Phosphorescence Quantum Efficiency and Intermolecular Interaction of Iridium(III) Complexes in Co-Deposited Films with O
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Phosphorescence Quantum Efficiency and Intermolecular Interaction of Iridium(III) Complexes in Co-Deposited Films with Organic Semiconducting Hosts Yuichiro Kawamura1, Kenichi Goushi2, Jason Brooks3, Julie J. Brown3, Hiroyuki Sasabe1,2, and *Chihaya Adachi1,2 1 CREST program, Japan Science and Technology Agency (JST), 1-32-12 Higashi, Shibuya, Tokyo 150-0011, Japan 2 Department of Photonics Materials Science, Chitose Institute of Science & Technology (CIST), 758-65 Bibi, Chitose, Hokkaido 066-8655, Japan 3 Universal Display Corporation, 375 Phillips Blvd., Ewing, NJ 08618, U.S.A. ABSTRACT We accurately measured the absolute photoluminescence (PL) quantum efficiency (ηPL) of organic solid-state thin films by using an integrating sphere. We measured the ηPL of conventional organic materials used in organic light emitting diodes, such as a tris (8-quinolionolato)aluminum(III) complex (Alq3), and a phosphorescent 1.5mol%-fac-tris(2-phenylpyridyl)iridium(III):4,4’-bis(carbazol-9-yl)-2,2’-biphenyl [Ir(ppy)3:CBP] co-deposited film. Alq3 and Ir(ppy)3:CBP showed a ηPL = 20 ± 1% and 97 ± 2%, which corresponded well to external electroluminescence efficiency using these materials. We also measured red emitting bis[2-(2’-benzothienyl)pyridinato-N,C3’] (acetylacetonato) iridium(III) [Btp2Ir(acac)] with CBP, and the blue complex, bis[(4,6-difluorophenyl)pyridinato -N,C2](picolinato)iridium(III) [FIrpic], with m-bis(N-carbazolyl)benzene. The maximum ηPL values for Btp2Ir(acac), and FIrpic were 51±1% (at 1.4mol%), and 99±1% (1.2mol%), respectively. These results suggest that the ηEL of red phosphorescent OLEDs using Btp2Ir(acac) as the dopant can be as high as 10%, and blue devices using FIrpic can reach the theoretical limit of 20%. INTRODUCTION There has been a great deal of interest in the last decade in developing organic optoelectronic devices. In particular, organic light emitting diodes (OLEDs)[1-2] have achieved nearly 100% electro-photo conversion efficiency[3,4], and ongoing research into light emitting devices such as organic laser diodes[5-8] and organic thin film light-emitting transistors[9] is continuing by many research groups. Recently, many kinds of new luminescent organic compounds used in these devices have also been extensively developed. Especially, cyclometalated Ir(III) complexes are recognized as promising candidates for phosphorescent dopants because they can emit with high efficiency in room temperature from the triplet metal-to-ligand charge-transfer (3MLCT) state[10,11]. We need to know detailed information about the basic luminescent properties of organic materials to understand the make-up of highly luminescent materials and device architectures. Absolute photoluminescent (PL) quantum efficiency (ηPL) is a principal characteristic of luminescent materials and informs us about photophysical characteristics of organic materials. Although some methods for measuring the ηPL in a solution are well established[12], there are few direct methods for obtaining the absolute ηPL of organic solid-state t
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