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Decoding the Polymer p–n Junction: Controlled Dedoping and Reverse Bias Electroluminescence
摘要： The polymer light-emitting electrochemical cell (PLEC) is a unique solid-state device possessing attractive attributes for low-cost applications, but also a junction structure that is still poorly understood. In a PLEC, the applied voltage causes in situ electrochemical p- and n-doping of the semiconducting polymer and the formation of a dynamic light-emitting p–n junction. Once the junction is fixed by cooling or chemical manipulation, the “frozen-junction” PLEC exhibits a unipolar electroluminescence (EL) and photovoltaic response. Repeated thermal cycling, however, can cause the frozen-junction PLEC to experience drastically enhanced EL under forward bias and the emergence of reverse bias EL. In this study, a combination of transport measurements and direct imaging is used to elucidate the origin of the mysterious reverse bias EL. A model is developed that explains the reverse bias EL as caused by the tunnel injection of electrons and holes from bandgap states into a dedoped “intrinsic” region between the p- and n-doped regions. The model explains the location, relative intensity, and evolution of EL under both forward and reverse bias. The results hint at a junction that is much narrower than previously resolved.
关键词： electrochemical doping,light-emitting polymer,p–n junction,electroluminescence
更新于2025-09-11 14:15:04
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Nanostructured colloidal quantum dots for efficient electroluminescence devices
摘要： The exceptional quality of light generated from colloidal quantum dots has attracted continued interest from the display and lighting industry, leading to the development of commercial quantum dot displays based on the photoluminescence down-conversion process. Beyond this technical level, quantum dots are being introduced as emissive materials in electroluminescence devices (or quantum dot-based light-emitting diodes), which boast high internal quantum efficiency of up to 100%, energy efficiency, thinness, and flexibility. In this review, we revisit various milestone studies regarding the core/shell heterostructures of colloidal quantum dots from the viewpoint of electroluminescence materials. Development of nanostructured colloidal quantum dots advanced from core/shell heterostructure, core/thick shell formulation, and delicate control of confinement potential shape has demonstrated close correlation of the photophysical properties of quantum dots with the performance of electroluminescence device, which provided useful guidelines on the heterostructured quantum dots for mitigating or eliminating efficiency limiting phenomena in quantum dot light emitting diodes. To enable practical and high performance quantum dot-based electroluminescence devices in the future, integration of design concepts on the heterostructures with environmentally benign systems will be crucial.
关键词： Electroluminescence,Nanocrystals,Colloidal Quantum Dots,Core/Shell Heterostructures,Light Emitting Diodes
更新于2025-09-11 14:15:04
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A low molecular weight OLED material: 2-(4-((2-hydroxyethyl)(methyl)amino)benzylidene)malononitrile. Synthesis, crystal structure, thin film morphology, spectroscopic characterization and DFT calculations
摘要： 2-(4-((2-Hydroxyethyl)(methyl)amino)benzylidene)malononitrile (HEMABM) was synthesized from 4-[hydroxymethyl(methyl)amino]benzaldehyde and propanedinitrile to obtain a low molecular weight fluorescent material with an efficient solid-state emission and electroluminescence properties comparable to the well-known poly(2-methoxy-5(20-ethyl)hexoxyphenylenevinylene) (MEH-PPV). The HEMABM was used to prepare an organic light-emitting diode by a solution process. Despite the title compound being a small molecule, it showed optical properties and notable capacity to form a film with smooth morphology (10.81 nm) closer to that of polymer MEH-PPV (10.63 nm). The preparation of the device was by spin coating, the electrical properties such as threshold voltage were about 1.0 V for both HEMABM and MEH-PPV, and the luminance 1300 cd m?2 for HEMABM and 2600 cd m?2 for MEH-PPV. IR, NMR, and EI. Besides this low molecular weight compound was characterized by SCXRD, a quantitative analysis of the intermolecular interactions by PIXEL, density functional theory (DFT) calculations are reported.
关键词： electroluminescence,OLED,MEH-PPV,low molecular weight,solution process,HEMABM
更新于2025-09-11 14:15:04
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Nanoplatelet modulation in 2D/3D perovskite targeting efficient light-emitting diodes
摘要： Light-emitting diodes (LEDs) based on two-dimensional (2D) perovskite nanoplatelets exhibit high electroluminescence (EL) efficiency because of the quantum confinement effect, which increases electron–hole recombination to promote radiative emission. It is well-known that a 2D nanoplatelet structure (?n? = 1) is detrimental for luminescence efficiency due to possible thermal quenching of excitons at room temperature. Here, a simple strategy is developed to suppress growth of NMA2PbBr4 (?n? = 1) nanoplatelets by carefully tuning the precursor ratio of cesium bromide (CsBr), formamidinium bromide (FABr) and 1-naphthylmethylammonium bromide (NMABr). The sub-domain size of the perovskite crystal decreases as the long-chain ligand NMABr ratio increases, leading to enhanced photoluminescence quantum yields (PLQY) due to size confinement effect when the NMABr ratio is below 60%. Unfortunately, the NMA2PbBr4 component in 2D/3D perovskites also grows with increasing NMABr ratio, which results in poor EL efficiency. FABr incorporation can provide additional control over suppression of NMA2PbBr4 growth in 2D/3D perovskites. A compact and uniform perovskite film with reduced NMA2PbBr4 content achieves PLQY of ～61%. Benefiting from these features, a green perovskite LED yields current efficiency of 46.8 cd A?1 with an external quantum efficiency of 14.9%. This study paves a new way to modulate the crystal structure in perovskites via a simple and effective method for high-performance LEDs.
关键词： light-emitting diodes,perovskite,quantum confinement,electroluminescence,nanoplatelets
更新于2025-09-11 14:15:04
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p-GaN/n-ZnO Nanorod/CsPbBr <sub/>3</sub> Quantum Dots Decorated with ZnO Nanoseeds for Light-Emitting Diodes
摘要： In this paper, we report the dual-wavelength green-light emission from zinc oxide (ZnO)-nanoseed-decorated p-GaN (gallium nitride)/n-ZnO nanorod/CsPbBr3 quantum dots (QDs) light-emitting diodes (LEDs). At the same time, the effect of ZnO nanoseeds on the p-GaN/n-ZnO nanorod/CsPbBr3 QDs LED performance is deeply studied. ZnO nanoseeds were fabricated by magnetron sputtering and the sol?gel method; then ZnO nanorods were obtained on GaN by hydrothermal treatment to form the p-GaN/n-ZnO nanorod heterojunction, and green CsPbBr3 QDs were further deposited on ZnO nanorod arrays to realize LEDs. The results show that magnetron-sputtering ZnO nanoseeds can induce regular vertical ZnO nanorod arrays, and the corresponding device presents a better electroluminescence (EL) performance. The X-ray diffraction, atomic force microscopy, and EL mechanisms indicate that the p-GaN/n-ZnO nanorod with magnetron-sputtering ZnO nanoseeds has a better crystalline interface. Our results indicate that the p-GaN/n-ZnO nanorod/CsPbBr3 QDs heterojunction structure can be served as dual-wavelength LEDs, and magnetron-sputtering ZnO nanoseeds can give rise to a better EL performance.
关键词： CsPbBr3 quantum dots,electroluminescence,ZnO nanoseeds,ZnO nanorods,light-emitting diodes
更新于2025-09-11 14:15:04
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Thermal droop in high-quality InGaN LEDs
摘要： Thermal droop is investigated in high-quality InGaN light-emitting diodes (LEDs). To determine whether it is caused by intrinsic variations in recombination or by transport effects, photoluminescence and electroluminescence measurements are compared. The former does not show signs of pronounced thermal droop, with a near-constant internal quantum efficiency and recombination lifetime, regardless of temperature. In contrast, strong thermal droop is observed in the latter, pointing to transport effects as a leading contributor. Finally, high-efficiency LEDs with near-ideal thermal droop are demonstrated.
关键词： Thermal droop,recombination lifetime,electroluminescence,internal quantum efficiency,transport effects,photoluminescence,InGaN LEDs
更新于2025-09-11 14:15:04
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[IEEE 2019 54th International Universities Power Engineering Conference (UPEC) - Bucharest, Romania (2019.9.3-2019.9.6)] 2019 54th International Universities Power Engineering Conference (UPEC) - Quality Check during Manufacturing of Custom Photovoltaic Modules with Back-Contact Cells
摘要： The Electroluminescence (EL) analysis and the current-voltage (I-V) curves determination of PhotoVoltaic (PV) generators are the most used diagnosis methods to check the presence of defects. In the present work, these tests are applied to Interdigitated Back Contact (IBC) PV modules with customizable shape after their manufacturing. A defect is detected in a large number of modules, suggesting an issue related to the semi-automatic manufacturing procedure. Therefore, a detailed analysis is carried out to localize the cause of the defect and a preventive action is proposed in order to reduce the occurrence frequency of the defect during manufacturing.
关键词： back contacts,electroluminescence,photovoltaic,electrical contacts,current-voltage characteristic,defects,interdigitated
更新于2025-09-11 14:15:04
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Hot-Electron Trapping and Hole-Induced Detrapping in GaN-Based GITs and HD-GITs
摘要： This paper investigates the trapping mechanisms in gate-injection transistors (GITs) without and with a pdrain electrode, referred to as GITs and Hybrid-Drain-embedded GITs (HD-GITs), respectively, used to inject holes and reduce charge trapping effects. We compare the two sets of devices under both the OFF-state and semi-ON state, to investigate the role of hot electrons in favoring the charge trapping. The analysis is based on combined pulsed characterization, transient measurements, and electroluminescence (EL) characterization. We demonstrate the following relevant results: 1) GITs and HD-GITs have comparable and negligible dynamic RON when trapping is induced in the OFF-state; under semi-ON state conditions, GITs suffer from significant dynamic RON, while HD-GITs show no additional trapping with respect to OFF-state; 2) EL characterization carried out until VDS = 500 V in semi-ON conditions shows comparable features, suggesting that the electric field and hot-carrier density are similar in GITs and HD-GITs. This result indicates that the hot-electron trapping rate is identical for the two sets of samples, so the difference observed in dynamic RON must be ascribed to a different detrapping rate; 3) transient RON measurements indicate that the traps filled in the OFF-state conditions are the same as those filled by hot electrons in semi-ON, with Ea = 0.8 eV (possibly CN); and 4) EL analysis under constant bias indicates that in GITs there is a time-dependent increase in the luminescence signal at the drain terminal, when the devices are biased with VDS = 300 V. Such effect, indicative of hot-electron trapping, is not observed in HD-GITs. Based on the experimental evidence collected within this paper, we conclude that—in the semi-ON state—the main difference between GITs and HD-GITs consists in a faster detrapping rate of hot electrons, achieved through hole injection from the pdrain terminal.
关键词： gate-injection transistors (GITs),Electroluminescence (EL),gallium nitride (GaN) HEMT,trapping,hot electron
更新于2025-09-10 09:29:36
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Two N,N-chelated difluoroboron complexes containing phenanthroimidazole moiety: Synthesis and luminescence properties
摘要： Two new N,N-chelated difluoroboron complexes, PIBF2-Cz and PI-BODIPY, containing phenanthroimidazole moiety were synthesized and characterized by elemental analysis, NMR spectroscopy and MS. Their photophysical and electrochemical properties and thermal stabilities were investigated systematically. The results showed that these N,N-chelated difluoroboron complexes not only exhibit excellent thermal stabilities but also emit strong green emissions with photoluminescence quantum efficiency of 95.71% and 67.22% in chloroform solutions. Furthermore, based on these N,N-chelated difluoroboron complexes, the green organic light-emitting devices with a configuration of ITO/NPB (20 nm)/TBADN: difluoroboron complex (x wt%, 30 nm)/TPBi (30 nm)/Liq (2 nm)/Al (100 nm) have been successfully fabricated by vacuum-deposition method, in which the devices fabricated from PIBF2-Cz exhibited the best electroluminescence performance with a maximum brightness of 20290 cd/m2 and a maximum luminous efficiencies of 7.97 cd/A and a maximum external quantum efficiency (EQE) of 1.88%.
关键词： Photoluminescence,Difluoroboron complex,Electroluminescence,Phenanthroimidazole
更新于2025-09-10 09:29:36
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A family of solution processable ligands and their Re(I) complexes towards light emitting applications
摘要： A series of trimine ligands incorporating 2,2′:6′,2′′-terpyridine (terpy), 2,6-di(thiazol-2-yl)pyridine (dtpy), and 2,6-di(pyrazin-2-yl)pyridine (dppy) frameworks, as well as their corresponding Re(I) tricarbonyl complexes were successfully designed and synthesized to investigate the impact of the peripheral rings (pyridine, thiazole and pyrazine) and phenyl– or naphthyl–based substituents attached to the triimine skeleton on their photophysical and electroluminescent properties. The experimental studies were accompanied with DFT/TDDFT calculations. DSC investigations showed that both the free ligands and Re(I) complexes melted at high temperature (164–309oC) and some of them are able to form amorphous materials. CV measurements revealed that energy band gaps calculated on the basis of ionization potential and electron affinity of the Re(I) complexes, which are correlated with energy levels of frontier molecular orbitals, fall in the range of 2.14–2.32 eV, being lower than the corresponding ligands, what makes the complexes promising for organoelectronic applications. The photophysical properties of the synthesized triimine ligands and Re(I) complexes were studied in detail by electronic absorption and emission. In solution they exhibited photoluminescence quantum yields ranging from 0.15% to 84.42% depending on the chemical structure. The presence of pyrazine units significantly reduced ability for radiative emission. All the compounds were emissive also in a solid state. Preliminary tests of electroluminescence ability demonstrated that most of the devices with Re(I) complexes exhibited red or orange emission, while diodes with ligands showed maximum of emission band located mainly in the green region. It should be noticed that diodes with active layer consisting of a neat complex (ITO:PEDOT:PSS/complex/Al) emitted light under applied voltage.
关键词： electroluminescence,photoluminescence,electrochemistry,Re(I) complexes,triimine ligands
更新于2025-09-10 09:29:36