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Hybrid organic-inorganic light-emitting diodes were developed with pristine ZnO (2.0 wt%) and Cu-doped ZnO (2.0 wt%) as electron injection layer and iridium(III)-bis-2-(4-fluorophenyl)-1-(naphthalen-1-yl)-1H-phenanthro[9,10-d] imidazole (acetylacetonate) [Ir(fpnpi)2 (acac)] as green emissive layer (521 nm). The pristine ZnO and Cu-doped ZnO are deposited at indium tin oxide cathode and emissive layer interface. The electroluminescent performances increased by electron injection layer-Cu-doped ZnO compared with ZnO-based device because Cu-doped ZnO injects electron efficiently result in balanced h+ - e- recombination in emissive layer than ZnO-based device. The Cu-doped ZnO (2.0 %) device shows luminance (L) of 10 982 cd/m2 at 23.0 V (ZnO, 1450 cd/m2 at 23.0 V). [ABSTRACT FROM AUTHOR]

A series of phenanthroimidazole derivatives have been synthesized and used as non-doped blue emitters in organic light-emitting devices. Hybrid local and charge transfer (HLCT) state molecules (D-π-A) have been designed by the incorporation of effective hot exciton RISC and high PL efficiency to maximize the external quantum efficiency of fluorescent OLEDs. These compounds show high fluorescent quantum yield as well as good thermal and film-forming abilities. The emissive properties of the materials have been found to be related to the dihedral angles in these compounds. Among the pyrene substituted phenanthrimidazoles, Py-SPICN based device shows excellent performances with maximum current efficiency of 3.41 cd A −1 , power efficiency of 2.80 Lm W −1 and EQE of 1.48%. The non doped device using Cz-TPICN dopant exhibits a maximum current efficiency of 3.65 cd A −1 , power efficiency of 3.10 Lm W −1 and external quantum efficiency of 1.64% with Commission Internationale de’Eclairage (CIE) coordinates of (0.15, 0.10). [ABSTRACT FROM AUTHOR]

Blue emitting devices based on N-(4-(4′-(1-(4-benzylpiperidine)-1H-diphenylimidazol-2-yl)-styryl-1)phenyl)-N-phenylbenzenamine (TPA-BDIS), N-(4-(4′-(1-(4-benzylpiperidine)-1H-phenanthro[9,10-d]imidazol-2-yl)-styryl-1)phenylbenzenamine (TPA-BPIS) and 2-(4′-9H-carbazol-9-yl)-[1,1′-styryl]-4-yl-1-benzylpiperidine-1H-phenanthro[9,10-d]imidazole (Cz-BPIS) have been synthesized and characterized. The fully twisted TPA-BDIS exhibits a narrow electroluminescence emission at 441 nm with a full-width at half maximum of 40 nm. Density functional theory (DFT) calculations show that the decreased energy barrier between the transitions of TPA-BDIS causes a strong orbital coupling resulting in a deep blue emission. The electroluminescence performance of the non-doped device based on TPA-BPIS shows a high brightness of 2852 cd m−2, a current efficiency of 1.88 cd A−1, a power efficiency of 1.51 lm W−1 and an external quantum efficiency of 2.53%. Compared with TPA-BPIS, the weak donor carbazole substituted Cz-BPIS exhibits an excellent performance: a blue emission with CIE coordinates of (0.16, 0.09), a current density of 1.91 cd A−1, a power efficiency of 1.63 lm W−1 and an external quantum efficiency of 2.61%. A fluorescent molecule with a combination of the HLCT state and hot excitons may be an ideal candidate in the design of high efficiency, low cost, fluorescent OLED materials. [ABSTRACT FROM AUTHOR]

Efficient blue-emitting isomers of bis(phenanthrimidazolyl)biphenyl derivatives, 4,4′-bis(1-methylnaphthyl-1H-phenanthro[9,10-d]imidazol-2-yl)biphenyl (4,4′-BNPIB), 3,4′-bis(1-methylnaphthyl-1H-phenanthro[9,10-d]imidazole-2-yl)biphenyl (3,4′-BNPIB) and 3,3′-bis(1-methylnaphthyl-1H-phenanthro[9,10-d]-imidazol-2-yl)-biphenyl (3,3′-BNPIB) have been synthesised by tuning the coupling position on the biphenyl from the para- to meta-position. These compounds exhibit excellent thermal properties with a high glass-transition temperature of 152–198 °C and emit intense blue light in solution at ca. 396 nm. Because of changes in the degree of conjugation at the C-2 position in the phenanthrimidazole unit, the emission of 3,4′-BNPIB (413/430 nm) and 3,3′-BNPIB (396/426 nm) is blue-shifted when compared with that of 4,4′-BNPIB (422/450 nm) in both solution and film. The fabricated non-doped devices based on these materials exhibit blue emission at 431 nm (4,4′-BNPIB), 412 nm (3,4′-BNPIB) and 400 nm (3,3′-BNPIB), and 3,4′-BNPIB exhibits efficient performance with a maximum luminance of 39 823 cd m−2, a current efficiency of 8.01 cd A−1, a quantum efficiency of 4.85% and a power efficiency of 7.02 lm W−1. [ABSTRACT FROM AUTHOR]

Blue emitting devices based on donor-linker-acceptor geometry such as p-methoxynaphthylphenanthroimidazole-phenyl-phenylbenzenamine (TPA-MPI) and p-methoxynaphthylphenanthroimidazole-styryl-phenylbenzenamine (TPA-MPS) were synthesized and characterized. Due to the rigid molecular backbone composed of phenanthro[9,10-d]imidazole (acceptor), phenyl (TPA-MPI) and styryl (TPA-MPS) spacers, and triphenylamine (donor), these compounds exhibit good thermal stability. The nondoped device based on TAP-MPS exhibits higher efficiencies, 1.73 cd A-1 (ηc), 1.46 lm W-1 (ηp), and 2.11% (ηex). The higher efficiency is attributed to the coemission from the intercrossed excited state of the emissive layer. [ABSTRACT FROM AUTHOR]

Organic light-emitting devices (OLEDs) were fabricated with Au-doped ZnO and or ZnO nanoparticles (NPs) as hole injection layer (HIL) and CBP: Ir (TSDPI) 2 (pic) as emissive layer to enhance device performances. The photoluminescence intensity of 4,4′-N,N’-dicarbazole-biphenyl(CBP): Ir (TSDPI) 2 (pic)/Au −ZnO film at 514 nm is increased by 2.01 times than device with CBP: Ir (TSDPI) 2 (pic)/ZnO film. The current efficiency(η c ) and luminance efficiency (L)of green OLEDs with CBP: Ir (TSDPI) 2 (pic)/10% wt Au −doped ZnO film was 58.6% and 57.0%, respectively higher than CBP: Ir (TSDPI) 2 (pic)/ZnO film and 71.6% and 66.0%, respectively higher than device without HIL. This enhanced efficiencies with Au-doped ZnO was correlated with the out-coupling efficiency due to localized surface plasmon resonance (LSPR) generated by Au NPs incorporated in Au-doped ZnO. [ABSTRACT FROM AUTHOR]