Quantum Efficiency Research Articles

Lead-Free Perovskite With Efficient Tellurium Ion Activation for Multifunctional Applications.

Lead-free perovskite materials have received extensive attention due to their non-toxicity, super environmental stability and adjustable photoelectric properties. However, the inherent problems of low luminous efficiency and low photoluminescence quantum yields (PLQYs) limit its development in multifunctional applications. Here, Te4+ doped Cs2ZrCl6 with high luminous efficiency and stability for multifunctional applications are developed. Te4+ ions are used as emission centers to improve the optical properties of Cs2ZrCl6 to make efficient and stable single-component white light-emitting diodes (WLEDs), and can be used as scintillator materials to improve scintillation performance to achieve high-resolution and low-dose X-ray imaging detection. In addition, it is found for the first time that Te4+ ions can be introduced into the trap center, so that the Cs2ZrCl6:Te4+ perovskite material exhibits excellent persistent luminescence (PersL) and mechanoluminescence (ML) after X-ray radiation, which has potential applications in the fields of delayed imaging and stress sensing. This work provides a method for designing lead-free perovskites with high optical performance and scintillating properties, as well as developing multifunctional applications.

A Facile Low Prevacuum Treatment to Enhance the Durability of Nonfullerene Organic Solar Cells

Herein, a straightforward vacuum‐assisted method is introduced to enhance the stability of nonfullerene organic solar cells (OSCs). The method, termed “prevacuum” involves subjecting the active layer (D18:Y6) to a low‐pressure vacuum (−1 bar) before thermal annealing at 100 °C. Compared to untreated devices, prevacuum‐treated OSCs exhibit a notable increase in power conversion efficiency from 13.71% to 14.90%. This enhancement is attributed to improved light absorption and charge extraction, as evidenced by external quantum efficiency measurements. Moreover, prevacuum treatment significantly improves device stability under operational conditions, with a 30% power loss occurring after 8.25 h compared to 4.5 h for untreated devices. This improvement is attributed to the removal of volatile components and impurities during the vacuum process, leading to a more hydrophobic and stable active layer. The study demonstrates the efficacy of prevacuum treatment as a simple and accessible method for enhancing the performance and longevity of OSCs, paving the way for their broader application in sustainable energy technologies.

Visible-Light-Induced Hydrogen Generation from Mixtures of Hydrogen Boride Nanosheets and Phenanthroline Molecules.

Hydrogen boride (HB) nanosheets are recognized as a safe and lightweight hydrogen carrier, yet their hydrogen (H2) generation technique has been limited. In the present study, nitrogen-containing organic heterocycles are mixed with HB nanosheets in acetonitrile solution for visible-light-driven H2 generation. After exploring various nitrogen-containing heterocycles, the mixture of 1,10-phenanthroline molecules (Phens) and HB nanosheets exhibited significant H2 generation even under visible light irradiation. The quantum efficiency for H2 generation of the mixture of HB nanosheets and Phens is 0.6%. Based on spectroscopic and electrochemical analyses and density functional theory (DFT) calculations, it is determined that radical species generated from Phens with electrons and protons donated by HB nanosheets are responsive to visible light for H2 generation. The HB nanosheets/Phens mixture presented in this study can generate H2 using renewable energy sources such as sunlight without the need for complex electrochemical systems or heating mechanisms and is expected to serve as a lightweight hydrogen storage/release system.

Hybrid Local and Charge Transfer Emitters Utilizing Hyperconjugation Effect Towards Solution-Processed Ultra-Deep-Blue OLEDs with External Quantum Efficiency Approaching 12.

Hybrid local and charge transfer (HLCT) excited state materials, which possess weak donor-acceptor (D-A) pure organic structures, deserve one of the most promising efficient and stable blue emitters. Through high-lying reverse intersystem crossing (hRISC) process, 75% triplet excitons generated by electrical excitation could be harvested and utilized in organic light-emitting diodes (OLEDs). However, there are still significant challenges to achieve high-efficiency ultra-deep-blue HLCT emitters with low Commission Internationale de l'Eclairage (CIE) 1931 chromaticity coordinate y values. Here, a series of novel blue HLCT emitters based on spiro[1,8-diazafluorene-9,2'-imidazole] structure were designed and synthesized by fine-tuning the spiro[fluorene-9,2'-imidazole] core structure in our previous work through heteroatom substitution and hyperconjugation effect. The target emitters were endowed with excellent photophysical and electrochemical merits, thermal stability and solution processibility. The solution-processed OLED device based on 4',5'-bis(4-(9H-carbazol-9-yl)phenyl)spiro[1,8-diazafluorene-9,2'-imidazole] (NFIP-CZ) achieved efficient ultra-deep-blue emission (CIEx,y = 0.1581, 0.0422) with the maximum external quantum efficiency (EQEmax), maximum current efficiency (CEmax) and maximum power efficiency (PEmax) of 11.94%, 4.07 cd·A-1 and 2.56 lm·W-1. The record EQE is a breakthrough in both solution-processed and vacuum vapor deposition ultra-deep-blue HLCT-OLEDs currently.

Enhancing device characteristics of InP quantum dot LED through structural modification with polyethylene glycol blend

This study explored the integration of polyethylene glycol (PEG) into InP-based quantum dot (QD) light-emitting diodes (LEDs). By 5 wt% of PEG 400 blended into the QD emission layer (EML), we achieved an enhancement in both current efficiency (100 %) and external quantum efficiency (91 %). X-ray reflectivity revealed significant morphological changes in the QD EML upon PEG incorporation, primarily manifesting as increased thickness in the dense surface region without affecting the total thickness. This adjustment influenced electron density distribution, impacting hole and electron flow. Overall, the addition of PEG not only improved the electrical properties of QD LEDs but also reshaped the internal morphology of the QD EML. Notably, the efficiency improvements observed rival those achieved by integrating traditional hole transport materials into QD EMLs.

Superbly Efficient and Stable Ultrapure Blue Phosphorescent Organic Light-Emitting Diodes with Tetradentate Pt(II) Complex with Vibration Suppression Effect.

Blue phosphorescent organic light-emitting diodes (PHOLEDs) are on the brink of commercialization for decades. However, the external quantum efficiency (EQE) and operational lifetime of PHOLEDs are not yet reached industrial standards. Here, a novel tetradentate Pt(II) emitter with a spirofluorene onto the carbazole unit that minimizes the vibration modes, corresponding to the structural relaxation during the de-excitation, called the vibration suppression effect is reported. This modification reduces the intensity of the second peak in the spectrum and Shockley-Read-Hall recombination by blocking direct hole injection into the emitter while enhancing Förster resonance energy transfer, resulting in 451h of LT50 (the time until a 50% decrease in initial luminance at 1000cdm-2) and 25.1% of the maximum EQE (EQEmax). Thanks to the vibration suppression effect, an extremely narrow full width at half a maximum of 22nm is obtained. In phosphor-sensitized thermally activated delayed fluorescent OLED, ultra-pure blue emission with Commission internationale de l'Eclairage (CIE) coordinates of (0.136, 0.096) is obtained with 28.1% of EQEmax. Furthermore, 50.3% of the EQEmax and 589h of LT70 are simultaneously recorded with the two-stack tandem PHOLED, which is the highest EQEmax among 2-tandem and bottom-emission PHOLEDs with CIEy<0.15.

Fe3+-doped broadband near-infrared phosphor with high quantum efficiency toward multifunctional pc-LEDs applications

A broadband near-infrared (NIR) luminescence that is comparable to chromium ions activated materials is fulfilled in Li3Sc2(PO4)3:Fe3+ phosphor, which is highly desired for environmental and biomedical applications due to the non-toxicity of Fe3+ ions. Structural and spectral analysis reveal that the broadband NIR emission peaked at 805 nm with a full width at half-maximum of 130 nm is derived from the non-selective two-site occupation of Fe3+ in the Sc3+ sites. A high internal/external quantum efficiency of 53 %/38.7 % is achieved via relaxing the selection rule for the forbidden 4T1(4G) → 6A1(6S) transitions of Fe3+ by larger lattice distortion. The influence of Fe3+ concentration and environment temperature on the broadband NIR luminescence properties of the as-prepared phosphors are also investigated. Finally, a NIR pc-LED prototype is fabricated and its electro-optical performance has guaranteed the applications in non-destructive detection and night vision. All the results have validated Li3Sc2(PO4)3 as a novel matrix system for access to highly efficient broadband NIR Fe3+-doping phosphor materials.

Delocalizing electron distribution in thermally activated delayed fluorophors for high-efficiency and long-lifetime blue electroluminescence.

Blue thermally activated delayed fluorescent emitters are promising for the next generation of organic light-emitting diodes, yet their performance still cannot meet the requirements for commercialization. Here we establish a design rule for highly efficient and stable thermally activated delayed fluorescent emitters by introducing an auxiliary acceptor that could delocalize electron distributions, enhancing molecular stability in both the negative polaron and triplet excited state, while also accelerating triplet-to-singlet up-conversion and singlet radiative processes simultaneously. Proof-of-concept thermally activated delayed fluorescent compounds, based on a multi-carbazole-benzonitrile structure, exhibit near-unity photoluminescent quantum yields, short-lived delays and improved photoluminescent and electroluminescent stabilities. A deep-blue organic light-emitting diode using one of these molecules as a sensitizer for a multi-resonance emitter achieves a remarkable time to 95% of initial luminance of 221 h at an initial luminance of 1,000 cd m-2, a maximum external quantum efficiency of 30.8% and Commission Internationale de l'Eclairage coordinates of (0.14, 0.17).

Spin-Valley-Locked Electroluminescence for High-Performance Circularly Polarized Organic Light-Emitting Diodes.

Circularly polarized (CP) organic light-emitting diodes (OLEDs) have attracted attention in potential applications, including novel display and photonic technologies. However, conventional approaches cannot meet the requirements of device performance, such as high dissymmetry factor, high directionality, narrowband emission, simplified device structure, and low costs. Here, we demonstrate spin-valley-locked CP-OLEDs without chiral emitters but based on photonic spin-orbit coupling, where photons with opposite CP characteristics are emitted from different optical valleys. These spin-valley-locked OLEDs exhibit a narrowband emission of 16 nm, a high external quantum efficiency of 3.65%, a maximum luminance of near 98,000 cd/m2, and a gEL of up to 1.80, which are among the best performances of active single-crystal CP-OLEDs, achieved with a simple device structure. This strategy opens an avenue for practical applications toward three-dimensional displays and on-chip CP-OLEDs.

Free carrier generation efficiency in organic photovoltaic films determined using photo-MIS-CELIV

Solution processed organic photovoltaic (OPV) devices are promising for low-embedded energy and large-scale renewable energy production. The efficiency of charge carrier generation is a critical factor influencing the performance of photovoltaic devices. However, quantifying charge carrier generation can be challenging, with the results from experimental methods not always being easily correlated with solar cell performance. In this paper, we describe how photoinduced metal-insulating-semiconductor charge-extraction-by-linearly-increasing-voltage (photo-MIS-CELIV) can be used to determine the free charge carrier generation efficiency (FCGE) in OPV films. One of the benefits of this approach is that the FCGE can be measured alongside the charge mobility to provide a holistic picture of the fate of charges, from generation to extraction. We demonstrate this method through quantifying the FCGE of bulk heterojunctions of PCE10:ITIC-4F, D18:Y6 and PPDT2FBT:PC71BM, obtaining values of 47.4 ± 1.6 %, 75.0 ± 2.5 % and 70.6 ± 4.6 %, respectively. The measured FCGEs for these blends were consistent with the device-based external quantum efficiencies (EQEs) at the excitation wavelength used. The use of photo-MIS-CELIV for quantifying the FCGE increases its utility beyond simple charge mobility measurements and provides an extra method to enable optimisation of OPV device performance.

A thermally stable narrow-band green phosphor Na2MgAl10O17: Eu2+, Mn2+ for NUV LED application

Thermally stable narrow-band green phosphor is important for phosphor-converted light emitting diodes (pc-LEDs). Herein, an efficient and stable Na2MgAl10O17: Eu2+, Mn2+ green phosphor is obtained using Eu2+-Mn2+ energy transfer strategy. The Mn2+ activator could be effectively sensitized by the addition of Eu2+ with significant UV absorption enhancement, then generates a bright green emission with peak at 515 nm and FWHM of 40 nm. The internal and external quantum efficiencies of optimal phosphor Na2MgAl10O17: 0.15Eu2+, 0.50Mn2+ are measured as 69.5 and 30.8 %, respectively. It is found that Na2MgAl10O17: Eu2+, Mn2+ phosphor shows good chemical and thermal stability, i.e. maintains no quenching after H2O/HCl soaking and keeps 90 % of RT intensity at 200 °C. By using Na2MgAl10O17: Eu2+, Mn2+ as converted phosphor, single-chromatic and white pc-LEDs were fabricated, which simultaneously achieve green and white emission with high brightness. Our results show that this Na2MgAl10O17: Eu2+, Mn2+ is a potential candidate as a thermally stable green phosphor for white LEDs.

Effect of magnesium doping on NiO hole injection layer in quantum dot light-emitting diodes

Abstract This study reports on the fabrication of quantum dot light-emitting diodes (QLEDs) with an ITO/Ni1−x Mg x O/SAM/TFB/QDs/ZnMgO/Al structure and investigates the effects of various Mg doping concentrations in NiO on device performance. By doping Mg into the inorganic hole-injection layer NiO (Ni1−x Mg x O), we improved the band alignment with the hole-injection layer through band tuning, which enhanced charge balance. Optimal Mg doping ratios, particularly a Ni0.9Mg0.1O composition, have demonstrated superior device functionality, underscoring the need for fine-tuned doping levels. Further enhancements were achieved through surface treatments of Ni0.9Mg0.1O with UV-Ozone (UVO) and thermal annealing (TA) of the ZnMgO electron transport layer. Consequently, by optimizing Mg-doped NiO in QLED devices, we achieved a maximum external quantum efficiency of 8.38 %, a brightness of 66,677 cd/m2, and a current efficiency of 35.31 cd/A, indicating improved performance. The integration of Mg-doped NiO into the QLED structure resulted in a device with superior charge balance and overall performance, which is a promising direction for future QLED display technologies.

High efficiency in blue TADF OLED using favorable horizontal oriented host

An appropriate host featuring a wide band gap (Eg) and high triplet energy (T1) is crucial for facilitating highly efficient blue-light emitting devices. In this study, 4Ac26CzBz, a new host comprising acridan and carbazole moieties linked to a benzimidazole core, has been synthesized and characterized. Notedly, 4Ac26CzBz exhibits a wide optical gap (Eg) and high triplet energy (T1) of 3.3 and 3.0 eV, respectively, and has been proven a suitable host for blue thermally activated delayed fluorescence (TADF) OLED. By adopting 4TCzBN as a blue-light dopant, a remarkably high device external quantum efficiency of 35.8 % (59.8 cd/A and 62.8 lm/W) and a low turn-on voltage (<3 eV) have been demonstrated, with significant suppression of the efficiency roll-off, maintaining a high efficiency of 29.7 % as luminance at 1000 cd/m2. This excellent performance is deduced from the host’s ambipolar carrier transporting properties, which refer to its ability to transport both electrons and holes effectively, high photoluminescence quantum yield (PLQY) of 98.6 %, and highly horizontal orientation of transition dipole, as determined through diverse analytical measurements. The good material properties of 4Ac26CzBz and the high OLED performance reveal its potential for the next generation’s advanced display and lighting applications.

Efficient thermally activated delayed fluorescence materials from symmetric anthraquinone derivatives for high-performance red OLEDs

Constructing efficient red thermally activated delayed-fluorescence (TADF) materials for high-performance organic light-emitting diodes (OLEDs) remains challenging due to the formidable barrier of energy gap law. In this work, a design strategy of connecting two donor units to the adjacent positions of electron acceptor is proposed for creating red luminescent materials, and four Y-shaped TADF molecules consisting of strong electron-withdrawing anthraquinone (AQ) acceptor and triphenylamine or acridine-based donors are designed and synthesized. They exhibit strong red emissions (604−618 nm) in toluene solutions and orange/red emissions (566−608 nm) with good photoluminescence quantum yields (43−68%) in doped films, and enjoy small singlet-triplet energy gaps (0.02−0.10 eV) and fast reverse intersystem crossing processes (1.5–7.3 × 105 s−1), which are attributed to the unique Y-shape structure. A maximum external quantum efficiency of 19.5% with an electroluminescence peak at 616 nm is achieved for AQ-PTPA-based red doped device, representing the highest level for red TADF-OLEDs based on AQ acceptor in the literature. This work can provide guidance for the design of efficient red delayed-fluorescence molecules for the application in OLEDs.

Pure-Phase Perovskite Quantum Well for Green Light-Emitting Diodes.

Perovskite multiple quantum wells (MQWs) have shown great potential in the field of light-emitting diodes (LEDs). However, the random formation of QWs with varying well widths (n numbers) often leads to suboptimal interface defects and charge transport issues. Here, we reveal that the crystallization sequence of bromide-based perovskite MQWs is large-n QWs preceding small-n QWs. With this insight, we prevent the crystallization of subsequent small-n QWs by reducing the crystallization rate, ultimately resulting in the crystallization of only n = 5 QWs. This reduction in the crystallization rate is achieved through the chemical interaction of dual additives with perovskite constituents. Additionally, the chemical interaction effectively passivates the uncoordinated lead ions defects. Consequently, pure-phase perovskite QWs with a high photoluminescence quantum efficiency of 75% are achieved. The resulting green LEDs achieve a peak external quantum efficiency of 17.1% and a maximum luminance of 29,480 cd m-2, which is attractive for full-color display applications of perovskites.

Clar's Aromatic π-Sextet Rule for the Construction of Red Multiple Resonance Emitter.

Despite the proliferation of multiple resonance (MR) materials in the blue to green spectral ranges, red MR emitters remain scarce in the literature, an area that certainly warrants attention for future applications. Here, through a clever application of classic Clar's aromatic π-sextet rule, we triumphantly constructed the first red MR emitter by substituting the conventional benzene ring core with anthracene (fewer π-sextets). Theoretical studies indicate that the quantity of π-sextets ultimately determines the optical bandgap of a molecule, rather than the number of fused benzene rings. Benefiting from the high photoluminescence quantum yield of ~94% and horizontal dipole ratio of ~90%, the corresponding narrowband red (luminescence wavelength: 608 nm) organic light-emitting diode shows a high external quantum efficiency of 27.3%, with only a slight decrease of 3.7% at an elevated luminance level of 100,000 cd/m2.

Internal quantum efficiency improvement of AlInGaN-based red LED by using double V-pits layers as strain relief layer

Internal quantum efficiency improvement of AlInGaN-based red LED by using double V-pits layers as strain relief layer

Performance improvement of red, green and blue InGaN micro-LEDs with distributed Bragg reflector

Abstract Red-green-blue (RGB) micro light-emitting diodes (micro-LEDs) without distributed Bragg reflector (DBR), with air-separating DBR, and with integrated DBR, were demonstrated. The effect of the DBRs as reflectors on the external quantum efficiency (EQE) and electroluminescence (EL) spectra enhancement of RGB micro-LEDs was systematically investigated for realizing higher-performance micro-LEDs for display applications. At 5 A/cm2, the EQEs of the RGB micro-LEDs with integrated DBR were improved by 38%, 33%, and 32%, respectively, with comparison to the RGB DBR free micro-LEDs. Further, the full width at half maximum (FWHM) of the red micro-LEDs was reduced by 4.3 nm at 50 A/cm2 with the integrated DBR due to the higher enhancement of the central wavelength spectrum. The green and blue micro-LEDs with integrated DBR had higher EQE and the red micro-LEDs with integrated DBR had narrower FWHM compared to those with air-separating DBR. However, the peak wavelength of the RGB micro-LEDs with integrated DBR shifted, resulting in a lower color gamut in CIE 1931. The above work provides guidance for future full-color micro-display applications based on RGB InGaN micro-LED technology.&amp;#xD;

Narrowband Emission in Pt(II) Complexes via Ligand Engineering for Blue Phosphorescent Organic Light‐Emitting Diodes

AbstractIn this study, three stable tetradentate Pt(II) complexes are synthesized and characterized, namely, Pt‐biPh, Pt‐biPh5tBu, and Pt‐biPh4tBu, tailored for blue phosphorescent organic light‐emitting diodes to realize high‐efficiency and narrowband emissions via ligand engineering. Biphenyl (Pt‐biPh) or tert‐butyl‐modified biphenyl (Pt‐biPh5tBu and Pt‐biPh4tBu) is introduced into the carbene unit of the ligand to control the intermolecular interactions between the Pt(II) phosphors. Pt‐biPh, Pt‐biPh5tBu, and Pt‐biPh4tBu exhibit high photoluminescence quantum yields of 74%, 84%, and 92% with exciton lifetimes of 2.2, 2.3, and 2.5 µs, respectively, demonstrating rapid and efficient light emission. Furthermore, Pt‐biPh, Pt‐biPh5tBu, and Pt‐biPh4tBu show maximum external quantum efficiency (EQE) values of 18.1%, 19.0%, and 21.8%, respectively. Pt‐biPh5tBu and Pt‐biPh4tBu exhibit narrowband emission with a full width at half maximum of 21 nm owing to the small vibrational emission because of their sterically hindered and bulky ligand structures. Moreover, phosphor‐sensitized thermally activated delayed fluorescence devices employing a Pt‐biPh4tBu sensitizer achieve a high EQE of 28.6%. In particular, Pt‐biPh4tBu performs better than the state‐of‐the‐art phosphor as the sensitizer of the blue phosphor‐sensitized thermally activated delayed fluorescence devices in terms of the EQE.

Synthesis, characterization and effective UV photo-sensing properties of Ga3+ doped NiO nanoparticles

In this work, resistive type photodetectors were fabricated using Gd3+ ions doped NiO nanoparticles to improve the detection of ultraviolet (UV) light. The occurrence of the simple cubic phase in NiO systems has been shown by X-ray diffraction patterns. The crystalline size of the NiO nanoparticles doped with different concentrations of Gd3+ at levels of pure, 1 %, 2 %, and 3 % were 6 nm, 8 nm, 9 nm, and 12 nm, respectively. The presence of dopants in the material was established by the Raman spectrum analysis. Transmission electron microscopy (TEM) pictures were used to validate the morphological properties of Gd3+ doped NiO nanoparticles nanoparticles at different degrees of dopant concentration (0 %, 1 %, 2 % and 3 %). The introduction and concentration of dopants alter the shape of NiO material. Based on the findings of UV–visible absorption spectroscopic studies, it can be concluded that the addition of Gd3+ ions to the system improved the absorption characteristics. The measured bandgap values for various degrees of Gd3+ doping, namely 0 %, 1 %, 2 %, and 3 %, are 3.51 eV, 3.45 eV, 3.36 eV, and 3.23 eV, respectively. According to the measured photoluminescence spectrum, Gd3+ ions may efficiently trap and maintain excited electrons within an energy level between the ground and excited states. This process greatly extends the lifespan of excitons from immediate recombination. The use of Gd3+-doped NiO sensors in UV photodetection resulted in a significant increase in conductivity and photocurrent. The photodetector fabricated using a 3 % concentration of Gd3+ doped NiO, has a responsivity of 24 × 10−2 AW−1, a detectivity of 14 × 109 Jones, and an external quantum efficiency (EQE) of 62 %.