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Low-Bandgap Polymer-based Infrared-to-Visible Up-Conversion Organic Light-Emitting Diodes with Infrared Sensitivity up to 1.1μm
摘要： All-organic infrared (IR)-to-visible up-conversion organic light-emitting diodes (OLEDs) with an IR sensitivity up to 1,100nm were fabricated using a low bandgap polymer as the organic IR sensitizing layer. A novel low bandgap (1 eV) polymer, poly 4-(4,8-bis(5-(2-butyloctyl)thiophen-2-yl)benzo[1,2-b:4,5-b']dithiophen-2-yl)-6,7-diethyl-[1,2,5] thiadiazolo[3,4-g]quinoxaline (PBDTT-BTQ), with a strong photo-response in near-IR wavelengths of 700-1,100nm was first synthesized using a thiadiazolo[3,4]quinoxaline (BTQ) and a thiophene-substituted benzo[1,2-b:4,5-b2-bdithiophene (BDTT) as the electron-withdrawing and donating building blocks, respectively. The near-IR photodetector was then fabricated for evaluating a PBDTT-BTQ as the IR sensitizing layer. The PBDTT-BTQ IR photodetector showed detectivity greater than 1011 Jones in multi-spectral region (300-1,100nm) and the maximum detectivity of 3.1× 1011 Jones at the wavelength of 1,000nm due to significantly reducing dark current (8.8 × 10-6 mA/cm2 at -1 V). Finally, the all-organic IR up-conversion OLED with a PBDTT-BTQ IR sensitizer successfully converted invisible near-IR light of 700nm-1,100nm directly to visible green light with a peak emission wavelength of 520nm. This is the first report of all-organic IR-to-visible up-conversion OLED with near-IR sensitivity up to 1,100nm.
关键词： Organic Light Emitting Diode,Low Bandgap Polymer,Up-Conversion,Near-Infrared
更新于2025-09-12 10:27:22
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Benzoylpyridine-based TADF emitters with AIE feature for efficient non-doped OLEDs by both evaporation and solution process
摘要： Fluorescent materials taking both advantages of evaporation and solution processes are urgently explored for the development of efficient and simplified organic light-emitting diodes (OLEDs). Furthermore, it is another huge challenge for such materials to achieve excellent electroluminescence performances in non-doped OLEDs. Herein, two new emitters, named as PyB-DPAC and PyB-DMAC with 4-benzoylpyridine moiety as the electron acceptor and 9,9-diphenyl-9,10-dihydroacridine or 9,9-dimethyl-9,10-dihydroacridineas the electron donor were synthesized and explored. Both emitters exhibit distinct TADF character, typical AIE feature and relatively high photoluminescence quantum yields. Accordingly, we demonstrated efficient non-doped vacuum-deposited OLED based on the PyB-DPAC with a maximum external quantum efficiency (EQE) up to 9.7%, and meanwhile an extremely low efficiency roll-off of 1.7% at a high brightness of 1000 cd m-2. In addition, an impressive EQE of 11.1% can be realized from the solution-processed non-doped devices with the using of PyB-DPAC emitter. These affirmative results manifest that TADF emitters incorporate with the benzoylpyridine acceptor enabling a promising molecular design strategy in adapt to the non-doped evaporation- and solution-processed highly efficient OLEDs.
关键词： benzoylpyridine,Organic light-emitting diode,thermally activated delayed fluorescence,aggregation-induced emission
更新于2025-09-12 10:27:22
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Integrated microsensor for precise, real-time measurement of junction temperature of surface-mounted light-emitting diode
摘要： Light-emitting diodes (LEDs) are widely used in many industrial applications owing to their high performance and efficiency compared with conventional lighting systems. However, a considerable amount of input power is inevitably dissipated into heat at the LED junction, which can degrade the performance and reliability of the LED; thus, it is important to monitor the change in the junction temperature of the LED. In this study, we present a micro-temperature sensor-integrated surface-mounted device (SMD) for accurate and real-time measurement of the junction temperature of an LED. The LED is mounted on a microfabricated Pt sensor in a similar way to the typical SMD assembly. The heat generated at the LED junction is conductively transferred to the microsensor, increasing the temperature and changing its electrical resistance. In contrast to the conventional techniques for thermal characterization of LEDs, the integrated microsensor provides real-time information on the junction temperature with high precision, reproducibility, and simplicity. Additionally, the temperature of the solder, which is not easily accessible but is closely related to the reliability of the LED, can be estimated by analyzing the thermal resistance of the LED package. Experimental and numerical results indicate a linear correlation (R2 = 0.988) between the junction and sensor temperatures, which is practically useful for the thermal management of the miniaturized SMD-LED.
关键词： Junction temperature,Light-emitting diode,Thermal transient test,Microsensor,Surface-mounted device,Thermal management
更新于2025-09-12 10:27:22
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Optical Characterization of III-V Multijunction Solar Cells for Temperature-Independent Band Gap Features
摘要： A recently developed method to characterize the band gap energies of III-V optosemiconductors was utilized to determine temperature-invariant band gap features of multijunction solar cells. The method is based on measuring electroluminescent spectra of the solar cells at different temperatures. The normalized spectra reveal temperature-invariant energy values of the different junctions which are further converted to band gap energies. The method utilization requires a calibrated spectroradiometer and a temperature controlled mounting base for the solar cell under test, however, no knowledge about the absolute temperature of the cell under measurement. The method was tested on GaAs and GaInP solar cells that consist of single and dual junctions. The band gap energies were also derived from spectral response measurements. The differences of the determined band gap energies from the literature values were smaller than 1.1%. Compared with other band gap determination methods, the developed method yields temperature-invariant band gap characteristics; with a known uncertainty, that separated the different junctions in a multijunction device without individual biasing for the different junctions. In addition, a temperature-independent characterization parameter ensures that the operating conditions of the device under test do not affect the results.
关键词： III-V solar cells,light-emitting diode (LED),spectral response,temperature,Band gap
更新于2025-09-12 10:27:22
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Effect of Different Combinations of Red and Blue LED Light on Growth Characteristics and Pigment Content of In Vitro Tomato Plantlets
摘要： The aim of this study was to evaluate the growth characteristics and pigment content of tomato plantlets grown under various ratios of red (R) (661 nm) and blue (B) (449 nm) LED light. In this study, three di?erent ratios of R and B (RB) light such as 5:01, 10:01, and 19:01 along with R (100%) were used. The photosynthetic photon ?ux density (PPFD), and photoperiod of the growth chamber was 120 ± 5 μmol m?2s?1 and 16/8 h (day/night), respectively. Tomato plantlets were cultured for six weeks in the growth chamber. It was shown that tomato plantlets had higher photosynthesis rate, higher pigments content, higher growth characteristics (e.g., number of leaves, leaf area, shoot number, root number, root length, dry, and fresh mass), and greater surviving rate under the R:B = 10:01 ratio among the treatments. The plantlets showed at least a threefold decrease in photosynthesis rate, as well as a signi?cant abnormal stem elongation when grown under 100% R light. It is concluded that the RB ratio of 10:01 showed excellent performance in all growth parameters. This result has shown that the optimum lighting environment improves tomato plantlet cultures in vitro.
关键词： tomato plantlets,pigments,light-emitting diode (LED),biomass,photosynthesis
更新于2025-09-12 10:27:22
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A Single-Stage High-Power-Factor Light-Emitting Diode (LED) Driver with Coupled Inductors for Streetlight Applications
摘要： This paper presents and implements a single-stage high-power-factor light-emitting diode (LED) driver with coupled inductors, suitable for streetlight applications. The presented LED driver integrates an interleaved buck-boost power factor correction (PFC) converter with coupled inductors and a half-bridge-type series-resonant converter cascaded with a full-bridge rectifier into a single-stage power conversion circuit. Coupled inductors inside the interleaved buck-boost PFC converter sub-circuit are designed to operate in discontinuous conduction mode (DCM) for achieving input-current shaping, and the half-bridge-type series resonant converter cascaded with a full-bridge rectifier is designed for obtaining zero-voltage switching (ZVS) on two power switches to reduce their switching losses. Analysis of operational modes and design equations for the presented LED driver are described and included. In addition, the presented driver features a high power factor, low total harmonic distortion (THD) of input current, and soft switching. Finally, a prototype driver is developed and implemented to supply a 165-W-rated LED streetlight module with utility-line input voltages ranging from 210 to 230 V. Experimental results demonstrate that high power factor (>0.99), low utility-line current THD (<7%), low-output voltage ripples (<1%), low-output current ripples (<10%), and high circuit efficiency (>90%) are obtained in the presented single-stage driver for LED streetlight applications.
关键词： converter,streetlight,light-emitting diode (LED),driver
更新于2025-09-12 10:27:22
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Coaxial GaAs/(In,Ga)As Dot-in-a-Well Nanowire Heterostructures for Electrically Driven Infrared Light Generation on Si in the Telecommunication O Band
摘要： Core-shell GaAs-based nanowires monolithically integrated on Si constitute a promising class of nanostructures that could enable light emitters for fast inter- and intrachip optical connections. We introduce and fabricate a coaxial GaAs/(In,Ga)As dot-in-a-well nanowire heterostructure to reach spontaneous emission in the Si transparent region, which is crucial for applications in Si photonics. Specifically, we achieve room temperature emission at 1.27 μm in the telecommunication O band. The presence of quantum dots in the heterostructure is evidenced by a structural analysis based on scanning transmission electron microscopy. The spontaneous emission of these nanowire structures is investigated by cathodoluminescence and photoluminescence spectroscopy. Thermal redistribution of charge carriers to larger quantum dots explains the long wavelength emission achieved at room temperature. Finally, in order to demonstrate the feasibility of the presented nanowire heterostructures as electrically driven light emitters monolithically integrated on Si, a light emitting diode is fabricated exhibiting room-temperature electroluminescence at 1.26 μm.
关键词： Electroluminescence,Si substrates,Dot-in-a-well,Light emitting diode,Nanowire heterostructures
更新于2025-09-12 10:27:22
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Controlled Surface for Enhanced Luminescence Quantum Yields of Silicon Nanocrystals; 蛍光シリコン粉末の機能増強を導く表面制御に関する研究;
摘要： In the current review paper, we provide the experimental evidences for the controlled structure of diamond cubic silicon nanocrystals (SiNCs) which enhances their photoluminescence quantum yields (PLQYs). Hydrogen-terminated Si provides a basic surface for further modification. Their enhancement was performed by a simple ligand exchange between the hydrogen atoms and hydrocarbon chains. On the basis of the systematic study on temperature dependence of PL properties along with relaxation dynamics, a long-accepted mechanism for enhancing absolute PL was recently revised. Specifically, combination of PL spectroscopic measurement from cryogenic to room temperature with structural characterization allows us to link the enhanced PLQYs with the notable difference in surface structure. The hydride-terminated surface suffers from the presence of a large amount of nonradiative relaxation channels whereas the passivation with alkyl monolayers suppresses the creation of the nonradiative relaxation channels to yield the high PLQY. This anchoring effect was responsible for the PLQYs as high as 56%. Tunability of PL bands was achieved in the wavelength ranging between 590 nm and 1064 nm. Next, the review considers the use of the highly emitting SiNCs for optoelectronic and biophotonic applications. The tunable light emitting diodes in which SiNCs serve as active layers are demonstrated. Si exhibits a high chemical affinity to covalent linkages with carbon, oxygen, and nitrogen, thereby producing almost unlimited variations in organic–Si architectures hybridized at the molecular level. Therefore, biomedical applications of SiNCs are attractive. Details of the biophotonic applications are not described in this review, but functional near-IR (NIR) emitting nanoparticles of SiNCs of narrow PL spectra having no long emission tails, continuously tunable over the 700–1000 nm window where the light absorption of water and the tissues including hemoglobin is minimal have a potential to become one of nontoxic biomarkers that is available in-vivo study. Finally, we provide perspective on the overall current status, challenges and potentials for this research field in near future.
关键词： Anchor effect,Silicon nanocrystals,Photoluminescence,Light emitting diode
更新于2025-09-12 10:27:22
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Fabrication of highly transparent and luminescent quantum dot/polymer nanocomposite for light emitting diode using amphiphilic polymer-modified quantum dots
摘要： Herein we present the fabrication of a highly transparent and luminescent quantum dot (QD)/polymer nanocomposite for application in optoelectronic devices. First, we encapsulated CdSe@ZnS/ZnS core/shell QDs with an amphiphilic polymer, i.e., poly(styrene-co-maleic anhydride) (PSMA). By encapsulating QDs with PSMA instead of ligand exchange, the photoluminescence intensity of the QDs could be preserved even after surface modification. Next, the PSMA-modified QDs were used as crosslinkers for the aminopropyl-terminated polydimethylsiloxane (PDMS) resin in a ring-opening reaction between the maleic anhydride of the QDs and the diamines of the PDMS, producing polymer networks at a low curing temperature. This method afforded a nanocomposite with uniform dispersion of QDs even at high QD concentrations (~30 wt%) and superior optical properties compared to a nanocomposite prepared from unmodified QDs and commercial resin. Owing to these enhanced properties, the nanocomposite was used to fabricate a light emitting diode (LED) device, and the luminous efficacy was found to be highest at 1 wt%.
关键词： quantum dots,dispersion,surface modification,amphiphilic polymer,light emitting diode
更新于2025-09-12 10:27:22
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An overview of energy efficient solid state LED driver topologies
摘要： LED lamps are projected as prospective successors of incandescent lamps with high efficiency and a long lifetime. Therefore, there is a need to develop energy efficient LED driver topologies for achieving constant current regulation, despite the effects of temperature on the LED V‐I characteristics. This paper presents the salient features of various LED driver topologies with a focus on power density, multi‐string operation, renewable energy utilization, soft switching, optical wireless communication, reliability and size. The performance of the above topologies is analysed in terms of the number of components, converter switching frequency, galvanic isolation, power rating and efficiency. This paper takes a look at efficiency improvement methods while dwelling on aspects of lifetime and reliability prediction of LED drivers. The paper will anticipate some of the future trends associated with the adaptation of wide bandgap power semiconductor materials, smart LED lighting for the internet of things (IoT) and programmable LED lamp drivers. This detailed technology review is extremely useful for researchers, designers and engineers in choosing the right topology.
关键词： photovoltaic,dimmable LEDs,light emitting diode,organic LEDs,DC‐DC converters
更新于2025-09-12 10:27:22