Development of Extremely High Efficacy White OLED with over 100 lm/W

Ide, Nobuhiro; Yamae, Kazuyuki; Kittichungchit, Varutt; Tsuji, Hiroya; Ota, Masuyuki; Komoda, Tsugikazu

doi:10.2494/photopolymer.27.357

Cited by 11 publications

(10 citation statements)

References 10 publications

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“…39 Under these conditions, a 2.4-fold improvement in outcoupling efficiency is possible. 51 In recent work by Yoo et al, the high-index PEN was used as a substrate on its own. 39 The drawback of refractive index matched substrates is clearly cost, and there is currently no direct pathway to bringing down the prize of high refractive index substrates to a degree that would facilitate upscaling to high-volume production.…”

Section: External Outcoupling Schemesmentioning

confidence: 99%

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Recent advances in light outcoupling from white organic light-emitting diodes

2015

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Organic light-emitting diodes (OLEDs) have been successfully introduced to the smartphone display market and have geared up to become contenders for applications in general illumination where they promise to combine efficient generation of white light with excellent color quality, glare-free illumination, and highly attractive designs. Device efficiency is the key requirement for such white OLEDs, not only from a sustainability perspective, but also because at the high brightness required for general illumination, losses lead to heating and may, thus, cause rapid device degradation. The efficiency of white OLEDs increased tremendously over the past two decades, and internal charge-to-photon conversion can now be achieved at ∼100% yield. However, the extraction of photons remains rather inefficient (typically <30%). Here, we provide an introduction to the underlying physics of outcoupling in white OLEDs and review recent progress toward making light extraction more efficient. We describe how structures that scatter, refract, or diffract light can be attached to the outside of white OLEDs (external outcoupling) or can be integrated close to the active layers of the device (internal outcoupling). Moreover, the prospects of using top-emitting metal-metal microcavity designs for white OLEDs and of tuning the average orientation of the emissive molecules within the OLED are discussed.

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Section: External Outcoupling Schemesmentioning

confidence: 99%

“…)51 the organic material needed for the actual device (∼100 nm compared to the 80 μm organic cone heights). Rather than using expensive high refractive index substrates, a high-index thin film and outcoupling structure are combined with conventional glass substrates.…”

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confidence: 99%

Recent advances in light outcoupling from white organic light-emitting diodes

2015

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“…[ 20 ] Thereby, the quenching of the triplet excitons of fac -Ir(mpim) 3 in the EML White organic light-emitting devices (OLEDs) are expected to be used in next-generation general lighting and large display applications. [1][2][3][4][5] Phosphorescent OLED technology is crucial to realize high-effi ciency white OLEDs because phosphorescent emitters enable an internal quantum effi ciency as high as 100% by converting all the molecular excitons of 75% of triplets and 25% of singlets. [6][7][8] In fundamental research, green, red, and blue phosphorescent OLEDs have already realized external quantum effi ciencies (EQEs) of 30% at a low brightness of 100 cd m −2 .…”

mentioning

confidence: 99%

Simultaneous Realization of High EQE of 30%, Low Drive Voltage, and Low Efficiency Roll‐Off at High Brightness in Blue Phosphorescent OLEDs

Udagawa

Sasabe

Igarashi

et al. 2015

Advanced Optical Materials

110

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86 wileyonlinelibrary.com COMMUNICATION challenge. For example, Lee and Lee [ 14 ] reported an iridium(III) bis [(4,6-difl uorophenyl)-pyridinate-N,C2 ′ ]picolinate (FIrpic)-based blue OLED with an EQE of 30% at 100 cd m −2 using a pyrido [2,3-b]indole derivative as a host material. However, the driving voltages at 100 cd m −2 are very high (over 4.5 V) compared with those of low-drive-voltage green devices. [ 15,16 ] Shin et al. [ 17a ] reported a FIrpic-based OLED with an EQE of 29.5% using an exciplex-forming co-host system. However, the driving voltages at 1000 cd m −2 are relatively high at around 5.0 V. Very recently, Lee et al. [ 17b ] further reduced the driving voltage of this exciplex system by changing the electron-transport layer (ETL) from B3PyMPM to PO-T2T. Therefore, reducing the drive voltage at high brightness is a critical issue in blue OLEDs.Recently, Lee et al. [ 18 ] reported a low-driving-voltage blue device using a mixed-host system consisting of two host materials: 2-(diphenylphosphoryl)spirofl uorene (SPPO1) as an n-type host material and 4,4,4-tris( N -carbazolyl)triphenylamine (TCTA) as a p-type host material. The mixed-host device showed two times higher EQE than a single-host device with SPPO1 at the high-luminance region over 1000 cd m −2 . The mixed-host device also realized a low driving voltage of 3.9 V at 1000 cd m −2 . Therefore, the use of a mixed-host system represents a promising method to realize a low drive voltage and high EQE at high brightness.In this study, we realized a high EQE of 30%, a low drive voltage, and a low effi ciency roll-off at the high-brightness region (>1000 cd m −2 ) in blue OLEDs using a mixed-host system. We used two types of host materials: TCTA as a p-type host material and 2,6-bis(3-(carbazol-9-yl)phenyl)pyridine (26DCzPPy) as an n-type host material. Consequently, the mixed-host device gave a high-performance blue OLED with a driving voltage of 3.25 V, an EQE of 32.6%, and a power efficiency of 77.6 lm W −1 at 1000 cd m −2 without any enhancement in light outcoupling. We also developed a white OLED based on this blue device and iridium(III) bis-(2-phenylquinoly-N , C 2 ′ ) dipivaloylmethane [PQ 2 Ir(dpm)] as an orange emitter. The white OLED achieved a driving voltage of 3.35 V and an EQE of 24.4% at 1000 cd m −2 .Very recently, we have reported a blue OLED with a driving voltage of 3.0 V and an EQE of 30% at 100 cd m −2 . [ 19 ] We used a carrier-and exciton-confi ning structure along with a double emission layer (DEML) strategy using high-triplet-energy ( E T ) materials. All the neighboring materials, the hole-transport layer (HTL), host materials, and ETL have higher values of E T than a blue phosphorescent emitter, fac -tris(mesityl-2-phenyl-1H-imidazole)iridium(III) [ fac -Ir(mpim) 3 ]. [ 20 ] Thereby, the quenching of the triplet excitons of fac -Ir(mpim) 3 in the EML White organic light-emitting devices (OLEDs) are expected to be used in next-generation general lighting and large display applications. [1][2][3][4][5] Phosphorescent OLE...

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“…The WOLED II without and with the VaNHA showed the maximum EQEs of 20.5% and 44.3%, respectively. The efficiency is the highest among reported WOLEDs without external light extraction structures except the devices with corrugated substrates as shown in Table 2 where the performances of highly efficient WOLEDs reported in literature over or close to 100 lm W −1 are summarized . The EQE of the WOLED II w/o the VaNHA is lower than WOLED I w/o VaNHA because the device is not optimized for the maximum air mode but optimized for large extractable mode.…”

Section: Performance Of Woleds II W/o and W/ Vanha And Half‐sphericalmentioning

confidence: 96%

High‐Quality White OLEDs with Comparable Efficiencies to LEDs

Jeon

Lee

Han

et al. 2018

Advanced Optical Materials

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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...

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Development of Extremely High Efficacy White OLED with over 100 lm/W

Cited by 11 publications

References 10 publications

Recent advances in light outcoupling from white organic light-emitting diodes

Recent advances in light outcoupling from white organic light-emitting diodes

Simultaneous Realization of High EQE of 30%, Low Drive Voltage, and Low Efficiency Roll‐Off at High Brightness in Blue Phosphorescent OLEDs

High‐Quality White OLEDs with Comparable Efficiencies to LEDs

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