Synthesis And Performance Research Of Organic Photoelectric Materials Based On Benzothiadiazole Derivatives

Polymer solar cells(PSCs)have attracted much attention for the generation of clean and renewable energy.Up to now,the power conversion efficiency(PCE)of single junction PSCs has achieved 13%.However,further development of conjugated polymers is essential to achieve high performance PSCs for commercialization.Within which,D-A copolymers are the most powerful strategy to design a low band gap conjugated polymer photovoltaic materials due to their advantage in tuning the absorption spectra,HOMO/LUMO energy levels,charge transport ability and blends morphology of donor and acceptor materials etc.In this dissertation,a series of D-A conjugated polymers materials based on benzothiadiazole are designed and synthesized,the relationship between optical properties,active layer morphology,carrier mobility and photovoltaic performance of target polymers is systematically studied.The main contents of this dissertation are as follows:1.Three low bandgap polymers(PSDTBT-DFDT,PSDTfBT-DFDT,and PSDTffBT-DFDT)based on alkylthio substituted benzothiadiazole-quaterthiophene alternating units were synthesized and applied as the donor materials for polymer solar cells.The effect of fluorination and thio-alkylation on photophysical,electrochemical,photovoltaic properties of the polymers was comparatively investigated.The results indicated that PSDTfBT-DFDT and PSDTffBT-DFDT showed better light-harvesting abilities,lower-lying HOMO energy levels and better morphology than that of PSDTBT-DFDT.Bulk heterojunction(BHJ)solar cells based on the as-synthesized polymers as donor and[6,6]-phenyl-C71-butyric acid methyl ester(PC71BM)as acceptor were fabricated.The power conversion efficiencies of 6.94%for PSDTfBT-DFDT and 7.50%for PSDTffBT-DFDT were attained,respectively,both of which are higher than that of PSDTBT-DFDT(4.48%)due to the increasement of the numbers of fluorine atom.This result demonstrates that both fluorine substitution and thio-alkylation are efficient to improve optoelectronic properties of polymers.2.Two donor-acceptor(D-A)polymers PSQT-4F,PSQT-Uz,consisting of alkylthio substituted difluorobenzothiadiazole-quaterthiophene as the acceptor moieties and different donor units,have been designed and synthesized.The effects of variant donor moieties on photophysical,electrochemical and photovoltaic properties of the polymers were investigated.Compared with the polymer PSQT-Uz with the ullazine with donor moieties,the polymer PSQT-4F with 3,3'-difluoro-2,2'-bithiophene as the donor moieties shows smaller band gap,broader and stronger light harvesting capacity,higher mobility.Therefore,the PSQT-4F-based bulk heterojunction polymer solar cell electron donor material exhibits a higher PCE of 2.0%than that of PSQT-Uz-based electron donor material(1.59%).