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Through‐space charge transfer (TSCT) polymers are an attractive class of luminescent polymers with spatial donor/acceptor architecture and thermally activated delayed fluorescence effect, different from conventional luminescent polymers with conjugated donor‐acceptor structure and through‐bond charge transfer emission. Their emission comes from the intramolecular charge transfer by through‐space pathway because the donor and acceptor segments are spatially proximate to each other in each repeating unit but are physically separated by nonconjugated polymer backbone. In this review, recent advances in TSCT polymers with linear, bottlebrush, and dendritic architectures are presented, with the focus on their molecular design, photophysical behavior, and device performance. We hope that this review shall provide a useful insight of new luminescent polymers with TSCT effect for use in solution‐processed organic light‐emitting diodes. Through‐space charge transfer (TSCT) polymers, with spatial donor/acceptor architecture and thermally activated delayed fluorescence effect, represent an attractive approach toward efficient solution‐processed organic light‐emitting diodes. In this review, recent advances in TSCT polymers with linear, bottlebrush, and dendritic architectures are presented, with the focus on their molecular design, photo‐physical behavior, and device performance.

Neonatal jaundice is a very common disease in newborns and can lead to brain damage or death in severe cases. Phototherapy with light‐emitting diode (LED) arrays is widely used as the easiest and fastest way to relieve jaundice in newborns, but it has distinct disadvantages such as loss of water in the patient, damage to the retina, and separation from parents. In this paper, a novel light source‐based phototherapy for neonatal jaundice is proposed using a textile‐based wearable organic light‐emitting diode (OLED) platform that can move flexibly and conform to the curvature of the human body. The soft and flexible textile‐based blue OLED platform is designed to have a peak wavelength of 470 nm, suitable for jaundice treatment, and shows performance (>20 µW cm−2 nm−1) suitable for intensive jaundice treatment even at low voltage (<4.0 V). The textile‐based OLEDs fabricated in this study exhibit an operating reliability of over 100 h and low‐temperature operation (<35 °C). The results of an in vitro jaundice treatment test using a large‐area blue OLED confirm that the bilirubin level decreases to 12 mg dL−1 with 3 h of OLED irradiation. Kyung Cheol Choi et al. develops a novel light source‐based photomedical approach for neonatal jaundice treatment, using a textile‐based wearable organic light‐emitting diode (OLED) platform that can move flexibly and conform to the curvature of the human body. The effectiveness of the blue OLED jaundice treatment is verified by in vitro test, and effective and uniform treatment performance is confirmed. 

Printing techniques for the fabrication of diodes have received increasing attention over the last decade due to their great potential as alternatives for high‐throughput and cost‐effective manufacturing approaches compatible with both flexible and rigid substrates. Here, the progress achieved and the challenges faced in the fabrication of printed diodes are discussed and highlighted, with a focus on the materials of significance (silicon, metal oxides, nanomaterials, and organics), the techniques utilized for ink deposition (gravure printing, screen printing, inkjet printing, aerosol jet printing, etc.), and the process through which the printed layers of diode are sintered after printing. Special attention is also given to the device applications within which the printed diodes have been successfully incorporated, particularly in the fields of rectification, light emission, energy harvesting, and displays. Considering the unmatched production scalability of printed diodes and their intrinsic suitability for flexible and wearable applications, significant improvement in performance and intensive research in development and applications of the printed diodes will continuously progress in the future. Recent progress regarding the material processing, device fabrication, and practical applications of printed diodes is reviewed, with an emphasis on the aspects of solution‐processing and material performance. The challenges and prospects of printed diodes are also discussed, providing fundamental insights and offering useful guidelines for the future design of high‐performance, cost‐effective diodes for industrial and consumer applications.

With the naturally separated frontier molecular orbitals, exciplexes are capable of thermally activated delayed fluorescence emitters for organic light‐emitting diodes (OLEDs). And, the current key issue for exciplex emitters is improving their exciton utilization. In this work, a strategy of building exciplex emitters with three components is proposed to realize multiple reverse intersystem crossing (RISC) channels, improving their exciton utilization by enhancing upconversion of nonradiative triplet excitons. Accordingly, a tricomponent exciplex DBT‐SADF:PO‐T2T:CDBP is constructed with three RISC channels respectively on DBT‐SADF, DBT‐SADF:PO‐T2T, and CDBP:PO‐T2T. Furthermore, its photoluminescence quantum yield and rate constant of the RISC process are successfully improved. In the OLED, DBT‐SADF:PO‐T2T:CDBP exhibits a remarkably high maximum external quantum efficiency (EQE) of 20.5%, which is the first report with an EQE over 20% for the OLEDs based on exciplex emitters to the best of our knowledge. This work not only demonstrates that introducing multiple RISC channels can effectively improve the exciton utilization of exciplex emitters, but also proves the superiority of the tricomponent exciplex strategy for further development of exciplex emitters. Schematic energy transfer illustrates that introducing multiple reverse intersystem crossing (RISC) channels can effectively improve the exciton utilization of exciplex emitters by enhancing upconversion of nonradiative triplet excitons. According to this strategy, a tricomponent exciplex DBT‐SADF:PO‐T2T:CDBP with three RISC channels is developed, and a remarkably high maximum external quantum efficiency of 20.5% is successfully realized in the organic light‐emitting diodes.

The enhancement of hole injection layers is strongly important issue for obtaining high-efficient and low-driving-voltage Organic Light-Emitting Devices (OLEDs). In this paper, we presented a comprehensive electroluminescence (EL) study of phosphazene-based ionic liquids (PzILs) used as a hole transport layer in solution-processed OLEDs. Charge transfer properties of PzILs were investigated by doping in poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) at different ratios (0.1, 0.2, 0.5, 1.0, 2.0). Previously synthesized four types of PzILs (namely PzIL1, PzIL2, PzIL3, and PzIL4) were prepared in de-ionized water with 10 mg/ml concentration, mixed with PEDOT:PSS and examined for their charge transport characteristics on OLED device performance due to their ionic nature. The device with PzIL1 exhibited the best performance with luminance 4185 cd/m 2 compared to other devices with and without PzILs. Further, Density Functional Theory (DFT) calculations and admittance spectroscopic analysis of OLEDs based on four types of PzILs were studied profoundly. Admittance spectroscopy has been used for revealing the carrier transport properties, mobility and the equivalent circuit modeling of the devices. Four types of PzILs OLEDs represented typical p-type transporting characteristics with moderate mobility up to 1.93 cm 2 /V.s.

Light has been sought and explored by human since ancient times. As the most important form of light, fluorescence is significant to applications in bioimaging and optoelectronic devices. However, fluorescence quenching problem constitutes a serious bottleneck in materials creation. Inspired from the core–shell structure in nature, we report an effective strategy to overcome this long‐standing problem by utilizing a molecular core–shell structure. With an emissive core and multifunctional shell fragments, these compounds show aggregation‐induced delayed fluorescence (AIDF) properties by restricting singlet oxygen (1O2) generation and suppressing the triplet–triplet annihilation (TTA). Protected by the functional shell, the aggregation‐induced emission luminogens (AIEgens) exhibit strong emission with high photoluminescent quantum yield and exciton utilization. Furthermore, because the shell materials can form exciplex with electron‐transport materials, the fully solution‐processed organic light‐emitting diodes (OLEDs) based on these core–shell materials show low turn‐on voltages, excellent device performance with current efficiency of 61.4 cd A–1 and power efficiency of 42.8 lm W–1, which is a record‐breaking efficiency based on all‐solution processed organic multilayer systems among the AIE‐OLEDs so far. This simple visualization strategy based on molecular core–shell structure provides a promising platform for AIEgens used in the fully wet‐processed optoelectronic field. Core–shell molecules are firstly designed and proposed to achieve aggregation‐induced delayed fluorescence (AIDF) by stabilizing and protecting the triplet exciton, then the fully solution‐processed OLEDs based on the core–shell structural emitters demonstrate superior device performance with maximum luminance of 30,000 cd m–2, excellent EL efficiencies of up to 21.8%, 61.4 cd A–1 and 42.8 lm W–1.

Short‐circuit defects caused by microscale dust particles in organic light‐emitting diodes (OLEDs) cause a decrease in production yield and hinder cost reduction. An organic layer coating by solution process is used to prevent short‐circuit defects of particles on a substrate. In this study, the coverage properties of a coated organic layer on size‐controlled particles are revealed. The surface of the substrate with size‐controlled SiO2 particles with a diameter of 0.2–5 µm is quantitatively contaminated, and the particle coverage properties of the solution‐processed hole injection layer are investigated. From the results of the leakage current measurement and cross‐sectional observation by a transmission electron microscope, it is observed that devices with 50 nm‐spin‐coated poly (3,4‐ethylenedioxythiophene): poly(styrene sulfonate) can cover SiO2 particles up to 1 µm in diameter without any increase in leakage current. It is revealed that larger‐sized particles cause electric defects, albeit with a low probability, owing to the larger space under the particles. To fabricate OLEDs with a high yield, the shape of the coverage at the bottom of the particle is important in preventing electric defects. The results of this study are useful not only for OLEDs but also for printed and coated devices. To prevent short‐circuit defects caused by dust particles on substrates, the particle coverage properties of the spin‐coated hole injection layer are reported. Quantitatively contaminating the substrate surface with size‐controlled SiO2 particles, poly(3,4‐ethylenedioxy‐thiophene):poly(styrene sulfonate) is spin‐coated, resulting in coverage up to SiO2 particles 10–20 times larger than the film thickness.

Despite stringent power consumption requirements in many applications, over years organic light‐emitting diode (OLED) displays still suffer unsatisfactory energy efficiency due to poor light extraction. Approaches have been reported for OLED light out‐coupling, but they in general are not applicable for OLED displays due to difficulties in display image quality and fabrication complexity and compatibility. Thus to date, an effective and feasible light extraction technique that can boost efficiencies and yet keep image quality is still lacking and remains a great challenge. Here, a highly effective and scalable extraction‐enhancing OLED display pixel structure is proposed based on embedding the OLED inside a three‐dimensional reflective concave structure covered with a patterned high‐index filler. It can couple as much internal emission as possible into the filler region and then redirect otherwise confined light for out‐coupling. Comprehensive multi‐scale optical simulation validates that ultimately high light extraction efficiency approaching ≈80% and excellent viewing characteristics are simultaneously achievable with optimized structures using highly transparent top electrodes. This scheme is scalable and wavelength insensitive, and generally applicable to all red, green, and blue pixels in high‐resolution full‐color displays. Results of this work are believed to shed light on the development of future generations of advanced OLED displays. A highly effective and scalable light‐extraction pixel structure, based on embedding an organic light‐emitting diode (OLED) inside a 3D reflective concave structure and patterned high‐index filler coverage, is reported for OLED displays. Comprehensive multiscale optical simulation indicates that ultimately high light extraction efficiency approaching 80% and excellent viewing characteristics are simultaneously achievable with optimized structures using highly transparent top electrodes.

We numerically investigate the effect of the dipole orientation on the light emission characteristics of a three-dimensional top-emitting organic light-emitting diode (TOLED) with square pixel boundary, based on the finite element method. The spatial profiles of the optical power flows and the output angular emission characteristics are calculated in various horizontal positions of a single dipole with the x-, y-and z-directed dipole orientations. The total angular emission characteristics of the TOLED are obtained by summing the individual angular emission characteristics of 100 dipole emitters, which are assumed to be uniformly distributed within the square pixel boundary. The angular emission pattern of the y-directed dipole emitters exhibits an approximately 10% higher intensity with a narrower linewidth than that of the x-directed dipole emitters. This difference in the angular emission patterns of the x- and y-directed dipole orientations can be attributed to the dipole orientation dependent internal radiation pattern, which has different spectral power densities as a function of the internal emission angle and light polarization. In addition, the average angular emission characteristics of the randomly oriented dipole emitter are calculated by averaging over those of the x- and y- directed dipole emitters.

Nowadays, the display industry is endeavoring to develop technology to provide large-area organic light-emitting diode (OLED) display panels with 8K or higher resolution. Although the selective deposition of organic molecules through shadow masks has proven to be the method of choice for mobile panels, it may not be so when independently defined high-resolution pixels are to be manufactured on a large substrate. This technical challenge motivated us to adopt the well-established photolithographic protocol to the OLED pixel patterning. In this study, we demonstrate the two-color OLED pixels integrated on a single substrate using a negative-tone highly fluorinated photoresist (PR) and fluorous solvents. Preliminary experiments were performed to examine the probable damaging effects of the developing and stripping processes upon a hole-transporting layer (HTL). No significant deterioration in the efficiency of the develop-processed device was observed. Efficiency of the device after lift-off was up to 72% relative to that of the reference device with no significant change in operating voltage. The procedure was repeated to successfully obtain two-color pixel arrays. Furthermore, the patterning of 15 μm green pixels was accomplished. It is expected that photolithography can provide a useful tool for the production of high-resolution large OLED displays in the near future.