The Application Research Of Counter Electrode For Dye-sensitized Solar Cell Based On Bismuth Oxides

Under the current background of the rapid development of economy and science,energy shortage and environmental issue became serious problems to be sloved,therefore,looking for green and environmental friendly new energy turn into a top priority.At present,the new and environmental friendly energy has involved in wind energy,hydroenergy,solar energy,bioenergy and so on.Solar cell is a kind of device using the photovoltaic effect of semiconductor for photoelectric conversion,which is due to take advantage of the non-pollution and renewable solar energy as the input energy of photoelectric conversion,thus gradually become hot spot of scientific research.Solar cell can be divided into many kinds,including silion solar cell,perovskite solar cell,polymer solar cell,dye-sensitized solar cell and quantum dot solar cell,etc.In which dye-sensitized solar cell?DSSC?owing to some advantages become a hot research,such as rich raw materials,low cost and simple technique,etc.Since the research team of M.Gr?tzel professor from Swiss made great breakthrough in the study of DSSC,all kinds of reports related DSSC have sprung up like mushrooms.Bismuth based oxide is a kind of functional material with a low conductivity,wide energy band gap,rich synthetic resource material and simple preparation method,thus it can be expected for photoelectric conversion,medicine,pharmacy,etc.This paper is mainly on account of studying the Bi₄Ti₃O₁₂?BTO?and Bi₅FeTi₃O₁₅?BFTO?in the bismuth based oxide,studying the effect in DSSC by the BTO/BFTO and graphene composites which act as the counter electrode material.BTO which is due to the oxygen octahedron stratified structure and the high Curie temperature becomes an important kind of perovskite ferroelectric materials;while BFTO can be regarded as a four layer perovskite(Bi₃Ti₃FeO₁₃)^2-along the c axis in between the two?Bi₂O₂?²⁺in order to form the four layers of perovskite structure.Of which there are a lot of literature reports on the ferroelectric,dielectric and piezoelectric properties of BTO and BFTO,but a rare rports about their electrochemical and photovoltaic performance.In this paper,we mainly research that BTO composite graphene act as counter electrode for DSSC,and the polarized,Ag-modified BFTO serve as counter electrode for DSSC.The first part mainly introduces the process of the preparation of BTO nanofibers with electrostatic spinning method.We use sol-gel method to prepare precursor solution,and employed the macromolecule organic matter polyvinylpyrrolidone?PVP?as the binder so as to increase the viscosity of the percursor solution;afterwards through a homemade electrostatic spinning equipment to realize spinning process?DC10 kV,receiving distance of about 15 cm?;finally obtain the BTO nanofibers with diameter of about 160nm by annealing at 690?in the muffle furnace.We mainly use some physical characterization means such as XRD,SEM,TEM,Raman and so on to characterize the BTO nanofibers.The second part systematacially study the various performance of DSSC whose counter electrode materials are BTO/graphene composites.As we know,the carbon atoms of graphene has become honeycomb-like structure by means of SP₂ hybridization,graphene turns into a favourite of scientific workers owing to some essential properties,such as high electron mobility,high electric and thermal conductivity and very large specific surface,etc.So we composite BTO nanofibers with graphene according to the weight percentage,and make it attached on the honeycomb graphene to improve the specific surface,leading to the I^3-/I^-electrons in the electrolyte contact more fully with the electrode,eventually improving the catalytic activity of the compound counter electrode?CE?.The composites will be prepared into film by the simple coating method,then under the protection of argon gas annealing at 400?in order to prepare CE,followed by forming the whole DSSC assembled with TiO₂ photoanode and N719dye,by the electrochemical workstation,we eventually test some performance indexes of the DSSC such as volt-ampere characteristic curve,tafel polarization curve,electrochemical impedance spectroscopy,etc.We know when the weight percentage of graphene is 2.5%,the photoelectric conversion efficiency of the DSSC assembled with the composites counter electrode is 9.7%via characterization,which reach to 79.6%of the DSSC assembled with Pt counter electrode and 86.2%of the DSSC assembled with pure graphene counter electrode.The third part mainly describes the preparation process of BFTO film by chemical solution method,and the effect of the ferroelectric polarization BFTO film counter electrode for DSSC.This chapter mainly adopts sol-gel method to prepare BFTO precursor solution,afterwards conducts spin-coating on FTO by spin coater,then calcines the samples as follows,namely 200?baking,400?pyrolysis,680?crystallization,then the BFTO film is obtained.The as-prepared BFTO films is applied to voltage?+8/-8V?to perfom the polarization..Finally we use the polarized BFTO counter electrode,TiO₂ photoanode and N719 dye to form the integrated DSSC in order to test the electrochemical performance.When the polarization voltage is+8v,the photoelectric conversion efficiency is about 2%,which is twice larger than that of BFTO counter electrode?0.9%?.This work indicate the photoelectrical properties of CE based on ferroelectric oxides film could indeed be improved by means of ferroelectric polarization.