| Since the industrial revolution,human consumption of energy is increasing with the rapid development of social material civilization.However,the traditional fossil resources on earth are limited,and the demand of human society for new,clean and renewable resources has become more and more urgent.Among the many new energy technologies,solar energy is considered as the most promising new energy source because of its abundant resources and easy development and utilization.Due to the advantages such as low cost,lightweight and mechanical flexibility,polymer solar cells have attracted many researchers' attention.At present,the power conversion efficiency of bulk-heterojunction polymer solar cells has exceeded 12%,but it also faces many obstacles from large-scale commercial applications.The relatively low efficiency and short life-time of devices are still the two major problems restricting its development.Currently,in order to solve the above problems of polymer solar cells,many researches focus on new type of donor polymers with strong absorption ability,suitable energy level and high carrier transport ability.Firstly,in this paper,we reviewed the recent progress of some of the most efficient donor polymers.In order to understand the relationship between the structure and properties of materials,we classify these polymers systematically and try to understand importiant rules.In this paper,a series of strong aggregation polymers were synthesized by adjusting the structures of the main chain and side chain,and their photoelectric properties were investigated in details.In the second chapter,we selected a simple and efficient synthetic route to synthesize the fused ring structure of DTfBO,anelectron withdrawing unit.Through the polymerizations by Stille coupling,with T,DT and TT as the D unit of copolymerization,respectively,D-A type alternating polymers PDTfBO-T,PDTf BO-DT and PDTfBO-TT were obtained.The measured OFET hole mobilities based on the three polymers were all higher than 0.2cm2/(Vs).Among them,PDTfBO-TT showed the best holemobility of 0.54cm2/(Vs).At the same time,the three polymers displayed excellent photovoltaic performances and the energy conversion efficiencies(PCEs)were about 5.61%.The results indicate that the DTfBO unit has great potential in the construction of high mobility polymers and high efficiency polymer donors.In chapter three,we introduced the six membered fused ring unit TPTTPT as electron donating groups,to copolymerize with BT,DPP and IID,respectively,from which three D-A type conjugated polymers PTPTTPT-BT-24,PTPTTPT-DPP-16 and PTPTTPT-IID-20 were obtained.And the optical absorptions,electrochemical levels and photovoltaic performances of polymers were also studied in details.It was found that the efficiency of the PSC devices based on PTPTTPT-BT-24 could be up to 4.94%,showing the good potential of the TPTTPT unit.In chapter four,we synthesized an alternating copolymer with saturated aliphatic side chain PffBT-TPT.Futhermore,three random copolymers PffBT-TPT-Si25%,PffBT-TPT-Si50% and PffBT-TPT-Si75% by replacing the side chain of the aliphatic side chain with siloxane-terminated side chain in different proportion were designed.The optical,electrochemistry,surface properties and photovoltaic properties of the four polymers were investigated for comparason.Among them,PffBT-TPT-Si75% showed excellent photovoltaic performance,and the efficiency of the device prepared by blending with ITIC was 7.17%.The results demonstrate that replacing the alkyl chain with siloxane-terminated side chain in an optimized proportion can be an effective method to improve the photovoltaic performance of an polymer.In chapter five,we synthesized a series of narrow band gap polymers with alkoxy benzene as a main chain building block.It was found that the intramolecular torsional angle could be reduced and the planarity of polymer chains could be improved through the noncovalent interaction between alkoxy benzene and neighboring groups.In addition,the influence of the length of the alkyl chain and the ratio of the siloxane-terminated side chain on the optoelectronic properties of the polymer were studied by keeping the main chain structure unchanged.Thus the band gaps of the polymers were about 1.4 eV,showing limited changing.But the designs could result in significant influences on their photovoltaic properties.At the same time,it was found that the processing solvent had a great influence on the photovoltaic performances.Compared with chlorobenzene,the mixed solvent based on ortho-dichlorobenzene and chloroform could improve the efficiency of the PSC devices by improving the morphology of the active layer.Finally,the solar cells based on PDPP-EH-TPT-EH-Si50% could achieve the best power conversion efficiency of 6.03%.On the basis of the work of the fifth chapter,a series of narrow gap random copolymers were synthesized with different proportions of tetrafluorobenzene to replace the alkoxy benzene,in the sixth chapter.In comparsion with oxygen atoms,fluorine atoms can enhance intramolecular planarity and intermolecular aggregation through noncovalent interactions.The absorption spectra and electrochemical measurements indicated that the fluorobenzene unit could lower the HOMO and LUMO levels of polymers simultaneously,but showed no obvious influence on optical band gaps.For the photovoltaic performances of the polymers,using the fluorobenzene unit could induce a highest open-circuit voltage of 0.75 V for PDPP-EH-TPT-BO-F40%.The calculated photon energy loss is only 0.63 eV.Our results demonstrate that introduction of fluorobenzene in a polymer can help the open-circuit voltage. |
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