Cyano-Substituted Head-to-Head Polythiophenes

Enabling High-Performance n-Type Organic Thin-Film Transistors

Hang Wang, Jun Huang, Mohammad Afsar Uddin, Bin Liu, Peng Chen, Shengbin Shi, Yumin Tang, Guichuan Xing, Shiming Zhang, Han Young Woo, Han Guo, Xugang Guo

Research output: Contribution to journalArticle

6 Citations (Scopus)

Abstract

Polythiophenes, built on the electron-rich thiophene unit, typically possess high-lying energy levels of the lowest unoccupied molecular orbitals (LUMOs) and show hole-transporting properties. In this study, we develop a series of n-type polythiophenes, P1-P3, based on head-to-head-linked 3,3′-dialkoxy-4,4′-dicyano-2,2′-bithiophene (BTCNOR) with distinct side chains. The BTCNOR unit shows not only highly planar backbone conformation enabled by the intramolecular noncovalent sulfur-oxygen interaction but also significantly suppressed LUMO level attributed to the cyano-substitution. Hence, all BTCNOR-based polymer semiconductors exhibit low-lying LUMO levels, which are -1.0 eV lower than that of regioregular poly(3-hexylthiophene) (rr-P3HT), a benchmark p-type polymer semiconductor. Consequently, all of the three polymers can enable unipolar n-type transport characteristics in organic thin-film transistors (OTFTs) with low off-currents (I off s) of 10 -10 -10 -11 A and large current on/off ratios (I on /I off s) at the level of 10 6 . Among them, polymer P2 with a 2-ethylhexyl side chain offers the highest film ordering, leading to the best device performance with an excellent electron mobility (μ e ) of 0.31 cm 2 V -1 s -1 in off-center spin-cast OTFTs. To the best of our knowledge, this is the first report of n-type polythiophenes with electron mobility comparable to the hole mobility of the benchmark p-type rr-P3HT and approaching the electron mobility of the most-studied n-type polymer, poly(naphthalene diimide-alt-bithiophene) (i.e., N2200). The change of charge carrier polarity from p-type (rr-P3HT) to n-type (P2) with comparable mobility demonstrates the obvious effectiveness of our structural modification. Adoption of n-hexadecyl (P1) and 2-butyloctyl (P3) side chains leads to reduced film ordering and results in 1-2 orders of magnitude lower μ e s, showing the critical role of side chains in optimizing device performance. This study demonstrates the unique structural features of head-to-head linkage containing BTCNOR for constructing high-performance n-type polymers, i.e., the alkoxy chain for backbone conformation locking and providing polymer solubility as well as the strong electron-withdrawing cyano group for lowering LUMO levels and enabling n-type performance. The design strategy of BTCNOR-based polymers provides useful guidelines for developing n-type polythiophenes.

Original languageEnglish
Pages (from-to)10089-10098
Number of pages10
JournalACS Applied Materials and Interfaces
Volume11
Issue number10
DOIs
Publication statusPublished - 2019 Mar 13

Fingerprint

Thin film transistors
Polymers
Molecular orbitals
Electron mobility
Conformations
Semiconductor materials
Thiophenes
Hole mobility
polythiophene
Electrons
Charge carriers
Sulfur
Electron energy levels
Substitution reactions
Solubility
Thiophene
Naphthalene
Oxygen
poly(3-hexylthiophene)

Keywords

  • conformation lock
  • cyano-functionalization
  • head-to-head linkage
  • n-type organic thin-film transistors
  • polythiophene

ASJC Scopus subject areas

  • Materials Science(all)

Cite this

Cyano-Substituted Head-to-Head Polythiophenes : Enabling High-Performance n-Type Organic Thin-Film Transistors. / Wang, Hang; Huang, Jun; Uddin, Mohammad Afsar; Liu, Bin; Chen, Peng; Shi, Shengbin; Tang, Yumin; Xing, Guichuan; Zhang, Shiming; Woo, Han Young; Guo, Han; Guo, Xugang.

In: ACS Applied Materials and Interfaces, Vol. 11, No. 10, 13.03.2019, p. 10089-10098.

Research output: Contribution to journalArticle

Wang, H, Huang, J, Uddin, MA, Liu, B, Chen, P, Shi, S, Tang, Y, Xing, G, Zhang, S, Woo, HY, Guo, H & Guo, X 2019, 'Cyano-Substituted Head-to-Head Polythiophenes: Enabling High-Performance n-Type Organic Thin-Film Transistors', ACS Applied Materials and Interfaces, vol. 11, no. 10, pp. 10089-10098. https://doi.org/10.1021/acsami.8b22457
Wang, Hang ; Huang, Jun ; Uddin, Mohammad Afsar ; Liu, Bin ; Chen, Peng ; Shi, Shengbin ; Tang, Yumin ; Xing, Guichuan ; Zhang, Shiming ; Woo, Han Young ; Guo, Han ; Guo, Xugang. / Cyano-Substituted Head-to-Head Polythiophenes : Enabling High-Performance n-Type Organic Thin-Film Transistors. In: ACS Applied Materials and Interfaces. 2019 ; Vol. 11, No. 10. pp. 10089-10098.
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T1 - Cyano-Substituted Head-to-Head Polythiophenes

T2 - Enabling High-Performance n-Type Organic Thin-Film Transistors

AU - Wang, Hang

AU - Huang, Jun

AU - Uddin, Mohammad Afsar

AU - Liu, Bin

AU - Chen, Peng

AU - Shi, Shengbin

AU - Tang, Yumin

AU - Xing, Guichuan

AU - Zhang, Shiming

AU - Woo, Han Young

AU - Guo, Han

AU - Guo, Xugang

PY - 2019/3/13

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N2 - Polythiophenes, built on the electron-rich thiophene unit, typically possess high-lying energy levels of the lowest unoccupied molecular orbitals (LUMOs) and show hole-transporting properties. In this study, we develop a series of n-type polythiophenes, P1-P3, based on head-to-head-linked 3,3′-dialkoxy-4,4′-dicyano-2,2′-bithiophene (BTCNOR) with distinct side chains. The BTCNOR unit shows not only highly planar backbone conformation enabled by the intramolecular noncovalent sulfur-oxygen interaction but also significantly suppressed LUMO level attributed to the cyano-substitution. Hence, all BTCNOR-based polymer semiconductors exhibit low-lying LUMO levels, which are -1.0 eV lower than that of regioregular poly(3-hexylthiophene) (rr-P3HT), a benchmark p-type polymer semiconductor. Consequently, all of the three polymers can enable unipolar n-type transport characteristics in organic thin-film transistors (OTFTs) with low off-currents (I off s) of 10 -10 -10 -11 A and large current on/off ratios (I on /I off s) at the level of 10 6 . Among them, polymer P2 with a 2-ethylhexyl side chain offers the highest film ordering, leading to the best device performance with an excellent electron mobility (μ e ) of 0.31 cm 2 V -1 s -1 in off-center spin-cast OTFTs. To the best of our knowledge, this is the first report of n-type polythiophenes with electron mobility comparable to the hole mobility of the benchmark p-type rr-P3HT and approaching the electron mobility of the most-studied n-type polymer, poly(naphthalene diimide-alt-bithiophene) (i.e., N2200). The change of charge carrier polarity from p-type (rr-P3HT) to n-type (P2) with comparable mobility demonstrates the obvious effectiveness of our structural modification. Adoption of n-hexadecyl (P1) and 2-butyloctyl (P3) side chains leads to reduced film ordering and results in 1-2 orders of magnitude lower μ e s, showing the critical role of side chains in optimizing device performance. This study demonstrates the unique structural features of head-to-head linkage containing BTCNOR for constructing high-performance n-type polymers, i.e., the alkoxy chain for backbone conformation locking and providing polymer solubility as well as the strong electron-withdrawing cyano group for lowering LUMO levels and enabling n-type performance. The design strategy of BTCNOR-based polymers provides useful guidelines for developing n-type polythiophenes.

AB - Polythiophenes, built on the electron-rich thiophene unit, typically possess high-lying energy levels of the lowest unoccupied molecular orbitals (LUMOs) and show hole-transporting properties. In this study, we develop a series of n-type polythiophenes, P1-P3, based on head-to-head-linked 3,3′-dialkoxy-4,4′-dicyano-2,2′-bithiophene (BTCNOR) with distinct side chains. The BTCNOR unit shows not only highly planar backbone conformation enabled by the intramolecular noncovalent sulfur-oxygen interaction but also significantly suppressed LUMO level attributed to the cyano-substitution. Hence, all BTCNOR-based polymer semiconductors exhibit low-lying LUMO levels, which are -1.0 eV lower than that of regioregular poly(3-hexylthiophene) (rr-P3HT), a benchmark p-type polymer semiconductor. Consequently, all of the three polymers can enable unipolar n-type transport characteristics in organic thin-film transistors (OTFTs) with low off-currents (I off s) of 10 -10 -10 -11 A and large current on/off ratios (I on /I off s) at the level of 10 6 . Among them, polymer P2 with a 2-ethylhexyl side chain offers the highest film ordering, leading to the best device performance with an excellent electron mobility (μ e ) of 0.31 cm 2 V -1 s -1 in off-center spin-cast OTFTs. To the best of our knowledge, this is the first report of n-type polythiophenes with electron mobility comparable to the hole mobility of the benchmark p-type rr-P3HT and approaching the electron mobility of the most-studied n-type polymer, poly(naphthalene diimide-alt-bithiophene) (i.e., N2200). The change of charge carrier polarity from p-type (rr-P3HT) to n-type (P2) with comparable mobility demonstrates the obvious effectiveness of our structural modification. Adoption of n-hexadecyl (P1) and 2-butyloctyl (P3) side chains leads to reduced film ordering and results in 1-2 orders of magnitude lower μ e s, showing the critical role of side chains in optimizing device performance. This study demonstrates the unique structural features of head-to-head linkage containing BTCNOR for constructing high-performance n-type polymers, i.e., the alkoxy chain for backbone conformation locking and providing polymer solubility as well as the strong electron-withdrawing cyano group for lowering LUMO levels and enabling n-type performance. The design strategy of BTCNOR-based polymers provides useful guidelines for developing n-type polythiophenes.

KW - conformation lock

KW - cyano-functionalization

KW - head-to-head linkage

KW - n-type organic thin-film transistors

KW - polythiophene

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