Effects Of Side-chains Modification Of Fused-ring Units On Photovoltaic Properties Of The Non-fullerene Acceptors

Non-fullerene small molecular acceptors are favored by researchers due to their structure diversity,easy modification,and easy purification.In recent years,the photoelectric conversion efficiency(PCE)values of organic solar cells(OSCs)based on non-fullerene acceptors has exceeded 18%,which greatly encouraged the researchers in this field.Usually,many efforts have been paid on the modification of backbone and side chains in order to exploit high-performance non-fullerene acceptors,only a few efforts have been paid on exploiting non-halogenated solvent processed non-fullerene acceptors by tuning side chains.On the one hand,some high-performance photovoltaic materials have briefly introduced,and the progress of non-fullerene small molecular acceptors has been detailly summarized in this dissertation.On the other hand,two series of non-fullerene small molecular acceptors have been designed and synthesized,and the influence of side chain structure on its photovoltaic performance was studied.The main research contents are shown as follows:(1)A novel non-fullerene acceptor(ITC-C8-Br)was designed and synthesized by introducing octyl side chains at both ends of the electron-donating indacenodithienothiophene(IDTT)derivative,and the 2'-bromothiophene-substituted3-dicyan-1-indanone(SDCN-Br)(Fig.2.1)as the terminal electron-withdrawing units.The small molecular acceptor ITC-C8-T was obtained by substituting thiophene for bromine.The research results show the absorption spectra of ITC-C8-Br and ITC-C8-T are both red-shifted by 10 nm in the film state compared with the congener acceptors ITC-2Br and ITC-T without octyl side chains at both ends of the IDTT core,impling that the introduction of octyl side chains enhances intermolecular?-?stacking.The OSCs were fabricated with PBDB-T as the donor and ITC-C8-Br and ITC-C8-T as the acceptors,and the OSCs showed the PCE of 9.76%and 4.33%,respectively,which are both higher than the PCE values of the devices based on ITC-2Br(8.53%)and ITC-T(3.16%).That is to say,the introduction of alkyl chains at both ends of the electron-donating building block is beneficial to increase molecular solubility and intermolecular interaction as well as improve photovoltaic performance.(2)Two novel non-fullerene acceptors,named as ZB-C48 and ZBT-C48,were designed and synthesized by extending the alkyl chain to 2-hexyl decyl group on the nitrogen atom,and shortening the alkyl chain to n-octyl group at both ends of the fused-ring core,and incorporating brominated 3-dicyan-1-indanone and2'-bromothiophene-substituted 3-dicyan-1-indanone as the terminal groups respectively,which possessed the similar conjugated backbone with the reported acceptor ZB.The results show that the energy levels and the absorption spectrum of ZB-C48 are similar as those of ZB,which indicates that side chain modification has little effect on the energy levels and the absorption spectrum of small molecules.However,ZBT-C48 shows higher-lying energy levels,more blue-shifted absorption spectrum,and lower absorption coefficient than ZB-C48.As a result,when CF was used as the solvent to prepare the OSCs,the PM6:ZB-C48 OSCs yielded a higher PCE of up to 15.98%with a J_SCof 25.75 m A cm^-2,a FF of 68.72%and a V_OCof 0.9 V,while the OSCs based on ZB and ZBT-C48 showed the relatively inferior PCEs of14.89%and 8.22%respectively.In addition,when o-xylene was used as solvent to prepare the OSCs,the PM6:ZB-C48-based devices still obtained a high PCE of15.75%,while the OSCs based ZB showed a low PCE of 6.01%for the poor solubility of ZB and the OSCs based on ZBT-C48 also showed a low PCE of 6.90%for its inferior absorption spectrum and unmatched energy levels.The result indicates that it is an efficient strategy to obtain high-performance nonhalogenated solvent-processed non-fullerene acceptors by tuning side chains of the fused-ring cores.