The Design,Synthesis And Photovoltaic Performances Of Naphthalene Diimide Based Acceptor Materials

Many drawbacks of fullerene acceptors have been demonstrated with the progress of organic of solar cells,such as relatively narrow absorption in the visible region,poor regulation ability of energy level and energy band because of the difficulty in modifying the structure.Lower thermal stability is usually caused by the spherical structure.These defects have encumbered the development of organic solar cell.Hence,for the further development of organic solar cells,the development of non-fullerene acceptor materials should be highly regarded.In this paper,a systematic review of the current highly efficient imide-based nonfullerene acceptor materials is systematically reviewed to clarify the current development of different kinds of nonfullerene acceptor materials,which is helpful to understand the relationship between material structure and its performance in organic solar cells.Nanphthalene diimide?NDI?has shown good potential in OFET and OPV with its excellent electron affinity and transport properties.A series of NDI-based polymer and small molecule acceptors were synthesized and their photovoltaic performances in organic solar cells were studied systematically.In the second chapter,we incorporated varying contents of siloxane-terminated side chain into the polymer consisted of NDI and bithiophene,thus two polymer acceptor materials,PNDI-Si25 and PNDI-Si50,have been synthesized by means of random copolymerization.And we have also systematically studied the influences surrounding light absorption,energy level and the photovoltaic device performance caused by the growth of the proportion of siloxane-terminated side chain.The fill factor of all-polymer solar cells?all-PSC?based on PNDI-Si25as acceptor and PBDB-T as donor can nearly approached to 0.7,as the result,the corresponding power conversion efficiency?PCE?is also up to 7.4%,which indicates that siloxane-terminated side chain has great potential in the field of polymer acceptor.In the third chapter,we introduced siloxane-terminated side chain into acceptor polymers consisted of NDI and selenophene,from which four polymer acceptor materials,PNSe-Si25,PNSe-Si50,PNSe-Si75 and PNSe-Si100,were synthesized.Thereinto,we found that the polymer with the 100%siloxane-terminated side chain is difficult to be processed because of its strong aggregation.Therefore,we studied the effect of contents of the side chain on opotoelectronic properties of three acceptor polymers of PNSe-Si25,PNSe-Si50 and PNSe-Si75.If compared with PNDI-Si25 and PNDI-Si50 in the third chapter,the three polymers PNSe-Si25,PNSe-Si50 and PNSe-Si75 can show a better process ability in chlorobenzene.When PBDB-T is selected as the donor and the structure of the device is ITO/ZnO/PFN/active layer/MoO₃/Al,the performance of PNSe-Si25 is the best,and the maximum efficiency of the solar cell is 6.07%.With the gradual increase of the content of siloxane-terminated side chain,the short circuit current and the fill factor of the all-PSCs decline in varying degrees.In addition,the SCLC electron mobility of the series polymer rises first and then decreases with the increasing content of siloxane-terminated side chain.In the fourth chapter,we firstly inserted p-difluorobenzene and o-difluorobenzene as the backbone units into the polymer composed of NDI and bithiophene resepectively.Strong interactions could be found between the fluorine atoms and sulfur atoms on adjacent thiophene.Also,side chain distributions of the two polymers were quite different,resulting in great effect on the morphology of active layer of the all-PSCs.On this basis,we further investigated the influences of molecular weight and length of side chain on optoelectronic properties of the polymers.With PBDB-T as the polymer donor and the high molecular weight PN20TffBT-O-H as acceptor,all-PSCs can show PCEs over 7%for active layers of 100 and 200 nm thicknesses,and the efficiency can still be close to 6%for the 300 nm thick active layer.The results indicate that PN20TffT-O is a promising polymer acceptor material.In the fifth chapter,we introduced different electron-donating unit thieno[3,2-b]thiophene and bithiophene to replace the electron-accepting unit difluorobenzene in charpter four,and two polymer acceptors PN12DT-TT and PN12DT-2T were synthesized.The absorption spectra of the two polymers can be expanded to the near-IR region.However,with PBDB-T as the polymer donor,the all-PSC devices of PN12DT-TT and PN12DT-2T acceptors exhibited low short-circuit current(J_SC)and fill factor?FF?,giving the poor efficiencies.Carrier recombinations and morphology of the active layers were investigated so as to reveal the problems and defects of these all-PSC devices,showing some guidance for the structural design of polymer acceptors.In the sixth chapter,in order to solve aggregation problem of NDI-based small molecule acceptors,two small molecule acceptors TPA-3NDI and TPE-4NDI with twisted chemical structures were constructed with triphenylamine?TPA?and 1,1,2,2-tetraphenylethene?TPE?as the core and multi-NDI unit as the peripheral units.With PTB7-Th as the donor,the PCEs of the nonfullerene solar cells based on the TPA-3NDI and TPE-4NDI were 3.61%and 3.81%,respectively.The efficiencies belong to good results for NDI-based small molecular acceptors.The SCLC electron mobility based on PTB7-Th:TPA-3NDI could reach 10^-44 cm²/?V s?.