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The rapid development of nanotechnology for the last 30 years has enabled a rapid expansion in the applications of functional nanoparticles (NPs) on optoelectronic devices. Especially, NPs are of high significance in organic light‐emitting diodes (OLEDs) as they provide feasible solutions to the enduring challenges related to higher device efficiency. The use of NPs with designed structure and functionality is demonstrated, indicative of their great application potentials in OLEDs. Herein, the recent advances in OLEDs with the utilization of functional NPs are summarized. Starting with a brief overview about the unique properties of NPs, comprehensive roles of NPs in OLEDs, which include improving carrier injection abilities, local surface plasmonic resonance, light scattering, and magnetic field effects, are discussed together with their latest research progresses. Furthermore, one‐component and multicomponent heterostructured NPs with multifunctional capabilities in OLEDs are overviewed. Following the summarization of the roles of NPs in OLEDs and their latest research progress, a brief conclusion and outlook regarding the future research directions of highly efficient OLEDs by incorporation of NPs are provided. [ABSTRACT FROM AUTHOR]

Organic single crystals are highly promising for applications in optoelectronic devices because of their higher mobility and thermal stability than amorphous thin films. Although white organic single crystals have been fabricated by the double-doped method and applied to realize white organic light‐emitting devices (WOLEDs), the unbalanced carrier transport properties of the unipolar crystals severely limit the device performance. Here, ambipolar white organic single crystals are obtained by using mixed p- and n-type molecules as an ambipolar host for the red and green dopants. The white crystal with balanced carrier transport and balanced blue, green, and red emission intensity was applied to the single-crystal WOLEDs. The highest brightness of 1956 cd m−2 and the current efficiency of 1.31 cd A−1 are achieved, which are the best performance of the single-crystal WOLEDs reported to date. A high color rendering index is obtained, which varies between 82 and 87 with increasing driving current. It is expectable that this strategy would support the practical applications of organic single crystal-based OLEDs. [ABSTRACT FROM AUTHOR]

Organic light‐emitting devices on fabrics (Fa‐OLEDs) are outstanding candidates for high‐quality wearable displays. High flexibility and conformality to clothes deformations are required for Fa‐OLEDs to keep wearing comfort during body movement. However, it is a great challenge to realize an ultrathin planarization layer with ultrasmooth surface simultaneously on the rough surface of fabrics for Fa‐OLEDs fabrication. Here, a template‐stripping process is employed to fabricate both ultrathin and ultrasmooth planarization layers for highly flexible and efficient Fa‐OLEDs. The thickness of the planarization layer is as small as 3 µm while its surface roughness is only 0.6 nm. The planarization process is insensitive to the textures and morphology of fabrics. As a result, the Fa‐OLEDs show excellent electroluminescent performance and flexibility. The maximum current efficiency of 78 cd A−1 is comparable with that of the conventional planar devices. The variation of current efficiency is as small as 8% after 1000 times of bending with 1 mm bending radius, which is the best bending stability of the flexible Fa‐OLEDs reported to date. The Fa‐OLEDs are successfully used as conformal wearable displays by sewing on clothes and keep working well with a series of arm movements. [ABSTRACT FROM AUTHOR]

The demonstration of high efficiency and color tunability has brought organic light-emitting devices (OLEDs) into the lighting and display market. High efficiency is one of the key issues for their commercial applications, for which much effort has been devoted to developing novel materials and device structures. It is well known that around 80% of the generated photons are trapped in OLED structure, so that there is still the greatest scope for significant improvements in its efficiency. This has driven the research towards the integration of micro/nano patterns into device structures that benefit from their abilities in manipulating the generation and propagation of photons. Micro/nano patterns with random or periodic morphologies have demonstrated their effect on the outcoupling of the trapped photons within the device. Moreover, the emitting properties other than the light extraction could be manipulated by introducing the micro/nano patterns. This article reviews the recent progresses in improving the light extraction and manipulating the emission properties of the OLEDs through the introduction of the micro/nano patterns by various fabrication strategies. The light manipulation of the micro/nano patterns in organic photovoltaics is briefly discussed considering its similar working principle and fabrication strategies to that of the OLEDs. [ABSTRACT FROM AUTHOR]

The next generation of optoelectronic devices requires transparent conductive electrodes to be flexible, inexpensive and compatible with large scale manufacturing processes. We report an ultrasmooth, highly conductive and transparent composite electrode on a flexible photopolymer substrate by employing a template stripping method. A random silver nanowire (AgNW) network buried in poly(3,4ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) film constituted the composite electrode. Besides the effectively decreased surface roughness, its sheet resistance and transmittance are comparable to those of conventional PEDOT:PSS electrode. As a result, the efficiency of the OLEDs based on the composite electrode exhibited 25% enhancement compared to the OLEDs with conventional PEDOT:PSS electrode. Moreover, the performance of the flexible OLEDs remains stable after over one hundred bending cycles. [ABSTRACT FROM AUTHOR]

We have demonstrated an indium-tin-oxide free organic light-emitting device (OLED) with improved efficiency by doping poly (3,4-ethylene dioxythiophene):poly (styrene sulfonate) (PEDOT:PSS) with graphene oxide (GO) as a composite anode. In comparison with a pure PEDOT:PSS anode, 55% enhancement in efficiency has been obtained for the OLEDs based on the PEDOT:PSS/GO composite anode at an optimal condition. The PEDOT:PSS/GO composite anode shows a lower hole-injection barrier, which contributes to the improved device efficiency. Moreover, both high transmittance and good surface morphology similar to that of the pure PEDOT:PSS film also contribute to the enhanced efficiency. It is obvious that composite anode will generally be applicable in organic optoelectronic devices which require smooth and transparent anode. [ABSTRACT FROM AUTHOR]

An improved efficiency from an encapsulated flexible top-emitting organic light-emitting device (FTOLED) has been demonstrated by integrating a microstructure onto the polymer encapsulation film. Soft-nanoimprint lithography is employed to integrate the microstructure onto the polymer surface, which enables large area fabrication with high quality, low cost, and repeatable use of the poly(dimethylsiloxane) mold. The light extraction of the FTOLEDs has been improved by integrating the microstructure with two-dimensional tapered micropillars array on the polymer encapsulation film, which can suppress the reflection by enhancing the critical angle of total reflection owing to its gradually changed refractive index. Moreover, the microstructured surface exhibits a hydrophobic property owing to its high contact angle, which results in a self-cleaning ability to protect the FTOLEDs from being polluted by water droplets and dust particles in practical applications. [ABSTRACT FROM AUTHOR]

Highlights: [•] An ITO-free flexible OLED with improved efficiency has been fabricated. [•] Template stripping process has been employed to fabricate the ITO-free OLEDs. [•] The smoothness and conductivity of the PEDOT: PSS anode has been improved. [•] The H2SO4 residues on the PEDOT: PSS anode has been eliminated. [•] The device stability has been improved by eliminating the H2SO4 residues. [ABSTRACT FROM AUTHOR]

Highlights: [•] Viewing-angle independent WTOLEDs have been fabricated. [•] A microcavity with a periodically and gradually changed cavity length has been constructed. [•] The periodic microstructured cavity has been introduced into the WTOLEDs. [•] The viewing-angle independence in both the spectrum and CIE coordinates are obtained. [•] The microstructured WTOLEDs show comparable efficiency to that of the planar TOLEDs. [ABSTRACT FROM AUTHOR]

Abstract: In this work, large-size tetracene- and pentacene-doped 1,4-Bis(4-methylstyryl)-benzene (BSB-Me) crystals were prepared with physical vapor transfer technique. The photoluminescence emission can be adjusted from blue to green and even to red by changing the doping. Their fluorescence features are investigated by both the steady-state fluorescence spectra and time-resolved fluorescence measurements, which indicate highly efficient energy transfer from the host BSB-Me to the acceptor. The PL efficiencies of the tetracene-doped BSB-Me and pentacene-doped BSB-Me crystals are as high as 79% and 47%, the energy transfer efficiency is 49.7% and 73.1%, respectively. Excitation intensity-dependent ultrafast dynamics was further probed, which shows that the kinetics in doped crystals exhibit much less excitation intensity dependence than that of the pure BSB-Me crystals. Our results are relevant to the understanding of ultrafast energy-transfer dynamics in doped crystals and are expected to be of interest for organic light emitting transistors, diodes, and lasers. [Copyright &y& Elsevier]

Fe3O4 has been demonstrated to be an efficient p-dopant in improving the performance of organic light-emitting devices. This paper investigates in detail the role of Fe3O4 in improving the hole injection and the hole transport by the ultraviolet/visible/near-infrared absorption, x-ray, and ultraviolet photoelectron spectroscopy. The results demonstrated that Fe3O4 as a p-dopant has different effectiveness when it is doped into different host materials. The improved properties of the OLEDs with the p-doped N, N'-diphenyl-N,N'-bis (1,1'-biphenyl)-4,4'-diamine layer is mainly due to the enhanced hole injection through the lowering of the hole injection barrier, while the enhanced hole transport plays a more important role for the OLEDs with the p-doped 4,4',4”-tris (3-methylphenylphenylamino) triphenylamine due to their higher ability in the formation of charge transfer complex. [ABSTRACT FROM PUBLISHER]

We propose a plasmonic ultrathin metal grid electrode as a promising light outcoupling strategy in a flexible organic light-emitting device (OLED). The plasmonic ultrathin metal grid electrode consists of an ultrathin Au grid film incorporating with plasmonic subwavelength corrugations, which was fabricated by lithography and nanoimprint technologies, demonstrates excellent optical and electrical properties as the substitute of ITO transparent electrode in flexible OLED. The transmittance of the plasmonic ultrathin Au grid electrode is 88.5% at 550 nm and the sheet resistance is about 36 Ω/sq. The periodic subwavelength corrugations of the plasmonic ultrathin Au grid electrode excite the surface plasmon-polariton (SPP) resonance which is an adverse optical mode with power loss in OLED, and the photons trapped in SPP mode are effectively outcoupled and extracted by the plasmonic corrugations. Compared to the ITO-based device, OLED based on plasmonic ultrathin Au grid electrode realizes a desirable enhancement of 60.3% in current efficiency. In addition, the flexible OLED based on the proposed electrode also exhibits decent mechanical robustness and flexibility with stable electroluminescence performances. Image 1 • A plasmonic ultrathin metal grid film incorporating with corrugations is reported. • The proposed electrode serves as a light extraction strategy in flexible OLED. • A 60.3% enhancement in current efficiency has been achieved. [ABSTRACT FROM AUTHOR]

Instability and large wire-wire contact resistance of silver nanowires (AgNWs) have seriously hindered their practical applications as electrodes in optoelectronic devices. Although various methods have been demonstrated to improve the stability and conductivity of the AgNWs, a simple and low-cost process, especially compatible to the flexible substrates for their applications in flexible devices, is still a challenge. Here, perfluorinated sulfonic acid (PFSA) polymer has been employed as a surface-passivation layer on the AgNWs through a simple surface coating. The PFSA passivation can simultaneously improve the conductivity, thermal stability and mechanical stability of the AgNWs. As a result, the PFSA-passivated AgNWs film maintains an almost constant conductivity under ambient condition after heating for 30 min at 250 °C or 10 days storage at room temperature, and 600 continuous bending cycles at a bending radius of 1 mm. The PFSA-passivated AgNWs have been applied to flexibly organic light emitting devices as their electrodes, and both mechanical stability and long-term operational stability have been improved. Image 1 • Simultaneous improvement of conductivity, stability and flexibility. • Excellent thermal and chemical durability. • Suitable for fabricating flexible OLEDs. [ABSTRACT FROM AUTHOR]

As the demand for display technology in consumer electronics and lighting panels increases, thin, light, high‐quality, and more cost‐effective light‐emitting devices are required. Organic light‐emitting devices (OLEDs), satisfying the criteria exactly, have been considered the most promising next‐generation display and lighting technique. In particular, an OLED based on flexible substrate enables the device to be applied to curved displays, electronic newspapers, wearable displays, and conceptual lighting panels, has been always in the spotlight both in science and industry. Great advances on flexible OLEDs (FOLEDs) have been made over the past three decades. The fundamental elements of FOLEDs including substrates, electrodes, fabrication and encapsulation techniques, as well as the strategies of efficiency improvement are discussed herein. Moreover, emerging electrodes such as graphene, carbon nanotubes, metal nanowire network and their composite, flexible perovskite light emitting devices, and stretchable light emitting devices are also considered. Finally, the future challenges and prospects for these devices are put forward. The fundamental elements of flexible organic light‐emitting devices including substrates, electrodes, fabrication and encapsulation techniques, as well as the strategies of efficiency improvement are discussed. Moreover, emerging electrodes such as graphene, carbon nanotubes, metal nanowire network and their composites, flexible perovskite light emitting devices, and stretchable light emitting devices are also considered. Finally, the challenges and prospects for the future are put forward. [ABSTRACT FROM AUTHOR]

A single crystal-based organic light-emitting device (OLED) with intrinsically polarized and color-tunable electroluminescence (EL) has been demonstrated without any subsequent treatment. The polarization ratio of 5:1 for the transversal-electric (TE) and transversal-magnetic (TM) polarization at the emission peak of 575 nm, and 4.7:1 for the TM to TE polarization at the emission peak of 635 nm, respectively, have been obtained. The emitting color is tunable between yellow, yellow-green and orange by changing the polarization angle. The polarized EL and the polarization-induced color tunability can be attributed to the anisotropic microcavity formed by the BP3T crystal with uniaxial alignment of the molecules. [ABSTRACT FROM AUTHOR]