Synthesis And Properties Of Non-fullerene Small Molecular Acceptor Photovoltaic Materials

Although fullerene and its derivatives such as PC61 BM and PC71 BM have been used as acceptors for organic solar cells,they have many drawbacks,such as expensive cost,narrow light absorption range and so on.Comparably,non-fullerene organic small molecules(OSMs)exhibit broad spectral absorption range,are simply prepared and purified,and they are easy to be modified chemically,which contributes to an emerging hot topic in the field of studying OSM photovoltaic(PV)materials.Hence,this paper designed and synthesized non-fullerene OSM acceptors with different groups and central units modification,and investigated the relationship between PV performance and chemical structure of materials.In this paper,benzothiadiazole(BT),single fluoro-substituted benzothiadiazole(fBT)and quinoxaline(Qx)were chosen as central withdrawing electron units,which linked by 2-cyanostyryl as ? bridge with different electron-withdrawing groups,including nitryl,trifluoromethylpyridine,trifluoromethylphenyl and fluorophenyl.Therefore,three series of nine novel A-?-A'-?-A–type non-fullerene OSMs were designed.In addition,to further investgate the impacts of different spatial stereostructure on the PV performance for materials,two D(-?-A)3 star-type OSMs were designed via triphenylamine(TPA)as central electron-donating unit that combined with trifluoromethylpyridine and trifluoromethylphenyl as terminal groups.Density functional theory(DFT)and time-dependent density functional theory(TD-DFT)method,UV-vis absorption spectrum and cyclic voltammetry(CV)respectively were performed in order to study molecular energy level,electronic density distribution,optical and electrochemical property.Finally,bulk heterojunction(BHJ)PV devices based on the above novel small molecules as acceptor,P3 HT as donor,respectively,were fabricated so as to explore their PV performance preliminarily.According to the above measurements,some conclusions could be drawn as follows:(1)BTTCNBF obtained a relatively high Jsc of 5.29 mA cm-2,a PCE of 1 %;(2)fluoro-substituted benzothiadiazole materials yielded a low Voc due to its lower HOMO level;(3)all BT,fBT and Qx series materials with large red-shifts ranging from 30 to 47 nm;(4)due to their different light absorption capacities,Jsc of four series increased in order of TPA,fBT,Qx and BT;(5)in the preliminary study of all-small-molecule organic solar cells(all-SMOSCs)based on fBTTCNBNO and BTTCNBF,a Voc of exceeding 0.90 V was yielded,which was higher than P3HT-SMs system.From the perspective of the relationship between different chemical structures and PV performance,the paper has totally synthesized eleven target molecules and initially conducted PV measurement.The effects produced by different central units,terminal segements and stereostructures on the photoelectric and PV performance of materials have been discussed,which would provide the idea for the design of non-fullerene OSM acceptors PV materials.In addition,PV device optimization based on the above four series materials is underway in our laboratory.