Design And Synthesis Of Conjugated Polymers Containing B And N Elements And Studies On The Performance Of Electronic Devices

Conjugated polymers are widely used in organic electronic devices,such as organic field effect transistors(OFET)and organic solar cells(OSC)due to their light weight,good flexibility,low cost,and easy processing features,The intrinsic optical and electrical properties of conjugated polymers,such as photophysical properties and frontier molecular orbital(FMO)energy levels,are one of the key factors determining the performance of electronic devices.Therefore,it is significant to adjust the optical and electrical properties of conjugated polymers through molecular structure design and tailoring to regulate device performance.Alternating copolymerization of electron-rich units(D)and electron-deficient units(A)is the main strategy for constructing conjugated polymers.In conjugated polymers,the carbon(C)-carbon(C)single-double bond alternating conjugated structure is mainly used,along with heteroatoms such as N,B,O,P,and S.Among them,B and N are adjacent to C in the periodic table and their atomic numbers are different from C only by 1.Although the atomic numbers of B,N and C are close,the properties are quite different.If two elements,B and N,can be introduced into the conjugated skeleton based on C to obtain a polymer containing B and N heteroelements,the optical and electrical properties of the materials can be finely adjusted to regulate the device performance feasibly.In this project,we chose an electron-deficient unit containing B?N bonds,namely,BNIDT to copolymerize with different conjugated units by D-A or A-A to obtain a series of copolymers containing B and N heteroelements.First,we investigated the synthesis of BNIDT and diketopyrrolopyrrole(DPP)copolymer(BNIDT-DPP)and the performance of electronic devices.It is found that compared with C-C polymers,the energy levels of polymers containing B and N elements are significantly reduced and the absorption spectrum is broadened.OFET device tests on these polymers show p-type semiconductor characteristics.Due to the higher HOMO energy levels and weaker n-type semiconductor characteristics,OSC devices using these polymers as the accetpors show very low efficiencies.In order to further reduce the HOMO energy level and enhance the characteristics of n-type semiconductors,a fluorinated benzotriazole unit was selected and copolymerized with BNIDT to prepare BN-BTZ-2f.Compared with BNIDT-DPP,the HOMO(-5.22 vs.-5.55 eV)of BN-BTZ-2f was significantly reduced.However,due to the weak characteristics of n-type semiconductors,the efficiencies of OSC devices using BN-BTZ-2f as the acceptor is still low(0.12%).In order to improve the efficiencies,the side groups of BNIDT units were methylated and fluorinated and they were copolymerized with difluorothiophene.The obtained polymers were used as an acceptor material to prepare an OSC devices,and showed an efficiency of 3.17%,which proves that modificating the side groups and screening copolymerization units has a significant effect on the photovoltaic performance of such B?N element-containing copolymers.Finally,two donor materials,PhI-T-BTZ-2f and ThI-T-BTZ-2f,were designed and synthesized for matching B?N embedded conjugated polymers.These results have proved that conjugated polymers containing B and N heteroelements are a new type of semiconductor materials with broad application prospects.