Efficient and saturated blue organic polymer light emitting devices with an oxadiazole containing poly(fluorene) polymer emissive layer (original) (raw)
Related papers
Efficient deep blue fluorescent polymer light-emitting diodes (PLEDs)
Journal of Materials Chemistry C, 2014
A new series of deep blue/blue emitting co-polymers are reported. Poly(9,9-dihexylfluorene-3,6-diyl and 2,7-diyl-co-2,8-dihexyldibenzothiophene-S,S-dioxide-3,7-diyl) derivatives p(F-S) of varying composition have been synthesised. The effects of two different S derivatives with dialkoxy sidechains, the F : S monomer feed ratio, and meta versus para conjugation with respect to the F units have all been investigated in terms of photophysics and polymer light-emitting diode (PLED) device performance in the architecture ITO/PEDOT:PSS/polymer/TPBi/LiF/Al. The meta polymers poly(9,9-dihexylfluorene-3,6diyl-co-2,8-di(O-methylenecyclohexyl)dibenzothiophene-S,S-dioxide-3,7-diyl) p(F m -S OCy ) in three different co-monomer ratios, P1-3, give deep blue electroluminescence peaking at 415 nm, with the ratio of 70 : 30 p(F m : S OCy ) producing a maximum external quantum efficiency (EQE) h ext, max 2.7%, whilst the ratio of 85 : 15 gave the highest maximum brightness L max of 81 cd m À2 , with CIE coordinates (0.17, 0.12) The analogous para series poly(9,9-dihexylfluorene-2,7-diyl-co-2,8-di(O-methylenecyclohexyl)dibenzothiophene-S,S-dioxide-3,7-diyl) p(F p -S OCy ) and poly(9,9-dihexylfluorene-2,7-diylco-2,8-dihexyloxydibenzothiophene-S,S-dioxide-3,7-diyl) p(F p -S O6 ) in two different ratios, P4-7, produced blue emission peaking at ca. 450 nm. The ratio of 70 : 30 F : S units consistently gave better devices than the corresponding 50 : 50 co-polymers. It was also observed that co-polymers incorporating the bulkier S OCy derivatives gave more efficient and brighter devices, with polymer P5 attaining a remarkable h ext, max 3.2%, 4.4 cd A À1 , 3.4 lm W À1 and maximum brightness 2500 cd m À2 with CIE (0.16, 0.18).
Performance and defects in phosphorescent organic light-emitting diodes
Solid State Sciences, 2010
Phosphorescent heavy metal complexes can utilize both singlet and triplet excitons and thus are interesting for doping polymer to obtain highly efficient organic light-emitting diodes. In this study, we have investigated devices using a new phosphorescent-metal complex containing fluorene and platinum added to a luminescent polymer blend, composed of 2-(4-biphenylyl)-5-(4-tert-butyl-phenyl)-(1,3,4oxadiazole) (PBD) and poly(9-vinylcarbazole) (PVK). The performance of devices (luminance and yield) is measured in indium tin oxide (ITO)/poly(3-4 ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS)/(PVK-PBD-complex)/Al diodes. The devices emit an orange light with a brightness of 607 cd/m 2 and an external quantum efficiency of 0.28 cd/A at 25 V. In order to investigate the structural modifications of the polymer by the incorporation of phosphorescent-metal complex, we have studied the defect states in diodes by charge-based Deep Level Transient Spectroscopy (Q-DLTS). Analysis of Q-DLTS spectra obtained in undoped and doped devices, revealed at least three trap levels distributed in the range 0.2-0.5 eV within the band gap of the hybrid composite with trap density in the range around 10 16 cm À3. Incorporation of Pt complex into the polymer blend modified the trap states by reducing the density of traps in the blend and by creating new trap levels in the band gap.
Organic Light Emitting Materials and Devices XIII, 2009
The properties of phosphorescent fac tris(2-phenylpyridine) iridium [Ir(ppy 3 )]-doped poly(N-vinyl carbazole) (PVK)/4,7-diphenyl-1,10-phenanthroline (Bphen) polymer/small molecular hybrid OLEDs are described. For optimal BPhen thickness, the power efficiency of the devices exceeds 30 lm/W. The low-temperature electroluminescence-detected magnetic resonance (ELDMR) exhibits the well-known negative spin 1/2 resonance attributed to enhanced formation of trions, but the positive spin 1/2 resonance, typically observed at low temperature or at high current density, is not observed. The OLEDs' performance and the ELDMR results are discussed in relation to the nature of the defects and their density in these devices.
Journal of Polymer Science Part A, 2006
A series of multilayer polymeric light-emitting diodes (PLEDs) containing an electron-transporting layer (ETL), that is tris(8-quinolinolato)-aluminum(III) (Alq) and 2,2 0 ,2 00-(1,3,5-phenylene)-tris[1-phenyl-1H-benzimidazole] (TPBI), were fabricated by doping fluorescent oligo(p-phenylene-vinylene)s (BIII and BV) and polymer derivatives (PBV) into poly(N-vinyl carbazole) (PVK). These PLEDs can be optimized by the design of multilayer device configurations (brightness increased 8-15 times by addition of ETL) and possess greenish electroluminescent (EL) spectra peaked about 500-540 nm. A remarkably high brightness of 56,935 cd/m 2 with a power efficiency of 3.25 lm/W was obtained in the device of PVK:BVOC 8-OC 8 (100:20)/Alq (60 nm/60 nm). It suggests that the emission mechanism (including the conjugated and excimer emissions of BVOC 8-OC 8 emitters) originates from both of BVOC 8-OC 8 and ETL (Alq and TPBI) by varying the concentration of chromophores and adjusting the thickness of ETL. The concentration effect of the emitters in PVK (i.e. PVK:BVOC 8-OC 8 ¼ 100:5, 100:20, and 100:100 wt %) and the influence of the ETL (including its thickness) on the EL characteristics are also reported. V
White-emissive tandem-type hybrid organic/polymer diodes with (033, 033) chromaticity coordinates
Optics Express, 2009
This study reports fabrication of white-emissive, tandem-type, hybrid organic/polymer light-emitting diodes (O/PLED). The tandem devices are made by stacking a blue-emissive OLED on a yellow-emissive phenyl-substituted poly(para-phenylene vinylene) copolymer-based PLED and applying an organic oxide/Al/molybdenum oxide (MoO 3) complex structure as a connecting structure or charge-generation layer (CGL). The organic oxide/Al/MoO 3 CGL functions as an effective junction interface for the transport and injection of opposite charge carriers through the stacked configuration. The electroluminescence (EL) spectra of the tandem-type devices can be tuned by varying the intensity of the emission in each emissive component to yield the visible-range spectra from 400 to 750 nm, with Commission Internationale de l'Eclairage chromaticity coordinates of (0.33, 0.33) and a high color rendering capacity as used for illumination. The EL spectra also exhibit good color stability under various bias conditions. The tandem-type device of emission with chromaticity coordinates, (0.30, 0.31), has maximum brightness and luminous efficiency over 25,000 cd/m 2 and ~4.2 cd/A, respectively.
Organic oxide/Al composite cathode in efficient polymer light-emitting diodes
Applied Physics Letters, 2006
This work presents the fabrication of efficient polymer light-emitting diodes ͑PLEDs͒ by thermally evaporating a salt-free neutral organic-oxide buffer layer onto the surface of the electroluminescent film in a vacuum before the device cathode, made of Al-rather than the low work function metals, such as Ca or Ba-is deposited. The electroluminescence ͑EL͒ efficiency of phenyl-substituted poly͑para-phenylene vinylene͒ copolymer-based PLEDs with an organic oxide/Al composite cathode, reaches 8.86 cd/ A, which is markedly higher than those, 5.26 cd/ A and 0.11 cd/ A, of devices with Ca/ Al and Al cathodes, respectively. The device performance is improved by the formation of a specific organic oxide/Al complex at the cathode interface during the deposition of Al, facilitating the injection of electrons and eliminating the metal-induced quenching sites of luminescence in the EL layer near the recombination region.
Advanced Materials, 2008
Polymer-based electronics has developed rapidly over the last decade. In particular, the phenomenon of electroluminescence in conjugated semiconducting polymers spurred wide interest in the field. Successful demonstration of basic optoelectronics devices such as lasers, polymer light emitting diodes (PLEDs), thin film transistors, photovoltaics (PVs), and optical sensors have been realized in research laboratories, and some are already incorporated into commercial applications. However, there is still scope for improvement in terms of device stability and specifically correct choice of charge injecting/transporting layers for LEDs. The conventional PLED structure employs low work function metal electrodes which require hermetical encapsulation since they can not operate in ambient conditions. Even relatively stable Mg-Ag cathodes have been found to degrade gradually in air due to oxidation. [7] State-of-art PLEDs use poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) as the hole injecting anode and Ca-Al bilayers as the electron injecting cathode. As an alternative, metal-oxides can be employed as charge transport and injection layers, as has been illustrated for charge collection electrodes in photovoltaic diodes. These metal-oxides have advantages of exceptional stability, mechanical and electrical robustness, low cost, transparency in the visible region, solution processable fabrication and the potential to control the film morphology and interfacial electronic structure through sol-gel and surface chemistry. Composite oxide-polymer based diodes are good substitutes to improve device stability, [11, and as we demonstrate here can compete well with conventional PLED architectures. In addition to being unsusceptible to oxidization, metal oxides also provide good double heterojunction structure for charge carrier confinements. Here, we present a comprehensive study of a variety of metal oxides in mesoporous and compact forms for electron injection in highly luminescent composite oxidepolymer light emitting diodes (COPLEDs). We demonstrate that the morphology of the polymer film cast on the metal oxide surface critically influences the ensuing photoluminescence and electroluminescence efficiency, and that wave-guiding is also extremely effective and causes an enhancement in the angular emission intensity. We report the highest efficiency of 2.8 Cd A À1 employing a compact ZnO electron transport and injection layer, and a MoO 3 hole injection layer. This demonstrates that these metal oxide inter-layers are real contenders to replace conventional low work function metals and conducting polymer electrodes currently employed in emissive polymer devices.