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Light extraction analysis and enhancement in a quantum dot light emitting diode

Ruidong Zhu, Zhenyue Luo, and Shin-Tson Wu

Open Access Open Access

Abstract

We apply a rigorous dipole model to analyze the light outcoupling and angular performance of quantum dot light emitting diode (QLED). To illustrate the design principles, we use a red QLED as an example and compare its performance with an organic light emitting diode (OLED). By combining a high refractive index glass substrate with macroextractors, our simulation results indicate that the light outcoupling efficiency is doubled from ~40% to ~80%. After analyzing the light emission spectra and angular radiation pattern of the device, we confirm that QLED has a much weaker color shift than OLED.

© 2014 Optical Society of America

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Figures (14)
Fig. 1
Fig. 1 (a) Structure of the proposed QLED stack and (b) PL spectra of the QDs taken from [19].

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Fig. 2
Fig. 2 (a) The device structure of the OLED stack and (b) the PL spectra of NPB:Ir(MDQ)2(acac) taken from [32].

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Fig. 3
Fig. 3 Schematic drawing of the simplified three layer structure.

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Fig. 4
Fig. 4 Simulated power dissipation spectra of (a) QLED and (b) BOLED.

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Fig. 5
Fig. 5 Amount of power coupled to different optical channels for (a) QLED device and (b) BOLED device.

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Fig. 6
Fig. 6 Simulated full power dissipation spectra of (a) QLED and (b) BOLED.

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Fig. 7
Fig. 7 (a) Changing the proportions of different optical channels by tuning the BPhen:Cs layer thickness for the OLED structure, and (b) Changing the proportions of different optical channels by tuning the NPB layer thickness for the QLED structure.

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Fig. 8
Fig. 8 Changing the fraction of power of different optical channels for the QLED structure by varying the ZnO layer thickness.

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Fig. 9
Fig. 9 Amount of power coupled to different optical channels for the QLED device with a high refractive index (n = 1.8) substrate.

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Fig. 10
Fig. 10 How the refractive index of the substrate affects different optical channel power proportion.

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Fig. 11
Fig. 11 Full power dissipation spectra of the QLED with different substrate refractive indices: a) nsub = 1.8 b) nsub = 2.0 c) nsub = 2.2 d) nsub = 2.4.

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Fig. 12
Fig. 12 Emission spectra of the (a) QLED stack (b) BOLED stack.

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Fig. 13
Fig. 13 Calculated color shift of the proposed red QLED and the red OLED.

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Fig. 14
Fig. 14 Simulated angular radiation pattern of the OLED and the QLED structures.

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Tables (1)

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Table 1 Fractions of power coupled to different modes for the QLED stack with substrates having different refractive indices.

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Equations (13)

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I(λ,θ)= 1+ R T +2 R T cos(− ϕ T + 4π n e acos( θ ′ ) λ ) (1− R T R B ) 2 +4 R T R B sin 2 ( Δϕ 2 ) T B I 0 (λ).
Δϕ= 4π n e dcos( θ ′ ) λ − ϕ B − ϕ T .
EQE=ηIQE=ηγ η S/T q eff ,
EQE=ηIQE=ηγ q eff .
q= k r k r + k nr ,
P=1−q+qF=1−q+q ∫ 0 ∞ K( k x )d k x .
q eff q = k r * k r * + k nr = F k r F k r + k nr = F qF+1−q .
K= 1 3 K TMv + 2 3 ( K TMh + K TEh ),
K TMv = 3 2 Re[ k x 3 (1+ r TMv b e 2i k z b )(1+ r TMv t e 2i k z a ) k e k z 3 (1− r TMv b r TMv t e 2i k z (a+b) ) ], K TMh = 3 4 Re[ k x k z (1− r TMv b e 2i k z b )(1− r TMv t e 2i k z a ) k e 3 (1− r TMv b r TMv t e 2i k z (a+b) ) ], K TEh = 3 4 Re[ k x (1+ r TEv b e 2i k z b )(1+ r TEv t e 2i k z a ) k e k z (1− r TEv b r TEv t e 2i k z (a+b) ) ].
ε e f f = ∑ i d i / ∑ i ( d i / ε i ) , n e f f = Re ( ε e f f ) .
K TEh = 3 8 k x k e k z [ | 1+ r TEv b e 2i k z b | 2 | 1− r TEv b r TEv t e 2i k z (a+b) | 2 ( T TEv t + A TEv t )+ | 1+ r TEv t e 2i k z t | 2 | 1− r TEv b r TEv t e 2i k z (a+b) | 2 ( T TEv b + A TEv b )] = 3 8 k x k e k z [ | 1+ r TEv b e 2i k z b | 2 | 1− r TEv b r TEv t e 2i k z (a+b) | 2 ( T TEv t + T TEv b )+ | 1+ r TEv t e 2i k z t | 2 | 1− r TEv b r TEv t e 2i k z (a+b) | 2 ( A TEv t + A TEv b )] = K TEh T + K TEh A .
P=1−q+qF=1−q+q ∫ λ 1 λ 2 S(λ) ∫ 0 ∞ K( k x )d k x dλ .
q eff η= P dir / P tot .
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