High Quantum Efficiency in Organic Light-Emitting Devices   with Iridium-Complex as a Triplet Emissive Center

Tsutsui, Tetsuo; Yang, Moon-Jae; Yahiro, Masayuki; Nakamura, Kenji; Watanabe, Taeko; Tsuji, Taishi; Fukuda, Yoshiro; Wakimoto, Takeo; Miyaguchi, Satoshi

doi:10.1143/jjap.38.l1502

Cited by 198 publications

(106 citation statements)

References 19 publications

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“…The triplet energy of the polymers 1 -3 of approximately 2.6 eV is significantly higher than that of poly-(fluorene) (2.2 eV -2.4 eV) 24 and poly-(para-phenylenevinylene) (1.3 eV -1.6 eV) 25 , and lower than that of PVK (~ 3 eV). In fact, the triplet energy of the carbazole polymers 1 -3 matches that of 4,4'-bis(9-carbazolyl)-biphenyl (CBP), which has a triplet energy of 2.56 V 25 .…”

Section: Phosphorescent Polymer Ledsmentioning

confidence: 77%

“…In fact, the triplet energy of the carbazole polymers 1 -3 matches that of 4,4'-bis(9-carbazolyl)-biphenyl (CBP), which has a triplet energy of 2.56 V 25 . For the copolymers the values of the half-wave oxidation potential (about 0.75 V, see table II) are slightly larger than that of the homopolymer (0.55 V, see Table II) but still considerably lower than that of PVK (ca.…”

Section: Phosphorescent Polymer Ledsmentioning

confidence: 98%

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High-efficiency polymer LEDs : triplets and novel devices

et al. 2004

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We present results and a discussion of highly efficient polymer Light-Emitting Diodes (polymer LEDs, PLEDs). The external quantum efficiency in current standard devices reaches up to 2-4% only. We have explored two routes to enhance this value. In the first route, PEDOT/PSS is replaced with a novel anode or hole injection layer. The efficiency with some Light Emitting Polymers (LEP) is improved significantly, resulting in an efficacy of 35 cd/A for a yellow emitting poly-(para-phenylene-vinylene) and 20 cd/A for a blue emitting poly-(spirobifluorene). We attribute the major improvement compared to standard devices, where about 10 and 5 cd/A are obtained, respectively, to a combination of improved exciton formation efficiency and light out-coupling efficiency, and to less quenching of the radiative decay under actual device operating conditions. In the second route, we developed a new host polymer with high triplet energy such that transition metal-based green-emitting phosphorescent dyes can be used without significant back transfer of triplet excitons to the polymer host. First results using this system showed about 25 cd/A using a soluble green Ir-based emitter. Importantly, all data are obtained in a standard two-layer device of a hole transport/injection layer and the LEP.

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Section: Phosphorescent Polymer Ledsmentioning

confidence: 77%

Section: Phosphorescent Polymer Ledsmentioning

confidence: 98%

High-efficiency polymer LEDs : triplets and novel devices

et al. 2004

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“…A maximum EQE of 12.4% and PE of 30.1 lm/W are obtained for the c-ITO/glass-based device, similar to the recently reported results. 19,20 The a-IZO/PC and a-IZO/glass-based devices result in almost the same device performance with the maximum EQE of 13.7% and the PE of 32.7 lm/W, and EQE of 13.2% and PE of 30.7 lm/W, respectively. Furthermore, the bended device of a-IZO/PC emits bright green light clearly visible under ordinary room light, as shown in the inset of Fig.…”

Section: J76mentioning

confidence: 89%

High-Performance Flexible Organic Light-Emitting Diodes Using Amorphous Indium Zinc Oxide Anode

Kang

Jeong

Kim

et al. 2007

Electrochem. Solid-State Lett.

105

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We demonstrate a high-performance flexible organic light-emitting diode ͑OLED͒ employing amorphous indium zinc oxide ͑IZO͒ anode. The amorphous IZO on flexible polycarbonate ͑PC͒ substrate shows similar electrical conductivity and optical transmittance with commercial ͑ITO͒ glass, even though it was prepared at Ͻ50°C. Moreover, it exhibits little resistance change during 5000 bending cycles, demonstrating good mechanical robustness. A green phosphorescent OLED fabricated on amorphous IZO on flexible PC shows maximum external quantum efficiency of ext = 13.7% and power efficiency of p = 32.7 lm/W, which are higher than a device fabricated on a commercial ITO on glass ͑ ext = 12.4% and p = 30.1 lm/W͒ and ITO on flexible PC ͑ ext = 8.5% and p =14.1 lm/W͒. The mechanical robustness and low-temperature deposition of IZO combined with high OLED performance clearly manifest that the amorphous IZO is a promising anode material for flexible displays. There has been increasing activity for flexible organic lightemitting diodes ͑OLEDs͒ over the past few years, and it has focused on developing indium tin oxide ͑ITO͒-coated polymer substrates, such as polyethylene terephthalate ͑PET͒, 1-5 polycarbonate ͑PC͒,polyimide, 8 polyethersulfone ͑PES͒, 9 polyethylene naphthalate ͑PEN͒, 9 and polycyclic olefin ͑PCO͒. 9 However, ITO electrode comes with its own set of problems such as chemical instability in a reduced ambient, poor transparency in the blue region, release of oxygen and indium into the organic layer, imperfect work function alignment with typical hole-transport layers, and easy deterioration of ITO targets. 5 In addition, the optimum properties of ITO film can only be obtained from fully crystallized film deposited at high temperature ͑ϳ300°C͒ or annealed in air or oxygen ambient. 10 With the increasing interest in the development of flexible OLEDs, there is great need for a more mechanically robust and transparent electrode because the resistance of crystallized ITO films on flexible substrate increases with increasing mechanical stain. The increase in resistance is related to the number of cracks generated in the electrode, which depends on applied strain and film thickness. 1,3 For this reason, new transparent conducting materials have been explored to replace ITO for flexible OLED anodes. To achieve better performance of flexible OLEDs, Zn-based transparent conducting oxide ͑TCO͒ films, such as ZnSn 2 O 4 , ZnSnO 3 , Zn 2 In 2 O 5 , and Al͑Ga͒-doped ZnO, have been applied as the anode.11-16 Among various Zn-based transparent conducting oxides, the Zn-doped In 2 O 3 ͑IZO͒ films recently have been recognized as promising TCO materials for OLEDs due to its good conductivity, high transparency, excellent surface smoothness, high etching rate, and low deposition temperature. [13][14][15][16] In particular, it has been confirmed that electrical and optical properties of amorphous IZO ͑a-IZO͒ films can be optimized at Ͻ50°C without a postannealing process. Therefore it is considered that a-IZO anode films can be applied to...

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“…11,[15][16][17][18][19][20] A particularly widely used host for organic LEDs is the organic semiconductor 4 , 4Ј-bis͑N-carbazolyl͒biphenyl ͑CBP͒. [2][3][4][5][6][7][8][9] CBP is also of current interest as a host for laser gain media, with the potential for low threshold or even electrical pumping. 11,12 Given the widespread use of guest-host systems it is important to understand the energy transfer process from host to guest and the role of exciton-exciton annihilation in the host material.…”

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confidence: 99%