Design,Synthesis And Photoelectric Properties Of D-A Conjugated Polymers

During the development of organic semiconductor materials,polymer semiconductor materials combine the advantages of inorganic semiconductors(outstanding photoelectric properties)and polymer materials(feasible design and synthesis)together,and they have attracted so much attention recently.For the synthesis of donor-acceptor(D-A)conjugated polymers,the frontier orbital energy levels and electron distribution over the backbone can be tuned by the rational design of electron-withdrawing groups and electron-donating groups,thus leading to the improvement of physicochemical properties and device performance of the polymer materials.Therefore,we focused on the design and synthesis,and comprehensive characterization of the D-A conjugated polymers.Meanwhile,the polymer materials were applied as donor materials in organic solar cells,and their charge carrier-transporting properties were also investigated.In this thesis,the design and synthesis of three series of conjugated polymer materials and their application in organic solar cells and organic filed-effect transistors were discussed,and then the effect of structural variation of the conjugated backbone and the side chain on the photovoltaic performance and charge carrier mobilities was studied.First of all,three D-A conjugated polymer materials,PBT2F-TT-a,PBT2F-TT and PBT2F-Se,with 5,6-difluorobenzothiadiazole as the acceptor unit and phenyl rings flanked with different heterocyclic units(thiophene and selenophene)as donor units were successfully prepared.All the polymer showed intense absorption in the visible range,which may contribute to the high power conversion efficiency(PCE).The active layer of bulk heterojunction polymer solar cells(PSCs)was prepared with polymers as donor units and PC71BM as acceptor.The effect of additives on photovoltaic performance of PSCs based on these polymers has been comprehensively investigated by means of AFM,TEM,ACIS,and SCLC analysis.The charge carrier mobilities of these blend films were greatly increased after the addition of diphenyl ether(DPE)additive(2%v/v),giving rise to enhanced photovoltaic performances.And the improvement of the efficiency of PBT2F-Se is the most obvious,from 3.01%to 4.18%,which is nearly 40%.Then,the D-A conjugated polymers PDPP20 and PDPP32 with diketopyrrolopyrrole(DPP)as the acceptor and the indolo[3,2-b]indole(IDID)as the donor were designed and synthesized.The length and branching position of side chain were modulated to investigate the effect of side chains on the charge carrier mobility of conjugated polymers.The variation of side chain showed negligible effect on optical and electrical properties of the materials.Organic field-effect transistor devices were fabricated to determine their charge carrier mobilities,and both polymers showed decent hole mobilitie around 10-3 cm2V-1s-1.Finally,we designed and synthesized two novel D-A conjugated polymers,PTIIG and PFIIG,with derivated isoindigo and fluorinated thiophene as building blocks.Now we have finished the characterization of their photophysical properties and thermal stability.The introducing of thiophene unit into the conjugated backbone of polymer PTIIG led to narrow bandgap.The photovoltaic performance and charge carrier transporting properties of these polymer based on isoindigo derivant are still under investigation.