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

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??_h?of more than 20 cm² V^–11 s^–1 have been achieved in p-type polymers.However,the reported electron mobilities??_e?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 a?_h/?_e 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 in?_e 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 a?_h/?_e 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 a?_h/?_e 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 a?_h/?_e 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.