Optoelectronic Properties Of Novel Supramolecular Fullerene Liquid Crystals With High Fullerene Content

With the development of supramolecular chemistry,[60]fullerene supramolecular liquid crystals(SLCs)have attracted a great deal of research attentions.However,to date,most research works focused on the molecular design and structure characterization of SLCs,while few studied their properties and application.In this paper,we study the optoelectronic properties of three series of fullerene supramolecular liquid crystals,Cn-Cg-C60(n=6,7,8,10,12,14,where n is the alkoxyl chain length),azobenzene-containing Cn-azo-C8-C60(n=4,7,8,9,12,where n is the alkoxyl chain length),and chiral center-containing C12-a-n-C60(n=6,8,10,12,n is the flexible spacer length).Here are the details:(1)The hierarchical structures in Cn-C8-C60(n＝6,8)dyads,which have two SLC phases,were studied by small angle X-ray scattering(SAXS),transmission electron microscopy(TEM)and density measurement.For dyad with n＝6,two smectic A SLC phases were observed during heating,where the fullerene balls form triple-layer 2D crystal packing in low temperature phase,while quadruple-layer packing in high temperature phase,leading to a stepwise layer thickness increment.For dyad with n=8,the fullerenes form triple-layer 2D crystal packing in low temperature smectic A phase,while quadruple-layer 2D crystal packing in high temperature smectic C phase.(2)The electron mobility of Cn-C8-C60(n=6,7,8,10,12,14)dyads were measured and calculated by space charge limited current(SCLC)method.It was found that with the increment of alkyl chain length,the electron mobility of materials decreased greatly.The reason of this change is due to the increased insulator layer thickness of alkyl chains,which greatly hinders the electron transfer,and the electron mobility dropped as a result.A high electron mobility of 1.92 × 10-3 cm2/V·s was obtained for dyad with n=6,which is comparable with PCBM,the traditional materials used in organic optoelectronics.For dyad with n=7,the highest electron mobility can reach 3.95×10-3 cm2/V·s,due to the unique layer-in-layer hierarchical structure.(3)The electron mobility of azobenzene-containing Cn-azo-C8-C60(n=4,7,8,9,12)compounds were measured and calculated by SCLC method.It was found that with the increment of alkoxyl chain length,the electron mobility dropped only slightly.The difference in the trend to the Cn-C8-C60 samples is the azobenzene functional groups in the alkyl chain layers,which can be the electron hoping media due to large area π-electron delocalization.(4)The electron mobility of chiral-center containing C12-a-n-C60(n=6,8,10,12)compounds were measured and calculated by SCLC method.The results show the charge mobility drops with the increment of intermediate flexible spacer length.(5)Organic solar cell devices based on P3HT/C7-C8-C60 are fabricated,similar to traditional P3HT/PCBM devices.By controlling the ratio of donor/acceptor materials,the performance of the device was increased first then decreased with the increment of the portion of the fullerene SLC receptor.The optical performance was revealed to be the donor/acceptor ratio at 1:2,with the best performance of PCE at 1.85%.