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The Quantum Efficiency Roll-Off Effect in Near-Infrared Organic Electroluminescent Devices with Iridium Complexes Emitters
摘要： The electroluminescence quantum e?ciency roll-o? in iridium(III)-based complexes, namely Ir(iqbt)2(dpm) and Ir(iqbt)3 (iqbt = 1 (benzo[b]thiophen-2-yl)-isoquinolinate, dpm = 2,2,6,6-tetramethyl-3,5-heptanedionate) utilized as near-infrared emitters in organic light emitting diodes with remarkable external quantum e?ciencies, up to circa 3%, 1.5% and 1%, are measured and analyzed. With a 5–6 weight% of emitters embedded in a host matrix, the double-layer solution-processed structure as well as analogous three-layer one extended by a hole-conducting ?lm are investigated. The triplet-polaron, the Onsager electron-hole pair dissociation and the triplet-triplet annihilation approaches were used to reproduce the experimental data. The mutual annihilation of triplets in iridium emitters was identi?ed as prevailingly controlling the moderate roll-o?, with the interaction between those of iridium emitters and host matrixes found as being less probable. Following the ?tting procedure, the relevant rate constant was estimated to be (0.5 ? 12) × 10?12 cm3/s, values considered to be rather too high for disordered organic systems, which was assigned to the simplicity of the applied model. A coexistence of some other mechanisms is therefore inferred, ones, however, with a less signi?cant contribution to the overall emission quenching.
关键词： infrared emitters,iridium complex,quantum e?ciency roll-o?,triplet-triplet annihilation,OLEDs
更新于2025-09-23 15:19:57
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Temperature-Independent Performance of an 8-Layer ?? ~1.3 ??m InAs/GaAs Quantum-Dot Laser
摘要： We report high-performance broad-area eight-layer InAs/GaAs quantum-dot lasers (QDLs) emitting at 1.3 μm in the pulse and continuous-wave (CW) operations. Operational characteristics of the fabricated QDLs, including the emission wavelength, output power, threshold-current density, di?erential quantum e?ciency, and characteristic temperature, are investigated at di?erent temperatures. For as-cleaved facets of 100 μm wide and 1 mm cavity-length device, an output power of 100 mW is achieved at 1 kHz with 5% duty cycle and 49 mW in the CW operation. The device exhibits a threshold-current density of 56 A/cm2 at room temperature in both the operating modes and increases to 71 and 80 A/cm2 the in the pulse and CW modes, respectively, at 343 K. Over a temperature range of 298 K to 343 K, we calculate the threshold characteristic temperature of 166 K and 119 K and slope-e?ciency characteristic temperature of 2061 K and 408 K in the pulse and CW modes, respectively. The laser exhibits di?erential quantum e?ciency of 41% and 32% in the pulse and CW mode, respectively. We observed that the device exhibited negligible dependence over a temperature range of 298 K to 343 K.
关键词： characteristic temperature,quantum-dot laser,di?erential quantum e?ciency,semiconductor laser
更新于2025-09-19 17:13:59
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Temperature-Dependent Luminescence of Red-Emitting Ba2Y5B5O17: Eu3+ Phosphors with Efficiencies Close to Unity for Near-UV LEDs
摘要： Solid state white light sources based on a near-UV LED chip are gaining more and more attention. This is due to the increasing e?ciency of near-UV-emitting LED chips and wider phosphors selection if compared to devices based on blue LED chips. Here, a brief overview is given of the concepts of generating white light employing near-UV LED and some optical properties of the available phosphors are discussed. Finally, the synthesis and optical properties of very e?cient red-emitting Ba2Y5B5O17:Eu3+ phosphor powder and ceramics is reported and discussed in terms of possible application as a red component in near-UV LED-based white light sources.
关键词： Eu3+,ceramics,near-UV LED,quantum e?ciency,luminous e?cacy,red phosphor,borate,CIE 1931 colour coordinates,thermal quenching
更新于2025-09-19 17:13:59
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Effect of impact ionization on the performance of quantum ratchet embedded intermediate band solar cell: An extensive simulation study
摘要： An investigation has been carried out on the performance of quantum ratchet embedded intermediate band solar cell by considering impact ionization in the sub-bandgap region. The architecture under investigation is modelled using Silvaco ATLAS TCAD. More emphasis has been provided in the analysis of important paradigms like quantum e?ciency, spectral response, generated electric ?eld and recombination involved in the cell, which are the sole reason behind the low e?ciency (E?), ?ll factor (FF), short circuit current density (Jsc) and open circuit voltage (Voc). The use of impact ionization solves the lower Jsc issue by generating more than one electron-hole pair by the use of single photon, while the use of ratchet band solves the voltage preservation problem by enhancing the carrier lifetime of the minority generated photocarriers. With this advanced feature, this architecture provides a higher e?ciency of > 80%.
关键词： Impact ionization,Intermediate band,Quantum e?ciency,Solar cell,Recombination,Sub-bandgap
更新于2025-09-16 10:30:52
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Mixed-Host Systems with a Simple Device Structure for Efficient Solution-Processed Organic Light-Emitting Diodes of a Red-Orange TADF Emitter
摘要： Charge balance, concentration quenching, and exciton con?nement are the most important factors for realizing the use of thermally activated delayed ?uorescence (TADF) emitters for organic light-emitting diodes. Red-orange organic light-emitting diodes of a TADF emitter 2-[4 (diphenylamino)phenyl]-10,10-dioxide-9H-thioxanthen-9-one (TXO-TPA) have been reported by doping in a mixed p-type host system of poly(N-vinylcarbazole) (PVK) and 1,3-bis(N-carbazolyl)benzene (mCP) via solution-processed. We have demonstrated the peak external quantum e?ciency of 9.75%, maximum current e?ciency of 19.36 cd/A, and power e?ciency of 12.17 lm/W along with a CIE coordinate of (0.45, 0.51). The devices were compared with di?erent doping concentrations of TXO-TPA, and a comparative investigation on the e?ect of the thickness electron transport layer was studied. The results clearly indicated that this solution-processed TXO-TPA device structure is a promising strategy to develop highly e?cient but simple OLED structures.
关键词： external quantum e?ciency,thermally activated delayed ?uorescence,red-orange,solution-processed,organic light-emitting diodes
更新于2025-09-16 10:30:52
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Optical Properties of Red-Emitting Rb2Bi(PO4)(MoO4):Eu3+ Powders and Ceramics with High Quantum Efficiency for White LEDs
摘要： There are several key requirements that a very good LED phosphor should meet, i.e., strong absorption, high quantum e?ciency, high colour purity, and high luminescence quenching temperature. The reported Rb2Bi(PO4)(MoO4):Eu3+ phosphors have all these properties. The Rb2Bi(PO4)(MoO4):Eu3+ phosphors emit bright red light if excited with near-UV radiation. The calculated colour coordinates show good stability in the 77–500 K temperature range. Moreover, sample doped with 50% Eu3+ possesses quantum e?ciency close to unity. Besides the powder samples, ceramic disks of Rb2Eu(PO4)(MoO4) specimen were also prepared, and the red light sources from these disks in combination with near-UV emitting LED were fabricated. The obtained results indicated that ceramic disks e?ciently absorb the emission of 375 and 400 nm LED and could be applied as a red component in phosphor-converted white LEDs.
关键词： thermal quenching,luminescent ceramics,red phosphor,colour coordinates,quantum e?ciency,luminous e?cacy
更新于2025-09-16 10:30:52
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Fabrication of Less Bowed Light-Emitting Diodes on Sapphire Substrates with a SiO2 Thin Film on Their Back Sides
摘要： In this study, less bowed light-emitting diodes (LEDs) were fabricated by preparing a LED structure on a sapphire substrate with a SiO2 thin ?lm on its back side. The SiO2 thin ?lm with a low thermal expansion coe?cient reduced the bow of the wafer generated by the thermal expansion coe?cient di?erence. As the thickness of SiO2 was increased from 1 μm to 4 μm, the compressive stress in the GaN ?lm was reduced from 16% to 62% with respect to that without SiO2 thin ?lm. The stress reduction in multiple quantum wells also enhanced the internal quantum e?ciency of the LED by reducing the piezoelectric ?eld.
关键词： Stress relaxation,Internal quantum e?ciency,Light-emitting diodes
更新于2025-09-12 10:27:22
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A Quarterthiophene-Based Dye as an Efficient Interface Modifier for Hybrid Titanium Dioxide/Poly(3-hexylthiophene)(P3HT) Solar Cells
摘要： This work focused on studying the in?uence of dyes, including a thiophene derivative dye with a cyanoacrylic acid group ((E)-2-cyano-3-(3,3,5,5-trihexyl-[2,2:5,2:5,2-quaterthiophene]-5-yl) acrylicacid)(4T), on the photovoltaic performance of titanium dioxide (TiO2)/poly(3-hexylthiophene)(P3HT) solar cells. The insertion of dye at the interface improved the e?ciency regardless of the dye used. However, 4T dye signi?cantly improved the e?ciency by a factor of three when compared to the corresponding control. This improvement is mainly due to an increase in short circuit current density (JSC), which is consistent with higher hole-mobility reported in TiO2/P3HT nanocomposite with 4T dye. Optical absorption data further revealed that 4T extended the spectral response of the TiO2/P3HT nanocomposite, which could also enhance the JSC. The reduced dark current upon dye insertion ensured the carrier recombination was controlled at the interface. This, in turn, increased the open circuit voltage. An optimized hybrid TiO2/P3HT device with 4T dye as an interface modi?er showed an average e?ciency of over 2% under-simulated irradiation of 100 mWcm?2 (1 sun) with an Air Mass 1.5 ?lter.
关键词： e?ciency,interface modi?er,photovoltaic,poly(3-hexylthiophene),oligothiophene dye,quantum e?ciency,titanium dioxide,absorption,polymers,hybrid solar cells
更新于2025-09-11 14:15:04