Spin-coating Preparation Of Transparent Nickel Sulfide Electrode And Its Application In Dye-sensitized Solar Cells

Counter electrode(CE)is one of the important components of a dye-sensitized solar cell(DSSC).It plays an important role of collecting electrons form external circuit and catalyze redox reactions,showing a great impact on the performance of DSSC devices.At present,the most commonly used CE material is platinum(Pt),which has excellent electrocatalytic activity.However,its high cost limits its application range.Transition metal sulfides,which have advantages of easy preparation,low cost and high electrocatalytic activity,are considered to be one kind of the most feasible alternatives to Pt electrode materials.In addition,the counter electrode with good light transmittance is conducive to the reuse of transmitted light,such as being used in bifacial DSSC devices and tandem cells,thereby increasing light utilization efficiency.This subject is mainly devoted to the simple preparation of nickel sulfide counter electrodes with high electrocatalytic performance and high light transmittance,that is,spin coating and low-temperature annealing methods.Many factors,such as solvent,annealing temperature/atmosphere,graphene composite,have been studied,and their effects on the performance of CE thin films have also been investigated.The photoelectric conversion efficiency of DSSC devices based on transparent nickel sulfide counter electrodes was evaluated when irradiated from the front/rear sides.The main research contents are as follows:(1)Ethanol and isopropanol as precursor solvents were employed to prepare nickel sulfide(Ni S)counter electrodes in the air,and their effects on CE electrocatalytic performance and DSSC device efficiency were studied.First,thiourea and nickel chloride were dissolved in ethanol at a ratio of 1:3to obtain a precursor solution,which was spin-coated on the ITO substrate,and the annealing temperature was optimized to 200~oC.In addition,the precursor solvent was replaced with isopropanol,and the influence of different spin coating speeds on the light transmittance and performance of the Ni S electrode was studied.The experimental results show that the light transmittance of the Ni S counter electrode prepared by using isopropanol as the solvent is equivalent to that of the Ni S counter electrode prepared by ethanol solvent,while its photoelectric performance is better than the Ni S counter electrode prepared by ethanol solvent.(2)Additionally,Ni S counter electrode was also prepared in a nitrogen atmosphere,and the effect of annealing temperature and rate of spin coating on the performance of Ni S electrode was investigated.The experimental results show that 200~oC is the best annealing temperature and 800r/min is the best spin coating rate.The transmittance of the Ni S counter electrode prepared under these conditions is 79.13%(at 550 nm,air calibration).Applying this pair of electrodes to DSSC,the photoelectric conversion efficiency(PCE)with the standard test light source irradiated from the front is 7.54%(the PCE is 3.96%when the reverse is irradiated,which is 52.52%of the front irradiated),which is similar to the value(7.48%)of platinum electrode DSSC device.Compared with the Ni S counter electrode DSSC device prepared in air(PCE is 3.7%),the photoelectric conversion performance is improved by 104%.(3)The Ni S/graphene composite counter electrode was prepared by the spin coating method,and the influence of amount of graphene incorporated on the performance of the DSSC device was studied.The incorporation of graphene improves the electrocatalytic performance of Ni S CE,where 0.05mg/m L is the optimal doping concentration,and the PCE of the DSSC with front-side irradiation is7.84%(the PCE when the back side is irradiated is 4.59%,which is 58.55%of the front-side irradiation).Compared with the pure Ni S counter electrode DSSC,PCE of graphene-incorporated device increases by 3.83%.The above results show that the Ni S counter electrode prepared by spin-coating method and low temperature annealing has high light transmittance and excellent electrocatalytic performance,showing great potential for application in bifacial DSSC devices or tandem cells.