Design,Synthesis And Properties Of Non-fullerene Acceptor Materials Based On "ADA'DA" Conjugated Skeleton

Due to the advantages of light weight,flexibility and roll to roll processing,organic solar cells have attracted much attention.At present,the power conversion efficiency(PCE)of a single organic photovoltaic device has exceeded 18%,which lays a foundation for the development of commercialization.In recent years,the development and application of non-fullerene acceptor materials has become one of the main ways to promote development of organic solar cells.However,there are still some problems in this kind of materials.Firstly,the PCE of solar cells based on polymer acceptor materials is lower than that of small molecule systems,mainly due to the lack of new polymer acceptor materials.Secondly,the complex structure and high cost of non-fullerene fused-ring small molecule acceptors greatly limit the commercial application of this kind of solar cells.In order to solve the above problems,we designed and synthesized new polymer acceptors based on the strategy of constructing polymer acceptors with small molecules.Meanwhile,we synthesized non-fused ring small molecule acceptors with simple structure and easy preparation by using non-covalent bond conformation lock design.The thermodynamic,optical,electrochemical and photovoltaic properties of these non-fullerene acceptor materials were systematically studied.The main contents of this paper are as follows:(1)Two narrow band gap polymer acceptors PY-2T and PY-2T2C1 were designed and synthesized by copolymerization of 2,2'-bithiophene(2T)and 3,3'-dichloro-2,2'-bithiophene(2T2C1)with Y5 derivatives of ADA'DA type as conjugated backbone.Compared with the polymers PIDIC-2T and PIDIC-2T2C1 with IDIC framework,the effect of chloride substituted ?-spacer on polymer acceptors was studied systematically.The results show that the polymer with the center core adjusted from IDIC to Y5 exhibits a relatively red shifted absorption,an up shifted energy level and a narrower band gap;Meanwhile,the introduction of chlorine substituted ?-spacer has little effect on the optical and electrochemical properties of the polymer,but it shows good crystallinity and good phase separation morphology after blending with the donor,and the PCE of the device based on PBDB-T:PY-2T2C1 reaches 9.35%.(2)The polymer acceptors PY-2T and PY-2Tz were prepared by copolymerization of Y5 with 2T and 2,2'-bithizole(2Tz)units,respectively.The results show that the thermal stability of the polymer acceptor PY-2Tz is improved compared with that of PY-2T,but the absorption is blue shifted;GIWAXS data show that PY-2Tz film presents mixed crystal orientation,and the short-circuit current of the device is low due to poor compatibility with the donor PBDB-T,which only shows 1.58%PCE,while the film of PY-2T is highly ordered,and its PCE reaches 5.34%.(3)Two ADA'DA type small molecule acceptors BDD-IC and BDD-IC4F were designed and synthesized with benzodithiophenedione(BDD)as the central core and 3-(Dicyanomethylidene)indan-1-one(IC)or 2-(5,6-difluoro-3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile(IC4F)as the terminal group.These two molecules have the advantages of simple preparation and low cost.The results show that BDD-IC4F has wider optical absorption,deeper homo and LUMO energy levels and higher thermodynamic stability than BDD-IC,and the photovoltaic device based on BDD-IC4F achieves 0.21%power conversion efficiency.(4)Using Four ADA'DA type small molecule semiconductor materials PTIC,PTIC-4F,PTTIC and PTTIC-4F with similar skeletons were designed and synthesized using alkoxybenzene ring as the core,thiophene and thieno[3,2-B]thiophene as ?-spacer,IC or IC4F as the end group,respectively.The results show that the fluorination of terminal group and the increase of ? bridge length will lead to the red shift of UV,the enhancement of molar absorptivity and the improvement of thermal stability;Meanwhile,the conformational lock of non-covalent bond in the molecule will increase the effective conjugation length of the molecular structure,and the four small molecules show good main chain planarity.