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Transparent organic light‐emitting diodes (TOLEDs) are exciting next‐generation electronic devices that can be embedded and integrated into walls, windows, head‐up panels in commercial and domestic buildings, cars, planes, and other segments of the consumer goods sector. TOLEDs are also fundamental components for the realization of the stacked OLEDs for various industrial and research applications. Furthermore, futuristic smart wearables for clothing as well as medical purposes will also benefit remarkably from the development of TOLEDs. However, the efficiency of TOLEDs is significantly lower than that of their opaque counterparts. The achievement of high‐performance TOLEDs is directly dependent on the properties of the chosen electrode materials as well as the used light extraction techniques. In this review, the reported perspectives of TOLEDs are discussed along with their types, design, and architectures, applied TOLED materials and properties, and the application fields of these transparent devices. The performance of the electrode materials and the commonly used light extraction methods are reviewed in detail as well. The main purpose is to shed light on some of the effective TOLED approaches and the underlying reasons for the frequently encountered issues in these diodes. Auspicious novel fabrication techniques as well as device structures are also highlighted. [ABSTRACT FROM AUTHOR]

Reported herein are solution-processed polymer anode electrodes for blue phosphorescent organic light-emitting diodes (PhOLEDs). The highly conductive anodes were made from 10-wt%-methyl-red-(MR)-doped poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) (PH1000) films. The red-colored and uniform polymer films demonstrated electrical conductivity values that significantly increased from 0.25 to 50 S·cm−1 after doping. The more than 200-fold enhancement in conductivity indicates that the doped films have a lower sheet resistance and better hole injection and transport properties than the pristine films. The resultant PhOLEDs based on the doped polymer anodes exhibited stable, broad, and intense blue emission at 468 nm with a 2616 cd·m−2 maximum luminance and a 4 V turn-on voltage. The obtained study results confirmed the effectiveness of the MR dye as a dopant for the significant enhancement of the conductivity and effective hole injection of PEDOT:PSS. Efficient future flexible optoelectronic applications can be built using this highly conductive polymer electrode obtained via a simple, solution-processed, and cost-effective doping approach. [ABSTRACT FROM AUTHOR]

We demonstrate high-performance down-conversion microlens array (DC-MLA) films for white organic light-emitting diodes (OLEDs). The DC-MLA films are readily fabricated by an imprinting method based on breath figure patterns, which are directly formed on the polymer substrate with a novel concept. The DC-MLA films result in high-quality white light as well as enhanced light outcoupling efficiency for white OLEDs. The external quantum efficiency and power efficiency of OLEDs with DC-MLA films are increased by a factor of 1.35 and 1.86, respectively, compared to OLEDs without outcoupling films. Moreover, the white OLEDs with DC-MLA films achieve a high color-rendering index of 84.3. It is anticipated that the novel DC-MLA films fabricated by the simple imprinting process with breath figure patterns can contribute to the development of efficient white OLEDs. [ABSTRACT FROM AUTHOR]

Highly conductive poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) films as transparent electrodes for organic light-emitting diodes (OLEDs) are doped with a new solvent 1,3-dimethyl-2-imidazolidinone (DMI) and are optimized using solvent post-treatment. The DMI doped PEDOT:PSS films show significantly enhanced conductivities up to 812.1 S cm−1. The sheet resistance of the PEDOT:PSS films doped with DMI is further reduced by various solvent post-treatment. The effect of solvent post-treatment on DMI doped PEDOT:PSS films is investigated and is shown to reduce insulating PSS in the conductive films. The solvent posttreated PEDOT:PSS films are successfully employed as transparent electrodes in white OLEDs. It is shown that the efficiency of OLEDs with the optimized DMI doped PEDOT:PSS films is higher than that of reference OLEDs doped with a conventional solvent (ethylene glycol). The results present that the optimized PEDOT:PSS films with the new solvent of DMI can be a promising transparent electrode for low-cost, efficient ITO-free white OLEDs. [ABSTRACT FROM AUTHOR]

Conventional planar organic light-emitting diodes (OLEDs) suffer from poor light extraction due to the total internal reflection at the waveguided interfaces. Therefore, the development of efficient light extraction structures is of great necessity and significance to realize practical applications in large area and cost-effective light sources. In this paper, a high-performance internal light outcoupling system for white OLEDs with spontaneously formed metal oxide nanostructures is developed. The fabrication process of the outcoupling system is simple and can be scaled to large area manufacturing. The enhancement of external quantum efficiency in white OLEDs comprising the outcoupling system reaches a factor of 1.7, and it is further increased to 2.9 when a hemispherical lens is employed. Together with the improvement of light extraction, excellent color stability over broad viewing angles is achieved. [ABSTRACT FROM AUTHOR]

Efficient transparent organic light-emitting diodes (OLEDs) with improved stability based on conductive, transparent poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) electrodes are reported. Based on optical simulations, the device structures are carefully optimized by tuning the thickness of doped transport layers and electrodes. As a result, the performance of PEDOT:PSS-based OLEDs reaches that of indium tin oxide (ITO)-based reference devices. The efficiency and the long-term stability of PEDOT:PSS-based OLEDs are significantly improved. The structure engineering demonstrated in this study greatly enhances the overall performances of ITO-free transparent OLEDs in terms of efficiency, lifetime, and transmittance. These results indicate that PEDOT:PSS-based OLEDs have a promising future for practical applications in low-cost and flexible device manufacturing. [ABSTRACT FROM AUTHOR]

High performance indium tin oxide (ITO)-free small molecule organic solar cells and organic light-emitting diodes (OLEDs) are demonstrated using optimized ZnO electrodes with alternative non-metallic co-dopants. The co-doping of hydrogen and fluorine reduces the metal content of ZnO thin films, resulting in a low absorption coefficient, a high transmittance, and a low refractive index as well as the high conductivity, which are needed for the application in organic solar cells and OLEDs. While the established metal-doped ZnO films have good electrical and optical properties, their application in organic devices is not as efficient as other alternative electrode approaches. The optimized ZnO electrodes presented here are employed in organic solar cells as well as OLEDs and allow not only the replacement of ITO, but also significantly improve the efficiency compared to lab-standard ITO. The enhanced performance is attributed to outstanding optical properties and spontaneously nanostructured surfaces of the ZnO films with non-metallic co-dopants and their straightforward integration with molecular doping technology, which avoids several common drawbacks of ZnO electrodes. The observations show that optimized ZnO films with non-metallic co-dopants are a promising and competitive electrode for low-cost and high performance organic solar cells and OLEDs. [ABSTRACT FROM AUTHOR]

We report on highly transparent conductive hybrid thin-films based on copper (Cu)-mesh structures combined with conductive polymer films. The hybrid films show outstanding optical and electrical properties (transmittance of 81.7% at a wavelength of 550 nm, sheet resistance of 71.3 Ω/sq). The effective current collecting property of metal mesh structures as well as the excellent current spreading property of the conducting polymer enables the high performance of the hybrid transparent electrodes. Organic light-emitting diodes (OLEDs) employing the hybrid transparent electrodes result in 2.0-fold enhanced current and power efficiencies, compared to the control polymer electrode-based OLED without current collecting metal mesh structures. The results present that Cu-mesh structures combined with conductive polymer films show great promise for applications in low-cost, flexible indium tin oxide-free OLEDs. Image 1 • Hybrid transparent conductive films with Cu-mesh/polymer are presented. • The hybrid electrodes show the greatly reduced sheet resistance of polymer films. • The efficiency of OLEDs with hybrid electrodes is greatly improved by a factor of 2.0. [ABSTRACT FROM AUTHOR]

We demonstrate high performance internal light outcoupling structures using nanoparicle-embedded hole transport layers (NE-HTLs) for solution-processed organic light-emitting diodes (OLEDs). The NE-HTLs show smoothly formed corrugated surfaces. The OLEDs with NE-HTLs show enhanced power efficiencies by a factor of 1.44 for polystyrene (PS) nanoparticles and 1.78 for SiO 2 nanoparticles, respectively. These improvements are mainly attributed to the reduced total internal reflection at the interfaces of organic layers and transparent electrodes in devices by introducing NE-HTLs. Because the internal light outcoupling structures are prepared on top of the transparent electrode, a damage of organic layers and deterioration of the electrical and optical properties of transparent electrodes are not induced. In addition, the OLEDs with NE-HTLs show the angle-independent light outcoupling enhancement. It is expected that the NE-HTLs fabricated by the simple solution process can contribute to the development of efficient internal outcoupling structures for OLEDs. [ABSTRACT FROM AUTHOR]

Highly conductive poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) films are prepared by introducing a new solvent 2-ethoxyethanol and are optimized by acid-free solvent post treatment. The behavior of samples are investigated with various coating conditions. The change of electrical performance for 2-ethoxyethanol added PEDOT:PSS films with various post treatment methods is studied. Upon post treatment, the sheet resistance greatly decreases attributed to a structural change with removal of insulating PSS in the film. Based on these conductive films, we demonstrate efficient ITO-free green phosphorescent organic light-emitting diodes (OLEDs). The efficiency of OLEDs with post-treated PEDOT:PSS electrodes is greater than that of OLEDs with untreated PEDOT:PSS electrodes. The results illustrate a promising future for flexible, low-cost, ITO-free OLEDs employing PEDOT:PSS electrodes optimized by 2-ethoxyethaol with acid-free solvent post treatment. [ABSTRACT FROM AUTHOR]

We demonstrate highly conductive poly (3,4-ethylenedioxythiophene):poly (styrenesulfonate) (PEDOT:PSS) films introduced with a newly investigated solvent 2-ethoxyethanol. The films are optimized by simple solvent post treatment and show enhanced conductivities and reduced sheet resistances. Solvent post treatment for 2-ethoxyethanol added PEDOT:PSS films reduces insulating PSS and forms conductive PEDOT networks in conductive films, resulting in improved electrical properties. ITO-free white OLEDs are fabricated with post-treated PEDOT:PSS electrodes and show almost equal performance to ITO-based OLEDs. Our work demonstrate that the conductive PEDOT:PSS electrode optimized by 2-ethoxyethanol and post treatment promises its potential as alternative transparent electrode in flexible, low-cost, high-performance ITO-free OLEDs. [ABSTRACT FROM AUTHOR]

We have developed down-conversion outcoupling films to enhance the light outcoupling efficiency in white organic light-emitting diodes (OLEDs). The down-conversion outcoupling films consist of outcoupling structures and color conversion materials, which are prepared by a simple solution-based micro-imprint process and are adopted into OLEDs. The down-conversion films successfully realize white light by converting blue rays from blue phosphorescent OLED. The OLEDs based on the down-conversion films with outcoupling structures show a great improvement of power efficiency by a factor of 1.32 compared to the reference OLED based on down-conversion films without outcoupling structures. Furthermore, the influence of a concentration of color conversion materials on color rendering index of OLEDs is investigated. The results strongly indicate that readily fabricated down-conversion light outcoupling films by a simple micro-imprint process are highly promising for enhanced light extraction performance and high color rendering index of white OLEDs. [ABSTRACT FROM AUTHOR]

We report outcoupling efficiency enhanced organic light-emitting diodes (OLEDs) using microlens array films prepared by a simple solution-processed imprinting technique with breath figure patterns. The films with breath figure micro-patterns (BFMP) effectively extract confined light in the glass substrate, which leads to the greatly improved outcoupling performance of OLEDs. We observe the enhancement of external quantum efficiency of the OLEDs employing the BFMP outcoupling film is about 1.51, corresponding to the enhancement of the power efficiency by a factor of 1.65. Moreover, the device with the outcoupling film shows the limited angle-dependency of emission spectrum over viewing angles. The BFMP films prepared with a low-cost, simple, and solution-processable fabrication process can pave the way to achieving high-performance OLEDs. • A facile approach to enhance the efficiency in OLEDs using breath figure-patterned outcoupling films is demonstrated. • The outcoupling films greatly suppress the angle-dependent spectral distortion of OLEDs. • The outcoupling films show a large enhancement of the power efficiency of OLEDs by a factor of 1.65. [ABSTRACT FROM AUTHOR]

A high-performance external light outcoupling film for organic light-emitting diodes (OLEDs) is developed using a novel phase-separated polymer (PSP) which is spontaneously formed from a homogeneous solution of poly(amic acid) and polyimide in dimethylacetamide. The phase separation during the spin-coating process leads to complex morphologies of film with random microdent and nanobump patterns by a self-assembly of polymers. The PSP film is utilized on the backside of a glass substrate in green OLEDs as a light outcoupling film, leading to a considerable enhancement of light outcoupling efficiency. Both the current efficiency and power efficiency of OLEDs with the PSP film are improved by a factor of 1.45 and 1.53, respectively, in comparison with those of the reference device. The results demonstrate that the PSP film could serve as a promising outcoupling film for OLEDs. [ABSTRACT FROM AUTHOR]