Study On ZCISeS Quantum Dots Sensitized Solar Cells Based On CNT+Cu₂S Counter Electrode

Quantum dot sensitized solar cells(QDSCs)have been widely studied due to their simplicity and the theoretical efficiency of more than 44%,but the current research level has only reached 13%.This is because there is no suitable materials found,such as metal oxide films with extremely high light transmittance,electrolytes with excellent catalytic reduction and counter electrodes with good electrical conductivity and catalytic properties.In addition,the recombination of charge at the interface between quantum dots,metal oxide films and electrolyte reduces the efficiency of the battery.In order to improve the overall performance of the battery,the light-harvesting material with narrow energy band and wide light absorption range should be found firstly.Secondly,the electrode,as an important part of collecting electrons and catalytic reduction electrolyte transmitted from the external circuit,should also be deeply studied.This paper is studied from two aspects:quantum dot light-harvesting material and pair electrode.(1)The preparation of ZCISeS quantum dots by thermal implantation.In this paper,the amount of zinc,copper and indium was kept unchanged,and then ZCISeS quantum dots were prepared by changing the molar ratio of selenium to sulfur.Through ligand conversion technology,the long-chain ligands of oleamine were converted into short-chain ligands of mercaptopropionic acid,which were loaded on titanium dioxide(TiO2)and assembled with cuprous sulfide brass sheet(Cu2S brass)to form a sandwich structure.It is found that with the increase of the ratio of selenium to sulfur,the photoelectric conversion efficiency of solar cells assembled by ZCISeS increases at first and then decreases.The photovoltaic conversion efficiency of the quantum dot solar cell prepared by Se:S=5:2 is the highest.Under a standard solar light intensity,the short-circuit current density is 20.01 mA/cm2,the open-circuit voltage is 0.56 V,the filling factor is 52%,and the photoelectric conversion efficiency is 5.8%.Compared with ZCISe QDSCs,the photoelectric conversion efficiency is increased by 23.4%.It is also found that when the molar ratio of selenium to sulfur continues to increase,from the characterization of TEM and XRD,it is found that the crystallinity of quantum dots becomes worse,and the number of defect sites increases,resulting in the decrease of the optical and electronic performance of solar cells.(2)The preparation of Copper oxalate microspheres by hydrothermal method.Copper oxalate was used as a self-sacrificing template to react with sodium sulfide to form cuprous sulfide(represented by Cu2S-1 in this paper).It is found that when the concentration of Na2S is low,the hollowed-out microsphere CuS,is formed with the increase of Na2S concentration,resulting in excellent catalytic performance of Cu2S-1.Because the Cu2S-1 with hollowed-out structure increases the contact area with the electrolyte,the catalytic performance is improved.The CU2S-1 counter electrode prepared by scraping method and ZCISeS quantum dots loaded on TiO2 form a sandwich structure.The photoelectric conversion efficiency of solar cells measured under a standard solar light intensity reaches 6.2%.Then the composite counter electrode was prepared by adding carbon nanotube(CNT)to Cu2S-1,and the photoelectric conversion efficiency of ZCISeS QDSCs was up to 6.7%.Compared with Cu2S brass as counter electrode,the efficiency of,ZCISeS QDSCs battery is increased by 8%.Compared with the single CNT as counter electrode,the efficiency of ZCISeS QDSCs battery is increased by 34%.(3)Cupric Hydroxide with parallel line structure is formed by reacting the prepared Copper Oxalate with sodium hydroxide(NaOH),and the product reacts with supersaturated Na2S ethanol solution to form cuprous sulfide with micron sphere structure composed of nanowires(represented by Cu2S-2 in this paper).After the preparation of the pair electrode,the short circuit current density of ZCISeS QDSCs is 22.2 mA/cm2,the open circuit voltage is 0.57 V,the filling factor is 50.6%,and the photoelectric conversion efficiency is 6.4%,compared with that when Cu2S brass is the opposite electrode alone.Then,the composite counter electrode was prepared by controlling the content of CNT and Cu2S-2.It was found that when Cu2S-2:CNT=7:3 was used,the photoelectric conversion efficiency of ZCISeS QDSCs was 7.1%,which was 22%higher than that when Cu2S brass was the opposite electrode,and 42%higher than that of the counter electrode composed of CNT alone.