Design,Synthesis,and Optoelectronic Performance Investigation of Ambipolar and N-type Semiconducting Polymers

Author:Yang Jie

Supervisor:wang shuai liu yun zuo


Degree Year:2019





Compared with inorganic field-effect transistors,organic field-effect transistors(OFETs)have unique advantages,including light weight,mechanical flexibility,solution processability,and tunable optoelectronic property.OFETs exhibit potential applications in logic circuits,intelligent sensors,flexible displays,electronic skins,and wearable electronic devices.Recently,impressive progress has been made in polymer-based OFETs.High hole mobilities(μh)of more than 20 cm2 V–11 s–1 have been achieved in p-type polymers.However,the reported electron mobilities(μe)of ambipolar or n-type polymers are generally below 5 cm2 V–11 s–1,which fall greatly behind those of p-type counterparts.It is of great importance to design and synthesize ambipolar or n-type polymers because of their potential applications in logic circuits and organic light-emitting field-effect transistors.The research work in this dissertation is focused on the design and synthesis of novel ambipolar or n-type polymers.Several effective design strategies of ambipolar or n-type polymers are summarized by investigating their structure-property relationship.The main contents are listed as follows:1.A bis-diketopyrrolopyrrole(2DPP)acceptor was developed by an“acceptor dimerization”strategy.Four 2DPP-based polymers,P2DPP-BT,P2DPP-TT,P2DPP-TVT and P2DPP-BDT were synthesized.The LUMO energy levels of 2DPP-based polymers(P2DPPs)were lowered by 0.1 eV compared with those of mono DPP-based polymers(PDPPs).PDPPs were nearly p-type semiconductors with negligible electron mobilities of10–33 cm2 V–11 s–1.However,all the P2DPPs showed remarkable ambipolar performance.Particularly,P2DPP-TT showed excellent performance with aμh/μe of 4.16/3.01 cm2 V–1s–1,which were among the highest values for ambipolar polymers.A remarkable improvement of up to two orders of magnitude inμe was observed from PDPPs to P2DPPs.These results demonstrated that“acceptor dimerization”was an effective strategy to synthesize ambipolar polymers.2.A tri-diketopyrrolopyrrole(3DPP)acceptor and its copolymer(P3DPP-BT)were developed.P3DPP-BT showed a narrow optical bandgap of 1.27 eV.The HOMO and LUMO energy levels of P3DPP-BT were-5.45 and-3.51 eV,respectively.OFET devices based on P3DPP-BT showed balanced transport behaviors with aμh/μe of 1.12/1.27 cm2V–11 s–1.3.Three isoindigo-based polymers of PIID-2FBT,P1FIID-2FBT and P2FIID-2FBT were developed by a“multifluorination”strategy.From PIID-2FBT to P2FIID-2FBT,the polymers showed enhanced coplanarity,lower LUMO energy levels,and higher crystallinity.From PIID-2FBT to P2FIID-2FBT,the polymers showed obvious mobility changes from p-channel dominant to balanced ambipolar,and n-channel dominant performance.Particularly,P2FIID-2FBT exhibited remarkable performance with aμh/μe of 2.75/9.70 cm2 V–11 s–1,which were among the highest values for ambipolar polymers.The concept of“effective mass”was introduced to further elucidate the reasons for the high performance of P2FIID-2FBT.P2FIID-2FBT showed small effective masses,indicating good intramolecular charge transport.The results indicated that high-performance ambipolar polymers could be achieved by designing polymers with fine-tuned energy levels,high crystallinity,and small effective masses.4.A general synthetic method to obtain substituted bay-annulated indigo(BAI)units was developed.This method was effective to introduce various groups(F,Cl,Br,CN or CF3)into BAI at different substituted positions.A series of BAI acceptors were reported for the first time based on this method.Four polymers of PBAI-V,P2FBAI-V,P2ClBAI-V,and P4OBAI-V were synthesized.All the polymers exhibited ambipolar transport behaviors.Particularly,P2ClBAI-V exhibited remarkable performance with aμh/μe of 4.04/1.46 cm2 V–11 s–1.The general synthetic method can be used to obtain other novel BAI acceptors and thus significantly enrich the library of ambipolar polymers.