Green Light-emitting Diodes Research Articles

Exceptional Stability against Water, UV Light, and Heat for CsPbBr3@Pb-MOF Composites.

All-inorganic lead halide perovskite nanocrystals (NCs) have been widely applied in optoelectronic devices owing to their excellent photoluminescence (PL) properties. However, poor stability upon exposure to water, UV light or heat strongly limits their practical application. Herein, CsPbBr3@Pb-MOF composites with exceptional stability against water, UV light, and heat are synthesized by ultrasonic processing the precursors of lead-based MOF (Pb-MOF), oleylammonium bromide (OAmBr) and cesium oleate (Cs-OA) solutions at room temperature. Pb-MOF can not only provide the lead source for the in situ growth of CsPbBr3 NCs, but also the protective layer of perovskites NCs. The formed CsPbBr3@Pb-MOF composites show a considerable PL quantum yield (PLQY) of 67.8%, and can maintain 90% of the initial PL intensity when immersed in water for 2 months. In addition, the outstanding PL stability against UV light and heat is demonstrated with CsPbBr3 NCs synthesized by the conventional method as a comparison. Finally, a green (light-emitting diode) LED is fabricated using green-emitting CsPbBr3@Pb-MOF composites and exhibits excellent stability without packaging when immersed in water for 30 days. This study provides a practical approach to improve the stability in aqueous phase, which may pave the way for future applications for various optoelectronic devices.

Do attenuation coefficients based on luminescence bleaching fronts reflect true light attenuation in rocks?

The emerging technique of rock surface luminescence dating employs a double-exponential fitting dating model based on the Bouguer-Lambert law. The accuracy of exposure age determination is sensitive to the light attenuation coefficient, μ, which is usually derived from fitting the luminescence profile as a function of depth into the rock. Alternatively, μ might be determined by direct measurement using a spectrophotometer. However, their directly measured values of μ were significantly larger than those estimated from field luminescence bleaching data. Here, we aim to confirm these previous results by measuring the luminescence-depth profiles of both IRSL and IRPL signals from granite rock exposed to different light sources, including sunlight, SOL2 and IR LEDs under controlled conditions. We also measured monochromatic light (blue LED: (470 ± 30) nm, green LED: (520 ± 30) nm, and infrared LED: (850 ± 30) nm) attenuation in granite rock slices of varying thickness (0.62–2.60 mm) using a high-sensitivity photodiode. Finally, we use a camera-based measurement system and a Risø Luminescence Imager to investigate spatial variation in transmitted light as a function of slice thickness. The spatial correlation between direct light transmission and luminescence emission is then investigated, to investigate the underlying reasons for the difference between direct measurement and luminescence-based estimates of μ. We find that light attenuation through a granite rock slice is very heterogeneous; most light penetrates through localized low attenuation light paths corresponding to transmission through the most transparent grains, presumably quartz. The light penetration and escape into the surrounding matrix are assumed to be influenced by the surface area of quartz grains. As a result, transmissive light paths result in a significant area of feldspar grains at depth in the slice being exposed to more light than might be expected from average attenuation measurement. When the incident light predominantly travels through feldspar minerals, simultaneously stimulating luminescence from within any potassium feldspar (K-feldspar), the attenuation coefficients derived from the luminescence-depth profiles tend to be smaller than the average of 1.18 ± 0.07 (n = 79) irrespective of the kinetic model used for fitting. Thus, luminescence-based attenuation coefficient estimates appear to be affected by the distribution of light attenuation across and within the rock slice, making such estimates preferable to directly measured (average) estimates of light attenuation coefficients. These insights are important for our understanding of the significance of light attenuation coefficients in rock samples; they contribute to the reassessment of parameters and measurement methods in dating models and so to improvements in accuracy of rock surface luminescence dating techniques.

Filter paper as electrolyte flow transport using vaporized methanol as fuel in a microfluidic fuel cell: Experimental and numerical simulation

In this work, we present a design of a paper-based microfluidic fuel cell (μFC), which employs the spontaneous capillary flow of reactant solutions in a filter paper to accomplish passive conveyance of the fuel and oxidant. This self-pumping device uses methanol vapor as a fuel. The gas phase in the microfluidic fuel cell increases the fuel supply to the anode due to a higher diffusion coefficient of 1.5 ​× ​10−5 ​m2 ​s−1 compared with 5 ​× ​10−9 ​m2 ​s−1 for liquid phase. An air-breathing cathode is incorporated to paper-based μFC through which atmospheric oxygen is continuously supplied. The paper-based μFC performance is studied by polarization curves and chronoamperometry to determinate the power output and stability. Peak power of 1.49 ​mW and a stable current of 1.35 ​mA at 0.35 ​V for 28 ​h can be achieved with this prototype under room temperature. To interpret the device performance a numerical model is developed and validated with the experimental polarization curve. The fuel and oxidant concentration profiles in the electrodes from the model demonstrates a constant species availability at the cathode and anode and explains the stable current obtained in the experimental measurements. Subsequently, a stack of four MμFCFP was developed and evaluated in both series and parallel connections. In the parallel configuration, a maximum open circuit potential (OCP) of 0.69 ​V with a maximum current and power output of 34.53 ​mA and 4.14 ​mW are delivered, respectively. Conversely, in the series connection, a total current of 7.35 ​mA, an OCP of 2.39 ​V and a maximum power of 3.57 ​mW are reached. As a proof of concept, the stack successfully operates a 3 green LEDs array, each requiring a 2.1–2.5 ​V and 4.2–5 ​mW power to function, for a continuous duration of 3 ​h.

Bright, efficient, and stable pure-green hyperfluorescent organic light-emitting diodes by judicious molecular design

To fulfill ultra-high-definition display, efficient and bright green organic light-emitting diodes with Commission Internationale de l’Éclairage y-coordinate ≥ 0.7 are required. Although there are some preceding reports of highly efficient devices based on pure-green multi-resonance emitters, the efficiency rolloff and device stabilities for those pure-green devices are still unsatisfactory. Herein, we report the rational design of two pure-green multi-resonance emitters for achieving highly stable and efficient pure-green devices with CIEx,ys that are close to the NTSC and BT. 2020 standards. In this study, our thermally activated delayed fluorescence OLEDs based on two pure-green multi-resonance emitters result in CIEy up to 0.74. In hyperfluorescent device architecture, the CIExs further meet the x-coordinate requirements, i.e., NTSC (0.21) and BT. 2020 (0.17), while keeping their CIEys ~ 0.7. Most importantly, hyperfluorescent devices display the high maximum external quantum efficiencies of over 25% and maximum luminance of over 105 cd m−2 with suppressed rolloffs (external quantum efficiency of ~20% at 104 cd m−2) and long device stabilities with LT95s of ~ 600 h.

Portable Air Quality Detector Using DSM501A Dust Sensor and Arduino Uno

Aims: The primary feature of this research is to design a circuit that can analyze the air around the system and determine the quality of the air.
 Study Design: This paper reports on the design and implementation of a portable air pollution analyzer using Arduino Uno, DSM501A dust sensor, LCD, switches, buzzer, and multiple LEDs. The air pollution analyzer system was designed using a combination of hardware and software techniques to measure air pollution properly.
 Place and Period of Study: The research was accomplished by the authors in a group of two students under the grasp of a professor as a part of one of his course capstone projects for the Bachelor of Science in Electrical and Electronic Engineering degree at the American International University Bangladesh (AIUB), Dhaka, Bangladesh. The authors performed their investigative tasks at AIUB from September 2023 to February 2024.
 Methodology: The air pollution analyzer was implemented using an Arduino Uno and dust sensor to generate and determine accurate air quality based on specific air contents. The system that was developed used a PM10 detection system that identified the amount of dust particles in the area. Based on PM10 readings, the air quality was identified. Moreover, the Air Quality Index (AQI) was determined using the PM10 readings. The LCD, buzzer, and multiple LEDs were used to display and indicate the air quality condition and levels.
 Results: The portable air pollution analyzer was successfully tested and found to be accurate and reliable in determining air quality. To indicate different hazardous states of air, red, green, and yellow color LEDs are used. The test outcomes were very satisfactory.
 Conclusion: This system demonstrates the use of a microcontroller in building a simple yet effective portable air quality detector. It can be scaled up for commercial production.

Novel indolocarbazole-based bipolar host materials for fabricating green phosphorescent organic light-emitting diodes with high efficiency and low roll-off

Herein we report two novel host materials, viz., 2-(dibenzo [b,d]furan-2-yl)indolo [3,2,1-jk]carbazole (ICz-DBF) and 3-(indolo [3,2,1-jk]carbazol-2-yl)furo [2,3-b:5,4-b']dipyridine (ICz-PFP), for fabricating highly stable and efficient organic light-emitting diodes (OLEDs). Green phosphorescent OLEDs (PhOLEDs) based on ICz-DBF and ICz-PFP exhibited less efficiency roll-off than those based on 4,4′-bis(N-carbazolyl)-1,1′-biphenyl (CBP) host, and especially, the ICz-DBF-based device achieved a high external quantum efficiency (EQE) of 20.5 %. Bipolar hosts composed of indolocarbazole (ICz) exhibit strong molecular rigidity, high triplet energy, and fast electron transport properties; therefore, they act as acceptors, but dibenzofuran (DBF) and dipyridofuran (PFP) substitutions endow them with controlled electron-donating characteristics. The bipolar properties of the new host materials were demonstrated by single-carrier device analysis, confirming the effectiveness of our research strategy for developing hosts for high-quality OLEDs.

Formation of homogeneous pyridinic emission states in carbon dots via solid-state carbonization of aminoquinoline: Optical design principles and light-emitting diode applications

Developing carbon dots (CDs) for practical applications faces significant hurdles due to non-homogeneity in their chemical structure, leading to broad spectral distribution and the excitation-energy-dependent behavior of their fluorescence (FL) emission properties. To address this challenge, we implemented solid-state carbonization of 6-aminoquinoline (6-AQ) devoid of any additives that could induce chemical non-homogeneity. This process yielded pyridinic-nitrogen-doped CDs (PN-CDs) characterized by homogenous, uniform emission states arising from pyridine-incorporated heteroatomic structures. Notably, these PN-CDs exhibited excitation-energy-independent FL at 520 nm with a full-width-half-maximum of 70 nm. To elucidate the structure-property relationship in PN-CDs, a comprehensive analysis encompassing time-resolved spectroscopy and ab initio calculations was conducted. Furthermore, we performed a comparative study by manipulating synthesis parameters and utilizing six AQ isomers, offering valuable insights to optimize the optical properties of PN-CDs. Finally, we successfully demonstrated high-color-purity and efficient green light-emitting diodes utilizing PN-CDs, highlighting their potential for future display applications. This paves the way for advancement in optical materials with enhanced performance and reduced environmental impact.

Efficient non-doped cluster light-emitting diodes based on semiconducting copper iodide hybrids

Copper iodide hybrid clusters have attracted lots of interest in solution-processed light-emitting diodes (LEDs) for solid-state lighting and display in recent years, benefiting from their simple synthesis, structural diversity, high photoluminescence quantum yield (PLQY), and non-toxicity. However, most efficient copper iodide cluster LEDs are made by host-guest doped emitters and thus suffer from cumbersome synthesis and increased costs from the expensive hosts. Here, we report a non-doped cluster LED based on a novel copper iodine hybrid [35DPPy]4Cu2I2 (35DPPy: 3,5-diphenylpyridine) with high PLQY and decent charge transport characteristic. The non-doped [35DPPy]4Cu2I2 film synthesized by a one-step spin-coating approach possess the flat and compact morphology, high PLQY of 59.6%, and excellent heat/ultraviolet (UV) light/moisture/oxygen stability. The efficient green PL of [35DPPy]4Cu2I2 is proved to originate from the synergistic contribution from thermally activated delayed fluorescence and phosphorescence. A non-doped green LED based on [35DPPy]4Cu2I2 emitters is fabricated, achieving a peak external quantum efficiency of 4.8% and a maximum luminance of 3895 cd/m2. More importantly, large-area LEDs with an emitting area of 4.00 cm2 are realized with homogeneous and bright electroluminescence, showing their attractive potentials as novel electroluminescent emitters in the application of non-doped cluster LEDs.

Cr3+ doped Cs2ZnCl4 microcrystals enabling near-infrared emission

As a promising lead-free metal halide, Cs2ZnCl4 has the potential to serve as a host for achieving various photoluminescence emissions with different colors through ion doping. Therefore, studying the optical properties of various ions doped into Cs2ZnCl4 with tetrahedron coordination is of great significance. However, there is still a lack of research on near-infrared (NIR) emission in Cs2ZnCl4. In this study, we successfully synthesized Cs2ZnCl4:Cr3+ crystals using a simple hydrothermal method. The Cs2ZnCl4:Cr3+ exhibits luminescence in the range of 800–1300 nm, with a peak position at 915 nm and a full width at half maximum (FWHM) of 150 nm under 375 nm excitation. Through the analysis of photoluminescence spectra, density functional theory (DFT), lifetime decay curves, temperature-dependent spectra, and time-resolved photoluminescence (TRPL), we confirmed the presence of two potential sites for Cr3+ ion occupancy. Additionally, NIR phosphor-converted light-emitting diodes (pc-LEDs) were fabricated by combining Cs2ZnCl4:Cr3+ with a green LED chip. The night-vision camera captured the distribution of blood vessels and bones in the fingers, demonstrating the promising potential of this material in the field of NIR imaging.

Field comparison of broad-spectrum white LED-baited traps with narrow-spectrum green LED-baited traps in the capture of Anopheles mosquitoes (Diptera: Culicidae).

Light-Emitting Diodes (LEDs) have been effective light sources in attracting Anopheles mosquitoes, but the broad-spectrum white light, even with a wide-ranging application in lighting, have not been evaluated yet. In this study, the white light was field evaluated against the green one in the light trapping of anopheline mosquitoes by using two non-suction Silva traps and two CDC-type suction light traps. Anopheline mosquitoes were captured for two 21-night periods of collecting (2022 and 2023). In the first period, two LEDs were used per Silva trap, but three were used in the second one to increase the luminance/illuminance at traps. A CDC-type suction light trap equipped with an incandescent lamp was used in 2022 and a CDC-type suction light trap equipped with a 6 V-white light (higher luminance/illuminance) in 2023. A total of eight species and 3,289 specimens were captured in both periods. The most frequent species were Anopheles triannulatus s.l., An. goeldii, An. evansae and An. argyritarsis. In 2022, white LEDs were less attractive to anopheline mosquitoes than the other light sources, but without statistical difference among treatments (F = 2.703; P = 0.0752; df = 2). In 2023, even with an increased luminance/illuminance at traps, no statistical difference was found between the two LED-baited Silva traps (F = 6.690; P = 0.0024; df = 2), but rather between the 6 V-white-baited CDC-type suction light trap and green-baited Silva traps. Due to some drawbacks and the lower abundance of individuals caught by using white LEDs, the narrow-banded green LEDs is preferable to white ones for attracting anophelines.

Erythrosine+KI with Multiple Sessions Green LED-mediated Photodynamic Therapy Potentiate Anticandidiasis Effect

SignificanceThe concurrent use of double photosensitizers with multiple irradiation sessions is emerging as a promising modality for photodynamic therapy. ApproachCandida albicans (ATCC10231) biofilm was treated with either erythrosine 220 μM, 100 mM KI, or 220 μM erythrosine+100 mM KI. Control groups were phosphate buffer saline, 1:100,000 U/ml nystatin solution, and Light-only respectively. After 60-secs incubation, experimental groups were irradiated with LED (520-540 nm, 250 mW/cm2, 20 J/cm2/session) for 1 or 3 sessions. The logarithmic transformation of biofilm count was calculated and a comparison at 1, 24 hrs was performed using median±interquartile range. The statistically significant difference was determined using Kruskal Wallis test with post hoc test at p<0.05 Results220 μM Erythrosine+100 mM KI with 60 J/cm2 (20 J/cm2x3 sessions) exerted the most anticandidal effect that comparable to nystatin effect. ConclusionsErythrosine 200 μM+KI 100 mM+3 sessions green LED (total energy 60 J/cm2) effectively reduced C. albicans biofilm.

Chromatic Wavelengths Luminescence: It’s Impact to Growth Response of Tsitsirika (Catharanthus Roseus)

This study seeks to analyze the complex interactions between color psychology, lighting technology, and the cultivation of Tsitsirika (Catharanthus roseus) in the Philippine agricultural environment. The study is organized around three main goals: first, to investigate the effect of several LED wavelengths, specifically red, blue, and green, on the overall growth parameters of Tsitsirika. Second, it intends to conduct a rigorous comparative analysis, carefully comparing the development patterns shown by various colored LEDs to those detected in natural solar irradiation. This comprehensive analysis seeks to identify significant differences and explain potential benefits or drawbacks related with the use of artificial lighting. Ultimately, the study aims to explain the physiological characteristics induced by red, blue, and green LED wavelengths on Tsitsirika, revealing their subtle effects on the plant's physiological and morphological aspects, including leaf pigmentation and stomatal behavior. By thoroughly addressing these objectives, this study hopes to provide nuanced and academically valuable insights on the prudent application of color psychology and lighting technology, ultimately influencing optimal cultivation practices for Tsitsirika. This scholarly endeavor is positioned to support sustainable and efficient agricultural practices, not just in the Philippines but also with potential for broader application.

Compositionally engineered NiCoLDH@rGO as bifunctional cathode catalyst for rechargeable Li-O2/Li-CO2 battery

Compositionally tuned nickel-cobalt layered double hydroxides (NCLDHs) and NCLDH@reduced graphene-oxide (NCLDH@rGO) were synthesized through a facile solvothermal synthesis route. The formation of the synthesized NCLDH and the NCLDH@rGO with the intercalated carbonate and nitrate anions, has been confirmed utilizing different characterization techniques. Microscopic results revealed the flaky morphology with thickness about 30 nm. Rotating ring disc electrode (RRDE) voltammetry was utilized to analyze the oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and carbon dioxide reduction reaction (CO2RR) kinetics on each of the pristine (1:1), (2:1), (3:1) and (4:1) NCLDH catalysts and the NCLDH@rGO composites. The RRDE data revealed that the electrochemical activity towards ORR/OER/CO2RR could be largely increased by tuning mole ratio of the (Ni2+/Co3+) or the amount of the rGO in the NCLDH. It turned out that among the pristine electrocatalysts, the (1:1) NCLDH catalyst exhibited enhanced ORR/OER kinetics. While the NCLDH acted as a catalyst center, the rGO provided conductive network that facilitated passable overpotential with increased current density for the ORR/OER/ CO2RR. Better adsorption of O2 and CO2 on the NCLDH@rGO catalyst also contributed for the electrocatalytic activity. Consequently, the NCLDH@rGO composites as cathode catalyst for Li-O2 battery in the CR2032 prototype coin-cell exhibited a stable open circuit voltage (OCV). Among the NCLDH@rGO composites, the NCLDH with 15 wt.% rGO (NCRGO15) exhibited a high discharge capacity of 3616 mAh g−1 at 50 Ag−1 for the Li-O2 battery and a discharge capacity of 45 mAh g−1 at a current density of 100 Ag−1 for the CR2032 coin-type Li-CO2 battery. As a practical use, a commercial 2.8 V green LED bulb was lit continuously for about 20 h using the fabricated Li-O2 battery that consisted of lithium anode and (1:1) NCLDH@rGO15 wt.% (NCRGO15) air-breathing cathode.

Investigating the annealing effects on the performance of polyvinyl alcohol-graphite-based triboelectric nanogenerator

Annealing plays a crucial role in enhancing the performance, stability, and durability of triboelectric nanogenerators (TENGs). By carefully controlling the annealing parameters, the material properties can be optimized and improve the overall efficiency of TENG devices for various practical applications. Herein, graphite (Gr) embedded polyvinyl alcohol (PVA) composite films are prepared by a solution casting technique and subjected to annealing at various temperatures below the glass transition temperature (Tg) of PVA. The annealed effects are thoroughly examined through characterizations involving PXRD, SEM, EDS, FTIR, and TGA. Subsequently, TENGs are fabricated utilizing the annealed composite films as the tribopositive material, polypropylene as the tribonegative material, and the impact of annealing on the device performance is investigated. At an annealing temperature of 80°C, the PVA-Gr TENG exhibited notably higher output voltage (VOC) and short-circuit current (ISC) of 200.24 V and 12.68 µA, respectively. In addition, the PVA-Gr TENG successfully charges electrolytic capacitors, powers a digital watch, operates a humidity and temperature sensor, and lights a series of green LEDs. Thus, the present study highlights the significant impact of annealing on the performance of PVA-Gr TENG, leading to enhanced output power and stability.

Analysis of Unique Motility of the Unicellular Green Alga Chlamydomonas reinhardtii at Low Temperatures down to -8 °C.

Previous studies of motility at low temperatures in Chlamydomonas reinhardtii have been conducted at temperatures of up to 15 °C. In this study, we report that C. reinhardtii exhibits unique motility at a lower temperature range (-8.7 to 1.7 °C). Cell motility was recorded using four low-cost, easy-to-operate observation systems. Fast Fourier transform (FFT) analysis at room temperature (20-27 °C) showed that the main peak frequency of oscillations ranged from 44 to 61 Hz, which is consistent with the 60 Hz beat frequency of flagella. At lower temperatures, swimming velocity decreased with decreasing temperature. The results of the FFT analysis showed that the major peak shifted to the 5-18 Hz range, suggesting that the flagellar beat frequency was decreasing. The FFT spectra had distinct major peaks in both temperature ranges, indicating that the oscillations were regular. This was not affected by the wavelength of the observation light source (white, red, green or blue LED) or the environmental spatial scale of the cells. In contrast, cells in a highly viscous (3.5 mPa·s) culture at room temperature showed numerous peaks in the 0-200 Hz frequency band, indicating that the oscillations were irregular. These findings contribute to a better understanding of motility under lower-temperature conditions in C. reinhardtii.

DESIGN AND IMPLEMENTATION OF IOT BASED HOTEL ROOMS OCCUPANCY REPORTING SYSTEM

Advances in technology applications are becoming more visible in everyday activities as the globe becomes more technologically skilled and evolved. Being able to receive and execute control is critical in the age of Internet of Things technology and control. This pattern eventually led to the development of an Internet of Things (IoT) system for reporting room occupancy as a promising technique or system for determining the availability of rooms and buildings. This method lowers human mistake, mismanagement, and energy use, all of which directly translate to decrease hotel running costs, possibly to zero. As a result, it is conceivable that the number of guests staying in Nigerian hotels has risen significantly. If this is the case, good management will most certainly result in an immense rise in profits. However, sharp practices among hotel employees tend to divert the profit met for the owners, thus this project is designed to automatically report hotel occupancy easily accessible to owners. An infrared detection circuit was used detect human movement and a lithium-ion battery that supplied 3.7 volts was used as the power supply for the circuit while a GPRS module (a SIM 800L GSM module) was utilized to receive and transmit data messages via radio waves, and an LGT8F328P microcontroller controlled every other component in the circuit. An android application was developed and installed on a mobile phone to gather all of the real-time readings and events that take place throughout the project’s system. The programming of the microcontroller was done using the Arduino Integrated Development Environment (IDE) software and C++ programming language. When the project was turned on, I saw that all of the LEDs turned on automatically. The first two LEDs (brown and green) were automatically turned on, as were the corresponding room LEDs. After that, the green LED turned off. When the infrared LEDs’ visibility is obscured, their input to the phototransistors in each room and the LEDs attached to each room automatically turn on, indicating that the rooms are occupied and vice versa. The various room compartments’ check-ins and check-outs are tracked, managed, and updated using the proposed hardware. The data is then transmitted to the IoT cloud and eventually to the Android application

Visible light photoresponse properties of Ag/n-ZnO-NRs/p-Si/Al photodiodes, the influence of optimal ZnO precursor concentration via CBD method

In this study, we studied the influence of zinc nitrate hexahydrate (Zn(NO3)2.6 H2O) precursor concentrations (0.03, 0.05, and 0.07 M) in Ag/n-ZnO-NRs/p-Si/Al photodiodes on the photoresponse of the samples to the blue, green, and red light LEDs. The layers were characterized by FESEM, EDX, XRD, PL, UV-Vis. reflectance spectra, and also, I-V and I-t in the dark and under light illuminations. We found, depending on the precursor concentration: (1) the ZnO layers, while having a polycrystalline structure with a hexagonal (wurtzite) phase mainly grown along the (002) direction, consist of nanorods (NRs) with different diameters and lengths; (2) the analysis of the dark I-V data showed the synthesized devices have rectifying behavior; (3) the analysis of the I-t data, operated at −5 V, showed that the fabricated samples have a fast-switching characteristic (≈ 65 ms); (4) the sample with a 0.05 M concentration as the optimal layer, with the lowest light reflectance feature, has the maximum light sensitivity (SIP/ID) and responsivity (R*) to various visible light illuminations (460, 31 mA/W for blue, 201, 14 mA/W for green, and 190, 13 mA/W for red).

Multifunctional TADF Additives for High-Performance Green Perovskite Light-Emitting Diodes

Multifunctional TADF Additives for High-Performance Green Perovskite Light-Emitting Diodes

High-Performance All-Inorganic Architecture Perovskite Light-Emitting Diodes Based on Tens-of-Nanometers-Sized CsPbBr3 Emitters in a Carrier-Confined Heterostructure.

Developing green perovskite light-emitting diodes (PeLEDs) with a high external quantum efficiency (EQE) and low efficiency roll-off at high brightness remains a critical challenge. Nanostructured emitter-based devices have shown high efficiency but restricted ascending luminance at high current densities, while devices based on large-sized crystals exhibit low efficiency roll-off but face great challenges to high efficiency. Herein, we develop an all-inorganic device architecture combined with utilizing tens-of-nanometers-sized CsPbBr3 (TNS-CsPbBr3) emitters in a carrier-confined heterostructure to realize green PeLEDs that exhibit high EQEs and low efficiency roll-off. A typical type-I heterojunction containing TNS-CsPbBr3 crystals and wide-bandgap Cs4PbBr6 within a grain is formed by carefully controlling the precursor ratio. These heterostructured TNS-CsPbBr3 emitters simultaneously enhance carrier confinement and retain low Auger recombination under a large injected carrier density. Benefiting from a simple device architecture consisting of an emissive layer and an oxide electron-transporting layer, the PeLEDs exhibit a sub-bandgap turn-on voltage of 2.0 V and steeply rising luminance. In consequence, we achieved green PeLEDs demonstrating a peak EQE of 17.0% at the brightness of 36,000 cd m-2, and the EQE remained at 15.7% and 12.6% at the brightness of 100,000 and 200,000 cd m-2, respectively. In addition, our results underscore the role of interface degradation during device operation as a factor in device failure.

Modulated Crystallization and Carrier Transport Properties for Green Perovskite Light-Emitting Diodes via Thermally Activated Delayed Fluorescent-Modified Hole Transport Layers

Modulated Crystallization and Carrier Transport Properties for Green Perovskite Light-Emitting Diodes via Thermally Activated Delayed Fluorescent-Modified Hole Transport Layers