Atom-Economic Synthesis Of Non-Fullerene Acceptors And Studies On Photovoltaic Applications

Organic photovoltaics（OPVs）have become the research hotspots of sustainable energy,owing to their low-cost,semitransparent,solution processibility,lightweight and flexibility.With the development of non-fullerene acceptors,the power conversion efficiency（PCE）of OPV increased rapidly in the last five years.The key synthesis of OPV materials lies in the construction of sp² C–C bond,which are mainly realized by Suzuki and Stille cross couplings.Although this type of reactions have played key roles in construction of organic electronic materials,it still has the disadvantage of high-cost,toxic by-products,pre-functionalization of C–M bonds（M=B or Sn）,and tedious synthetic procedures,which limit their large-scale applications.C–H direct arylation（DACH）can be used to construct sp² C–C bonds by directly activating C-H bonds,which has the advantages of fewer synthesis steps,higher atom utilization,low cost,non-toxic and simple by-products compared with classical Suzuki and Stille couplings.With these in mind,in this paper,we synthesized a series of novel oligomerized unfused non-fullerene acceptors（NFAs）and star-shaped electronic materials by DACH reaction.Meanwhile,the structures,light absorption,energy levels and photovoltaic performance of these novel materials have been systematically studied.1.We developed,for the first time,that the combination of pot economy strategy with DACH reaction to prepare unfused oligomeric NFAs with gradually increasing chain length,namely IDB-IC-n and IDBF-IC-n（n=1～3）.These oligomeric NFAs have varied conjugation lengths but the same backbones of alternating indacenodithiophene and benzothiadiazole or difluoro benzothiadiazole.It is worth noting that IDB-IC-3 and IDBF-IC-3 have the longest conjugation lengths among the oligomeric NFAs ever reported.The optimal PCE of PM6:IDBF-IC-1 device is 12.12%,and the PCE decreases with the increase of the chain length of oligomer NFAs.The results demonstrate that the photoelectric properties can be fine-tuned effectively by changing con Jugation lengths or introducing fluorinated building units.2.We implement a proof-of-concept of welding DPP and PDI together as propellers for the design of novel molecules with star-shaped or three-dimensional（3D）geometries and minimized self-aggregation.Three novel rigid con Jugation molecules Ph（DPP-PDI）₃ Py（DPP-PDI）₄ and SF（DPP-PDI）₄with different central cores（e.g.,benzene,pyrene and spirofluorene）were synthesized by atomic and steps economical DACH coupling reaction.The opto-electrochemical and photovoltaic properties of molecules with different geometric configurations were systematically studied by UV-Vis,cyclic voltammetry and BHJ device measurement.Compared to DPP-PDI molecule,target molecules have broader light absorption range,higher molar absorption coefficient and more favorable frontier molecular orbital levels.