Improved hole-injection and external quantum efficiency of organic light-emitting diodes using an ultra-thin K-doped NiO buffer layer

Malvin, Chi Ting Tsai, Chen Tao Wang, Yih Yuan Chen, Po Ching Kao, Sheng-Yuan Chu

Research output: Contribution to journalArticle

1 Citation (Scopus)

Abstract

In this paper, we used the thermal evaporation method to deposit K-doped NiO (KNO) films as the inorganic buffer layer in thermally activated delayed fluorescence (TADF)-based organic light emitting diode (OLED) devices, and investigated how it improved device performance. The device configuration was ITO/NiO:K2CO3 (X mol%, 1 nm)/NPB (40 nm)/CBP:4CzIPN (5 wt%, 20 nm)/TPBi (50 nm)/LiF (1 nm)/Al (150 nm). We used various concentrations of alkali metal-doped metal oxide on the ITO, which was then subjected to UV-O3 surface treatment. We studied the effects and mechanisms of the improved hole-injection properties of the OLEDs with different measurement methods. X-ray Photoelectron Spectroscopy (XPS) was used to measure the molecular binding energy and confirm formation of the K-doped NiO films. In comparison with the ITO electrode's work function, the KNO film increased the work function from 4.8 to 5.3 eV. Contact angle measurement showed that the deposition of the buffer layer increased both polarity and surface energy. The K-doped NiO film was found to have a smoother surface than that of the ITO electrode, as determined by Atomic Force Microscopy. Reduction in the sheet resistance of the OLEDs was revealed by Admittance Spectroscopy measurement. The opto-electrical performances of the devices showed an increase in luminance from 18420 cd/m2 to 36740 cd/m2, a decrease in turn-on voltage from 4.3 V to 3.9 V at 100 cd/m2, and an increase in external quantum efficiency (EQE) from 7.1% to 9.76% when a 1-nm-thick KNO film with a doping concentration of 1 mol% was inserted into the OLEDs.

Original languageEnglish
Pages (from-to)159-165
Number of pages7
JournalJournal of Alloys and Compounds
Volume797
DOIs
Publication statusPublished - 2019 Aug 15

Fingerprint

Organic light emitting diodes (OLED)
Buffer layers
Quantum efficiency
Alkali Metals
Electrodes
Thermal evaporation
Sheet resistance
Alkali metals
Angle measurement
Binding energy
Interfacial energy
Oxides
Contact angle
Surface treatment
Luminance
Atomic force microscopy
Deposits
X ray photoelectron spectroscopy
Metals
Fluorescence

All Science Journal Classification (ASJC) codes

  • Mechanics of Materials
  • Mechanical Engineering
  • Metals and Alloys
  • Materials Chemistry

Cite this

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title = "Improved hole-injection and external quantum efficiency of organic light-emitting diodes using an ultra-thin K-doped NiO buffer layer",
abstract = "In this paper, we used the thermal evaporation method to deposit K-doped NiO (KNO) films as the inorganic buffer layer in thermally activated delayed fluorescence (TADF)-based organic light emitting diode (OLED) devices, and investigated how it improved device performance. The device configuration was ITO/NiO:K2CO3 (X mol{\%}, 1 nm)/NPB (40 nm)/CBP:4CzIPN (5 wt{\%}, 20 nm)/TPBi (50 nm)/LiF (1 nm)/Al (150 nm). We used various concentrations of alkali metal-doped metal oxide on the ITO, which was then subjected to UV-O3 surface treatment. We studied the effects and mechanisms of the improved hole-injection properties of the OLEDs with different measurement methods. X-ray Photoelectron Spectroscopy (XPS) was used to measure the molecular binding energy and confirm formation of the K-doped NiO films. In comparison with the ITO electrode's work function, the KNO film increased the work function from 4.8 to 5.3 eV. Contact angle measurement showed that the deposition of the buffer layer increased both polarity and surface energy. The K-doped NiO film was found to have a smoother surface than that of the ITO electrode, as determined by Atomic Force Microscopy. Reduction in the sheet resistance of the OLEDs was revealed by Admittance Spectroscopy measurement. The opto-electrical performances of the devices showed an increase in luminance from 18420 cd/m2 to 36740 cd/m2, a decrease in turn-on voltage from 4.3 V to 3.9 V at 100 cd/m2, and an increase in external quantum efficiency (EQE) from 7.1{\%} to 9.76{\%} when a 1-nm-thick KNO film with a doping concentration of 1 mol{\%} was inserted into the OLEDs.",
author = "Malvin and Tsai, {Chi Ting} and Wang, {Chen Tao} and Chen, {Yih Yuan} and Kao, {Po Ching} and Sheng-Yuan Chu",
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pages = "159--165",
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Improved hole-injection and external quantum efficiency of organic light-emitting diodes using an ultra-thin K-doped NiO buffer layer. / Malvin; Tsai, Chi Ting; Wang, Chen Tao; Chen, Yih Yuan; Kao, Po Ching; Chu, Sheng-Yuan.

In: Journal of Alloys and Compounds, Vol. 797, 15.08.2019, p. 159-165.

Research output: Contribution to journalArticle

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AB - In this paper, we used the thermal evaporation method to deposit K-doped NiO (KNO) films as the inorganic buffer layer in thermally activated delayed fluorescence (TADF)-based organic light emitting diode (OLED) devices, and investigated how it improved device performance. The device configuration was ITO/NiO:K2CO3 (X mol%, 1 nm)/NPB (40 nm)/CBP:4CzIPN (5 wt%, 20 nm)/TPBi (50 nm)/LiF (1 nm)/Al (150 nm). We used various concentrations of alkali metal-doped metal oxide on the ITO, which was then subjected to UV-O3 surface treatment. We studied the effects and mechanisms of the improved hole-injection properties of the OLEDs with different measurement methods. X-ray Photoelectron Spectroscopy (XPS) was used to measure the molecular binding energy and confirm formation of the K-doped NiO films. In comparison with the ITO electrode's work function, the KNO film increased the work function from 4.8 to 5.3 eV. Contact angle measurement showed that the deposition of the buffer layer increased both polarity and surface energy. The K-doped NiO film was found to have a smoother surface than that of the ITO electrode, as determined by Atomic Force Microscopy. Reduction in the sheet resistance of the OLEDs was revealed by Admittance Spectroscopy measurement. The opto-electrical performances of the devices showed an increase in luminance from 18420 cd/m2 to 36740 cd/m2, a decrease in turn-on voltage from 4.3 V to 3.9 V at 100 cd/m2, and an increase in external quantum efficiency (EQE) from 7.1% to 9.76% when a 1-nm-thick KNO film with a doping concentration of 1 mol% was inserted into the OLEDs.

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