Highly branched green phosphorescent tris-cyclometalated iridium(III) complexes for solution-processed organic light-emitting diodes (original) (raw)
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Organic Electronics, 2008
Solution processed organic field-effect transistors (OFETs) usually have high on/off ratios but suffer from low mobilities, while transistors based on graphene usually exhibit very high mobilities but low on/off ratios. We demonstrate a straightforward route to solve the challenging problem of enhancing the effective mobility in OFETs while keeping the on/off ratio sufficiently high. We achieve this by developing hybrid FETs incorporating both organic semiconductors and graphene. Compared against OFETs with only pure organic semiconductors, our hybrid FETs exhibit up to 20 times higher effective mobilities, and yet they keep the on/off ratios comparable or better. P3HT/graphene hybrid FETs exhibit mobility as high as 0.17 cm 2 V À1 s À1 , and PQT-12/graphene hybrid FETs show effective mobility up to 0.6 cm 2 V À1 s À1 . We expect that incorporating graphene is a general route to enhance the performance of OFETs, providing a low-cost avenue for enhancing OFET performance.
Macromolecules, 2010
A poly(styrene) with pendant dendronized iridium(III) complexes attached to every repeat unit was prepared in good yields using a free radical polymerization of a "macromonomer". The dendronized pendant groups were heteroleptic iridium(III) complexes comprised of two 2-phenylpydridyl ligands, to which first generation biphenyl dendrons with 2-ethylhexyloxy surface groups were attached, and a phenyltriazolyl coligand that formed the attachment point to the polymer backbone. Dendronization of the pendant iridium(III) complexes was found to improve thermal stability, solubility, and solution (61%) and solid-state (13%) photoluminescence quantum yields (PLQYs) relative to the nondendronized homopolymer. Viscosity under normal solution processing conditions of 25 mg/mL was found to be 1.23 cSt. Importantly, although the phosphorescent iridium(III) chromophores are held closely along the polymer backbone, they do not significantly reduce the PLQY in solution by intrachain chromophore interactions. Simple bilayer organic light-emitting diodes comprising a blend of the poly(dendrimer) with 4,4-bis(N-carbazolyl)biphenyl and an electron transporting layer had good performance with an external quantum efficiency of 6.2% at 100 cd/m 2 .
Tetrahedron, 2018
Two novel dendrimer-like blue-emitting dinuclear cyclometalated iridium (III) complexes, namely (DNaTPA) 2 DBF(FIrpic) 2 and (DPyTPA) 2 DBF(FIrpic) 2 , have been successfully synthesized and characterized. In which FIrpic is an iridium (III) bis[(4,6-difluorophenyl)pyridinato-N,C2 0 ]picolate blue-emitting phosphorescent chromophore core, DBF is a 2,7-diphenyl-9H-fluorene bridging core, DNaTPA and DPyTPA are deep blue-emitting fluorescent chromophores composed by rigid high-triplet-energy dendrons of triphenylamine-functionalized naphthalene or pyrene units, and the peripheral dendrons are connected with the ancillary ligand of the emitting core through nonconjugated ether linkage. Their photophysical, thermal, electrochemical, as well as electrophosphorescent properties were primarily studied. Both iridium (III) complexes exhibit high efficient blue emission in solution (38.5% and 19.2%) and a typical FIrpic emission in 1,3-bis(N-carbzolyl)benzene (mCP) matrix (27.0% and 24.1%). Simple bilayer phosphorescent organic light-emitting diodes (PHOLEDs) with a configuration of ITO/PEDOT:PSS/ mCP:dopants/TmPyPB/Liq/Al achieved high efficiencies of 12.96 cd/A for current efficiency (CE), 6162 cd/ m 2 for brightness, 6.22% for external quantum efficiency (EQE), and 3.13 lm/W for power efficiency (PE) with Commission International de L'Eclairage (CIE) coordinates of (0.19 ± 0.01, 0.35 ± 0.02) at only 2 wt% blend of (DNaTPA) 2 DBF(FIrpic) 2. (DPyTPA) 2 DBF(FIrpic) 2-doped devices also reach efficiencies of (9.14 cd/ A, 7167 cd/m 2 , 4.41%, 2.61 lm/W) at the same doping concentration. The results demonstrate that the introduction of dendritic blue-emitting fluorescent chromophore grafted into the blue phosphorescent chromosphere core through nonconjugated linkage is an efficient way to achieve high-efficiency skyblue emission.
Journal of the American Chemical Society, 2009
This is a first report on a novel divergent procedure to synthesize higher generation polyphenylene dendrimers with an Ir(III) core up to G4, which up to now is the largest Ir(III) dendrimer, having a molecular diameter of 8 nm. Our synthetic method provides a much higher yield (>80%) than earlier reported traditional convergent strategies (<35%). Moreover, with a stepwise synthesis, the molecular sizes are controlled by different dendrimer generations from G1 (R 1 ≈ 15 Å) to G4 (R 4 ≈ 40 Å). In this case, polyphenylene dendrons are used as a "matrix" which prevent iridium phosphorescent cores from triplet-triplet annihilation and improve their photoluminescence quantum yields (PLQYs). All dendrimers show strong phosphorescence at room temperature, and interestingly, their PLQYs tend to increase with subsequent generations up to 36% for G4 in solid state, almost 4 times of that of the nondendritic iridium complex. We also fabricated all generation dendrimers in phosphorescent organic light-emitting diodes (PhOLEDs) and investigated the relationship between the Ir(III) dendrimer sizes and the device performances. Our results indicate that dendrimer G3 possesses the highest efficiency device compared to other generation dendrimers, since its appropriate dendrimer size (R 3 ≈ 30 Å) can not only prevent intermolecular triplet-triplet annihilation, thereby increasing the PLQY, but also provide an effective charge carrier mobility from the periphery to the Ir(III) core.
White organic light emitting diodes based on fluorene-carbazole dendrimers
Journal of Luminescence, 2014
In this paper, we report on the Prod. Type: FTP fabrication and characterization of blue and white light emitting devices based on two fluorene-carbazole containing dendrimers and para-sexiphenyl (6P) oligomers. Blue light emitting diodes were fabricated using 9′,9″-(9,9-dioctyl-9H-fluorene-2,7-diyl)bis-9′ H-9,3′:6′,9″-tercarbazole (OFC-G2) and 9′,9″-(9,9′-spirobi[fluorene]-2,7-diyl)bis-9′H-9,3′:6′,9″-tercarbazole (SBFC-G2) dendrimers as a hole transport and emissive layer (EML) and 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) as an electron transport layer. White light emitting diodes were fabricated using 6P and these two dendrimers as an EML. OLED device with the structure of ITO/PEDOT:PSS (50 nm)/OFC-G2 (40 nm)/6P (20 nm)/LiF:Al (0.5:100 nm) shows maximum luminance of nearly 1400 cd/ m 2 and a Commission Internationale de l'Eclairage chromaticity coordinates of (0.27, 0.30) at 12 V.
Influence of molecular structure on the properties of dendrimer light-emitting diodes
Organic Electronics, 2003
Iridium-based phosphorescent dendrimers have shown much promise as highly efficient light emitting materials for organic light emitting diodes (OLEDs). Here we report the effects of modifying the chemical structure on the emissive and charge transport properties of Ir(ppy) 3 based electrophosphorescent dendrimers. We investigate a novel para linked first generation (G1) iridium dendrimer. This material is compared to G1 and G2 meta linked dendrimers. We show that by blending these dendrimers into a CBP host, high external quantum efficiencies of over 10% and luminous efficiencies of 27 lm/W can be achieved.
npj Flexible Electronics
Controlling the orientation of the emissive dipole has led to a renaissance of organic light-emitting diode (OLED) research, with external quantum efficiencies (EQEs) of >30% being reported for phosphorescent emitters. These highly efficient OLEDs are generally manufactured using evaporative methods and are comprised of small-molecule heteroleptic phosphorescent iridium(III) complexes blended with a host and additional layers to balance charge injection and transport. Large area OLEDs for lighting and display applications would benefit from low-cost solution processing, provided that high EQEs could be achieved. Here, we show that poly(dendrimer)s consisting of a non-conjugated polymer backbone with iridium(III) complexes forming the cores of firstgeneration dendrimer side chains can be co-deposited with a host by solution processing to give highly efficient devices. Simple bilayer devices comprising the emissive layer and an electron transport layer gave an EQE of >20% at luminances of up to ≈300 cd/ m 2 , showing that polymer engineering can enable alignment of the emissive dipole of solution-processed phosphorescent materials.
High-efficiency green phosphorescence from spin-coated single-layer dendrimer light-emitting diodes
Applied Physics Letters, 2002
We demonstrate very high-efficiency green phosphorescence from a single-layer dendrimer organic light-emitting diode formed by spin-coating. A first generation fac-tris͑2-phenylpyridine͒ iridium cored dendrimer doped into a wide-gap 4,4Ј-bis(N-carbazole) biphenyl host displays a peak external quantum efficiency of 8.1% ͑28 Cd/A͒ at a brightness of 3450 Cd/m 2 and a current density of 13.1 mA/cm 2 . A peak power efficiency of 6.9 lm/W was measured at 1475 Cd/m 2 and 5 mA/cm 2 . We attribute this exceptionally high quantum efficiency for a single-layer device to the excellent film forming properties and high photoluminescence quantum yield of the dendrimer blend and efficient injection of charge into the emissive layer. These results suggest that dendrimers are an effective method for producing efficient phosphorescent devices by spin-coating.
2010
a b s t r a c t 24 A uniform dispersion of highly soluble phosphorescent dendrimer emitters is achieved by 25 blending with a polymer host poly(9-vinylcarbazole) (PVK) containing N,N 0 -diphenyl-N, 26 N 0 -(bis(3-methylphenyl)-[1,1-biphenyl]-4,4 0 -diamine (TPD) and 2-(4-biphen-4 0 -yl)-5-(4-27 tert-butylphenyl)-1,3,4-oxadiazole (PBD). No visible aggregation or self-quenching was 28 observed for guest-to-host weight ratios of up to 33:67. The dendrimers contain a fac-29 tris(2-phenylpyridyl)iridium(III) [Ir(ppy) 3 ] core, first generation biphenyl-based dendrons, 30 and 2-ethylhexyloxy surface groups. The guest-host blend is used for all solution pro-31 cessed organic light-emitting diodes. A maximum external and current efficiency of 32 10.2% and 38 cd/A (at 5 V and a brightness of 50 cd/m 2 ), and a maximum brightness of 33 27,000 cd/m 2 (at 14.5 V), were obtained when a CsF/Al cathode was used. Blade coating 34 was used to fabricate a multi-layer structure that also contained an electron-transport 35 layer. The device that had a LiF/Al cathode had a maximal efficiency of 40 cd/A correspond-36 ing to an external quantum efficiency of 10.8% (at 5 V and a brightness of 19 cd/m 2 ). The 37 maximum brightness of the second device was 17,840 cd/m 2 at 14 V.