High-performance Polymer Light-emitting Diodes Research Articles

Hyperbranched Conjugated Polymer with Multiple Charge Transfer Enables High-Efficiency Nondoped Red Electroluminescence with Low Driving Voltage

Conjugated polymers featuring thermally activated delayed fluorescence (TADF) attract tremendous attention in both academic and industry communities due to their easy solution processing for fabricating large-area and low-cost high-performance polymer light-emitting diodes (PLEDs). However, current nondoped solution-processed PLEDs frequently encounter significant efficiency roll-offs and unreasonably high operating voltages at high brightness, especially for red-emitting polymers. Herein, we design hyperbranched conjugated polymers (HCPs) with D-A-D type TADF characteristics for high-performance red-emitting PLEDs. Multiple intramolecular charge transfer (ICT) channels induced by quasi-equivalent donors of the TADF core strongly boost the reverse intersystem crossing (RISC) process and singlet excitons radiative transition. Coupling with the efficient energy transfer process generated by structure advantages of HCPs, the strongly electron-withdrawing oxygen atoms located on the TADF cores further accelerate hole transportation from the host chains to the TADF cores. Under a rational regulation of the TADF core ratio, the related nondoped red-emitting device performs an outstanding performance with an EQEmax of 8.39% and exhibits no roll-off while the luminance is less than 100 cd/m2 and only 3.3% decrease at 500 cd/m2. Simultaneously, the EQE can maintain 7.4% under 1000 cd/m2. Furthermore, the corresponding nondoped device exhibits a low turn-on voltage of around 2.5 V and achieves a luminance of 500 cd/m2 at 3.5 V and even 1000 cd/m2 at 3.9 V. To our knowledge, this is the best performance among all nondoped red PLEDs with high brightness obtained at low operating voltage.

Halogenated π-conjugated polymeric emitters with thermally activated delayed fluorescence for highly efficient polymer light emitting diodes

Benefiting from the facile solution-processed fabrication, superior electrical and photophysical properties, π-conjugated polymers with thermally activated delayed fluorescence (TADF) have drawn much more attention. But the credible designing principle for gaining high-performance TADF polymeric emitters is still demanded. Herein, we designed and synthesized the fluorinated and chlorinated π-conjugated TADF polymers, and their non-halogenated analog, respectively. The halogenation can aggrandize the locally excited component of triplet states ( 3 LE), which is favorable to enhance spin-orbit coupling (SOC) and reverse intersystem crossing (RISC) processes. Therefore, two halogenated polymers gain high photoluminescence quantum yield (PLQY) of nearly 80%, meanwhile keep the small overlap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). In addition, the high molecular dipole moments in halogenated polymers induce the preferentially horizontal emitting dipole orientation and thus high optical out-coupling efficiency. Eventually, the halogenated emitters based polymer light-emitting diodes (PLEDs) can reach high external quantum efficiency (EQE) of over 20%, and extremely low efficiency roll-off with sustaining over 18% EQE at luminance of 1000 cd/m 2 . This study opens a way to design high efficiency TADF materials by halogenation and thus guides the future research on the high-performance PLEDs. • The halogenated polymers with obvious TADF features are prepared by condensation polymerization. • The halogenation can enhance the triplet locally excited component and thus enhance reverse intersystem crossing processes. • The increased dipole moments can improve the horizontal emitting dipole orientation and optical out-coupling efficiency. • OLEDs employing the halogenated polymers as emitters can achieve the EQE value of over 20% with the good colour stability. • The EQE value of the fluorinated polymer can reach 18.2% at luminance of 1000 cd/cm 2 with extremely low efficiency roll-off.

Mechanically and thermally stable, transparent electrodes with silver nanowires encapsulated by atomic layer deposited aluminium oxide for organic optoelectronic devices

Abstract Flexible conductive electrodes are essential components for organic optoelectronic devices (OODs). One of the main challenges in the development of flexible OODs is to achieve an optimal combination of photoelectrical properties, enhanced flexibility and stability in transparent conductive electrodes (TCEs). In this work, high-performance flexible nonfullerene organic solar cells (OSCs) and polymer light-emitting diodes (PLEDs) based on TCEs of silver nanowires (AgNWs) encapsulated with an ultra-thin atomic layer deposited aluminum oxide (Al2O3) have been demonstrated. The hybrid AgNWs/Al2O3 composite electrodes with enhanced thermal, ambient and mechanical stabilities enable an efficient flexible transparent electrode with high transmittance and conductivity, which can synergistically optimize the device performance of nonfullerene OSCs and PLEDs. The maximum power conversion efficiency value of 7.03%, as well as a current efficiency of 7.26 cd A−1 for flexible OSCs and PLEDs are achieved, respectively. Notably, excellent flexibility, long-term atmospheric and thermal stabilities have been systematically investigated and demonstrated. These results provide a new design platform for the fabrication of high-performance, flexible transparent electrodes, which can be further explored in a wide range of organic optoelectronics field.

Dual hole transport layers for blue-light-emitting PLED: Suppress the formation of exciplex towards high device performance and color purity

The realization of high-performance blue polymer light-emitting diodes typically requires a hole transport layer to facilitate hole injection, primarily due to the deep highest occupied molecular orbital (HOMO) energy levels of the blue light-emitting polymers. However, the widely-used hole transport layers (HTLs) are prone to induce exciplex with longer wavelength emission when cooperating with those n-type blue-light-emitting layers, due to the HOMO and lowest unoccupied molecular orbital (LUMO) energy levels offsets. To avoid formation of exciplex and improve device performance of blue light-emitting, we employed two hole-transport layers consisting of a cross-linkable poly(indenofluorene-co-triphenylamine) copolymer and an additional poly(9-vinylcarbazole) (PVK) layer. The devices with dual HTLs have an enhanced luminous efficiency of 7.67 cd A−1 while keep the electroluminescent spectrum identical to the device based on PVK devices. The resulting blue light-emitting device based on such two-layer HTL exhibited remarkable stability, with luminous efficiency remained about 6.6 cd A−1 at a luminance of 10000 cd m−2. Our results shown that the dual HTLs device structure is a promising strategy for constructing high performance solution-processed blue polymer light-emitting diodes.

Improving efficiency and color purity of poly(9,9-dioctylfluorene) through addition of a high boiling-point solvent of 1-chloronaphthalene

In this work, the β-phase of poly(9,9-dioctylfluorene) (PFO) was used as a probe to study the effects of the addition of a high boiling-point solvent of 1-chloronaphthalene on the nanostructures and electroluminescence of PFO films. Both absorption and photoluminescence spectra showed that the content of the β-phase in PFO film was obviously enhanced as a result of the addition of a small amount of 1-chloronaphthalene into the processing solvent of p-xylenes. Apparently rougher morphology associated with the effectively enhanced ordering of polymer chains across the entire film was observed for films processed from p-xylene solutions consisting of a certain amount of 1-chloronaphthalene, as revealed by atomic force microscopy and grazing incidence x-ray diffraction measurements. In addition to the effects on the nanostructures of films, of particular interest is that the performance and color purity of polymer light-emitting devices can be noticeably enhanced upon the addition of 1-chloronaphthalene. These observations highlight the importance of controlling the nanostructures of the emissive layer, and demonstrate that the addition of a low volume ratio of high boiling-point additive can be a promising strategy to attain high-performance polymer light-emitting diodes.

Solution-processed bottom-emitting polymer light-emitting diodes on a textile substrate towards a wearable display

Proposed herein are textile-based polymer light-emitting diodes (PLEDs) prepared via a spin coating process for a wearable display. Multilayers consisting of alumina (Al2O3) and poly(vinyl alcohol) were used as a planarization layer to fabricate PLEDs on a textile, and non-inverted bottom-emitting PLEDs were fabricated on a planarized textile. Despite the light loss caused by the woven and opaque textile substrate, the fabricated device showed high maximum luminous efficiency (9.72 cd/A) and high maximum power efficiency (7.17 lm/W), and no angular dependency of the EL spectrum was observed on the textile-based PLEDs. In addition, the fabricated PLEDs showed stable operation under bending stress with a bending radius of 2.5 mm. In summary, high-performance PLEDs were developed using a solution process on a real textile, and the feasibility of realizing textile-based PLEDs for a large-area wearable display is suggested.

Using d-limonene as the non-aromatic and non-chlorinated solvent for the fabrications of high performance polymer light-emitting diodes and field-effect transistors

Aiming to environment protection, green solvents are crucial for commercialization of solution-processed optoelectronic devices. In this work, d-limonene, a natural product, was introduced as the non-aromatic and non-chlorinated solvent for processing of polymer light-emitting diodes (PLEDs) and organic field effect transistors (OFETs). It was found that d-limonene could be a good solvent for a blue-emitting polyfluorene-based random copolymer for PLEDs and an alternating copolymer FBT-Th4(1,4) with high hole mobility (μh) for OFETs. In comparisons to routine solvent-casted films of the two conjugated polymers, the resulting d-limonene-deposited films could show comparable film qualities, based on UV–vis absorption spectra and observations by atomic force microscopy (AFM). With d-limonene as the processing solvent, efficient blue PLEDs with CIE coordinates of (0.16, 0.16), maximum external quantum efficiency of 3.57%, and luminous efficiency of 3.66cd/A, and OFETs with outstanding μh of 1.06cm2 (Vs)−1 were demonstrated. Our results suggest that d-limonene would be a promising non-aromatic and non-chlorinated solvent for solution processing of conjugated polymers and molecules for optoelectronic device applications.

P.119: High‐Performance Polymer Light‐Emitting Diodes with a Conjugated Polyelectrolyte

AbstractWe demonstrated red, yellow, green and blue polymer light‐emitting diodes (PLEDs) with high performances using a conjugated polyelectrolyte electron injection layer and high work function metal (Ag). PLEDs using a conjugated polyelectrolyte layer show improved performances in terms of the luminance and efficiency, as compared to the devices without this layer. Furthermore, it is providing a new possibility of all solution‐processed PLEDs with Ag electrodes.

High-Performance Polymer Light-Emitting Diodes Based on a Gallium-Doped Zinc Oxide/Polyimide Substrate

Conducting atomic force microscopy and scanning surface potential microscopy were used to study the surface electrical properties of gallium-doped zinc oxide (GZO) films on the nanoscale. GZO films on a polyimide (PI) substrate were prepared by pulsed laser deposition at various substrate temperatures. Our experimental results show a correlation between the local conductivity and work function (WF) and the gallium dopant concentration and the number of oxygen vacancies on the GZO surface. When the substrate temperature was approximately 150 °C, the root-mean-square roughness, the percent surface area of the conducting regions, and the mean WF on the GZO surface were 2.17 nm, 88.91%, and 4.74 eV, respectively. When the GZO/PI substrate was used as an anode material in a polymer light-emitting diode (PLED), the electroluminescence intensity was increased by nearly onefold compared with the standard PLED, which is based on a commercial-indium tin oxide/glass substrate.

Alkali metal salts doped pluronic block polymers as electron injection/transport layers for high performance polymer light-emitting diodes

A series of alkali metal salts doped pluronic block copolymer F127 were used as electron injection/transport layers (ETLs) for polymer light-emitting diodes with poly[2-(4-(3′,7′-dimethyloctyloxy)-phenyl)-p-phenylenevinylene] (P-PPV) as the emission layer. It was found that the electron transport capability of F127 can be effectively enhanced by doping with alkali metal salts. By using Li2CO3 (15%) doped F127 as ETL, the resulting device exhibited improved performance with a maximum luminous efficiency (LE) of 13.59 cd/A and a maximum brightness of 5529 cd/m2, while the device with undoped F127 as ETL only showed a maximum LE of 8.78 cd/A and a maximum brightness of 2952 cd/m2. The effects of the doping concentration, cations and anions of the alkali metal salts on the performance of the resulting devices were investigated. It was found that most of the alkali metal salt dopants can dramatically enhance the electron transport capability of F127 ETL and the performance of the resulting devices was greatly improved.

Tuning the energy levels and photophysical properties of triphenylamine-featured iridium(iii) complexes: application in high performance polymer light-emitting diodes

Download options Please wait... Article information DOI https://doi.org/10.1039/C2JM30928A Article type Paper Submitted 15 Feb 2012 Accepted 28 Mar 2012 First published 03 Apr 2012 Download Citation J. Mater. Chem., 2012,22, 11128-11133 BibTex EndNote MEDLINE ProCite ReferenceManager RefWorks RIS Permissions Request permissions Tuning the energy levels and photophysical properties of triphenylamine-featured iridium(III) complexes: application in high performance polymer light-emitting diodes M. Zhu, Y. Li, C. Li, C. Zhong, C. Yang, H. Wu, J. Qin and Y. Cao, J. Mater. Chem., 2012, 22, 11128 DOI: 10.1039/C2JM30928A To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page. If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given. If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page. Read more about how to correctly acknowledge RSC content. Search articles by author Minrong Zhu Yanhu Li Chen'ge Li Cheng Zhong Chuluo Yang Hongbin Wu Jingui Qin Yong Cao

Workfunction-Tunable, N-Doped Reduced Graphene Transparent Electrodes for High-Performance Polymer Light-Emitting Diodes

Graphene is a promising candidate to complement brittle and expensive transparent conducting oxides. Nevertheless, previous research efforts have paid little attention to reduced graphene, which can be of great benefit due to low-cost solution processing without substrate transfer. Here we demonstrate workfunction-tunable, highly conductive, N-doped reduced graphene film, which is obtainable from the spin-casting of graphene oxide dispersion and can be successfully employed as a transparent cathode for high-performance polymer light-emitting diodes (PLEDs) as an alternative to fluorine-doped tin oxide (FTO). The sheet resistance of N-doped reduced graphene attained 300 Ω/□ at 80% transmittance, one of the lowest values ever reported from the reduction of graphene oxide films. The optimal doping of quaternary nitrogen and the effective removal of oxygen functionalities via sequential hydrazine treatment and thermal reduction accomplished the low resistance. The PLEDs employing N-doped reduced graphene cathodes exhibited a maximum electroluminescence efficiency higher than those of FTO-based devices (4.0 cd/A for FTO and 7.0 cd/A for N-doped graphene at 17,000 cd/m(2)). The reduced barrier for electron injection from a workfunction-tunable, N-doped reduced graphene cathode offered this remarkable device performance.

High performance polymer light-emitting diodes with N-type metal oxide/conjugated polyelectrolyte hybrid charge transport layers

We present an interfacial engineering strategy employing n-type-metal-oxide/conjugated-polyelectrolyte (CPE) hybrid charge-transport layers for highly efficient polymer light-emitting diodes (PLEDs). The hybrid metal-oxide/CPE layer facilitates electron-injection, while blocking hole-transport, and thereby maximizes electron-hole recombination within the emitting layer. A series of metal-oxide/CPE combinations were tested in inverted PLEDs (FTO/metal-oxide/CPE/F8BT/MoO3/Au). Specifically, HfO2/CPE double layer achieved an electroluminescence (EL) efficiency of up to 25.8 cd/A (@ 6.4 V, one of the highest values reported for fluorescent PLEDs).

Poly(ethylene oxide)-functionalized Al cathodes of tunable electron-injection capabilities for efficient polymer light-emitting diodes

Poly(ethylene oxide)-functionalized aluminum (Al) cathodes of tunable electron-injection capabilities are reported in this study for the fabrication of high-performance polymer light-emitting diodes (PLEDs). The composite cathodes are prepared by thermally co-evaporating poly(ethylene glycol) dimethyl ether (PEGDE, Mnca. 2000) polymer with Al metal simultaneously in vacuum as the cathode buffer. We attribute the formation of the carbide-like/Al complex as characterized by X-ray photoelectron spectroscopy (XPS) to the instant chemical reactions between the ethylene oxide functional groups with Al, which markedly enhances the device performance. The electron-injection capabilities of PEGDE : Al/Al cathodes are correlated with the contents of the carbide-like/Al complex in the buffer layer and can, therefore, be modulated by varying the co-evaporation ratios of PEGDE and Al. The luminous efficiency of green polyfluorene-based PLEDs applying an PEGDE : Al (2 : 1)/Al cathode is of 10.46 cd A−1, which is much higher than that of ∼0.04, 5.19, 6.40 cd A−1 for PLEDs with Al, PEGDE/Al and calcium/Al cathodes, respectively. This research leads to an alternative cathode design, free of salts, additives, complicated synthesis, and of tunable electron-injection capabilities to balance the opposite charge carriers for fabricating high-performance PLEDs.

Conjugated Zwitterionic Polyelectrolyte as the Charge Injection Layer for High-Performance Polymer Light-Emitting Diodes

A new zwitterionic conjugated polyelectrolyte without free counterions has been used as an electron injection material in polymer light-emitting diodes. Both the efficiency and maximum brightness were considerably improved in comparison with standard Ca cathode devices. The devices showed very fast response times, indicating that the improved performance is, in addition to hole blocking, due to dipoles at the cathode interface, which facilitate electron injection.

High performance polymer light-emitting diodes doped with a novel phosphorescent iridium complex

High performance polymer light-emitting diodes (PLEDs) based on a phosphor of noble metal complex bis(1,2-dipheny1-1H-benzoimidazole) iridium (acetylacetonate) [(pbi) 2Ir(acac)] doped in poly( N-vinylcarbazole) (PVK) host with various concentration were demonstrated. The photoluminescence (PL) and electroluminescence (EL) spectra of the PLEDs exhibited an emission intensity decrease of PVK and a gradually enhanced feature of (pbi) 2Ir(acac) with increased doping concentration. The device with a 5 wt% (pbi) 2Ir(acac) doped PVK system showed a high power efficiency of 3.84 lm/W and a luminance of 26,006 cd/m 2. The results indicated that both energy transfer and charge trapping have a significant influence on the performance of PLEDs. The devices have a broadened EL spectrum of full-width at half-maximum (FWHM) more than 100 nm, which can be realized for WOLEDs.

Design of Hole Blocking Layer with Electron Transport Channels for High Performance Polymer Light‐Emitting Diodes

Design of Hole Blocking Layer with Electron Transport Channels for High Performance Polymer Light‐Emitting Diodes

High-performance polymer light-emitting diodes fabricated with a polymer hole injection layer

Enhanced luminance (L) and luminous efficiency (LE) of polymer light-emitting diodes (PLEDs) is demonstrated using poly(bis(tetraphenyldiamino)biphenyl-perfluorocyclobutane), poly(BTPD-Si-PFCB), as the hole injection layer. The monomer is cast directly onto the indium-tin-oxide anode and thermally polymerized in situ. Hole injection from poly(BTPD-Si-PFCB) into the “super yellow” derivative of poly(phenylene vinylene) and into several blue-emitting polymers is comparable to or better than that from poly(ethylenedioxythiophene):poly(styrene sulfonic acid) (PEDOT:PSSA). With poly(BTPD-Si-PFCB) as the hole injecting layer into “super yellow,” the performance is identical to that obtained with PEDOT:PSSA (LE≈8 cd/A with little fall-off, even at L>104 cd/m2).

High-performance polymer light-emitting diodes doped with a red phosphorescent iridium complex

High efficiency has been achieved in polymer light-emitting diodes (PLEDs) exhibiting red emission by doping a fluorescence host material, poly(vinylcarbazole) (PVK), with an iridium(III) complex, bis[2-(2′-benzothienyl)-pyridinato-N,C3′]iridium(acetylacetonate) (BtpIr). The electroluminescence spectrum has a maximum wavelength of 614 nm. The highest external quantum efficiency is 3.3%. Due to its short triplet excited lifetime (∼5 μs), the quenching of the triplet exciton in BtpIr-doped PVK PLEDs has been shown to be suppressed compared to platinum(II)-2,8,12,17-tetraethyl- 3,7,13,18-tetramethylporphyrin-doped PVK PLEDs. 65% of the peak efficiency can be sustained at high-current density and at the very high brightness of 1350 cd/m2. We suggest that both triplet–triplet annihilation and polaron–triplet annihilation involves exciton quenching.

High Performance Polymer Light-Emitting Diodes Fabricated by a Low Temperature Lamination Process

We report on the successful demonstration of high performance polymer light-emitting diodes (PLEDs) using a low temperature, plastic lamination process. Blue- and red-emitting PLEDs were fabricated by laminating different luminescent polymers and organic compounds together to form the active media. This unique approach eliminates the issue of organic solvent compatibility with the organic layers for fabricating multi-layer PLEDs. In addition, a template activated surface process (TAS) has been successfully applied to generate an optimum interface for the low temperature lamination process. Atomic force microscopy analysis reveals a distinct difference in the surfaces created by the TAS and the spin-coating process. This observation coupled with the device data confirms the importance of the activated interface in the lamination process.