Electroluminescent Properties Research Articles

Enhanced Electroluminescence Properties of Tin-based Perovskites by Vitamin C Additives

Enhanced Electroluminescence Properties of Tin-based Perovskites by Vitamin C Additives

Effects of the nature of donor substituents on the photophysical and electroluminescence properties of derivatives of perfluorobiphenyl: donor–acceptor versus donor–acceptor–donor type AIEE/TADF emitters

The synthesis and properties of a group of organic electroactive compounds based on electron-deficient perfluorobiphenyl (PFBP) are described.

Synthesis and Electroluminescence Properties of Deep Blue Materials Based on Anthracene Core

Synthesis and Electroluminescence Properties of Deep Blue Materials Based on Anthracene Core

The impact of structural modification on the electrochromic and electroluminescent properties of D–A–D benzothiadiazole derivatives with a fluorene linker and (Bi)thiophene units

Two derivatives of benzothiadiazole (BTD) symmetrically functionalized with a dihexylfluorene units serving as a linker between the BTD core and the thiophene or bithiophene were designed, synthesized and comprehensively characterized.

Interfacial Passivation Engineering for Highly Efficient Quantum Dot Light-Emitting Diodes via Aromatic Amine-Functionalized Dipole Molecules.

Blue quantum dot (QD) light-emitting diodes (QLEDs) exhibit unsatisfactory operational stability and electroluminescence (EL) properties due to severe nonradiative recombination induced by large numbers of dangling bond defects and charge imbalance in QD. Herein, dipolar aromatic amine-functionalized molecules with different molecular polarities are employed to regulate charge transport and passivate interfacial defects between QD and the electron transfer layer (ETL). The results show that the stronger the molecular polarity, especially with the -CF3 groups possessing a strong electron-withdrawing capacity, the more effective the defect passivation of S and Zn dangling bonds at the QD surface. Moreover, the dipole interlayer can effectively reduce electron injection into QD at high current density, enhancing charge balance and mitigating Joule heat. Finally, blue QLEDs exhibit a peak external quantum efficiency (EQE) of 21.02% with an operational lifetime (T50 at 100 cd m-2) exceeding 4000 h.

Preparation of Si nanoparticles from bamboo leaves and measurement of their photoluminescence and electroluminescence spectra

In this study, Si nanoparticles were prepared by the Mg reduction of SiO2 extracted from bamboo leaves, and their optical properties were investigated. Si nanoparticles were filtered under reduced pressure to separate the residue and filtrate specimens. Although RT photoluminescence (PL) was observed for both Si nanoparticle specimens, the PL intensity of the filtrate specimens was approximately seven times higher than that of the residue specimens. An electroluminescence (EL) device was fabricated using the Si nanoparticles of the filtrate as the active layer, and its EL properties were evaluated. With an applied voltage of 15 V, red luminescence was observed in the active layer. The Si nanoparticles from the bamboo leaves had relatively broad EL spectra with a peak wavelength approximately 700 nm, similar to that of the PL spectra. These results indicated that Si nanoparticles from bamboo leaves can be recycled for light-emitting devices.

Synthesis, structure and optoelectronic properties of iridium(III) complexes bearing a four-membered Ir-N-C[sbnd]N chelate structure

Herein four novel iridium(III) complexes (tfpmd)2Ir(dpppy) (Ir1a, tfpmd = 2-(4-(trifluoromethyl) phenyl) pyrimidine, dpppy = P,P-diphenyl-N-(pyridin-2-yl)phosphinic amide), (tfpmd)2Ir(dppq) (Ir1b, dppq = P,P-diphenyl-N-(quinolin-2-yl)phosphinic amide), (tfpqz)2Ir(dpppy) (Ir2a, tfpzq = 4-(4-(trifluoromethyl) phenyl) quinazoline) and (tfpqz)2Ir(dppq) (Ir2b) were synthetized, and their structures, opto-physical, and electro-chemical properties were investigated in detail. The crystal structure shows that these complexes exhibit pseudo-octahedral geometry around iridium atom coordinated by C, N atoms from cyclometalated and ancillary ligands. Interestingly, two coordinated nitrogen atoms from the ancillary ligand form an unusual quaternary ring with the central iridium ion. Ir1a and Ir1b emit pure-green light with Commission Internationale de L'Eclairage (CIE) color coordinates of (0.25, 0.67) and (0.22, 0.67), respectively, in CH2Cl2 solution. With the increase of the degree of conjugation of the cyclometalated ligand from tfpmd to tfpqz, the luminescence of complexes Ir2a and Ir2b is greatly red-shifted, and pure-red emission with CIE coordinates of (0.66, 0.34) and (0.66, 0.34), respectively, is obtained. The photophysical behaviors were reasonably explained by quantum chemical calculations. The calculation results shows that their emission is ascribed to the mixed 3MLCT (metal-ligand charge transfer, dπ(Ir)→π*(cyclometalated ligand)) and 3LLCT (ligand-ligand charge transfer, π(ancillary ligand)→π*(cyclometalated ligand)) states. Owing to their good thermal and electrochemical stabilities, organic light emitting diode (OLED) devices with dual-emitting layer structure and a space interlayer were fabricated and exhibited high electroluminescent properties and mild efficiency roll-off (14%-21%).

Utilizing direct Zener tunneling in Germanium for cryogenic quantum applications

The temperature-dependent electroluminescent properties of Ge-Diodes, especially the Ge-Zener-Emitter, with tunnel transitions are investigated. The direct band-gap behavior of Germanium below a temperature of 140 K is demonstrated, facilitated by Zener tunneling. Pulsed excitation of the Ge-Zener-Emitter results in an optical output power density of 6 μW, which is sufficient to excite quantum dots for single-photon emission. The peak energy of 0.86 eV suits the non-resonant excitation of InGaAs quantum dots at cryogenic temperatures. This paper presents a potential optical pump source for a quantum photonic integrated circuit.

Enhanced LED Performance by Ion Migration in Multiple Quantum Well Perovskite.

Here we study the effect of ion migration on the performance of perovskite light emitting diodes (PeLEDs). We compared aromatic and linear barrier molecules in Ruddlesden-Popper and Dion-Jacobson two-dimensional perovskites having multiple quantum well (MQW) structures. PeLED devices were fabricated by using the same conditions and architecture, while their electroluminescence properties and ion migration behavior were investigated. Impedance spectroscopy measurements were used to analyze the PeLEDs, which found a direct link between the barrier molecule type, the device efficiency, and ion migration. The best performing LEDs were based on the aromatic barriers, which present dominant inductive impedance, indicating an earlier onset voltage of radiative recombination. These findings present an approach of how to control radiative emission in perovskite LEDs which opens the way for further improvement in PeLEDs and memristors.

Trifluoromethyl substituted cationic cyclometallated iridium(III) complexes: Photophysical properties and theoretical studies

Three new trifluoromethyl substituted (–CF3) cationic iridium(III) complexes 1–3, with 3,5-dimethyl-1-(3-(trifluoromethyl)phenyl)-1H-pyrazole (DTPP) as the cyclometallated ligand, namely, [Ir(DTPP)2bpy](PF6) (1, bpy = 2, 2′–bipyridine), [Ir(DTPP)2phen](PF6) (2, phen = 1,10-phenanthroline) and [Ir(DTPP)2pphen](PF6) (3, pphen = pyrazino[2,3-f][1,10]phenanthroline) have been rationally designed and synthesized in good yields (60–77%). The photophysical, electrochemical, and electroluminescent properties were fully characterized. Complexes 1–3 show bright blue to yellow emission in the both solution and neat film states with maximum emission wavelength in the range of 484–560 nm. Photoluminescence quantum yields (PLQYs) are very high ranging from 62% to 72% in the solution state with microsecond excited-state lifetimes (0.39–0.77 μs). More detailed photophysical and theortical calculation studies reveal that introduction of –CF3 substituent onto the cyclometallated ligand can induce a blue-shift emission compared with conventional fluorinated phenylpyridine or phenylpyrazole complexes, which can be contributed to the decline in HOMO energy level of complexes. Single-crystal structure analysis of complex 3 shows a distorted octahedral geometry with strong intermolecular π–π stacking (face-to-face) interactions between ancillary ligands in adjacent molecules, which might be responsible for the obviously red-shifted emission compared with complexes 1 and 2 in the aggregated state. In addition, electroluminescent properties of all three new complexes have been studied in the application of light-emitting electrochemical cells (LECs), which show green to yellow electroluminescence (λmax, EL = 516–540 nm).

Green-Light GaN p-n Junction Luminescent Particles Enhance the Superconducting Properties of B(P)SCCO Smart Meta-Superconductors (SMSCs)

Superconducting materials exhibit unique physical properties and have great scientific value and vast industrial application prospects. However, due to limitations, such as the critical temperature (TC) and critical current density (JC), the large-scale application of superconducting materials remains challenging. Chemical doping has been a commonly used method to enhance the superconductivity of B(P)SCCO. However, satisfactory enhancement results have been difficult to achieve. In this study, we introduce green-light GaN p-n junction particles as inhomogeneous phases into B(P)SCCO polycrystalline particles to form a smart meta-superconductor (SMSC) structure. Based on the electroluminescence properties of the p-n junction, the Cooper pairs were stimulated and strengthened to enhance the superconductivity of B(P)SCCO. The experimental results demonstrate that the introduction of inhomogeneous phases can indeed enhance the critical temperature TC, critical current density JC, and complete diamagnetism (Meissner effect) of B(P)SCCO superconductors. Moreover, when the particle size of the raw material of B(P)SCCO is reduced from 30 to 5 μm, the grain size of the sintered samples also decreases, and the optimal doping concentration of the inhomogeneous phases increases from 0.15 wt.% to 0.2 wt.%, further improving the superconductivity.

Theoretical and experimental investigation of exciplex-forming and electroluminescent properties of 4-ethyl-3,5-bis[40-(N, N-diphenylamine)biphenyl-4-yl]-4H-1,2,4-triazole

The recently synthesized 4-ethyl-3,5-bis [40-(N, N-diphenylamine)biphenyl-4-yl]-4H-1,2,4-triazole (TPA-TZ) is in this work thoroughly studied as an efficient luminophore with an account of density functional theory. The intense fluorescence is explained as an intramolecular charge-transfer transition from the diphenylamine (donor) moiety to the central part of the dye with a characteristic electron redistribution in the triazole ring (acceptor). The photoluminescence (PL) and phosphorescence (Ph) spectra of TPA-TZ in the film and in THF solution at 77 K were studied together with the well-known 2,4,6-tris [3-(diphenylphosphinyl)phenyl]-1,3,5-triazine (PO-T2T) dye. The latter compound was used as an electron-withdrawing component of the investigated TPA-TZ: PO-T2T exciplex, which is characterized by a relatively high energy level of the excited lowest triplet state. The films of a solid-state mixture of TPA-TZ and PO-T2T showed exciplex-type emission being slightly red-shifted compared to the PL of the individual donor and acceptor compounds. Two OLED devices with emitting layers of TPA-TZ and of the exciplex-forming molecular mixture of TPA-TZ and PO-T2T were prepared. The exciplex–based OLED demonstrated 4 103 cd/m2 brightness, a current efficiency of 22 cd/A, a power efficiency of 6.77 lm/W, and an external quantum efficiency (EQE) of 7%. This confirms the possibility of triplet harvesting in the molecular mixture of TPA-TZ and PO-T2T, since the theoretical EQE limit for OLED based on the prompt fluorescence is 5%.

Carrier Injection Tailoring and Electroluminescence Properties of Carbon Dots in Electroluminescent Light‐Emitting Diodes

Fantastic carbon dots (CDs) are demonstrated as carrier injection tailoring and emitters of electroluminescent light‐emitting diodes (LEDs). Using N‐Methyl‐2‐pyrrolidone as a carbon source, CDs are facilely synthesized by hydrothermal method. Transmission electron microscopy, X‐Ray photoelectron spectroscopy, atomic force microscopy, and photoluminescence measurements confirm that the CDs show good film morphology and particular electronic properties. With CDs‐doped poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) tailoring hole injection, the 2‐(4‐biphenyl)‐5‐(4‐tert‐butylphenyl)‐1,3,4‐oxadiazole‐based UV organic LED (OLED) gives maximum radiance of 2.34 mW cm−2 and external quantum efficiency (EQE) of 1.51%. With CDs as electron injection layer, the inverted UV OLED shows a maximum radiance of 1.13 mW cm−2 and EQE of 0.38%. The hole/electron injection characteristics are further elucidated using current–voltage characteristics and impedance spectroscopy. Electroluminescent LEDs using pure CDs and CDs‐doped poly(9‐vinylcarbazole) (PVK) as emitters are demonstrated. The CDs‐based electroluminescent LED shows superior electro‐optical properties with a maximum luminance of 48.67 cd m−2 at 8 V, luminous efficiency of 0.022 cd A−1, power efficiency of 0.023 lm W−1, and EQE of 0.023%, owing to the energy transfer from PVK to CDs. The research paves an alternative approach for broadening CDs applications and advancing novel electroluminescent LEDs.

Donor-Acceptor Copolymers with 9-(2-Ethylhexyl)carbazole or Dibenzothiophene-5,5-dioxide Donor Units and 5,6-Difluorobenzo[c][1,2,5]thiadiazole Acceptor Units for Photonics.

Semiconducting polymers, particularly of the third generation, including donor-acceptor (D-A) copolymers, are extensively studied due to their huge potential for photonic and electronic applications. Here, we report on two new D-A copolymers, CP1 and CP2, composed of different electron-donor (D) units: 9-(2-ethylhexyl)carbazole or dibenzothiophene-5,5-dioxide, respectively, and of 4,7-bis(4'-(2-octyldodecyl)thiophen-2'-yl)-5,6-difluorobenzo[c][1,2,5]thiadiazole building block with central 5,6-difluorobenzo[c][1,2,5]thiadiazole electron-acceptor (A) units, which were synthesized by Suzuki coupling in the high-boiling solvent xylene and characterized. The copolymers exhibited very good thermal and oxidation stability. A copolymer CP1 with different molecular weights was prepared in order to facilitate a comparison of CP1 with CP2 of comparable molecular weight and to reveal the relationship between molecular weight and properties. The photophysical, electrochemical, and electroluminescence properties were examined. Intense red photoluminescence (PL) with higher PL efficiencies for CP1 than for CP2 was observed in both solutions and films. Red shifts in the PL thin film spectra compared with the PL solution spectra indicated aggregate formation in the solid state. X-ray diffraction measurements revealed differences in the arrangement of molecules in thin films depending on the molecular weight of the copolymers. Light-emitting devices with efficient red emission and low onset voltages were prepared and characterized.

Single Atom Silver‐Phosphors in Titanosilicate Matrix for Enhanced LED Applications

AbstractSmall metal oligomers have gained significant attention due to their exceptional optoelectronic properties and versatile applications, ranging from sensors to imaging and catalysis. However, the need for matrices (silica, zeolites, or metal‐organic frameworks) to prevent aggregation into larger metallic particles reduces their potential applicability in light‐emitting devices (LEDs) due to their poor electrical properties. To address this issue, a novel semiconductor stabilizer, titanosilicate, is proposed as an innovative solution for Ag‐based luminescent materials. These results show that titanosilicate, characterized by high thermochemical stability and well‐defined semiconducting properties, is an ideal scaffold for Ag‐luminescent species. Optical spectroscopic techniques reveal that Ag‐titanosilicates feature an orange fluorescence with a photoluminescence quantum yield reaching 20%. In contrast, a combination of X‐ray diffraction, TEM, and XEOL‐X‐ray absorption spectroscopic techniques show that, unlike zeolites, the luminescent species consist of single Ag atoms. The electroluminescent properties of the proposed Ag‐titanosilicate are further investigated within a conventional LED architecture by using the new material as an emissive layer. The developed proof‐of‐concept LED exhibits a significant improvement of the ZEOLEDs, where a smaller low turn‐on voltage of 2 V (enabling energy‐efficient operation) and high color rendering index of 80 introduces exciting prospects for developing advanced Ag‐LED phosphors.

Time-dependent electrical and electroluminescence properties of In-substituted CaSnO3 and CaSnO3:Pr thin films prepared by a chemical solution deposition method

CaSnO3, CaSn0.9In0.1O3−δ, and Ca0.995Pr0.005Sn0.9In0.1O3−δ thin films sandwiched between (In0.975Sn0.025)2O3−δ thin-film electrodes were prepared by a chemical solution deposition method. The electric and electroluminescence properties were investigated by applying dc (direct current) voltages to the films. No appreciable current was detected for the CaSnO3 thin film. When constant dc voltage was applied to the CaSn0.9In0.1O3−δ and the Ca0.995Pr0.005Sn0.9In0.1O3−δ thin films, current was close to zero just after applying the voltage, increased with increasing time at the beginning, reached a maximum at a certain time, and then decreased with increasing time. The current increased by annealing at 673 K in air and decreased reversibly by quenching from 1323 K. Ca0.995Pr0.005Sn0.9In0.1O3−δ thin film showed reddish white electroluminescence due to f-f transitions of Pr3+ ions. The time dependence of the luminance was similar to that of the current. The results were discussed in relation to oxygen absorption and desorption at high temperatures and electromigration of oxygen vacancies at room temperature.

Simultaneously Realizing High Efficiency and High Color Rendering Index for Hybrid White Organic Light-Emitting Diodes by Ultra-Thin Design of Delayed Fluorescence Sensitized Phosphorescent Layers.

In consideration of energy economization and light quality, concurrently attaining high external quantum efficiency (ηext ) and high color rendering index (CRI) is of high significance for the commercialization of hybrid white organic light-emitting diodes (WOLEDs) but is challenging. Herein, a blue luminescent molecule (2PCz-XT) consisting of a xanthone acceptor and two 3,6-diphenylcarbazole donors is prepared, which exhibits strong delayed fluorescence, short delayed fluorescence lifetime, and excellent electroluminescence property, and can sensitize green, orange, and red phosphorescent emitters efficiently. By employing 2PCz-XT as sensitizer and phosphorescent emitters as dopants, efficient two-color and three-color WOLED architectures with ultra-thin phosphorescent emitting layers (EMLs) are proposed and constructed. By incorporating a thin interlayer to modulate exciton recombination zone and reduce exciton loss, high-performance three-color hybrid WOLEDs are finally achieved, providing a high ηext of 26.8% and a high CRI value 83 simultaneously. Further configuration optimization realizes a long device operational lifetime. These WOLEDs with ultra-thin phosphorescent EMLs are among the state-of-the-art hybrid WOLEDs in the literature, demonstrating the success and applicability of the proposed device design for developing robust hybrid WOLEDs with superb efficiency and color quality.

Synthesis, characterization, photophysical and electroluminescent properties of iridium complexes with CF3-substituted 1,3,4-oxadiazole amide ancillary ligands

Utilizing 1,3,4-oxadiazole amide that possesses outstanding electron mobility to serve as auxiliary ligands, four novel iridium (III) complexes of Ir1–Ir4 were prepared. Their structure, photophysical, and electrochemical characteristics were examined in detail, and quantum chemical calculations were used to interpret their photophysical behaviors. At room temperature, complexes Ir1 and Ir2 exhibit almost coincident green phosphorescence with peaks at 506 nm. Ir3 and Ir4 complexes produce greenish blue and greenish yellow light with a double-peak structure located at 496 and 531 nm. Organic light-emitting diodes utilizing Ir1–Ir4 as emitters exert extremely moderate efficiency roll-off, which is caused by the emitters bearing CF3-substituted 1,3,4-oxadiazole amide possessing excellent electron mobility.

Single-layer SrTiO3 film and SiO2/SrTiO3 composite film white electroluminescence performance comparison

Single-layer SrTiO3 film and SiO2/SrTiO3 composite film electroluminescence (EL) devices were fabricated on n-Si substrate though vacuum electron vapor deposition (EBVD) technique. The film layers in the device were analyzed using various detection methods to determine their microstructure and composition, and the EL properties of both types of devices were compared. EL experimental results show that both devices can emit white light visible to the naked eye when the forward bias is applied. Moreover luminescence intensity of SiO2/SrTiO3 composite thin film devices is much higher than that of single-layer SrTiO3 thin film devices. The EL spectrum analysis of the device samples shows that there are three luminescence peaks in both types of devices, and they are located in the blue, yellow and red regions. Three emission peaks of single-layer SrTiO3 thin film devices are located at 460 nm (blue region), 580 nm (yellow region) and 685 nm (red region). Three luminescence peaks of SiO2/SrTiO3 composite thin film devices are located at 460 nm (blue region), 585 nm (yellow region) and 716 nm (red region). In composite film devices, SiO2 acts as an electron barrier layer, confining electrons to the SrTiO3 film layer and increasing the chance for the electrons in the SrTiO3 conduction band to participate in the composite luminescence. As a result, the blue peak emission intensity of the SrTiO3 composite film device is significantly enhanced, while the overall white light emission intensity of the composite thin film device is greatly improved. Additionally, the color coordinates of SiO2/SrTiO3 composite film device is closer to those of standard white light according to CIE standards.

High-efficiency long-wavelength NIR iridium complexes constructed by extending rigid coordination and optimizing peripheral donor position to break cocoon into butterfly

Due to the non-radiative decay of excited states, it is extremely complicated for iridium (III) complexes to simultaneously harvest high-efficiency and long-wavelength emission in the near-infrared (NIR) region based on the energy-gap law. In order to address this issue, we designed and synthesized two butterfly-type iridium(III) complexes of (PyPz-TPA)2Ir(acac) and (PyQl-TPA)2Ir(acac), in which pyrene-pyrazine (PyPz) and pyrene-quinoxaline (PyQl) are respectively used as the rigid C^N bidentate coordinated cocoons, peripherally with two triphenylamine (TPA) units at 4, 5-positions. Their photophysical, electrochemical and electroluminescent properties are primarily investigated. It is found that the (PyQl-TPA)2Ir(acac) presents stronger spin-orbital coupling effect, a smaller ΔEST energy difference, and lower reorganization energy than (PyPz-TPA)2Ir(acac) by selecting rigid pyrene-quinoxaline coordination and optimizing peripheral TPA position. Furthermore, the (PyQl-TPA)2Ir(acac)-doped OLEDs exhibit a red-shifted NIR emission peaked at 784 nm with a record external quantum efficiency of 5.42% using CBP as host matrix by solution process, which is a rare representation to shrink the limitation of energy-gap law in NIR region for iridium(III) complexes. This study provides a feasible strategy to construct high-efficiency NIR-emitting iridium(III) complexes by an artfully motivated strategy of extending and breaking the C^N coordinate cocoon into butterfly.