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We are introducing an innovative organic semiconductor electroluminescent device capable of emitting light with unprecedented characteristics: high directionality (divergence angle of 1.1°) and high color purity (full width at half‐maximum of 2.5 nm). This achievement was realized through intricate design techniques aimed at enhancing gain via meticulous recombination zone control, complemented by the reduction of losses through minimizing the overlap of the optical mode with the electrodes. These groundbreaking results mark the world's first demonstration of simultaneously achieving a narrow spectrum and superior directionality in an organic electroluminescent device. [ABSTRACT FROM AUTHOR]

The control of laser emission angles in laser devices is essential for many optoelectronic and photonic applications such as optical sensing and displays. In this context, we studied the light diffraction pattern of laser beams in a one-dimensional sampled distributed feedback resonator having organic gain media. The gratings consist of the repetition of supercells having a mixed-order sampled grating in which 1st-order gratings surround a 2nd-order grating. The experimental results showed that the diffraction angles of the laser beams are quite diverse depending on the supercell structures. We demonstrate that the interval of the diffraction angle (θ) of the laser beams is inversely proportional to the length of the supercell experimentally and theoretically. By tuning the length of supercells as well as the length of 1st-order and 2nd-order regions, the interval θ was tuned from 0.1° to 43° with the different arc emission patterns. With the reduction of θ, i.e., the longer 1st-order region, a significant decrease in the laser threshold was obtained, resulting in the lowest lasing threshold of 2.5 ± 0.1 μJ/cm2 with ∼3.5 ns of a long pulse width excitation source. [ABSTRACT FROM AUTHOR]

Laser diodes based on organic semiconductor materials have high threshold current densities that require the suppression of various inherent loss processes. One way to study such loss processes is to analyze the external quantum efficiency (EQE) roll-off in organic light-emitting diodes (OLEDs). In this work, we used electrical simulations to analyze the origin of the experimental EQE roll-off of an OLED based on 4,4′-bis[(N-carbazole)styryl]biphenyl (BSBCz) under extremely high current injection (∼1 kA/cm2). We considered various singlet exciton annihilations and quenching processes (i.e., singlet-singlet annihilation, singlet-triplet annihilation, singlet-polaron annihilation, singlet-heat quenching, and electric field quenching of singlet excitons). These results showed that the EQE roll-off can be attributed to Joule heating and/or singlet-triplet annihilation and/or the dissociation of singlet excitons under a high applied electric field. The electric field quenching of singlet excitons was confirmed by a field-induced photoluminescence (PL) quenching experiment. By applying an electric field-induced charge dissociation model to both the EQE and field-induced PL quenching, we estimated the singlet exciton binding energy of a BSBCz film to be in the range of 0.64–0.71 eV. [ABSTRACT FROM AUTHOR]

We report on the cavity numerical characterization of a second order one-dimensional distributed feedback organic laser. The gain medium containing 6wt. % of 4,4'-bis[(N-carbazole) styryl]biphenyl) in a 4,4'-bis[9-dicarbazolyl]-2,20-biphenyl) host is vacuum deposited to form an organic thin film on a SiO2 grating. The influence of the organic film thickness on the properties of the resonant cavity is investigated through numerical calculations of both the confinement factor Γ and the Q-factor. The Q-factor is obtained using two methods, one by calculating the eigenmodes of the resonant cavity and the other by calculating the reflection spectrum. It was found that while the Γ increases with the organic film thickness, the Q-factor shows a non-monotonic function with a maximum value for a thickness of 200 nm. Published by AIP Publishing. [ABSTRACT FROM AUTHOR]

Abstract: Spectroscopic ellipsometry has been used to extract the optical indices of blend organic donor:ZnO (1:2) thin films. Four different donor molecules are investigated in this study: P3HT, PCPDTBT, PTB7 and DTS(PTTh2)2. Using these optical indices as input parameters, the optical performances and the color range for human eyes of donor:ZnO (1:2) hybrid organic–inorganic solar cells have been investigated through optical simulations. These calculations suggest that a tradeoff between reflectance for human eyes and photonic absorption of the AM1.5 spectrum can be reached depending on the composition of the active layer. While the total device reflectance in the visible range is closely correlated to the photonic absorption in the case of a high band gap semiconducting material, a tradeoff is easier to obtain in the case of low band gap semi-conducting materials. Finally, we show that the color range of devices depends both on the active layer compositions and the geometrical parameters of the cells. [Copyright &y& Elsevier]

Two-dimensional perovskites containing an organic fluorophore can be a unique emitter for light-emitting diodes (LEDs). However, external quantum efficiencies (EQEs) of fluorophore-containing perovskite LEDs reported thus far are still very low. In this study, these are able to boost the EQE to ≈10% by choosing an organic fluorophore with appropriate energy levels for the perovskite structure organization. In the fluorophore-containing perovskite LEDs, carrier transport and exciton formation take place in the perovskite's metal halide framework, thereby avoiding the direct formation of nonradiative triplet excitons on the organic fluorophores. Subsequently, the bright triplet excitons formed in the metal halide framework are transferred to form the radiative singlet states of the organic fluorophores, leading to efficient electroluminescence (EL) from the organic fluorophores regularly dispersed inside the perovskite structure. Unexpectedly higher light-outcoupling efficiency, which is caused by the light scattering in the polycrystalline perovskite layer, will be another reason for efficient EL. These findings will contribute toward the fabrication of LED-based products with high performance at a low cost., (© 2024 Wiley‐VCH GmbH.)

Conventional materials discovery is a laborious and time-consuming process that can take decades from initial conception of the material to commercialization. Recent developments in materials acceleration platforms promise to accelerate materials discovery using automation of experiments coupled with machine learning. However, most of the automation efforts in chemistry focus on synthesis and compound identification, with integrated target property characterization receiving less attention. In this work, an automated platform is introduced for the discovery of molecules as gain mediums for organic semiconductor lasers, a problem that has been challenging for conventional approaches. This platform encompasses automated lego-like synthesis, product identification, and optical characterization that can be executed in a fully integrated end-to-end fashion. Using this workflow to screen organic laser candidates, discovered eight potential candidates for organic lasers is discovered. The lasing threshold of four molecules in thin-film devices and find two molecules with state-of-the-art performance is tested. These promising results show the potential of automated synthesis and screening for accelerated materials development., (© 2022 The Authors. Advanced Materials published by Wiley-VCH GmbH.)

Polaron-induced exciton quenching in thermally activated delayed fluorescence (TADF)-based organic light-emitting diodes (OLEDs) can lead to external quantum efficiency (EQE) roll-off and device degradation. In this study, singlet-polaron annihilation (SPA) and triplet-polaron annihilation (TPA) were investigated under steady-state conditions and their relative contributions to EQE roll-off were quantified, using experimentally obtained parameters. It is observed that both TPA and SPA can lead to efficiency roll-off in 2,4,5,6-tetra(9H-carbazol-9-yl)isophthalonitrile (4CzIPN) doped OLEDs. Charge imbalance and singlet-triplet annihilation (STA) were found to be the main contributing factors, whereas the device degradation process is mainly dominated by TPA. It is also shown that the impact of electric field-induced exciton dissociation is negligible under the DC operation regime (electric field < 0.5 MV cm -1 ). Through theoretical simulation, it is demonstrated that improvement to the charge recombination rate may reduce the effect of polaron-induced quenching, and thus significantly decrease the EQE roll-off., (© 2022. The Author(s).)

The photophysical analysis of thermally activated delayed fluorescence (TADF) materials has become instrumental for providing insights into their stability and performance, which is not only relevant for organic light-emitting diodes but also for other applications such as sensing, imaging, and photocatalysis. Thus, a deeper understanding of the photophysics underpinning the TADF mechanism is required to push materials design further. Previously reported analyses in the literature of the kinetics of the various processes occurring in a TADF material rely on several a priori assumptions to estimate the rate constants for forward and reverse intersystem crossing. In this report, we demonstrate a method to determine these rate constants using a three-state model together with a steady-state approximation and, importantly, no additional assumptions. Further, we derive the exact rate equations, greatly facilitating a comparison of the TADF properties of structurally diverse emitters and providing a comprehensive understanding of the photophysics of these systems.

Quantum chemical calculations are necessary to develop advanced emitter materials showing thermally-activated delayed fluorescence (TADF) for organic light-emitting diodes (OLEDs). However, calculation costs become problematic when more accurate functionals were used, therefore it is judicious to use a multimethod approach for efficiency. Here we employed combinatorial chemistry in silico to develop the deep blue TADF materials with a new concept of homo-junction design. The homo-junction materials containing TADF candidates designed by calculation were synthesized and analyzed. We found that these materials showed the emission from charge transfer (CT) state, and the clear delayed emission was provided in solid state. Because the homo-junction TADF materials showed three exponential decayed emission in solid state, we employed novel four-state kinetic analysis., (Copyright © 2020 Tsuchiya, Tsuji, Inada, Bencheikh, Geng, Kwak, Mustard, Halls, Nakanotani and Adachi.)

Organic light-emitting diode (OLED) technology is promising for applications in next-generation displays and lighting. However, it is difficult-especially in large-area mass production-to cover a large substrate uniformly with organic layers, and variations in thickness cause the formation of shunting paths between electrodes 1,2 , thereby lowering device production yield. To overcome this issue, thicker organic transport layers are desirable because they can cover particles and residue on substrates, but increasing their thickness increases the driving voltage because of the intrinsically low charge-carrier mobilities of organics. Chemical doping of organic layers increases their electrical conductivity and enables fabrication of thicker OLEDs 3,4 , but additional absorption bands originating from charge transfer appear 5 , reducing electroluminescence efficiency because of light absorption. Thick OLEDs made with organic single crystals have been demonstrated 6 , but are not practical for mass production. Therefore, an alternative method of fabricating thicker OLEDs is needed. Here we show that extraordinarily thick OLEDs can be fabricated by using the organic-inorganic perovskite methylammonium lead chloride, CH 3 NH 3 PbCl 3 (MAPbCl 3 ), instead of organics as the transport layers. Because MAPbCl 3 films have high carrier mobilities and are transparent to visible light, we were able to increase the total thickness of MAPbCl 3 transport layers to 2,000 nanometres-more than ten times the thickness of standard OLEDs-without requiring high voltage or reducing either internal electroluminescence quantum efficiency or operational durability. These findings will contribute towards a higher production yield of high-quality OLEDs, which may be used for other organic devices, such as lasers, solar cells, memory devices and sensors.

Thermally activated delayed fluorescence (TADF) based on through-space donor and acceptor interactions constitute a recent and promising approach to develop efficient TADF emitters. Novel TADF isomers using a dithia[3.3]-paracyclophane building block as a versatile 3D platform to promote through-space interactions are presented. Such a 3D platform allows to bring together the D and A units into close proximity and to probe the effect of their orientation, contact site and distance on their TADF emission properties. This study provides evidence that the dithia[3.3]paracyclophane core is a promising platform to control intramolecular through-space interactions and obtain an efficient TADF emission with short reverse-intersystem crossing (RISC) lifetimes. In addition, this study demonstrates that this design can tune the energy levels of the triplet states and leads to an upconversion from 3 CT to 3 LE that promotes faster and more efficient RISC to the 1 CT singlet state., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The development of single-component organic dual light-emitting molecules is of interest for a range of applications including white organic light-emitting diodes. Herein, a new thermally-activated delayed fluorescent molecule containing 4,6-bis-phenyl phenothiazine as donor units and 2-thiophene-1,3,5-triazine as acceptor unit was synthesized using a simple cost-effective method. This compound shows two stable molecular conformations due to the presence of the phenothiazine units in its molecular structure. These conformers exhibit different photophysical properties in both solution and thin films. The electroluminescence properties of this novel emitter were then examined in organic light-emitting diodes and the results provide useful insights into the influence of the device architecture on the dual emission characteristics. The experimental results were consistent with the optical simulations and the optimized architecture led to the fabrication of electroluminescent devices with an external quantum efficiency of 11.5% and a maximum luminance value of 10 370 cd m -2 ., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

The development of host materials with high performance is essential for fabrication of efficient and stable organic light-emitting diodes (OLEDs). Although host materials used in OLEDs are typically organics, in this study, it is shown that the organic-inorganic perovskite CH 3 NH 3 PbCl 3 (MAPbCl 3 ) can be used as a host layer for OLEDs. Vacuum-evaporated MAPbCl 3 films have a wide band gap of about 3 eV and very high and relatively balanced hole and electron mobilities, which are suitable for the host material. Photoluminescence and electroluminescence take place through energy transfer from MAPbCl 3 to an organic emitter in films. Incorporation of an MAPbCl 3 host layer into OLEDs leads to a reduction of driving voltage and enhancement of external quantum efficiency as compared to devices with a conventional organic host layer. Additionally, OLEDs with an MAPbCl 3 host layer demonstrate very good operational stability under continuous current operation. These results can be extensively applied to organic- and perovskite-based optoelectronics., (© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Organic light-emitting diodes have become a mainstream display technology because of their desirable features. Third-generation electroluminescent devices that emit light through a mechanism called thermally activated delayed fluorescence are currently garnering much attention. However, unsatisfactory device stability is still an unresolved issue in this field. Here we demonstrate that electron-transporting n-type hosts, which typically include an acceptor moiety in their chemical structure, have the intrinsic ability to balance the charge fluxes and broaden the recombination zone in delayed fluorescence organic electroluminescent devices, while at the same time preventing the formation of high-energy excitons. The n-type hosts lengthen the lifetimes of green and blue delayed fluorescence devices by > 30 and 1000 times, respectively. Our results indicate that n-type hosts are suitable to realize stable delayed fluorescence organic electroluminescent devices.

The demonstration of continuous-wave lasing from organic semiconductor films is highly desirable for practical applications in the areas of spectroscopy, data communication, and sensing, but it still remains a challenging objective. We report low-threshold surface-emitting organic distributed feedback lasers operating in the quasi-continuous-wave regime at 80 MHz as well as under long-pulse photoexcitation of 30 ms. This outstanding performance was achieved using an organic semiconductor thin film with high optical gain, high photoluminescence quantum yield, and no triplet absorption losses at the lasing wavelength combined with a mixed-order distributed feedback grating to achieve a low lasing threshold. A simple encapsulation technique greatly reduced the laser-induced thermal degradation and suppressed the ablation of the gain medium otherwise taking place under intense continuous-wave photoexcitation. Overall, this study provides evidence that the development of a continuous-wave organic semiconductor laser technology is possible via the engineering of the gain medium and the device architecture.

We report on the realization of polymer light-emitting diodes (PLEDs) based on fluorescent polythiophene (PT)-based insulated molecular wires (IMWs). PLEDs using PT emitting layers traditionally have low external quantum efficiencies (η eqe ) below 0.1%. Moreover, IMWs lack a thorough exploitation for electroluminescent applications due to concerns about reduced charge transport between their chains. We constructed multilayer PLEDs containing PT IMW emitting layers that show the maximum η eqe close to 1.4%, luminance at 3700 cd/m 2 , and low turn on voltage at 2.5 V. We also show a strong influence of the thickness of electron transport layer on η eqe through device optimization and optical simulations.

Cypermetherin has been implicated in the development of a variety of reproductive disorders in humans and infertility in wild life, where it increases the death rate of the offspring and induces aggressiveness (Elbetieha et al., 2001). Studies in workers exposed to handling of agro pesticides indicate that they have defects in their reproduction capabilities characterized by infertility and/or a decrease in the fertilizing potential, fetal death. In this study, mice weighing 30-35 g were used, separated in 3 groups, (1) control (2) vehicle (oil) and (3) experimental (Cypermetherin and oil). The animals were gavaged by 1/5, 1/20 LD50 for 2 and 4 weeks respectively, and with 1/5 LD50 for 12 weeks, then sacrificed. Epididymal spermatozoa were evaluated with respect to quantity, motility and morphology. The histology of testis and epididymis was also studied. Sperm count decreased by around 20% in treated animals compared with control. Teratology observations showed a clear modification of sperm morphology, especially the flagella. Testicular and epididymal morphology was also impaired. It is concluded that Cypermetherin may cause morphological and functional alteration of the male reproductive tract.