Interference effects in bilayer organic light-emitting diodes

Abstract

The electroluminescent spectra and the light intensities of Alq3-based organic light-emitting diodes were measured as a function of the thickness of the light-emitting layer. A maximum in the light intensity occurs when the thickness of this layer is approximately 600 Å, whereas a minimum in the light intensity occurs at about 1400 Å. The electroluminescent spectra were also found to vary strongly with the thickness of the light-emitting layer. Computer simulation, based on wide-angle interference of light-emitting dipoles from a reflective mirror, can account for the experimental observations.

Device optimization of tris-aluminum (Alq3) based bilayer organic light emitting diode structures

“…There have been several works on calculating the emission pattern [5] and external coupling in OLEDs [6]. It has been shown that the emission from an OLED can be varied through interference effects by changing the thickness of the organic layer in an OLED with a dielectric layer located below the ITO anode [7] or by changing the thickness of a ZnSe layer on top of the metal cathode [8][9]. For an OLED with SiO 2 layer below the ITO, it was shown that the emission spectrum from an OLED is strongly dependent on the Alq 3 thickness, so that with the increase of Alq 3 thickness the emission peak shifts from ~525 nm to ~555 nm, and with further increase of the thickness even splits into two peaks, one located ~495 nm and the other ~590-600 nm [7].…”

“…It has been shown that the emission from an OLED can be varied through interference effects by changing the thickness of the organic layer in an OLED with a dielectric layer located below the ITO anode [7] or by changing the thickness of a ZnSe layer on top of the metal cathode [8][9]. For an OLED with SiO 2 layer below the ITO, it was shown that the emission spectrum from an OLED is strongly dependent on the Alq 3 thickness, so that with the increase of Alq 3 thickness the emission peak shifts from ~525 nm to ~555 nm, and with further increase of the thickness even splits into two peaks, one located ~495 nm and the other ~590-600 nm [7]. It was also shown that, by changing the thickness of ZnSe layer deposited on top of the cathode, the efficiency of the OLED can be optimized so that for optimal ZnSe thickness efficiency as high as 64 cd/A can be achieved [8][9].…”

Effects of a Dielectric Multilayer Mirror on the Lighting Efficiency of Organic Light-Emitting Diodes Studied by Optical Simulation

“…또 하나의 접근 방법은 OLED가 가지는 미소공진(microcavity) 구조를 이용하는 것이다 [32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51] . 배면발광형 OLED는 기본적 으로 음극인 금속과 양극인 투명전극 사이에 약한 미소공진 구조가 형성되는데, 이 때 금속이나 유전체 다층박막 등으로 공진구조를 강화시키면 OLED 발광색의 순도가 강화되어 색 재현성이 증가하거나 발광효율의 상승을 기대할 수 있다.…”

Optimization of organic light emitting diode structures

“…8,9 For an OLED with SiO 2 layer below the ITO, it was shown that the emission spectrum from an OLED is strongly dependent on the Alq 3 thickness, so that with the increase of Alq 3 thickness the emission peak shifts from ~525 nm to ~555nm, and with further increase of the thickness even splits into two peaks, one located ~495 nm and the other ~590-600 nm. 7 It was also shown that, by changing the thickness of ZnSe layer deposited on top of the cathode, the efficiency of the OLED can be optimized so that for optimal ZnSe thickness efficiency as high as 64 cd/A can be achieved. 8,9 The spectral and angular distribution of the emission from an OLED has been studied in more details in organic microcavity devices 10,11 than in non-cavity devices.…”

“…3,4 There have been several works on calculating the emission pattern 5 and external coupling in OLEDs. 6 It has been shown that the emission from an OLED can be varied through interference effects by changing the thickness of the organic layer in an OLED with a dielectric layer located below the ITO anode 7 or by changing the thickness of a ZnSe layer on top of the metal cathode. 8,9 For an OLED with SiO 2 layer below the ITO, it was shown that the emission spectrum from an OLED is strongly dependent on the Alq 3 thickness, so that with the increase of Alq 3 thickness the emission peak shifts from ~525 nm to ~555nm, and with further increase of the thickness even splits into two peaks, one located ~495 nm and the other ~590-600 nm.…”