Qiu-Lei Xu

Highly Efficient Green and Blue-Green Phosphorescent OLEDs Based on Iridium Complexes with the Tetraphenylimidodiphosphinate Ligand

Two novel bis-cyclometalated iridium complexes are successfully applied in organic light-emitting diodes (OLEDs). Because of their better carrier transport ability and shorter excited stated lifetimes, good electroluminescence performances of the complexes are observed.

Syntheses, photoluminescence, and electroluminescence of a series of iridium complexes with trifluoromethyl-substituted 2-phenylpyridine as the main ligands and tetraphenylimidodiphosphinate as the ancillary ligand.

Five bis-cyclometalated iridium complexes with tifluoromethyl-substituted 2-phenylpyridine (ppy) at different positions of its phenyl group as the main ligands and tetraphenylimidodiphosphinate (tpip) as the ancillary ligand, 2-6 (1 is a trifluoromethyl-free complex), were prepared, and their X-ray crystallography, photoluminescence, and electrochemistry were investigated. The number and positions of trifluoromethyl groups at the phenyl ring of ppy greatly affected the emission spectra of Ir(3+) complexes, and their corresponding emission peaks at 533, 502, 524, 480, and 542 nm were observed at room temperature, respectively. Constructed with complexes 2-6 as the emitters, respectively, the organic light-emitting diodes (OLEDs) with the structure of indium-tin oxide/1,1-bis[4-(di-p-tolylamino)phenyl]cyclohexane (30 nm)/Ir (x wt %):bis[3,5-bis(9H-carbazol-9-yl)phenyl]diphenylsilane (15 nm)/1,3,5-tris(1-phenyl-1H-benzo[d]imidazol-2-yl)phenyl (45 nm)/LiF (1 nm)/Al (100 nm) showed good performances. Particularly, device G4 based on 4-trifluoromethyl-substituted complex 4 with x = 8 wt % obtained a maximum luminance of over 39000 cd m(-2) and maximum luminance efficiency (η(L)) and power efficiency (η(p)) of 50.8 cd A(-1) and 29.0 lm W(-1), respectively. The results suggested that all of the complexes 2-6 would have potential applications in OLEDs.

Highly efficient green phosphorescent OLEDs based on a novel iridium complex

A new iridium(III) complex Ir(tfmppy)2(tfmtpip) (1, tfmppy = 4-trifluoromethylphenyl-pyridine, tfmtpip = tetra(4-trifluoromethylphenyl)imidodiphosphinate) was synthesized and applied in organic light-emitting diodes (OLEDs). The devices with the structures of ITO/TAPC (1,1-bis[4-[N,N-di(p-tolyl)amino]phenyl]cyclohexane, 40 nm)/1 (x wt%): mCP (N,N′-dicarbazolyl- 3,5-benzene, 20 nm)/TmPyPB (1,3,5-tri(m-pyrid-3-yl-phenyl)benzene, 40 nm)/LiF (1 nm)/Al (100 nm) exhibited a maximum power efficiency (ηp,max) of 113.23 lm W−1 and a maximum current efficiency (ηc,max) of 115.39 cd A−1 (0.01342 mA cm2) at the doping level of 5 wt%, which is among the best performances for Ir(III) complex based OLEDs in the green-light-emitting region. Compared with our former work, the excellent device efficiencies are due to the use of TmPyPB as the electron-transporting/hole-blocking layer which has a relatively higher electron mobility than that of TPBi (2,2′,2′′-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole)) and the introduction of the –CF3 moiety to the Ir(III) complex, which can increase the electron mobility of the complex. The device performances proved that the complex has potential applications as an efficient green emitter in OLEDs.

Efficient OLEDs with low efficiency roll-off using iridium complexes possessing good electron mobility

Two bis-cyclometalated iridium complexes (Ir1 and Ir2) with trifluoromethyl substituted bipyridine (2′,6′-bis(trifluoromethyl)-2,3′-bipyridine (L1) and 2′,6′-bis(trifluoromethyl)-2,4′-bipyridine (L2)) as the main ligands and tetraphenylimidodiphosphinate as the ancillary ligand were prepared, and their X-ray crystallography, photoluminescence, electrochemistry properties were investigated. The Ir1 and Ir2 complexes show green emissions at about 500 and 502 nm with high quantum efficiencies of 0.63 and 0.93, respectively. Moreover, they also exhibit higher electron mobility than that of Alq3 (tris-(8-hydroxyquinoline)aluminium). The organic light emitting diodes (OLEDs) with the structure of ITO/TAPC (1,1-bis[4-(di-p-tolylamino)phenyl]cyclohexane, 40 nm)/mCP (1,3-bis(9H-carbazol-9-yl)benzene, 10 nm)/Ir complex (8 wt%): PPO21 (3-(diphenylphosphoryl)-9-(4-(diphenylphosphoryl)phenyl)-9H-carbazole, 25 nm)/TmPyPB (1,3,5-tri(m-pyrid-3-yl-phenyl)benzene, 50 nm)/LiF (1 nm)/Al (100 nm) showed excellent performances, partly due to their high quantum efficiency and high electron mobility. For the devices G1 and G2, the maximum current efficiency (ηc) values are as high as 101.96/99.97 cd A−1 and the maximum external quantum efficiencies of 31.6% and 30.5% with low electroluminescence efficiency roll-off. The ηc data still remain over 90 cd A−1 even at the luminance of 10000 cd m−2, which proves that the complexes have potential applications as efficient green emitters in OLEDs.

Two blue iridium complexes for efficient electroluminescence with low efficiency roll-off

Two bis-cyclometalated iridium complexes ((dfpypy)2Ir(tpip) and (dfpypy)2Ir(Ftpip)) with fluorinated substituted bipyridine (2′,6′-difluoro-2,3′-bipyridine, dfpypy) as the main ligand and tetraphenylimidodiphosphinate derivatives (tpip and Ftpip) as the ancillary ligands were prepared, and their X-ray crystallographic, photoluminescence and electrochemical properties were investigated. The (dfpypy)2Ir(tpip) and (dfpypy)2Ir(Ftpip) complexes showed blue emission at 457 nm with quantum efficiency yields of 7.0% and 7.1%, respectively. Organic light emitting diodes (OLEDs) with the structure of ITO/TAPC (1,1-bis[4-(di-p-tolylamino)phenyl]cyclohexane, 40 nm)/mCP (1,3-bis(9H-carbazol-9-yl)benzene, 10 nm)/(dfpypy)2Ir(tpip) or (dfpypy)2Ir(Ftpip) (8 wt%): PPO21 (3-(diphenylphosphoryl)-9-(4-(diphenylphosphoryl)phenyl)-9H-carbazole, 25 nm)/TmPyPB (1,3,5-tri(m-pyrid-3-yl-phenyl)benzene, 50 nm)/LiF (1 nm)/Al (100 nm) (B2 and B3) exhibit performances with the maximum current efficiency (ηc) values of 22.83 and 20.79 cd A−1, respectively, with low efficiency roll-off. For example, at 100 cd m−2 display brightness, the current efficiencies of devices B2 and B3 are 19.78, 13.74 cd A−1, respectively. At 1000 cd m−2 light brightness, these values are still 20.39 and 20.75 cd A−1, respectively. Even at the high luminance of 5000 cd m−2, these data also remained at 19.95 and 20.08 cd A−1, respectively.

Highly efficient yellow phosphorescent organic light-emitting diodes with novel phosphine oxide-based bipolar host materials

Two bipolar host materials, (4-((4-(naphthalen-1-yl(phenyl)amino)naphthalen-1-yl)(phenyl)amino)phenyl)diphenylphosphine oxide (POpN) and (3-((4-(naphthalen-1-yl(phenyl)amino)naphthalen-1-yl)(phenyl)amino)phenyl)diphenylphosphine oxide (POmN), comprising a hole-transporting N1-(naphthalen-1-yl)-N1,N4-diphenylnaphthalene-1,4-diamine (NPNA2) donor and an electron-transporting phosphine oxide (PO) acceptor at different positions of the phenyl bridge have been synthesized. POpN (glass transition temperature Tg = 119 °C) and POmN (Tg = 115 °C) exhibit high morphological stability. Two yellow phosphorescent organic light-emitting diodes (PhOLEDs, ITO (indium tin oxide)/TAPC (1,1-bis[4-(di-p-tolylamino)phenyl]cyclohexane, 40 nm)/POpN or POmN: Ir(bt)2(acac) (bis(2-phenylbenzothiozolato-N,C2′)iridium(acetylacetonate), 15 wt%, 20 nm)/TmPyPB (1,3,5-tri(m-pyrid-3-yl-phenyl)benzene, 40 nm)/LiF (1 nm)/Al (100 nm)) exhibit maximum luminances (Lmax) of 82057 and 78385 cd m−2, maximum current efficiencies (ηc,max) of 68.28 and 44.95 cd A−1, respectively, with low efficiency roll-off.

Yellow electrophosphorescent devices with hosts containing N1-(naphthalen-1-yl)-N1,N4-diphenylnaphthalene-1,4-diamine and tetraphenylsilane units

Two novel host materials, N1-(naphthalen-1-yl)-N1,N4-diphenyl-N4-(4-(triphenylsilyl)phenyl) naphthalene-1,4-diamine (SiP) and N1-(naphthalen-1-yl)-N1,N4-diphenyl-N4-(3-(triphenylsilyl) phenyl)naphthalene-1,4-diamine (SiM), were synthesised by incorporating a hole-transporting moiety, N1-(naphthalen-1-yl)-N1,N4-diphenylnaphthalene-1,4-diamine (NPNA2) and typical electron-transporting tetraphenylsilane moiety. SiP and SiM materials exhibit high thermal and morphological stability with a glass transition temperature higher than 110 °C and decomposition temperature above 350 °C. Using Ir(bt)2(acac) (bis(2-phenylbenzothiozolato-N,C2′)iridium(acetylacetonate)) as an emitter, yellow phosphorescent organic light-emitting diodes of ITO/TAPC (1,1-bis[4-(di-p-tolylamino)phenyl]cyclohexane, 40 nm)/host: Ir(bt)2(acac) (15 wt%, 20 nm)/TmPyPB (1,3,5-tri(m-pyrid-3-yl-phenyl)benzene, 40 nm)/LiF (1 nm)/Al (100 nm) show maximum current and power efficiency of 40.81 cd A−1 and 33.60 lm W−1 with low efficiency roll-off. The current efficiency of 40.10 cd A−1 is still observed at the practically useful brightness value of 1000 cd m−2.

Color changeable OLEDs controlled by doping ratio and driving voltage with an anthracene derivative doped layer

With 9,10-bis(3,3,3-triphenylprop-1-ynyl)anthracene (BTPYA) doped TPBi as an emissive layer, tunable OLED devices exhibited different emission colors (blue, near-white, green-yellow) controlled by the dopant ratio and driving voltage. The emissions were composed of the electrofluorescence of BTPYA, TPBi, and the electromer of BTPYA, an electroplex formed between BTPYA and TPBi.

Highly efficient yellow phosphorescent OLEDs based on two novel bipolar host materials

Two bipolar host materials, N1-(naphthalen-1-yl)-N1,N4-diphenyl-N4-(4-(5-phenyl-1,3,4-oxadiazol-2-yl)phenyl)naphthalene-1,4-diamine (NONP) and N1-(naphthalen-1-yl)-N1,N4-diphenyl-N4-(3-(5-phenyl-1,3,4-oxadiazol-2-yl)phenyl)naphthalene-1,4-diamine (NONM), comprising a hole-transporting N1-(naphthalen-1-yl)-N1,N4-diphenylnaphthalene-1,4-diamine (NPNA2) donor and an electron-transporting 1,3,4-oxadiazole (OXD) acceptor at different phenyl bridge positions, have been synthesized. NONP (glass transition temperature Tg = 127 °C) and NONM (Tg = 105 °C) exhibit high morphological stability. The theoretical calculations on both hosts show that the HOMOs (highest occupied molecular orbitals) are mainly dispersed on the electron-donating groups, and the LUMOs (lowest unoccupied molecular orbitals) are predominantly dispersed on the electron-accepting units, suggesting bipolar charge transporting property. Two yellow phosphorescent organic light-emitting diodes (PHOLEDs, ITO (indium tin oxide)/TAPC (1,1-bis[4-(di-p-tolylamino) phenyl]cyclohexane, 40 nm)/host: Ir(bt)2(acac) (bis(2-phenylbenzothiozolato-N,C2′) iridium(acetylacetonate), 15 wt%, 20 nm)/TmPyPB (1,3,5-tri(m-pyrid-3-yl-phenyl) benzene, 40 nm)/LiF (1 nm)/Al (100 nm)) fabricated using NONP and NONM as the host and Ir(bt)2(acac) as the emitter exhibit maximum current efficiencies (ηc,max) of 43.2 and 44.4 cd A−1, respectively, with low current efficiency roll-off. The values of 40.4 and 43.6 cd A−1 can still be achieved at the luminance of 3000 cd m−2, respectively.

CCDC 818982: Experimental Crystal Structure Determination

Related Article: Yu-Cheng Zhu, Liang Zhou, Hong-Yan Li, Qiu-Lei Xu, Ming-Yu Teng, You-Xuan Zheng, Jing-Lin Zuo, Hong-Jie Zhang, Xiao-Zeng You|2011|Adv.Mater.|23|4041|doi:10.1002/adma.201101792