstructure making more dyes absorbance. Different DSSCs based on TiO2with different temperature post-treatment shows130℃、30min treatment made the Jsc(6.1mA/cm2) andη(2.3%) maximum, achieving66%and91%improvement compared with the untreatednanofibers. Branched structures could form hetero-junctions with anatase TiO2, having high dyemolecules absorbed，low electron recombination and more light harvesting. But excessive rutilescould make electron loss in transfer process, leading a Jscand conversion decreasing.The study about the effect of different proportions and multilayer films thicknesses of theanode consisting0.7wt%Graphene/TiO2nanofibers as electron transfer way and thesenanofibers treated in130℃and30min as light-haresting were taken. The total thickness ofphotoanode was settled. From the proportions of branched nanofibers increased, the dyeabsorbance, IPCE, Jscand energy conversion all increased to highest and then got decreased. Theratio1:2of NFs and BNFs had a highest energy conversion1.2%, having a21%increasedcompared with the energy conversion of2.3%with a ratio1:0.5. The results showed branchedfilm could increase IPCE value and light harvest because of the more dye molecules absorbance.Meanwhie the rutiles suppressed electron recombination. Too much branch structures hinderedthe dye penetration, increased the electronic transmission loss, making a decreasement of totalconversion. Then setting the ratio of1:2, the effect of different photoanode thickness (45,33and26μm) on DSSCs conversion was studied.With the thickness decreased, dye absorbance, IPCE,Jsc, FF and energy conversion increased. The highest conversion was3.8%with the thickness of26μm，having a35%improvement compared with the thickness of45μm. The thicknessdecrease could improve the dye permeation, shorten the electron transfer distance,decreaseelectronic transmission loss and the electron recombination.