High‐Quality White OLEDs with Comparable Efficiencies to LEDs

Abstract

high luminous efficacy (LE) overcoming LEDs at high luminance are believed to be a distant goal at present even with large advances in light extraction during the last couple of decades. Those advances include scatter, [1][2][3][4][5][6][7][8][9] low refractive index layer, [10] micro lens array, [11][12][13][14] photonic crystal, [15][16][17][18] low/high refractive index grid, [19][20][21] high refractive index substrate, [9,22,23,27] corrugated structure, [24][25][26][27][28][29][30][31][32] graded index, [33] randomly distributed pillar array, [34,35] biomimetic structure, [36,37] plasmonic nanocavity, [38] and so on. Among the proposed methods, the insertion of extraction medium between the glass and the indium tin oxide (ITO) electrode is regarded to have potential for further efficiency enhancement by extracting the waveguide mode in combination with the extraction method at the glass-air interface. However, despite the efficiency improvement due to the extraction layer, many of these methods often have limitations such as diffraction pattern and color distortion to be applied to general illumination systems and high-performance electronic devices. [15][16][17][18][24][25][26][27][28][29][30][31] To solve these problems such as the angular dependence and diffraction pattern, a random pattern is introduced, but the currently reported random patterns are obtained by using spontaneous methods which have difficulty in quantitative control of randomness and poor reproducibility. [34,35] It would also be recommended that the internal extraction structure does not distort the planar structure in OLEDs to prevent the potential degradation issue coming from the rough structure because active layers of OLEDs are very thin.Here, we report novel WOLEDs approaching the theoretical limit by using the highly effective extraction layer based on a randomly dispersed vacuum nanohole array (VaNHA). The random VaNHA pattern was designed with random number generation function in the unit cell of 10 × 10 µm 2 to show no specific symmetry in the reciprocal space. The random VaNHA WOLEDs in combination with a half-spherical lens exhibited comparable performance with LED lighting with unprecedentedly high LE of 164 lm W −1 , originating from high maximum external quantum efficiency (EQE) of 78% and low efficiency roll-off. In addition, the WOLEDs showed uniform emission of high-quality light with high correlated color temperature (CCT) of 3400 K, high color rendering index (CRI) around 80, no color variation with viewing angle. The light extraction structure does not have any additional detrimental effect on the device The solid-state lighting sources require high efficiency and high-quality illumination at the same time. Here, highly efficient white organic light emitting diodes (WOLEDs) comparable to LEDs are demonstrated using a random vacuum nanohole array and a half-spherical lens as internal and external light extraction layers, respectively, exhibiting the maximum external quantum efficiency of 78% and luminous efficacy of...

High Light Outcoupling Efficiency from Periodically Corrugated OLEDs

“…Our simulated outcoupling with periodic corrugations can be compared to previously studied random corrugations 11 − 15 that display local order in the nearest-neighbor shell. Similar to our results, OLEDs patterned with a complex graded photonic super crystal were theoretically predicted to have efficiencies >70%, 31 with the triangular lattice outperforming the square lattice.…”

“… 14 Random vacuum nano-hole arrays in the substrate in conjunction with a half-spherical lens as internal and external light extraction layers achieved ∼78% EQE and luminous efficacy of 164 lm/W when emissive dipoles were preferentially oriented in the in-plane direction. 15 …”

Eliminate angular color shift in top‐emitting OLEDs through cavity design

“…Many methods have been developed to reduce the optical losses in TEOLEDs. The waveguide mode can be extracted by incorporating corrugations within the device stack, attaching a hemisphere lens/micro lens arrays (MLAs), or coating scattering films on top of the devices . The SPP mode can be suppressed by replacing the metal electrode with transparent conductive oxide (TCO) such as indium tin oxide (ITO) or indium zinc oxide (IZO) …”

5‐1: Distinguished Paper: Eliminate Angular Color Shift in Top Emitting OLEDs through Cavity Design

“…Many methods have been developed to reduce the optical losses in TEOLEDs. The waveguide mode can be extracted by incorporating corrugations within the device stack [9,10], attaching a hemi-sphere lens/micro lens arrays (MLAs) [11,12], or coating scattering films on top of the devices [8]. The SPP mode can be suppressed by replacing the metal electrode with transparent conductive oxide (TCO) such as indium tin oxide (ITO) or indium zinc oxide (IZO) [11,12,13].…”