Electroluminescence Characteristics Research Articles

Achieving deep red to near-infrared emission in dinuclear platinum (II) complexes with the donor-π-acceptor-type cyclometalated ligand

A novel deep red-emitting dinuclear platinum (II) complex, (TPA2niq)2Pt2(C8OXT)2, featuring a donor-π-acceptor (D-π-A) type ligand, was synthesized and characterized. Here, TPA2niq represents the 4-(tert-butyl)-N-(4-(tert-butyl)phenyl)-N-(4-(6-(isoquinolin-1-yl)naphthalen-2-yl)phenyl)aniline unit, while C8OXT was the abbreviation for the bridging ligand 5-(4-octyloxyphenyl)-1,3,4-oxadiazole-2-thiol. Its photophysical, electrochemical, and electroluminescent characteristics were primarily studied. It was found that (TPA2niq)2Pt2(C8OXT)2 exhibited a saturated deep red emission with a peak at 686 nm in dichloromethane. Furthermore, the (TPA2niq)2Pt2(C8OXT)2-doped polymer electroluminescent devices (PLEDs), fabricated through a solution process, exhibited outstanding electroluminescence (EL) properties, with an emission peak at 684 nm, a maximum external quantum efficiency (EQE) of 3.78%, and a maximum radiant emittance of 4478 mW/Sr/m2. By incorporating the D-π-A type ligand into the dinuclear platinum (II) complex, the PLEDs achieved efficient deep red emission.

Highly efficient AlGaN-based deep-ultraviolet light-emitting diodes: from bandgap engineering to device craft

AlGaN-based light-emitting diodes (LEDs) operating in the deep-ultraviolet (DUV) spectral range (210–280 nm) have demonstrated potential applications in physical sterilization. However, the poor external quantum efficiency (EQE) hinders further advances in the emission performance of AlGaN-based DUV LEDs. Here, we demonstrate the performance of 270-nm AlGaN-based DUV LEDs beyond the state-of-the-art by exploiting the innovative combination of bandgap engineering and device craft. By adopting tailored multiple quantum wells (MQWs), a reflective Al reflector, a low-optical-loss tunneling junction (TJ) and a dielectric SiO2 insertion structure (IS-SiO2), outstanding light output powers (LOPs) of 140.1 mW are achieved in our DUV LEDs at 850 mA. The EQEs of our DUV LEDs are 4.5 times greater than those of their conventional counterparts. This comprehensive approach overcomes the major difficulties commonly faced in the pursuit of high-performance AlGaN-based DUV LEDs, such as strong quantum-confined Stark effect (QCSE), severe optical absorption in the p-electrode/ohmic contact layer and poor transverse magnetic (TM)-polarized light extraction. Furthermore, the on-wafer electroluminescence characterization validated the scalability of our DUV LEDs to larger production scales. Our work is promising for the development of highly efficient AlGaN-based DUV LEDs.

Improved Photoluminescence, Electroluminescence, and Laser Characteristics of 1-Naphthylmethylamine-Based Quasi-Two-Dimensional Perovskite Films at Lower Temperatures

Improved Photoluminescence, Electroluminescence, and Laser Characteristics of 1-Naphthylmethylamine-Based Quasi-Two-Dimensional Perovskite Films at Lower Temperatures

Electroluminescence and infrared imaging of fielded photovoltaic modules: A complementary analysis of series resistance-related defects

Fielded photovoltaic (PV) modules often exhibit series resistance-related defects, mainly due to solder bond degradation and metallization corrosion. To quantitatively analyze the series resistance increase in fielded modules, we conducted a detailed investigation on two sets of modules, employing two complementary techniques, electroluminescence (EL) and infrared (IR) imaging. The dependence of EL image characteristics on module temperature, as revealed in IR images, was a key focus of this study. The first and second sets of modules were exposed in Florida (hot and humid climate) and Arizona (hot and dry climate) over 10 years and 18 years, respectively. The resistive defect patterns obtained using EL and IR images showed a closer correlation for the Florida modules compared to the Arizona modules as the Florida modules primarily experience solder bond degradation. EL and IR images were acquired at five current injection levels (i.e., 0.1, 0.3, 0.5, 0.7, 1.0 x short circuit current) and two exposure times (i.e., 60 s and 300 s) and used to develop and report a new curve fitting method for estimating the external series resistance. The results indicate that inaccurate temperature determinations from IR images can lead to underestimations (up to 23 %) in EL-based external series resistance estimates. For the most accurate series resistance estimation, especially in modules with severe thermal defects and series resistance deterioration, the study recommends obtaining EL and IR images within 60 s of the current injection time. This study also reports a Monte Carlo simulation assessing the impact of EL and IR characteristics on the accuracy of external series resistance estimations.

Bidirectional UV/violet heterojunction light-emitting diode with In0.27Al0.73N alloy film as electron transport layer

In this paper, the p-GaN/n-In0.27Al0.73N heterojunction light-emitting diode (LED) was fabricated by radio frequency magnetron sputtering (RF-MS) and the electroluminescence (EL) characteristics of the p-GaN/n-In0.27Al0.73N heterojunction diode was investigated. Based on the preparation of the InXAl1-XN thin films at different substrate temperatures (Ts), the crystal structure, optical and electrical properties were investigated by XRD, SEM and other material characterization techniques. With increasing Ts, the grain size and surface morphology of the InXAl1-XN thin films change dramatically. The film has the best optical and electrical properties when the Ts is 300℃. On the basis of this, the compositional content of indium in the InXAl1-XN film was calculated to be 0.27. The heterojunction LED was fabricated on a commercial p-GaN substrate and the In0.27Al0.73N alloy film. The EL was successfully achieved at various forward and reverse voltages at room temperature and the temperature-dependent EL has been investigated. Furthermore, research is being conducted on the characteristics of the interface of p-GaN/n-In0.27Al0.73N heterojunction and the elucidation of the light-emitting mechanism of diode. The present work uses a simple and low-cost RF-MS method to fabricate UV/Violet bidirectional drive p-GaN/n-In0.27Al0.73N heterojunction LED, which provides a new reference for the fabrication of LED using InXAl1-XN alloy material.

P‐155: A High‐resolution Patterning of Electroluminescent Quantum Dot Pixels via Photo‐crosslinking

The emergence of near‐eye displays for an extended reality (XR) has promoted the development of high‐resolution electroluminescence quantum dot (EL‐QD) devices. Direct photo‐lithography using photosensitive moieties is an effective technique for producing micrometer‐sized patterns of colloidal quantum dots. Here, we fabricated red, green, and blue quantum dot patterns with a resolution of >4,500 pixels per inch using an azide‐based photo‐crosslinking method, which is a simple and applicable to a versatile patterning or integrating process. The effect of QD ligands and solvents on the electroluminescence characteristics and pattern fidelity of QD films during the patterning process was studied.

An n-type host with a high triplet energy level and wide bandgap for RGB phosphorescent OLEDs

We applied 4,6-Bis(3,5-di(pyridin-2-yl)phenyl)-2-methylpyrimidine (B2PyMPM), a material with a wide bandgap and excellent electron mobility, as the host for the emissive layer in red, green, and blue organic phosphorescence-emitting devices. In the case of red emission, it exhibited a stable and outstanding external quantum efficiency (EQE) of 10.2% along with color coordinates (0.68, 0.31), indicating its potential as a candidate material for smartphone displays. For green and blue emissions, relatively low electroluminescence characteristics were observed due to insufficient energy transfer. With a high triplet energy level (T1) of 2.89 eV, B2PyMPM holds promise for use with other phosphorescent dopants in the future.

Luminescent color control and electroluminescent characteristics of iridium(III) complexes containing a four-membered chelating ring from ancillary ligand

Six dpppy (P,P-diphenyl-N-(pyridin-2-yl)phosphinic amide)- and dppq (P,P-diphenyl-N-(quinolin-2-yl)phosphinic amide)-based iridium(III) complexes 1a, 1b, 2a, 2b, 3a and 3b containing four-membered chelate architecture were synthetized. Their crystal structure and photophysical properties were investigated. The crystal structure shows that two coordinating N atoms from the ancillary ligand dpppy and dppq form a four-membered chelate architecture with the centered iridium(III). By changing the substituent groups and conjugation of the cyclometalated ligand, the control of the luminescent color of the complexes was achieved. In CH2Cl2 solution, complexes 1a, 1b, 2a, 2b, 3a and 3b emitted phosphorescence peaked at 509, 506, 479, 478, 620 and 618 nm with CIE color coordinates of (0.29, 0.60), (0.27, 0.61), (0.13, 0.37), (0.14, 0.35), (0.67, 0.33) and (0.67, 0.33), respectively. The quantum chemical calculation shows that their emitting light is primarily from 3LC π−π* states of the cyclometalated ligand. Electroluminescent devices with dual light-emitting layers were fabricated and exhibited mild efficiency roll-off.

Synthesis and Electrical Properties of a New Bipolar Material Using Spacer Moiety

To develop a deep-blue emitter, a molecule with bipolar characteristics was designed as a donor-spacer-acceptor type, in which 9-(4-(4,6-diphenyl-1),3,5-triazin-2-yl)-2,5-dimethylphenyl)-9H-carbazole (DTPCZ)—with carbazole as an electron donating group and a diphenyl triazine moiety as an electron accepting group—was successfully synthesized. The photoluminescence (PL) maxima of DTPCZ were 421 nm in the solution state and 425 nm in the film state, indicating emission in the deep-blue region. DTPCZ also exhibited high thermal stability, with a degradation temperature of 349 °C. To confirm the electroluminescence (EL) characteristics, DTPCZ was applied as a dopant at 10, 20, and 30 wt% in a blue-fluorescent organic light-emitting diode (OLED) device. The highest efficiency was achieved using the 20 wt% doped device, with a current efficiency of 1.2 cd/A, an external quantum efficiency of 2.3%, and a Commission Internationale de l’Eclairage proceedings y-value of 0.06. Thus, deep-blue emission could be realized in the film state. These molecular design strategies can be applied to various fields, such as organic semiconductors.

Structural and optical properties of position-controlled n-ZnO nanowire arrays: Potential applications in optoelectronics

Highly position-controlled ZnO nanowire (NW) arrays and nanowire-cluster (NW–C) arrays are grown on mask-patterned gallium nitride (GaN) substrates by hydrothermal method. Electroluminescence (EL) emissions with blue-violet light at forward-bias(fb) voltage, EL emissions with yellow light at reverse-bias(rb) voltage, and EL emission at both rb voltages and rb voltages were achieved by the adjustment of the size of the heterojunction interface between wire arrays and film. The high rb current is attributed to electron tunneling transport edge effect via a narrow tunnel barrier. The obtained results highlight that the EL characteristics of ZnO NWs can be tuned and controlled through the size of the heterojunction interface between wire arrays and film. Besides, the nonplanar heterogeneous structure of ZnO NW arrays/GaN film also shown a great spectral response characteristic in the ultraviolet(UV) band, which proves that the structure of is worthy of being studied to achieve high performance UV photodetectors.

High-Performance Tandem Quantum-Dot Light-Emitting Diodes Based on Bulk-Heterojunction-Like Charge-Generation Layers.

In this study, the fundamental but previously overlooked factors of charge generation efficiency and light extraction efficiency (LEE) are explored and collaboratively optimized in tandem quantum-dot light-emitting diodes (QLEDs). By spontaneously forming a microstructured interface, a bulk-heterojunction-like charge-generation layer composed of a poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate)/ZnO bilayer is fabricated and an ideal charge-generation efficiency surpassing 115% is obtained. The coupling strength of the waveguide mode for the top unit and the plasmon polariton loss for the bottom unit are highly suppressed using precise thickness control, which increases the LEE of the tandem devices. The red tandem QLED achieves an exceptionally low turn-on voltage for electroluminescence at 4.0V and outstanding peak external quantum efficiency of 42.9%. The ultralow turn-on voltage originates from the sequential electroluminescence turn-on of the two emissive units of the tandem QLED. Benefiting from its unique electroluminescent features, an easily fabricated optical-electrical dual anti-counterfeiting display is built by combining a dichromatic tandem QLED with masking technology.

Study on blue and white electroluminescence based on Ga2O3 composite films

Diamond/Ga2O3 composite film (DGCF) and diamond/SiO2/Ga2O3 composite film (DSGCF) were prepared on heavy doped n-type silicon substrate by integrating Ga2O3 with diamond and SiO2. DGCF structure electroluminescence (EL) devices use the electron acceleration and local electric field enhancement characteristics of diamond thin film to excite Ga2O3 and obtain blue EL, while DSGCF structure EL devices show brighter and more uniform white EL characteristics due to the introduction of SiO2 layer. The introduction of SiO2 film layer not only introduces the defect energy level related to red light emission of the device, but also improves the green light emission intensity of Ga2O3. In addition, the SiO2 film layer brings a more uniform electron injection to the Ga2O3 film, resulting in a brighter and more uniform white EL.

Unveiling the Potential of Electroluminescence Characteristics in Investigating Different Types of Defects and Degradations in c-Si PV Module

Photovoltaic (PV) cells can be characterized using current-voltage (I-V) as well as electroluminescence (EL) characteristics. However, unlike I-V, the potential of EL characteristics has not been well discussed in the literature. In this work, the impact of different types of defects on the EL characteristics is studied, and the possible use of EL characteristics in the qualitative and quantitative investigation of defects is unveiled. Defective field-aged and new modules with artificially induced defects were taken for experimental study. EL current-intensity (I-ɸ) and EL voltage-intensity (V-ɸ) characteristics were studied for the cells suffering from major defects such as cracks, busbar interconnect failure, and PID-shunting. It is observed that I-ɸ characteristic is useful in the investigation of shunting defects, whereas V-ɸ characteristic is in diagnosing defect that increases series resistance. Bulk defects within a cell affect EL calibration constants and increase cell-to-cell mismatch within a module. The findings of this work would be useful for extracting valuable information from EL images regarding defects and degradations.

Formation of Distributed Local Heterojunction to Enhance NIR Emission Due to the Effective Carrier Transfer

AbstractPerovskite light‐emitting devices (PeLEDs) have emerged as a highly promising contender for the next generation of lighting and display technologies. During the nucleation and crystallization process, numerous defects are commonly formed on the surface and grain boundaries as a result of the ionic characteristics of perovskite, especially in an air environment. These defects ultimately contribute to the deterioration of the photoelectron properties. In this study, CsPbI3 nanocrystals (NCs) solution is introduced into ethyl acetate antisolvent as an additive, resulting in the high‐quality perovskite films under ambient conditions. The introduction of CsPbI3 NCs has been found to increase the grain size and improve the uniformity of perovskite films while also effectively passivating defects. More significantly, the utilization of CsPbI3 NCs leads to the formation of a 0D/3D local heterojunction that is distributed throughout the MAPbI3 film. These distributed heterojunctions significantly increase both the carrier concentration and the photoluminescence performance. With the incorporation of doped perovskite films, Silicon (Si) ‐based PeLEDs demonstrate enhanced efficiency, achieving a maximum external quantum efficiency of 12.6% in ambient conditions. Additionally, these devices exhibit a prolonged operational half‐life of 80 minutes. This study presents a novel methodology for fabricating high‐efficiency Si‐based PeLEDs that exhibit exceptional electroluminescence characteristics.

Unraveling the Origin of an Unusual Shift in the Electroluminescence of 1D CsCu2I3 Light-Emitting Diodes.

Lead-free low-dimensional copper-based metal halides are promising luminescent materials for broadband LEDs owing to their broad self-trapped exciton (STE) emission. However, recently, in 1D CsCu2I3, a discrepancy between their electroluminescence (EL) and photoluminescence (PL) has been observed. As a result, the overall output color from LEDs is significantly different than the anticipated emission. To unveil the origin of this discrepancy, here, we provide comprehensive analyses and show that the shift in the EL is caused neither by any structural/optical interactions between CsCu2I3 and electron transport layers (ETL) nor by the degradation of 1D CsCu2I3. Instead, it depends on the carrier imbalance on CsCu2I3, mainly due to the difference in the electron mobility of the ETLs and the electron density on the CsCu2I3 layer. By varying the ETLs, different colored 1D CsCu2I3 LEDs with peaks at 556, 590, and 647 nm are fabricated, and a maximum luminance of over 2000 cd/m2 is achieved for a 556 nm LED. Further, by limiting the electron mobility and injection to 1D CsCu2I3 using an insulating LiF layer at the CsCu2I3/ETL interface, more red-shifted LEDs are achieved confirming the critical role of electron density on the EL characteristics of 1D CsCu2I3.

Improvement of Cd-Free Quantum Dot Electroluminescent Characteristics by Inorganic Ion Treatment

Improvement of Cd-Free Quantum Dot Electroluminescent Characteristics by Inorganic Ion Treatment

The preparation of CuO film under different annealing atmospheres and investigation of the excellent electrical and undoped tunable electroluminescence characteristics of Au/i-CuO/n-GaN LED

Copper oxide (CuO) film is widely used in optoelectronic devices. The CuO films were fabricated by radio frequency (RF) magnetron sputtering and then annealed at 700 °C under different atmospheres (unannealed, O2, N2, vacuum). The physical characteristics of the films were analyzed systematically. In addition, we prepared Au/i-CuO/n-GaN metal-insulator-semiconductor (MIS) structure devices using optimized conditions. The devices had excellent rectifying characteristics at different ambient temperatures and the turn-on voltage was about 1.7 V. The working mechanism of the diode was analyzed through electroluminescence (EL) spectra and band structure. The EL spectra observed at positive and negative bias were compounded by holes and electrons on the gold electrode passing through the insulating layer into the n-GaN side. The EL spectra exhibited that a dominant ultraviolet (UV) emission peak at ∼376 nm was observed under forward bias (FB), and a strong near-white light emission peak at ∼530 nm was observed under reverse bias (RB). The device exhibited unique electroluminescent spectra tunability varying with bias conditions. The chrominance coordinate of the device under RB was (0.3067,0.3604), and the color temperature was 6585 K. This study proved the application potential of i-CuO as an insulating layer in the preparation of new reference for MIS structured GaN-based tunable light-emitting diodes.

Dynamical characteristics of AC-driven hybrid WSe2 monolayer/AlGaInP quantum wells light-emitting device

The exploration of functional light-emitting devices and numerous optoelectronic applications can be accomplished on an elegant platform provided by rapidly developing transition metal dichalcogenides (TMDCs). However, TMDCs-based light emitting devices encounter certain serious difficulties, such as high resistance losses from ohmic contacts or the need for complex heterostructures, which restricts the device applications. Despite the fact that AC-driven light emitting devices have developed ways to overcome these challenges, there is still a significant demand for multiple wavelength emission from a single device, which is necessary for full color light emitting devices. Here, we developed a dual-color AC-driven light-emitting device by integrating the WSe2 monolayer and AlGaInP–GaInP multiple quantum well (MQW) structures in the form of capacitor structure using AlOx insulating layer between the two emitters. In order to comprehend the characteristics of the hybrid device under various driving circumstances, we investigate the frequency-dependent EL intensity of the hybrid device using an equivalent RC circuit model. The time-resolved electroluminescence (TREL) characteristics of the hybrid device were analyzed in details to elucidate the underlying physical mechanisms governing its performance under varying applied frequencies. This dual-color hybrid light-emitting device enables the use of 2-D TMDC-based light emitters in a wider range of applications, including broad-band LEDs, quantum display systems, and chip-scale optoelectronic integrated systems.Graphical

Improve characteristics of GaN-based green mini-LEDs with double dielectric sidewall passivation

The technique of double dielectric sidewall passivation could improve the electroluminescence characteristics of green mini-LED, including the leakage current, electroluminescence intensity and external quantum efficiency (EQE). According to the analysis of EQE with ABC + f(n) model, both the increment of size and the sidewall passivation could reduce the fraction of SRH recombination. Then, the results of time-resolved photoluminescence measurement indicated that the carrier lifetime of mini-LEDs with higher surface-volume ratio and sidewall passivation would be reduced. Moreover, the communication performances such as modulation bandwidth and frequency response of green mini-LEDs could also be improved by adopting double dielectric sidewall passivation, and the smaller sized green mini-LEDs could achieve higher modulation bandwidth and frequency response.

Strategic molecular engineering of blue phosphorescent Pt(II)compounds for the development of high-efficiency single-doped white OLEDs

We synthesized two novel Pt(Ⅱ) β-diketonate compounds, 2′,6′-dimethoxy-4-tert-butyl-2,3′-bipyridinato-N,C4′)platinum(Ⅱ)(acetylactonate-O,O) (1) and 2′,6′-dimethoxy-4-trimethylsilyl-2,3′-bipyridinato-N,C4′)platinum(Ⅱ)(acetylactonate-O,O) (2), to develop blue phosphorescent compounds and systematically investigated their photoluminescent and electroluminescent characteristics. The compounds 1 and 2 exhibited bright sky-blue phosphorescence, with a phosphorescence maximum (λmax) at 465 nm and 475 nm, respectively. The luminescence quantum yields were found to be 0.63 for 1 and 0.93 for 2. At high concentrations, both compounds exhibited bright red emission originating from the formation of excimer. However, compound 2, due to effective intermolecular interactions, exhibited a more red-shifted emission than compound 1 at the same concentration.For fabricating phosphorescent organic light-emitting diodes, the compounds 1 and 2 were used as dopants, and a 50:50 mixture of 3′-di(9H-carbazol-9-yl)-1,1′-biphenyl:9-(3′-carbazol-9-yl-5-cyano-biphenyl-3-yl)-9H-carbazole-3-carbonitrile was used as the mixed host. When doped with 20 wt% of compound 2, the electroluminescent device exhibited the best performance, achieving an external quantum efficiency (EQE) of 13.7% at 100 cd/m2 and current efficiency of 35.5 cd A−1. Remarkably, the single-doped compound 2-based device achieved emission with Commission Internationale de L'Eclairage coordinates (x, y) of (0.40, 0.48). To the best of our knowledge, this is one of the highest performing single-doped white organic light-emitting diodes.