Preparation Of Flexible Carbon Nanofibers Films And Its Application In Dye-sensitized Solar Cells

In recent years,because the carbon nanofibers(CNFs)films have excellent thermal stability,conductivity and tensile strength,it is widely used in DSSCs.However,due to the brittleness of carbon materials,its application in the field of flexible product is limited.Therefore,in order to improve the defect of carbon materials,the flexible CNFs films was prepared based on polyacrylonitrile(PAN),polyvinyl pyrrolidone(PVP)and titanate isopropyl(TiP)by electrospinning process.And then,the flexible CNFs films,TiO_x/C NFs,was prepared by pre oxidation and carbonization.After that,the effects of different pre oxidation temperature on the tensile strength,electrical conductivity and flexibility of TiO_x/CNFs were investigated.With the increase of pre oxidation temperature,the values of tensile strength,elongation at break and bending elastic modulus increased first,and reached the maximum value,then decreased,the maximum value appeared in the pre oxidation temperature is 240 °C,they were 7.10 MPa,3.56% cN/cm~2.and 9.0 cN/cm~2,respectively.Moreover,with the pre-oxidation temperature no more than 260 °C,the average square resistances of TiO_x/C NFs films were about 10 ?/sq.With the temperature being over 280 °C,the average square resistances of TiO_x/C NFs films greatly increased and reached about 22 ?/sq.Therefore,the pre oxidation temperature have great influence on conductivity of TiO_x/C NFs films.As to the three aspects of mechanical properties,flexibility and conductivity,when the pre oxidation temperature is 240 °C,the flexible TiO_x/C NFs films have the best performance.In order to improve the catalytic activity of flexible CNFs films,CoS particles with electrocatalytic properties were prepared by hydrothermal method,and then,the CNFs films loaded with CoS(CNFs-CoS)were prepared by electrostatic spraying method.CoS has excellent electrocatalytic performance,but its conductivity is poor.Therefore,the value of the square resistances of CNFs-CoS is too large,which is not good for the improvement of the electrocatalytic performance of CNFs-CoS.So,in order to improve the conductivity of CNFs-CoS,the Ag nano particles were introduced to the CNFs-CoS to prepare the CNFs-CoS-Ag,as the result,the conductivity was improved.In addition,the Ag nano particlesalso has electrocatalytic properties,it can cooperat with CoS,improving the electrocatalytic performance.But on the other hand,because the existence of CoS and Ag nano particles,the mechanical properties and the flexibility of CNFs-CoS and CNFs-CoS-Ag decreased.Luckily,CNFs-CoS and CNFs-CoS-Ag still have enough flexibility to be used for preparing the FDSSCs.CNFs-CoS and CNFs-CoS-Ag were used as counter electrodes to assemble FDSSCs,and the photoelectric conversion efficiency of FDSSCs with CNFs-CoS-Ag as the counter electrode was greatly improved compared with CNFs-CoS as the counter electrode of FDSSCs.CoS has good electrocatalytic performance,but its conductivity is poor,so the charge transfer resistance of interface between electrolyte and CNFs-CoS was up to 15.96 ?.Therefore,introducing the Ag nano particles to the CNFs-CoS can overcame its disadvantage of poor conductivity caused by CoS,and makes the charge transfer resistance of interface between electrolyte and CNFs-CoS-Ag decrease to 6.17?,The values of charge transfer resistance is directly related to the conversion efficiency of the battery,so the photoelectric conversion efficiency of FDSSCs with CNFs-CoS-Ag as the counter electrode is up to 1.28%,which is about 1.48 times of the FDSSCs with CNFs-CoS as the counter electrode.When used the Pt-FTO to substitute CNFs-CoS-Ag as the counter electrode of DSSCs,the photoelectric conversion efficiency is higher than FDSSCs with CNFs-CoS-Ag as the counter electrode,reached 1.74%.But compared with the DSSCs prepared by conductive glass FTO and liquid electrolyte,the photoelectric conversion efficiency is still low,this is mainly because the resistance values of flexible conductive substrate and quasi solid electrolyte is too large,which is not good for improving the efficiency of the battery.