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Frequency Response Characteristics of Fluorescent OLED with Alternating Current Driving Method

교류구동방식에 의한 형광 OLED의 주파수 응답 특성

  • Seo, Jung-Hyun (Department of Advanced Materials Science & Engineering, Daejin University) ;
  • Ju, Sung-Hoo (Department of Advanced Materials Science & Engineering, Daejin University)
  • 서정현 (대진대학교 신소재공학과) ;
  • 주성후 (대진대학교 신소재공학과)
  • Received : 2018.08.21
  • Accepted : 2018.09.04
  • Published : 2019.01.01

Abstract

To study the frequency response characteristics of alternating-current-driven organic light-emitting diodes (OLEDs), we fabricated blue-fluorescent OLEDs and analyzed their electroluminescent characteristics according to the alternating current voltage and frequency. The luminance-frequency characteristics of alternating-current-driven OLED was similar to that of a low-pass filter, and the luminance of high-voltage OLED decreased at higher frequency than low-voltage OLED. The luminance characteristics of the OLED according to the frequency is due to the capacitive reactance in the OLED, generated during the alternating current driving. The frequency response characteristics of the OLED according to the voltage is due to the decrease in internal resistance of the organic layer. In addition, the negative voltage component of the alternating current did not affect the frequency response of the OLED. Therefore, the electroluminescent characteristics of OLED with an alternating current power of 60 Hz are not influenced by the frequency.

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Fig. 1. Structure of blue fluorescent OLED.

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Fig. 2. Schematic diagram of current-voltage-luminance and impedance measurement system for frequency response characteristic of OLEDs.

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Fig. 3. Electroluminescent intensity vs frequency characteristics of OLED with AC application.

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Fig. 4. Equivalent circuit of OLED with AC.

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Fig. 5. Cole-Cole plot of blue fluorescent OLED.

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Fig. 6. Electroluminescent intensity vs frequency characteristics of OLED with AC sine and square wave application.

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Fig. 7. Luminance vs peak voltage characteristics of OLED with various AC wave application.

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Fig. 8. Electroluminescent intensity vs frequency characteristics of OLED with various AC wave application.

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Fig. 9. Fourier series of various waveform.

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Fig. 10. Electroluminescent intensity vs frequency characteristics of OLED with AC full and half square wave application.

Table 1. Comparison of cut-off frequency. A: cut-off frequency of OLED driven by sine wave, B: cut-off frequency of OLED driven by square wave, and C: cut-off frequency by impedance measurement of OLED.

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Table 2. Comparison of cut-off frequency with impedance measurement and simulation.

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