Browsing by Author "Chien, Chen-Han"

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A Bipolar Host Material Containing Triphenylamine and Diphenylphosphoryl-Substituted Fluorene Units for Highly Efficient Blue Electrophosphorescence
(2009-09-09)
Hsu, Fang-Ming
;
Chien, Chen-Han
;
Shu, Ching-Fong
;
Lai, Chin-Hung
;
Hsieh, Cheng-Chih
Highly efficient blue electrophosphorescent organic light-emitting diodes incorporating a bipolar host, 2,7-bis(diphenylphosphoryl)-9-[4-(N,N-diphenylamino)phenyl]-9-phenylfluorene (POAPF), doped with a conventional blue triplet emitter, iridium(III) bis[(4,6-difluorophenyl)pyridinato-N,C(2)]picolinate (FIrpic) are fabricated. The molecular architecture of POAPF features an electron-donating (p-type) triphenylamine group and an electron-accepting (n-type) 2,7-bis(diphenylphosphoryl)fluorene segment linked through the sp(3)-hybridized C9 position of the fluorene unit. The lack of conjugation between these p- and n-type groups endows POAPF with a triplet energy gap (ET) of 2.75 eV, which is sufficiently high to confine the triplet excitons on the blue-emitting guest. In addition, the built-in bipolar functionality facilitates both electron and hole injection. As a result, a POAPF-based device doped with 7 wt% FIrpic exhibits a very low turn-on voltage (2.5 V) and high electroluminescence efficiencies (20.6% and 36.7 lm W(-1)). Even at the practical brightnesses of 100 and 1000cd m(-2), the efficiencies remain high (20.2%/33.8 lm W(-1) and 18.8%/24.3 lm W(-1), respectively), making POAPF a promising material for use in low-power-consumption devices for next-generation flat-panel displays and light sources.
A new organic/inorganic electroluminescent material with a silsesquioxane core
(2009-04-01)
Cheng, Chih-Chia
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Chien, Chen-Han
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Yen, Ying-Chieh
;
Ye, Yun-Sheng
;
Ko, Fu-Hsiang
This paper describes a new polyhedral oligomeric silsesquioxane (POSS)-based blue-light electroluminescent nanoparticle, octakis[N-(9-ethyl-9-H-carbazol-3-yl)undecanamide-11-dimethylsiloxy]silsesquioxane (POSS-C11-Cz), which contains eight carbazole chromophore arms, synthesized through the hydrosilation reaction of octakis(dimethylsiloxy)silsesquioxane with the terminal olefin Cz-C11ene. POSS-C11-Cz exhibits good thermal and electrochemical stabilities and good film-forming properties. The optical and photoluminescence spectra of POSS-C11-Cz in solution and in the solid state indicate a reduction in the degrees of aggregation and excimer formation because inter-chain interactions were prohibited by the bulky POSS core. Moreover, photoluminescence spectra of a POSS-C11-Cz (3 wt.%,)/polyfluorene (97 blend revealed that the color was stable after heating the sample at 200 degrees C for 5 h; in contrast, the pure polyfluorene exhibited a significant green emission at 530 nm. A triple-layer device based on this blend exhibited higher maximum brightness and luminance efficiencies relative to those of the pure polyfluorene. Thus, the organic/inorganic POSS-C11-Cz/polyfluorene blend has potential for use in polymeric light-emitting diodes because of its improved thermal and optoelectronic characteristics. Published by Elsevier Ltd on behalf of Acta Materialia Inc.
A novel fluorene-triphenylamine hybrid that is a highly efficient host material for blue-, green-, and red-light-emitting electrophosphorescent devices
(2007-11-23)
Shih, Ping-I
;
Chien, Chen-Han
;
Wu, Tang-Iy
;
Shu, Ching-Fong
;
應用化學系
TFTPA (tris[4-(9-phenylfluoren-9-yl)phenyl]amine), a novel host material that contains a triphenylamine core and three 9-phenyl-9-fluorenyl peripheries, was effectively synthesized through a Friedel-Crafts-type substitution reaction. Owing to the presence of its sterically bulky 9-phenyl-9-fluorenyl groups, TFTPA exhibits a high glass transition temperature (186 degrees C) and is morphologically and electrochemically stable. In addition, as demonstrated from atomic force microscopy measurements, the aggregation of the triplet iridium dopant is significantly diminished in the TFTPA host, resulting in a highly efficient full-color phosphorescence. The performance of TFTPA-based devices is far superior to those of the corresponding mCP- or CBP-based devices, particularly in blue- and red-emitting electrophosphorescent device systems. The efficiency of the FIrpic-based blue-emitting device reached 12% (26 cd A(-1)) and 18 lm W-1 at a practical brightness of 100 cd m(-2); the Ir(piq)(2)acac-based red-emitting device exhibited an extremely low turn-on voltage (2.6 V) and a threefold enhancement in device efficiency (9.0 lm W-1) relative to those of reference devices based on the CBP host material.
A solution-processable bipolar molecular glass as a host material for white electrophosphorescent devices
(2008)
Chien, Chen-Han
;
Kung, Liang-Rern
;
Wu, Chen-Hao
;
Shu, Ching-Fong
;
Chang, Sheng-Yuan
A solution-processable bipolar material tBu-OXDTFA comprising an electron-rich triphenylamine core and electron-deficient oxadiazole/ fluorene peripheries was synthesized. This dendrimer-like molecule not only possesses a high triplet energy (2.74 eV) but also exhibits excellent film-forming properties upon solution processing. We achieved highly efficient white electrophosphorescent OLEDs (22.3 cd A(-1), 11.6%) through solution processing, wherein the single white emitting layer was readily formed after spin-coating a solution of blue- and red-phosphor co-dopants containing tBu-OXDTFA as the host matrix.
Bright-white light-emitting devices based on a single polymer exhibiting simultaneous blue, green, and red emissions
(2007-01-23)
Chuang, Chu-Ying
;
Shih, Ping-I
;
Chien, Chen-Han
;
Wu, Fang-Iy
;
Shu, Ching-Fong
We have developed efficient white-light-emitting polymers through the incorporation of low band gap green-light-emitting benzothiadiazole and red-light-emitting bisthiophenylbenzothiadiazole moieties into the backbone of a blue-light-emitting bipolar polyfluorene copolymer. Partial energy transfer from the blue-fluorescent polyfluorene backbone to the green- and red-fluorescent components resulted in individual emissions from the three emissive species. By carefully controlling the concentrations of the low-energy-emitting species in the resulting copolymers, the emission of white light, with contributions from each of the three primary colors, was achieved. Efficient polymer light-emitting devices prepared using these copolymers exhibited luminance efficiencies as high as 4.87 cd/A with color coordinates (0.37, 0.36) that were very close to the ideal CIE chromaticity coordinates for pure white light (0.33, 0.33). In addition, the color coordinates remained almost unchanged over a range of operating potentials. A mechanistic study suggested that energy transfer from the fluorene segments to the low band gap units, rather than charge trapping, was the main operating process involved in the electroluminescent process.
Efficient non-doped blue-light-emitting diodes incorporating an anthracene derivative end-capped with fluorene groups
(2009)
Wu, Chen-Hao
;
Chien, Chen-Han
;
Hsu, Fang-Ming
;
Shih, Ping-I
;
Shu, Ching-Fong
We have synthesized and characterized a novel blue-emitting material, 2-tert-butyl-9,10-bis[40-(9-ptolylfluoren- 9-yl) biphenyl-4-yl] anthracene (BFAn), containing an anthracene core end-capped with 9-phenyl-9-fluorenyl groups. The presence of the sterically congested fluorene groups imparts BFAn with a high thermal decomposition temperature (T(d) = 510 degrees C) and results in its forming a stable glass (T(g) = 227 degrees C). Atomic force microscopy measurements revealed that BFAn forms high-quality amorphous films and possesses good morphological stability after annealing. Organic light-emitting diodes (OLEDs) featuring BFAn as the emitter exhibited an excellent external quantum efficiency of 5.1% (5.6 cd A(-1)) with Commission Internationale de L'Eclairage coordinates of (0.15, 0.12) that are very close to the National Television Standards Committee's blue standard. The power efficiency of our BFAn-based devices reached as high as 5.7 lmW(-1), making them superior to other reported non-doped deep-blue OLEDs.
Efficient red electrophosphorescence from a fluorene-based bipolar host material
(2009-08-01)
Chien, Chen-Han
;
Hsu, Fang-Ming
;
Shu, Ching-Fong
;
Chi, Yun
;
應用化學系
We have prepared efficient red organic light-emitting diodes (OLEDs) incorporating 2,7-bis(diphenylphosphoryl)-9-[4-(N,N-diphenylamino)phenyl]-9-phenylfluorene (POAPF) as the host material doped with the osmium phosphor Os(fptz)(2)(PPh(2)Me)(2) (fPtZ = 3-trifluoromethyl-5-pyridyl-1,2,4-triazole). POAPF, which possesses bipolar functionalities, can facilitate both hole- and electron-injection from the charge transport layers to provide a balanced charge flux within the emission layer. The peak electroluminescence performance of the device reached as high as 19.9% and 34.5 lm/W - the highest values reported to date for a red phosphorescent OLED. In addition, we fabricated a POAPF-based white light OLED - containing red-[doped with OS(fPtZ)(2)(PPh(2)Me)(2)] and blue-emitting [doped with iridium(III) bis[(4,6-difluorophenyl)pyridinato-N,C(2')] picolinate, Firpic} layers - that also exhibited satisfactory efficiencies (18.4% and 43.9 lm/W). (C) 2009 Elsevier B.V. All rights reserved.
Efficient red-emitting electrophosphorescent polymers
(2008-02-26)
Yang, Xiao-Hui
;
Wu, Fang-Iy
;
Neher, Dieter
;
Chien, Chen-Han
;
Shu, Ching-Fong
We report the synthesis and characterization of a series of electrophosphorescent polymers with a polyfluorene backbone, containing a red-emitting iridium complex and carrier-transporting units as the substitutes of the C-9 position of fluorene. Different specimens and contents of the hole-transporting moieties were found to influence the electroluminescent properties of the polymers. Incorporation of a hole-transporting/electron-blocking interfacial layer and utilization of an efficient electron injection cathode led to the saturated red-emitting electrophosphorescent polymer devices with the peak luminance efficiency and power conversion efficiency of 9.3 cd A(-1) and 10.5 lm W-1, respectively. The efficiencies were 8 cd A(-1)/8 lm W-1 and 5.9 cd A(-1)/4.6 lm W-1, respectively, at 100 and 1000 cd m(-2).
Electrophosphorescent polyfluorenes containing osmium complexes in the conjugated backbone
(2008-05-09)
Chien, Chen-Han
;
Liao, Song-Fu
;
Wu, Chen-Hao
;
Shu, Ching-Fong
;
Chang, Sheng-Yuan
Electrophosphorescent copolymers have been synthesized by covalent bonding of a red-emitting osmium complex Os(bpftz), which contains two 3-trifluoromethyl-5-(4-tert-butyl-2-pyridyl)triazolate (bpftz) cyclometalated ligands, into the backbone of a bipolar polyfluorene (PF) copolymer. Employing these copolymers, a highly efficient red polymer light-emitting diode has been realised that has an external quantum efficiency of 18.0%, a maximum brightness of 38000 cd m(-2), and an emission centered at 618 nm. In addition, after incorporating appropriate amounts of green-emitting benzothiadiazole (BT) and the aforementioned Os(bpftz) into the bipolar PF, an efficient white-light electroluminescent polymer is obtained that displays simultaneous blue, green, and red emissions.
Highly efficient non-doped blue-light-emitting diodes based on an anthrancene derivative end-capped with tetraphenylethylene groups
(2007-11-05)
Shih, Ping-I
;
Chuang, Chu-Ying
;
Chien, Chen-Han
;
Diau, Eric Wei-Guang
;
Shu, Ching-Fong
A novel blue-emitting material, 2-tert-butyl-9,10-bis[4-(1,2,2-triphenylvinyl)phenyl]anthracene (TPVAn), which contains an anthracene core and two tetraphenylethylene end-capped groups, has been synthesized and characterized. Owing to the presence of its sterically congested terminal groups, TPVAn possesses a high glass transition temperature (155 degrees C) and is morphologically stable. Organic light-emitting diodes (OLEDs) utilizing TPVAn as the emitter exhibit bright saturated-blue emissions (Commission Internationale de L'Eclairage (CIE) chromaticity coordinates of x = 0.14 and y = 0.12) with efficiencies as high as 5.3% (5.3 cd A(-1)) - the best performance of non-doped deep blue-emitting OLEDs reported to date. In addition, TPVAn doped with an orange fluorophore served as an authentic host for the construction of a white-light-emitting device that displayed promising electroluminescent characteristics: the maximum external quantum efficiency reached 4.9% (13.1 cd A(-1)) with CIE coordinates located at (0.33, 0.39).
Highly efficient red electrophosphorescent device incorporating a bipolar triphenylamine/bisphenylsulfonyl-substituted fluorene hybrid as the host
(2009)
Hsu, Fang-Ming
;
Chien, Chen-Han
;
Hsieh, Ya-Jou
;
Wu, Chen-Hao
;
Shu, Ching-Fong
We have fabricated highly efficient red phosphorescent organic light-emitting diodes (PHOLEDs) incorporating a bipolar host material, 2,7-bis(phenylsulfonyl)-9-[4-(N,N-diphenylamino)phenyl]-9-phenylfluorene (SAF), doped with 7 wt% tris(1-phenylisoquinolinolato-C(2),N)iridium(III) [Ir(piq)(3)]. Attaching the electron-donating (p-type) triphenylamine group onto the electron-accepting (n-type) 2,7-bis(phenylsulfonyl)fluorene segment (through the C9 position of the fluorene unit) imparts SAF with good morphological stability, high triplet energy gap (ET), bipolar transporting ability, and matching energy levels with adjacent carrier-transporting layers. Consequently, the SAF-based red-PHOLED exhibited a very low turn-on voltage (2.4 V) and high electroluminescence efficiencies of 15.8% and 22.0 lm W(-1), superior to those of the corresponding device incorporating a conventional host material, 4,4'-N,N'-dicarbazolbiphenyl (CBP; 3.2 V, 8.5%, and 8.4 lm W(-1), respectively). At a practical brightness of 1000 cd m(-2), the efficiencies of the SAF-based red-PHOLED remained high (13.1%, 14.4 lm W(-1)).
Highly Emitting Neutral Dinuclear Rhenium Complexes as Phosphorescent Dopants for Electroluminescent Devices
(2009-08-24)
Mauro, Matteo
;
Procopio, Elsa Quartapelle
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Sun, Yinghui
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Chien, Chen-Han
;
Donghi, Daniela
A series of neutral, dinuclear, luminescent rhenium(I) complexes suitable for phosphorescent organic light emitting devices (OLEDs) is reported. These compounds, of general formula [Re(2)(mu-Cl)(2)(CO)(6)(mu-1,2-diazine)], contain diazines bearing alkyl groups in one or in both the beta positions. Their electrochemical and photophysical properties are presented, as well as a combined density functional and time-dependent density functional study of their geometry, relative stability and electronic structure. The complexes show intense green/yellow emissions in toluene solution and in the solid state and some of the complexes possess high emission quantum yields (phi = 0.18-0.22 for the derivatives with disubstituted diazines). In butyronitrile glass, at 77 K, due to the charge transfer character of the lowest (emitting) excited state, strong blue shift of the emission is observed, accompanied by a strong increase in the lifetime values. The highest-performing emitting complex, containing cyclopentapyridazine as ligand, is tested in a polymer-based light-emitting device, with poly(9-vinylcarbazole) as matrix, as well as in a device obtained by vacuum sublimation of the complex in the 2,7-bis(diphenylphosphine oxide)-9-(9-phenylcarbazol-3-yl)-9-phenylfluorene (PCF) matrix. This represents the first example of devices obtained with a rhenium complex which can be sublimed and is solution processable. Furthermore, the emission is the bluest ever reported for electrogenerated luminescence for rhenium complexes.
Multifunctional Deep-Blue Emitter Comprising an Anthracene Core and Terminal Triphenylphosphine Oxide Groups
(1970-01-01)
Chien, Chen-Han
;
Chen, Ching-Kun
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Hsu, Fang-Ming
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Shu, Ching-Fong
;
Chou, Pi-Tai
"A highly efficient blue-light emitter, 2-tert-butyl-9,10-bis[4'-diphenyl-phosphoryl)phenyl]anthracene (POAn) is synthesized, and comprises electron-deficient triphenylphosphine oxide side groups appended to the 9- and 10-positions of a 2-tert-butylanthracene core. This sophisticated anthracene compound possesses a non-coplanar configuration that results in a decreased tendency to crystallize and weaker intermolecular interactions in the solid state, leading to its pronounced morphological stability and high quantum efficiency. In addition to serving as an electron-transporting blue-light-emitting material, POAn also facilitated electron injection from the Al cathode to itself. Consequently, simple double-layer devices incorporating POAn as the emitting, electron-transporting, and -injecting material produce bright deep-blue lights having Commission Internationale de L'Eclairage coordinates of (0.15,0.07). The peak electroluminescence performance was 4.3% (2.9 cd A(-1)). For a device lacking an electron-transport layer or alkali fluoride, this device displays the best performance of any such the deep-blue organic light-emitting diodes reported to date."
Novel host material for highly efficient blue phosphorescent OLEDs
(2007)
Shih, Ping-I
;
Chien, Chen-Han
;
Chuang, Chu-Ying
;
Shu, Ching-Fong
;
Yang, Cheng-Han
We report the synthesis and characterization of a novel silane - fluorene hybrid, triphenyl-(4-(9-phenyl- 9H-fluoren-9-yl) phenyl) silane (TPSi-F), used as the host material for blue phosphorescent devices. TPSi-F is constructed by linking p-substituted tetraphenylsilane to the fluorene framework through a non-conjugated, sp(3)-hybridized carbon atom (C- 9) to enhance thermal and morphological stabilities, while maintaining the much needed higher singlet and triplet energy gap. Highly efficient sky-blue phosphorescent OLEDs were obtained when employing TPSi-F as the host and iridium(III) bis[(4,6-difluorophenyl) pyridinato-N,C-2'] (FIrpic) as the guest. The maximum external quantum efficiency (max. E. Q. E.) of this device reached as high as 15% (30.6 cd A(-1)). Furthermore, upon switching the guest from FIrpic to a new blue phosphor FIrfpy, better blue-emitting OLEDs were produced with a max. E. Q. E. of 9.4% (15.1 cd A(-1)). These TPSi-F based blue phosphorescent devices show a 2-fold enhancement in device efficiency compared with reference devices based on the conventional host material 1,3-bis(9-carbazolyl) benzene (mCP).
Phosphine-Oxide-Containing Bipolar Host Material for Blue Electrophosphorescent Devices
(1970-01-01)
Hsu, Fang-Ming
;
Chien, Chen-Han
;
Shih, Ping-I
;
Shu, Ching-Fong
;
應用化學系
"We report highly efficient blue electrophosphorescent organic light-emitting diodes (OLEDs) incorporating a bipolar host, 2,7-bis(diphenylphosphine oxide)-9-(9-phenylcarbazol-3-yl)-9-phenylfluorene (PCF), doped with iridium(III) bis[(4,6-difluorophenyl)pyridinato-NC2']picolinate (FIrpic). PCF, which contains diphenylphosphine oxide groups appended onto a carbazole/fluorene hybrid, displays both electron- and hole-tran sporting characteristics, resulting in a low turn-on voltage (2.6 V) and greatly improved power efficiencies. In addition, the sterically hindered structure of PCF provides a compatible environment for the FIrpic dopant, alleviating concentration quenching of the phosphor at high doping levels. The device doped with 28 wt % FIrpic exhibited maximum EL efficiencies of 30.8 cd/A and 26.2 lm/W (at 121 cd/m(2)) /m(2), Even at a high brightness of 1000 cd/m(2) the efficiencies remained high (26.9 cd/A and 19.6 lm/W)."
Polyfluorene presenting dipolar pendent groups and its application to electroluminescent devices
(2007-06-01)
Chien, Chen-Han
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Shih, Ping-I
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Wu, Fang-Iy
;
Shu, Ching-Fong
;
Chi, Yun
We have synthesized a blue-light-emitting polyfluorene derivative (PF-TPAOXD) that presents sterically hindered, dipolar pendent groups functionalized at the C-9 positions of alternating fluorene units. The incorporation of the dipolar side chains, each comprising an electron-rich triphenylamine group and an electron-deficient oxadiazole group connected through a pi-conjugated bridge, endows the resultant polymer with higher highest occupied molecular orbital and lower lowest unoccupied molecular orbital energy levels, which, consequently, lead to an increase in both hole and electron affinities. An electroluminescent device incorporating this polymer as the emitting layer exhibited a stable blue emission with a maximum brightness of 2080 cd/ m(2) at 12 V and a maximum external quantum efficiency of 1.4% at a brightness of 137 cd/m(2). Furthermore, atomic force microscopy measurements indicated that the dipolar nature of PF-TPAOXD, in contrast to the general nonpolarity of polydialkylfluorenes, provided a stabilizing environment allowing the polar organometallic triplet dopant to be dispersed homogeneously. We also fabricated an electrophosphorescent device incorporating PF-TPAOXD as the host material doped with a red-emitting osmium complex to realize red electroluminescence with Commission Internationale de l'Eclairage color coordinates of (0.66, 0.34). The resulting device exhibited a maximum external quantum efficiency of 7.3% at a brightness of 1747 cd/m(2) and a maximum brightness of 7244 cd/ m(2). (C) 2007 Wiley Periodicals, Inc.
Polymers derived from 3,6-fluorene and tetraphenylsilane derivatives: Solution-processable host materials for green phosphorescent OLEDs
(2008-06-10)
Yeh, Huan-Chi
;
Chien, Chen-Han
;
Shih, Ping-I
;
Yuan, Mao-Chuan
;
Shu, Ching-Fong
We have synthesized two fluorene-based polymeric host materials, P1 and P2, through palladium-catalyzed Suzuki couplings of monomers containing tetraphenylsilane and 3,6-disubstituted fluorene frameworks, respectively. The resultant copolymers exhibited high glass transition temperatures (T-g >= 215 degrees C) and excellent thermal stability. The conjugation lengths of polymers P1 and P2 were effectively confined through the presence of the 3,6-linkages and silane units in the polymer skeleton. The structural features endowed these copolymers with UV-violet emissions in the solid state, together with high triplet energies (E-T = 2.60 eV), which were sufficiently high for PI and P2 to serve as appropriate hosts for green-emitting phosphors. In the case of polymer P2, the incorporation of pendent carbazole groups increased the HOMO level markedly and balanced the rates of charge injection and transportation. Employing P2 doped with green-emitting fac-tris(2-phenylpyridine)iridium as the emissive layer, we fabricated highly efficient polymer light-emitting diodes (32 cd/A, 9.2%) that exhibited significantly enhanced EL performance relative to that of the system employing P1 (14.5 cd/A, 4.2%).
Switching On Luminescence by the Self-Assembly of a Platinum(II) Complex into Gelating Nanofibers and Electroluminescent Films
(2011)
Strassert, Cristian A.
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Chien, Chen-Han
;
Lopez, Maria D. Galvez
;
Kourkoulos, Dimitrios
;
Hertel, Dirk
Syntheses, Photophysics, and Application of Iridium(III) Phosphorescent Emitters for Highly Efficient, Long-Life Organic Light-Emitting Diodes
(2009)
Lee, Tsang-Chi
;
Chang, Chiung-Fang
;
Chiu, Yuan-Chieh
;
Chi, Yun
;
Chan, Tzu-Ying
Rational design and synthesis of Ir(III) complexes (1-3) bearing two cyclometalated ligands (C boolean AND N) and one 2-(diphenylphosphino)phenolate chelate (P boolean AND O) as well as the corresponding Ir(III) derivatives (4-6) with only one (C boolean AND N) ligand and two P boolean AND O chelates are reported, where (C boolean AND NH) = phenylpyridine (ppyH), 1-phenylisoquinoline (piqH), and 4-phenylquinazoline (nazoH). Single crystal X-ray diffraction studies of 3 reveal a distorted octahedral coordination geometry. in which two nazo ligands adopt an eclipsed Configuration, with the third P boolean AND O ligand located trans to the phenyl group of both nazo ligands, confirming the general skeletal pattern for 1-3. In sharp contrast, complex 4 reveals a trans-disposition for the PPh(2) groups, along with the phenolate groups residing opposite the unique cyclometalated ppy ligand, which is the representative structure for 4-6. These Ir(III) complexes exhibit green-to-red photoluminescence with moderate to high quantum efficiencies in the degassed fluid state and bright emission in the solid state. For 1-6, the resolved emission spectroscopy and relaxation dynamics are well rationalized by the Computational approach. OLEDs fabricated using 12 wt.% of 3 doped in CBP and with BCP as hole blocking material, give bright electroluminescence with lambda(max) = 628 nm and CIE(xy) coordinates (0.65, 0.34). The turn-on voltage is 3.2 V, while the current efficiency and the power efficiency reach 11.2cd A(-1) and 4.5 lm W(-1) at 20 mA cm(-2). The maximum efficiency reaches 14.7 cd A(-1) and 6.8 lm W(-1) upon switching to TPBI as hole blocking material. For evaluating device lifespan, the tested device incorporating CuPc as a passivation layer, 3 doped in CTP as an emitting layer, and BAlq as hole blocking material, shows a remarkably long lifetime up to 36 000 h at an initial luminance of 500 cd m(-2).
Synthesis and characterization of a polyfluorene containing carbazole and oxadiazole dipolar pendent groups and its application to electroluminescent devices
(2007-07-15)
Yuan, Mao-Chuan
;
Shih, Ping-I
;
Chien, Chen-Han
;
Shu, Ching-Fong
;
應用化學系
We have synthesized a blue-light-emitting polyfluorene (PF) derivative (PF-CBZ-OXD) that presents bulky bole-transporting carbazole and electron-transporting oxadiazole pendent groups functionalized. at the C-9 positions of alternating fluorene units. The results from photoluminescence and electrochemical measurements indicate that both the side chains and the PF main chain retain their own electronic characteristics in the copolymer. An electroluminescent device incorporating this polymer as the emitting layer was turned on at 4.5 V; it exhibited a stable blue emission with a maximum external quantum efficiency of 1.1%. Moreover, we doped PF-CBZ-OXD and its analogue PF-TPA-OXD with a red-light-emitting iridium phosphor for use as components of phosphorescent red-light emitters to investigate the effect of the host's HOMO energy level on the degree of charge trapping and on the electrophosphorescent efficiency. We found that spectral overlap and individual energy level matching between the host and guest were both crucial features affecting the performance of the electroluminescence devices. Atomic force microscopy measurements indicated that the dipolar nature of PF-CBZ-OXD, in contrast to the general nonpolarity of polydialkylfluorenes, provided a stabilizing environment that allowed homogeneous dispersion of the polar iridium triplet dopant. (c) 2007 Wiley Periodicals, Inc.