Studies On The Design,Synthesis And Photovoltaic Properties Of Non-fullerene Electron Acceptors

In last two decades,people have paid considerable attention to organic solar cells(OSCs)due to their unique features,such as low cost,light weight,flexibility and large area device fabrication.Fullerene derivatives are the classical electron acceptors in OSCs during the last two decades due to high electron mobility and isotropic charge transport.However,fullerenes also have drawbacks,such as weak absorption in visible and NIR rigion,limited tunability of energy levels,and poor device stability.Recently,Nonfullerene acceptors attracted increasing attention.In this thesis,perylene diimide(PDI),naphthalene diimide(NDI)and 1,1-dicyanomethylene-3-indanone(IC),fluornated IC were employed as electron withdrawing units,and a series of nonfullerenes electron acceptors were synthesized.Optical,electrochemical,thermal stability and photovoltaic performance of these compounds were investigated.The thesis,is divided into seven parts:(1)Two PDI small molecules with different side chains(BU and ME)were synthesized.diPDI-BU showed better solubility than diPDI-ME,but lower power conversation efficiencies than diPDI-BU.(2)Two rylene diimide polymers(PDI-CNTVT and NDI-CNTVT)were synthesized and both showed good solubilities.With PTB7-Th as donor,PDI-CNTVT and NDI-CNTVT based device yielded efficiencies of up to 1.74%and 3.8%,respectively.(3)Four random copolymers based on PDI and NDI units were synthesized(PDI-co-NDI).With PTB7-Th as donor,the best PCE was up to 4.63%when NDI ratio was 100%.(4)Five PDI/NDI copolymers were synthesized.With P3HT as donor,the device based on PPDI25-co-NDI75 achieved a higher PCE of up to 1.54%than that based on PPDI100/PNDI100(3:0.25:0.75,w/w)(PCE = 0.83%).The random copolymer based-devices yield higher PCE than those with physical blending.(5)The fused ring electron acceptor IDIC-Th was synthesized.When blending with a series of donor PBnDT-FTAZ,PTFBDT-BZS and PTB7-Th,the device based on the wide bandgap donor PBnDT-FTAZ and IDIC-Th acceptor achieved the best efficiency of up to 6.46%.The results suggest absorption complementarity has an influence on device efficiencies.(6)A series of new fused-ring electron acceptors,INIC,INIC1,INIC2 and INIC3,were designed and synthesized.Fluorinated molecules INIC1,INIC2 and INIC3 exhibit higher PCEs than nonfluorinated INIC devcie.The devices based on difluorinated INIC3 show the best PCE of 11.5%.(7)A new fused-ring electron acceptor,ITIC-Th1,was synthesized with fluorinated IC withdrawing unit.Compared with ITIC-Th,fluorinated ITIC-Th1 red-shifted the absorption and enhanced the π-π stacking.The devices based on ITIC-Th1 showed PCE as high as 12.1%.