Enhancement of hole injection and electroluminescence characteristics by a rubbing-induced lying orientation of alpha-sexithiophene

Toshinori Matsusima, Hideyuki Murata

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Abstract

The authors find that rubbing a film of alpha-sexithiophene (α-6T) with a nylon cloth induces a change from standing to lying orientations in a film surface region. While current densities of hole-only devices based on 4,4′,4″-tris(N-3-methylphenyl-N-phenyl-amino)triphenylamine (m-MTDATA) are independent of the rubbing number of α-6T, current densities of hole-only devices based on N-N′-diphenyl-N-N′-bis(1- naphthyl)-1,1′-biphenyl-4,4′-diamine (α-NPD) and 4,4′-bis(carbazol-9-yl)-2,2′-biphenyl (CBP) markedly increase (≈42 times at 1 V for the α-NPD devices and ≈236 times at 1 V for the CBP devices) as the rubbing number of α-6T is increased. The increase in current density is ascribed to enhanced hole injection through a -5.28 eV energy level of lying α-6T domains instead of a -4.95 eV energy level of standing α-6T domains and improved overlaps between an electronic cloud of indium tin oxide, π orbitals of lying α-6T molecules, and π orbitals of molecules of α-NPD and CBP at heterojunction interfaces. The rubbing of α-6T is also demonstrated to reduce drive voltages (by ≈40 at 10 mA/cm 2) and increase power conversion efficiency (by ≈26 at 10 mA/cm 2) of organic light-emitting diodes. Finally, half lifetimes are significantly enhanced (4.3 times) at a current density of 50 mA/cm 2.

Original languageEnglish
Article number024503
JournalJournal of Applied Physics
Volume112
Issue number2
DOIs
Publication statusPublished - Jul 15 2012
Externally publishedYes

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electroluminescence
injection
current density
augmentation
energy levels
orbitals
Nylon (trademark)
diamines
indium oxides
tin oxides
heterojunctions
molecules
light emitting diodes
life (durability)
electric potential
electronics

All Science Journal Classification (ASJC) codes

  • Physics and Astronomy(all)

Cite this

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abstract = "The authors find that rubbing a film of alpha-sexithiophene (α-6T) with a nylon cloth induces a change from standing to lying orientations in a film surface region. While current densities of hole-only devices based on 4,4′,4″-tris(N-3-methylphenyl-N-phenyl-amino)triphenylamine (m-MTDATA) are independent of the rubbing number of α-6T, current densities of hole-only devices based on N-N′-diphenyl-N-N′-bis(1- naphthyl)-1,1′-biphenyl-4,4′-diamine (α-NPD) and 4,4′-bis(carbazol-9-yl)-2,2′-biphenyl (CBP) markedly increase (≈42 times at 1 V for the α-NPD devices and ≈236 times at 1 V for the CBP devices) as the rubbing number of α-6T is increased. The increase in current density is ascribed to enhanced hole injection through a -5.28 eV energy level of lying α-6T domains instead of a -4.95 eV energy level of standing α-6T domains and improved overlaps between an electronic cloud of indium tin oxide, π orbitals of lying α-6T molecules, and π orbitals of molecules of α-NPD and CBP at heterojunction interfaces. The rubbing of α-6T is also demonstrated to reduce drive voltages (by ≈40 at 10 mA/cm 2) and increase power conversion efficiency (by ≈26 at 10 mA/cm 2) of organic light-emitting diodes. Finally, half lifetimes are significantly enhanced (4.3 times) at a current density of 50 mA/cm 2.",
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N2 - The authors find that rubbing a film of alpha-sexithiophene (α-6T) with a nylon cloth induces a change from standing to lying orientations in a film surface region. While current densities of hole-only devices based on 4,4′,4″-tris(N-3-methylphenyl-N-phenyl-amino)triphenylamine (m-MTDATA) are independent of the rubbing number of α-6T, current densities of hole-only devices based on N-N′-diphenyl-N-N′-bis(1- naphthyl)-1,1′-biphenyl-4,4′-diamine (α-NPD) and 4,4′-bis(carbazol-9-yl)-2,2′-biphenyl (CBP) markedly increase (≈42 times at 1 V for the α-NPD devices and ≈236 times at 1 V for the CBP devices) as the rubbing number of α-6T is increased. The increase in current density is ascribed to enhanced hole injection through a -5.28 eV energy level of lying α-6T domains instead of a -4.95 eV energy level of standing α-6T domains and improved overlaps between an electronic cloud of indium tin oxide, π orbitals of lying α-6T molecules, and π orbitals of molecules of α-NPD and CBP at heterojunction interfaces. The rubbing of α-6T is also demonstrated to reduce drive voltages (by ≈40 at 10 mA/cm 2) and increase power conversion efficiency (by ≈26 at 10 mA/cm 2) of organic light-emitting diodes. Finally, half lifetimes are significantly enhanced (4.3 times) at a current density of 50 mA/cm 2.

AB - The authors find that rubbing a film of alpha-sexithiophene (α-6T) with a nylon cloth induces a change from standing to lying orientations in a film surface region. While current densities of hole-only devices based on 4,4′,4″-tris(N-3-methylphenyl-N-phenyl-amino)triphenylamine (m-MTDATA) are independent of the rubbing number of α-6T, current densities of hole-only devices based on N-N′-diphenyl-N-N′-bis(1- naphthyl)-1,1′-biphenyl-4,4′-diamine (α-NPD) and 4,4′-bis(carbazol-9-yl)-2,2′-biphenyl (CBP) markedly increase (≈42 times at 1 V for the α-NPD devices and ≈236 times at 1 V for the CBP devices) as the rubbing number of α-6T is increased. The increase in current density is ascribed to enhanced hole injection through a -5.28 eV energy level of lying α-6T domains instead of a -4.95 eV energy level of standing α-6T domains and improved overlaps between an electronic cloud of indium tin oxide, π orbitals of lying α-6T molecules, and π orbitals of molecules of α-NPD and CBP at heterojunction interfaces. The rubbing of α-6T is also demonstrated to reduce drive voltages (by ≈40 at 10 mA/cm 2) and increase power conversion efficiency (by ≈26 at 10 mA/cm 2) of organic light-emitting diodes. Finally, half lifetimes are significantly enhanced (4.3 times) at a current density of 50 mA/cm 2.

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