Singlet-singlet and singlet-heat annihilations in fluorescence-based organic light-emitting diodes under steady-state high current density

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Abstract

We observed a significant decrease in electroluminescence (EL) in the high-current-density region (J>1 A cm2) in organic light-emitting diodes (OLEDs). The decreased external quantum efficiency (ηext) in an OLED with a cathode diameter of d=50 μm was in excellent agreement with the singlet-singlet annihilation (SSA) model. In contrast, the decreased ηext in an OLED with a cathode diameter of d=1000 μm coincided well with the singlet-heat annihilation (SHA) model. These results suggest that large OLEDs generate significant Joule heat, which causes additional exciton dissociation in addition to SSA. We also used a very thermally conductive sapphire substrate (46 kW m-1 K-1) combined with a small cathode diameter of 50 μm in an OLED to alleviate the ηext roll off characteristics and achieved injection at a much higher current density. With this device configuration, a maximum current density of Jmax =447 A cm2 was achieved. However, decreased ηext based on SHA was observed in the high current region, indicating that significant Joule heat was generated under a few hundred A cm2 that induced additional exciton dissociation even when the sapphire substrate was used.

Original languageEnglish
Article number213506
Pages (from-to)1-3
Number of pages3
JournalApplied Physics Letters
Volume86
Issue number21
DOIs
Publication statusPublished - May 23 2005
Externally publishedYes

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high current
light emitting diodes
current density
heat
fluorescence
cathodes
sapphire
excitons
dissociation
electroluminescence
quantum efficiency
injection
causes
configurations

All Science Journal Classification (ASJC) codes

  • Physics and Astronomy (miscellaneous)

Cite this

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title = "Singlet-singlet and singlet-heat annihilations in fluorescence-based organic light-emitting diodes under steady-state high current density",
abstract = "We observed a significant decrease in electroluminescence (EL) in the high-current-density region (J>1 A cm2) in organic light-emitting diodes (OLEDs). The decreased external quantum efficiency (ηext) in an OLED with a cathode diameter of d=50 μm was in excellent agreement with the singlet-singlet annihilation (SSA) model. In contrast, the decreased ηext in an OLED with a cathode diameter of d=1000 μm coincided well with the singlet-heat annihilation (SHA) model. These results suggest that large OLEDs generate significant Joule heat, which causes additional exciton dissociation in addition to SSA. We also used a very thermally conductive sapphire substrate (46 kW m-1 K-1) combined with a small cathode diameter of 50 μm in an OLED to alleviate the ηext roll off characteristics and achieved injection at a much higher current density. With this device configuration, a maximum current density of Jmax =447 A cm2 was achieved. However, decreased ηext based on SHA was observed in the high current region, indicating that significant Joule heat was generated under a few hundred A cm2 that induced additional exciton dissociation even when the sapphire substrate was used.",
author = "Hajime Nakanotani and Hiroyuki Sasabe and Chihaya Adachi",
year = "2005",
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TY - JOUR

T1 - Singlet-singlet and singlet-heat annihilations in fluorescence-based organic light-emitting diodes under steady-state high current density

AU - Nakanotani, Hajime

AU - Sasabe, Hiroyuki

AU - Adachi, Chihaya

PY - 2005/5/23

Y1 - 2005/5/23

N2 - We observed a significant decrease in electroluminescence (EL) in the high-current-density region (J>1 A cm2) in organic light-emitting diodes (OLEDs). The decreased external quantum efficiency (ηext) in an OLED with a cathode diameter of d=50 μm was in excellent agreement with the singlet-singlet annihilation (SSA) model. In contrast, the decreased ηext in an OLED with a cathode diameter of d=1000 μm coincided well with the singlet-heat annihilation (SHA) model. These results suggest that large OLEDs generate significant Joule heat, which causes additional exciton dissociation in addition to SSA. We also used a very thermally conductive sapphire substrate (46 kW m-1 K-1) combined with a small cathode diameter of 50 μm in an OLED to alleviate the ηext roll off characteristics and achieved injection at a much higher current density. With this device configuration, a maximum current density of Jmax =447 A cm2 was achieved. However, decreased ηext based on SHA was observed in the high current region, indicating that significant Joule heat was generated under a few hundred A cm2 that induced additional exciton dissociation even when the sapphire substrate was used.

AB - We observed a significant decrease in electroluminescence (EL) in the high-current-density region (J>1 A cm2) in organic light-emitting diodes (OLEDs). The decreased external quantum efficiency (ηext) in an OLED with a cathode diameter of d=50 μm was in excellent agreement with the singlet-singlet annihilation (SSA) model. In contrast, the decreased ηext in an OLED with a cathode diameter of d=1000 μm coincided well with the singlet-heat annihilation (SHA) model. These results suggest that large OLEDs generate significant Joule heat, which causes additional exciton dissociation in addition to SSA. We also used a very thermally conductive sapphire substrate (46 kW m-1 K-1) combined with a small cathode diameter of 50 μm in an OLED to alleviate the ηext roll off characteristics and achieved injection at a much higher current density. With this device configuration, a maximum current density of Jmax =447 A cm2 was achieved. However, decreased ηext based on SHA was observed in the high current region, indicating that significant Joule heat was generated under a few hundred A cm2 that induced additional exciton dissociation even when the sapphire substrate was used.

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