Search Results (637)

Organic optoelectronic devices receive appreciable attention due to their low cost, ecology, mechanical flexibility, band-gap engineering, brightness, and solution process ability over a broad area. In this study, we designed and studied organic light-emitting diodes (OLEDs) consisting of an assembly of natural dyes, extracted from noble fir leaves (evergreen) and blue hydrangea flowers mixed with poly-methyl methacrylate (PMMA) as light emitters. We experimentally demonstrate the effective conversion of blue light emitted by an inorganic laser/photodiode into longer-wavelength red and green tunable photoluminescence due to the excitation of natural dye–PMMA nanostructures. UV-visible absorption and photoluminescence spectroscopy, ellipsometry, and Fourier transform infrared methods, together with optical microscopy, were performed for confirming and characterizing the properties of light-emitting diodes based on natural dyes. We highlighted the optical and physical properties of two different natural dyes and demonstrated how such characteristics can be exploited to make efficient LED devices. A strong pure red emission with a narrow full-width at half maximum (FWHM) of 23 nm in the noble fir dye–PMMA layer and a green emission with a FWHM of 45 nm in blue hydrangea dye–PMMA layer were observed. It was revealed that adding monolayer MoS₂ to the nanostructures can significantly enhance the photoluminescence of the natural dye due to a strong correlation between the emission bands of the inorganic–organic emitters and back mirror reflection of the excitation blue light from the monolayer. Based on the investigation of two natural dyes, we demonstrated viable pathways for scalable manufacturing of efficient hybrid OLEDs consisting of assembly of natural-dye polymers through low-cost, purely ecological, and convenient processes. Full article

Organic light-emitting diodes (OLEDs) have attracted remarkable interest in display and lighting. To effectively address triplet exciton harvesting and enhance external quantum efficiency (EQE), delayed fluorescence AIEgens have gained significant prominence. The primary luminescence mechanism involves the efficient harvesting of triplet excitons via reverse intersystem crossing (RISC) channels, categorized into three types: thermally activated delayed fluorescence (TADF), hybridized local and charge transfer (HLCT), and triplet–triplet annihilation (TTA). In this review, we summarize the recent development of doped and non-doped delayed fluorescent AIEgens-based OLEDs. This review mainly discusses the molecular design strategies and photophysical properties of delayed fluorescent AIEgens and the electroluminescent properties of OLEDs as emitting layers. Finally, the challenges and prospects of delayed fluorescent AIEgens for the fabrication of OLEDs are also briefly discussed. Full article

Organic light-emitting diodes (OLEDs) have emerged as a leading high-resolution display and lighting technology, as well as for photo-therapeutic applications, due to their light weight, flexibility, and excellent color rendering. However, achieving long-term thermal stability and high energy efficiency remains a principal issue for their widespread adoption. Strong thermal robustness in OLED emitter materials is a critical parameter for achieving long device lifetimes, stable film morphology, reliable high-temperature processing, and sustained interface integrity in high-performance hosts. Bipolar emitters RB14 (N-(9-ethylcarbazole-3-yl)-4-(diphenylamino)phenyl-9H-carbazole-9-yl-1,8-naphthalimide), RB18 (N-phenyl-4-(diphenylamino)phenyl-9H-carbazole-9-yl-1,8-naphthalimide), and RB22 (N-phenyl-3-(2-methoxypyridin-3-yl)-9H-carbazole-9-yl-1,8-naphthalimide) were newly synthesized. RB18 is a yellow bipolar OLED emitter that has a glass transition temperature (T_g) of 162 °C and thermal durability (T_d) of 431 °C, which is the highest reported value for naphthalimide-based bipolar emitter derivatives for yellow OLEDs. Meanwhile, RB14 and RB22 are green OLED emitters that have glass transition temperatures (T_g) of 133 °C and 167 °C, and thermal durabilities (T_d) of 336 °C and 400 °C, respectively. We have fabricated OLED devices using these bipolar emitters dispersed in CBP host matrix, and we have found that the maximum EQEs (%) for RB14, RB18, and RB22 emitter-based devices are 7.93%, 3.40%, and 4.02%, respectively. For confirmation of thermal stability, we also used UV-visible spectroscopy measurements at variable temperatures on annealed spin-coated glass films of these emitter materials and found that RB22 is the most thermally stable emitter among these materials. Full article

Organic light-emitting diodes (OLEDs) have the advantages of high efficiency and high color purity, which gives them great potential and application prospects in the field of display technology, and thus they have been of wide interest for scholars and industry. Due to their nature, when using the first generation of fluorescent materials, only 25% of the excitons are used, while the rest are wasted, meaning the device efficiency does not exceed 25%. The second generation of phosphorescent materials solves this problem by utilizing 25% singlet excitons while utilizing 75% triplet excitons, achieving 100% internal quantum efficiency. Therefore, a third generation of materials, namely Thermally Activated Delayed Fluorescence (TADF) materials, has been developed, and these are able to use the small singlet–triplet energy gap to allow excitons on the triplet state to upconvert back to the single state, which improves the utilization of triplet excitons. These TADF materials can also reach 100% maximum internal quantum efficiency, but they have many problems, such as low color purity and serious efficiency roll-off. Therefore, researchers have designed hyperfluorescent materials, which possess high efficiency, high color purity, and a long lifetime, showing tremendous potential and application prospects in the field of display technology. This report takes hyperfluorescent OLEDs as the entry point and the molecular design and luminescence mechanism of hyperfluorescent materials are reviewed, considering blue, green, red, and white light. Full article

White organic light-emitting diodes (OLEDs) offer a promising solution for next-generation lighting technologies and their ability to emit white light through various mechanisms make them an attractive option for illumination and display applications. Here, we design and prepare a series of N,N-difluorenevinylaniline-based small molecules and polymer, and realize white OLEDs based on these luminescent materials with combined blue monomer emission and orange electromer emission upon electronic excitation in the solution-processed devices. Impressively, the single-component nonconjugated polymer exhibits the best device performance, because the nonconjugated structure favors good solubility of the polymers, while the conjugated starburst unit functions as highly luminescent fluorophore in both single molecular and aggregated structures for the blue and orange emissions, respectively. Specifically, the non-doped solution-processed OLEDs achieve warm white electroluminescence with a maximum luminance of 1806 cd/m² and a maximum external quantum efficiency of 2.63%. And, the OLEDs based on the monomer also exhibit white electroluminescence with Commission Internationale de L’Eclairage coordinates of (0.30, 0.32). These results highlight a promising strategy for the material design and preparation of single-component nonconjugated polymers with rich emissive behaviors in solid states towards efficient and solution-processable white OLEDs. Full article

Host engineering is one of the most efficient approaches to maximizing the electroluminescent performance of organic light-emitting devices. Herein, two carbazole-based N,N′-Dicarbazolyl-4,4′-biphenyl (CBP) derivatives, (9-(4′-(9H-carbazol-9-yl)-[1,1′-biphenyl]-4-yl)-3-(3-(1-phenyl-1H-benzo[d]imidazol-2-yl)phenyl)-9H-carbazole (CBPmBI), and (9-(4′-(9H-carbazol-9-yl)-[1,1′-biphenyl]-4-yl)-9H-carbazol-3-yl)diphenylphosphine oxide (CBPPO), were designed as bipolar hosts for blue phosphorescent devices. By introducing the electron-withdrawing groups to the backbone of CBP, the bipolar hosts exhibited high triplet energy, enhanced thermal stability, and balanced charge transport. The device constructed with the blue guest emitter bis[2-(4,6-difluorophenyl) pyridinato-C2,N]iridium (III) (FIrpic) showed the excellent electroluminescence performance. For instance, the CBPPO-based devices achieved a maximum current efficiency of 28.0 cd/A, a power efficiency of 25.8 lm/W, and an external quantum efficiency of 14.4%. Notably, the external quantum efficiency retained at14.1% under the brightness of 5000 cd/m², featuring the negligible efficiency roll-off. Full article

Tandem white organic light-emitting diodes (OLEDs), formed by stacking red, green, and blue organic electroluminescent units, offer a promising route toward high-resolution microdisplays. However, their performance is constrained by the intrinsically short lifetime of blue OLED sub-units. Replacing the unstable blue OLED with a long-lived GaN-based LED could address this limitation, but practical hybridization remains difficult because of incompatible fabrication routes and significant current imbalance between the inorganic and organic units. Here, we demonstrate the first hybrid GaN–OLED tandem white LEDs enabled by an interface-engineered charge-generation unit (CGU). By introducing an ITO/HAT-CN/LiNH₂-doped Bphen CGU, we simultaneously enhance the work function, strengthen the built-in electric field, and smooth the interfacial morphology. These synergistic effects promote efficient charge generation, yielding near-ideal voltage summation and well-balanced electron–hole injection. As a result, the hybrid tandem device shows a nearly twofold increase in current efficiency (from 28.1 to 58.6 cd A^–1) and significantly reduced spectral shift under varying current densities. We further demonstrate the generality of this approach by integrating the GaN emission with yellow OLEDs to produce stable blue–yellow hybrid white emission. This work establishes an applicable strategy for integrating GaN-LEDs and OLEDs, opening a pathway toward efficient, stable, and compact white light engines for next-generation microdisplay technologies. Full article

Thermally activated delayed fluorescence (TADF) often achieves high device efficiencies in organic light-emitting diodes. Here we develop TADF dyes, 1-H and 1-Me, based on an N,N-diphenylaminophenyl–phenylene–quinoxaline donor–π–acceptor system, which contains an unsubstituted 1,4-phenylene and a 2,5-dimethyl-1,4-phenylene π-spacer, respectively. In UV–vis absorption spectra in toluene at room temperature, 1-H showed a relatively intense shoulder band at 400 nm, whereas 1-Me had a weak, blue-shifted shoulder at 386 nm, indicating 1-Me adopts a more twisted π-conjugation system. On the other hand, the photoluminescence (PL) wavelength of 1-Me (λ_PL; 558 nm) under the same conditions was slightly red-shifted in comparison with that of 1-H (λ_PL; 552 nm), due to larger structural relaxation of 1-Me. From PL lifetime measurements, both the dyes showed TADF in 10 wt%-doped poly(methyl methacrylate) film, and their PL quantum yields were moderate (Φ_PL; ca. 0.5 at 300 K). As for the photokinetics, 1-Me exhibited larger rate constants for intersystem crossing and reverse intersystem crossing than 1-H due to the small excited-state singlet–triplet energy gap (ΔE_ST) of 1-Me. Furthermore, theoretical calculations indicated the triplet state of 1-Me is destabilized by localization of the spin density, resulting in the reduced ΔE_ST to facilitate TADF. Full article

Quantum dots (QDs) have tremendous potential for next-generation displays due to their high color purity, photoluminescence efficiency, and power efficiency. In this work, we present a simple and cost-effective method for fabricating flexible single- and multiple-layer films, and they can be detached and attached to the outside of OLEDs as a light-scattering and color-conversion layer. Light extraction efficiency is enhanced by forming low-density structures by using the reactive ion etching (RIE) process. As a result, the QD/PDMS composite film allowed for color conversion and achieved an excellent light extraction efficiency of up to 9.2%. Furthermore, the QD/PDMS composite film and greenish-blue OLED produced white light (CIEx,y = 0.28, 0.41), demonstrating the potential for application in broad areas, from flexible displays to lighting. The method provides a simple and cost-effective alternative to conventional processes. Full article

The non-linear optical and antitumoral properties of cis-Ir(N,C-ppy)₂(O,O-THC) have previously been established (where ppy and THC are the deprotonated forms of 2-phenylpyridine and tetrahydrocurcumin, respectively). In the present study, this complex is investigated as a green phosphorescent emitter for an OLED fabricated by solution processing. The device efficiency is similar to that of an analogue employing the archetypal complex cis-Ir(N,C-ppy)₂(O,O-acac), but shows a higher luminance at low applied voltages (<6 V). In order to explore whether this effect might be observed in the blue region too, a new derivative has been prepared and characterized, namely cis-Ir(N,C-F₂ppy)₂(O,O-THC) (F₂ppyH = 2-(2,4-difluorophenyl)pyridine). It, too, gives an OLED with a particularly high luminance at low voltage, suggesting a beneficial effect of substituting acetylacetonate by tetrahydrocurcuminate. Full article

Addressing the limitations of conventional inorganic light-emitting diodes (LEDs) in flexible visible light communication (VLC) applications, this study investigates the feasibility of organic light-emitting diodes (OLEDs) as an integrated platform for illumination, display, and communication. The optoelectronic characteristics and modulation bandwidth of red, green, and blue (RGB) OLEDs were systematically measured. Based on the experimental data, a wavelength division multiplexing (WDM) VLC system employing non-return-to-zero on-off keying (NRZ-OOK) modulation was constructed in simulation software for validation. The results indicate stable optoelectronic performance for all three primary-color OLEDs, with a maximum modulation bandwidth of 466 kHz achieved for the blue device. The system simulation demonstrates stable parallel transmission of three independent data channels, attaining a minimum bit error rate (BER) as low as $3.74\times {10}^{-35}$ achieved for the green device. This work confirms the potential of OLEDs for emerging communication applications such as flexible displays and wearable devices. Full article

Gate driver-on-array (GOA) circuits employing amorphous indium–gallium–zinc oxide (IGZO)-based thin-film transistors (TFTs) have been successfully utilized to generate the driving signals for the commercialization of active-matrix organic light-emitting diode (AMOLED) displays. The depletion-mode TFTs in GOA circuits can be completely turned off by the introduction of series-connected, two-transistor, dual low-voltage-level power signals. Simulation results demonstrate that a GOA exhibits high process stability with a threshold voltage margin from −5 V to +5 V. Furthermore, the GOA output characterization and mobility compensation effect are evaluated by the integration of the GOA and pixel in a 31-inch 4K AMOLED display. Experimental results demonstrate that full-swing driving pulses can be obtained with the GOA. Finally, the stripe mura in the display caused by mobility variation can be successfully eliminated by the introduction of GOA circuits. Full article

Background: Early childhood caries (ECC) remains a critical public health challenge, yet recent prevalence data and risk factors are scarce in rapidly urbanizing regions like Shenzhen City, China. Objectives: This study aimed to assess ECC prevalence and identify risk factors among 5-year-old children in Shenzhen City. Methods: This cross-sectional survey was conducted in Shenzhen City in 2024, recruiting 5-year-old children through multistage sampling from kindergartens. Self-administered parental questionnaires were distributed to collect data such as demographic characteristics, socioeconomic background and oral health-related behaviors. One trained dentist conducted the oral examination in kindergartens using ball-ended community periodontal index probes and disposable dental mirrors with an intra-oral light-emitting diode light attached. Dental caries was assessed using diagnosis criteria recommended by World Health Organization. The decayed, missing, and filled primary teeth (dmft) were recorded. Zero-inflated negative binomial regression was applied to identify associations between risk factors and ECC. Results: Among 1462 participants (86% response rate), ECC prevalence was 58% (mean dmft: 2.5 ± 3.4), with untreated decay (dt) accounting for 92% of cases. Socioeconomic factors, including low family income (p < 0.001), non-local residency (p < 0.001), and low caregiver education level (p = 0.012), were significantly associated with higher dmft scores. Behavioral factors such as frequent sugary drink consumption (p = 0.005), lack of parental brushing assistance (p = 0.027), and non-fluoride toothpaste use (p = 0.008) also contributed to the risk of ECC. Conclusions: Over half of Shenzhen City’s 5-year-olds suffered from ECC, predominantly untreated, driven by socioeconomic disparities and modifiable behavioral factors. Public health strategies must prioritize parental education, fluoride use and early preventive practices to reduce the burden of ECC. Full article

In this study, we fabricated a nanostructure on the surface of the micro-lens array (MLA), which is one of the light extraction technologies of organic light-emitting diodes (OLEDs), by performing the Reactive Ion -Etching (RIE) process. The MLA consists of a lensed area and a lens-less bottom (flat film area). We performed a systematic analysis to find ways to improve the light extraction efficiency of the MLA surface and flat film area. By controlling the RIE process time and type of gas plasma, nanostructures were formed on the surface of the MLA. O₂ and CF₄ gas plasmas resulted in nanostructures with tall heights and high aspect ratios, whereas CHF₃ and Ar gas plasmas resulted in nanostructures with small heights and low aspect ratios. Furthermore, it was found that the nanostructures were not covered over the entire area, and the extent to which the nanostructures were distributed varied depending on the process time. As the RIE process time increases, the nanostructure expands from the top surface of the MLA to the flat film area. This limited the light extraction efficiency improvement. At a short process time of 50 s, nanostructures were formed only on the upper surface of the MLA hemisphere, which increased the light extraction efficiency. However, at long process times over 50 s, the surface of the hemisphere of MLA was covered with vertically aligned nanostructures, which decreased the efficiency. While the flat film area was covered with nanostructures at the longest process time of ~3200 s, it was effective, but the total efficiency was further decreased by the trade-off between them. As a result, the high-aspect-ratio nanostructured MLA patterned only on the top surface of the hemispherical MLA with a 50 s O₂ plasma treatment showed the highest efficiency, which was slightly higher than that of the bare MLA. We expect that if the nanostructures can be formed in a direction perpendicular to the MLA surface and the flat film area simultaneously, the light extraction efficiency would be further improved. Full article

We report the synthesis and characterization of the two enantiomeric forms of a thienyl-substituted diketopyrrolopyrrole (DPP) derivative bearing chiral alkyl chains. Thin films were prepared either by spin-coating and drop-casting and analyzed by UV–Visible absorption, electronic circular dichroism (ECD), and circularly polarized (CP) luminescence (CPL). ECD spectra confirmed the opposite chirality of the (R) and (S) isomers, while CPL measurements of the S enantiomer demonstrated solid-state chiroptical activity. Preliminary device tests showed promising optoelectronic behavior, highlighting these chiral DPP materials as potential candidates for CP organic light-emitting diodes (CP-OLEDs) applications, combining strong chiroptical response with good film quality. Full article