Synthesis And Properties Of Fused-ring Non-fullerene Small Molecule Acceptor Materials

Since the 21st century,traditional fossil energy has been declining.In the future,it will not be able to meet the human demand for energy,and will cause serious environmental dilemmas.Solar cells are a new choice of energy for human beings.Organic solar cells have many advantages,such as low manufacturing cost,light weight,large-scale production by solution processing and relatively simple processing,so they have received a lot of attention.Traditional small molecule acceptor materials of organic solar cell,such as fullerenes,have been widely used because of their excellent charge transfer ability.However,due to the limitations of molecular structure,the absorption of fullerenes is poor,and there is almost no visible light absorption.Moreover,it is difficult to regulate the energy levels.Nonfullerene acceptor materials have developed rapidly in recent years.Compared with fullerene acceptor materials,nonfullerene acceptor materials are favored for their simple synthesis,Iow eost,adjustable energy levels and broad spectral absorption range by molecular structure design.In recent years,scientists have attempted to introduce electron-deficient groups into aromatic fiused rings to obtain nonfullerene small molecule acceptor materials with excellent performance,eollectively known as fused ring electron acceptors.In this paper,a series of A-D-A type nonfullerene small molecule acceptor materials were designed and synthesized by using Stille coupling reaction and Knoevenagel condensation reaction to bond different substituents by covalent bond based on indacenodithiophene(IDT)unit,indacenodithienothiophene(IDTT)unit and indeno[1,2-blfluorene(IFT)unit.The thermal,photophysical,electrochemical properties and photovoltaic properties of the target compounds were analyzed and discussed.In chapter 1,the development history,device structure,basic working principle and mam paraneters of organic solar cells are briefly introduced.And then we emphatically introduced the research progress of small molecule acceptor materials of organic solar cell,especially nonfullerene electron acceptor materials.Finally,the design ideas and research contents are briefly explained.In chapter 2,six small molecule acceptor materials,IDT-DMIO,IDT-IC2F,IDT-ICTh,IDT-ERN,IDT-FOD and IDT-DMBA,were synthesized by linking different terminal groups to the fused ring IDT unit which is used as a donor unit.First,we studied and analyzed the thermal properties of these six small molecule compounds.It was concluded that their decomposition temperatures were very high,showing excellent thennal and morphological stability.Secondly,their photophysical and electrochemical properties were measured.Among them,IDT-DMIo,IDT-IC2F and IDT-ICTh have strong absorption from 300 to 800 nm.The maximum absorption wavelength is around 700 nm,so it benefits for absorbing sunlight.Their LUMO levels are close to-3.70 eV,which facilitates the charge transport.Therefore,we focus on solar cell devices based on these three materials.Through the preparation and optimization of the device,all these three acceptor materials have relatively good photovoltaic performance.Among them,the solar cell device based on PM6:IDT-ICTh has the best performance with a power conversion efficiency(PCE)value of 8.69%.Besides,the external quantum efficiency(EQE)of PM6:IDT-IC2F solar cell device could reach more than 80%at 700 nm.After optimizing,the device could obtain an open circuit voltage(Voc)of 0.91 V,a short circuit current density(Jsc)of 14.82 mA/cm2 and an excellent PCE of 9.47%.In chapter 3,four A-D-A type small molecule acceptors,IDTT-TFBN,IDTT-TFMB,IDTT-ERN and IDTT-FOD were synthesized by Stille coupling reaction and Knoevenagel condensation reaction by using IDTT unit as the donor unit.The thermal properties of these four materials are relatively good.However,the maximum absorption wavelength in the film state is less than 600 nm,and the energy gap is very wide.Therefore,the prepared organie solar cell deviee has almost no photocurrent.We changed our mind and doped IDTT-FOD into(FA)0.8(MA)0.2PbI3 perovskite solar cells.The experimental results show that doping IDTT-FOD can effectively improve the performance of(FA)0.8(MA)0.2PbI3 perovskite solar cells.It can be seen from atomic force microscopy(AFM)and scanning electron microscopy(SEM)that doping can make up for the defects of perovskites and obtain larger crystallite perovskites.Doping with 20%and 40%concentration IDTT-FOD can improve performance of perovskite solar cells.The device with 40%IDTT-FOD can obtain a PCE of 18.20%,a Jsc of 25.53 mA/cm2.a Voc of 1.05 V and a fill factor(FF)of 67.90%.Compared with the non-doped perovskite solar cells,the PCE increased by more than 14%and other performances have been improved.In chapter 4,we synthesized IFT-DMIO,IFT-IC2F,IFT-IC2C1 and IFT-ICTh,based on IFT unit by simple condensation reaction.It was found that the thermal decomposition temperatures of these four materials were higher than 300℃,showing good thermal stability.The four materials have wide and strong absorption from 300 to 800 nm.The maximum absorption wavelength is around 650 nm and the energy gap is moderate,matching donor materials with wide or narrow energy gap for blending.The LUMO energy levels are deep and exhibit a gradient change with the difference of electron-withdrawing ability of terminal groups.Along them,the LUMO level of IFT-IC2C1 is the deepest,which is-3.92 eV.The PCE values of devices based on IFT-DMIO,IFT-IC2F,IFT-IC2C1 and IFT-ICTh as acceptors and polymer PM6 as donor are 1.48%,4.05%,3.50%and 2.89%,respectively.It can be concluded that the solar cell device based on IFT-IC2F as the acceptor has the best performance.The EQE of PM6:IFT-IC2F solar cell device could reach more than 40%at 600 nm.The Voc is 0.84 V,Jsc is 8.82 mA/cm2 and FF is 54.42%.The devices based on IFT-DMIO,IFT-IC2C1 and IFT-ICTh have relatively poor performance,which can be improved by optimizing the devices.Finally,the fifth chapter gives a brief summary of all the research contents of this paper,and makes a reasonable prospect for the development of organic solar cells in the future.