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

5 Citations (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

All Science Journal Classification (ASJC) codes

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

Fingerprint Dive into the research topics of 'Improved hole-injection and external quantum efficiency of organic light-emitting diodes using an ultra-thin K-doped NiO buffer layer'. Together they form a unique fingerprint.

  • Cite this