Pure Green Emission Research Articles

Silicon-based perovskite plasmonic diode with highly polarized emission

Abstract Here, we propose and develop a silicon (Si)-based perovskite plasmon-emitting diode (PED) with controlled linear polarization in this study. Such polarization originates from the efficient excitation of surface plasmons by excitons in the active layer of the device and the efficient outcoupling by a wedged boundary of a metal electrode. Furthermore, a p-type Si substrate serves as an anode of the diode, and a hole blocking layer of SiO2 is introduced in the PEDOT:PSS/Si heterojunction for carrier injection balance. Pure green emission light has been achieved from devices with varied thicknesses of the emitting layer, and the maximum degree of polarization is measured to be 0.79. The field distribution and polarization of the PED were simulated and measured. Such a low-cost Si-based plasmonic diode provides a promising way to realize simpler and more compact multiple-functional light sources, which are extensively demanded for optoelectronic integration.

Enhanced performance of ambient-air processed CsPbBr3 perovskite light-emitting electrochemical cells via synergistic incorporation of dual additives

Metal halide perovskite light-emitting electrochemical cells (MHP-LECs) are promising due to their facile solution processability and exceptional optoelectrical properties. However, commercialization is hindered by poor thin-film coverage and the need for glovebox processing. This study addresses these issues by incorporating poly(ethylene oxide) (PEO) and potassium hexafluorophosphate (KPF6) into cesium lead bromide perovskite (CsPbBr3) emitting layers (EML), processed under ambient-air conditions. These perovskite composite thin films were spin-coated on a preheated substrate, and the device structure was ITO/PEDOT:PSS/EML/Al. Notably, the MHP-LEC based on CsPbBr3:PEO:KPF6 (100:65:0.2, weight ratio) exhibited pure-green emission with a peak at 524 nm and a narrow full width at half-maximum of 27 nm. Compared to a reference device (CsPbBr3:PEO (100:65, weight ratio)), the new device showed 1.5-, 4-, and 5-fold improvements in current density, electroluminescence (EL) intensity, and lifetime, respectively. These enhancements are attributed to reduced non-radiative current leakage, improved film surface coverage and passivation, and balanced charge carrier injection and transportation. This study offers a straightforward approach for processing CsPbBr3 thin films under ambient-air conditions, enhancing the EL performance of MHP-LECs.

Surface-binding molecular multipods strengthen the halide perovskite lattice and boost luminescence

Reducing the size of perovskite crystals to confine excitons and passivating surface defects has fueled a significant advance in the luminescence efficiency of perovskite light-emitting diodes (LEDs). However, the persistent gap between the optical limit of electroluminescence efficiency and the photoluminescence efficiency of colloidal perovskite nanocrystals (PeNCs) suggests that defect passivation alone is not sufficient to achieve highly efficient colloidal PeNC-LEDs. Here, we present a materials approach to controlling the dynamic nature of the perovskite surface. Our experimental and theoretical studies reveal that conjugated molecular multipods (CMMs) adsorb onto the perovskite surface by multipodal hydrogen bonding and van der Waals interactions, strengthening the near-surface perovskite lattice and reducing ionic fluctuations which are related to nonradiative recombination. The CMM treatment strengthens the perovskite lattice and suppresses its dynamic disorder, resulting in a near-unity photoluminescence quantum yield of PeNC films and a high external quantum efficiency (26.1%) of PeNC-LED with pure green emission that matches the Rec.2020 color standard for next-generation vivid displays.

A diphenylphosphine oxide decorated multi-resonance TADF emitter for narrowband green electroluminescence with an EQE of 32.4.

A new narrowband thermally activated delayed fluorescence emitter, PhCzBN-PO, was developed by incorporating the diphenylphosphine oxide (DPPO) group into a multi-resonance core. The unique properties of DPPO enabled PhCzBN-PO to achieve pure green emission and a nonplanar structure. The resulting electroluminescent devices achieved high external quantum efficiencies up to 32.4% with extremely low efficiency roll-off and pure-green emission with Commission Internationale de L'Eclairage (CIE) coordinates of (0.24, 0.67).

53‐3: Distinguished Paper: Developing Pure Green Polycyclo‐Heteraborin MR‐TADF Scaffolds for Efficient, Stable Narrowband OLEDs

We developed two symmetrical green MR‐TADF emitters, BpIC‐DPA and BpIC‐Cz, based on the rigidification and regulation of molecular orbitals (MO) engineering strategies. Both emitters exhibited pure green emission with narrow FWHM below 25 nm and high PLQY over 84%. Among the fabricated OLEDs, BpIC‐Cz‐device showed maximum external quantum efficiency (EQEmax) of 25.7% with alleviated efficiency roll‐off characteristics (EQE1000nits = 24.3%) and longer device‐lifetime (LT90) of 291 h at the initial luminance of 1000 nits.

Pure Tunable Emissions from Cesium Manganese Bromide by Monitoring the Crystal Fields Through a Sustainable Approach

AbstractResearch on manganese (Mn) halide perovskite derivatives with tunable emissions and high color purity have gathered a significant amount of attention for display technology. Despite of mesmerizing optical properties, the synthesis of these all‐inorganic Mn halide compounds is followed by complex and toxic processes. Second, a precise control over the synthesis parameters is mandatory to achieve their pure emissions. Therefore, an ecologically sustainable water‐based solution approach is adapted here to tailor the phases and emissions of cesium manganese bromide (Cs‐Mn‐Br) perovskite derivatives. It is observed that a controlled injection of solution stabilizer plays a pivotal role in engineering the intrinsic properties of Mn halide perovskites. This solution stabilizer interacts with the Mn‐ions of those perovskite derivatives influencing their surrounding coordination environment and pure emission from then. A pure green emission with PLQY of 82% is achieved from as prepared Cs3MnBr5, whereas CsMnBr3 showed a red emission with PLQY of ≈20%. Encouraged by these properties phosphor‐driven light emitting diodes (LED) are designed that show a steady electroluminescence intensity. The CIE coordinates of the Cs3MnBr5 and CsMnBr3 LED prototypes are at (0.224, 0.659) and (0.688, 0.316). This study showcases simple, eco‐friendly tactics for developing green and red LED prototypes contributing toward sustainable device design.

Developing sensitized green fluorescence for efficient, stable narrowband organic light emitting diodes

AbstractThe thermally activated delayed fluorescence (TADF) or phosphorescence‐sensitized organic light‐emitting diodes (OLEDs) based on multi‐resonance TADF (MR‐TADF) emitters are greatly studied to develop an effective narrowband emitting system for wide color gamut display applications. However, developing pure green OLEDs to meet BT2020 and NTSC requirements is challenging. In this study, we investigated the TADF and phosphorescence‐sensitized OLEDs based on two green MR‐TADF final emitters, namely, BpIC‐DPA and BpIC‐Cz. The unique molecular structure of these emitters resulted in a pure green emission with narrow full width at half‐maximum (FWHM) and high PLQY in both solution and solid state. Notably, under optimal conditions, the BpIC‐Cz‐based OLEDs demonstrated a maximum external quantum efficiency (EQEmax) of 25.7% with alleviated efficiency roll‐off characteristics even at high luminescence (EQE5000 nits = 22.6%). The corresponding CIE coordinates are almost at the level of BT2020 and NTSC green‐color industrial standards. Additionally, the BpIC‐Cz‐based device displayed remarkable stability as seen by a noticeably longer device lifetime (LT90) of 25.3 h at a high initial luminance of 5000 nits.

Structural Optimization of BODIPY Derivatives: Achieving Stable and Long-Lived Green Emission in Hyperfluorescent OLEDs.

Boron dipyrromethene (BODIPY) derivatives are widely studied as terminal emitters in organic light-emitting diodes (OLED) due to their narrow emission and high photoluminescence quantum yield (PLQY). However, the strategy for precisely tuning their emission toward a high color purity is still challenging. Herein, we developed a new design strategy to regulate the emission of BODIPY derivatives by modifying the electronic and steric dominance using functionalities, such as nitrile, pentafluorophenyl, diethyl, and monobenzyl. These rational modifications yielded a series of four novel green BODIPY emitters, namely, tPN-BODIPY, tPPP-BODIPY, tPBn-BODIPY, and tPEN-BODIPY, each benefited with a tuned emissions range of 517 to 542 nm with a narrow fwhm of 25 nm and high photoluminescence quantum yield up to 96%. Among these synthesized BODIPYs, an unsymmetrical tPBn-BODIPY was chosen as a final dopant (FD) to explore its application in OLED devices. The fabricated TADF sensitized fluorescence-OLED (TSF-OLED) exhibits a narrow band pure green emission at 531 nm with corresponding CIE coordinates of (x, y) = (0.27, 0.68) and a maximum external quantum efficiency (EQE) of 20%. Furthermore, the TSF-OLED displayed an exceptionally prolonged device operational lifetime (LT90) of 210 h at an initial luminescence of 3000 cd m-2.

Colorless Polyamide–Imide films with tunable coefficient of thermal expansion and their application in flexible display devices

In a previous study, our group reported the fabrication of a series of colorless polyamide–imide (PAI) films (named TFDB-DABPO-TPC-6FDA) with good thermal stability. To further improve their properties, herein, the effect of adding blocks in molecules on the performance of polyimide (PI) films was studied. By changing the order and amount of the four reactants added each time, seven PAIs with different structures and block lengths were obtained. Their glass transition temperatures (Tg) ranged from 359 °C to 368 °C, and their transmittance at 430 nm (T430) was 82.7%–85.1 %. Importantly, the coefficient of thermal expansion (CTE) of these seven PAIs decreased almost linearly from 31.1 to 18.5 ppm/K, making it possible to fabricate PI films with a desired CTE value for specific applications. Furthermore, the PAI-6-T film, which had the longest polyamide block and the best overall performance (Tg = 362 °C, CTE = 18.5 ppm/K, T430 = 83.1 %, tensile strength = 179.4 MPa, dielectric constant (Dk) = 2.53, and dielectric loss (Df) = 0.0088 at 10 GHz) was used as a substrate to fabricate a flexible printed circuit board (FPCB) and an organic light-emitting diode (OLED). Mechanical–electrical test shows that Ag was firmly bonded with the PAI-6-T film, and the resistance of FPCB@PAI-6-T only increased by 14.8 % after 150,000 folding tests. The flexible OLED@PAI-6-T exhibited pure green emission, a turn-on voltage of 3.0 V, a luminance of 1000 cd/m2 at 6 V, a current efficiency of 1.31 cd/A, and an external quantum efficiency of 0.44 %.

Dual‐Hole‐Transport‐Layer‐Facilitated Efficient Perovskite Light‐Emitting Diode

The improved luminescence and colour purity of solution‐processable perovskite materials have positioned them as promising candidates for advanced lighting technologies. Herein, a simple method is presented for fabricating dual hole‐transport layers (HTLs) of green perovskite light‐emitting diodes (PeLEDs), for improved charge balance in the emissive layer (EML). With well‐matched energy levels, and lowered charge injection barrier of the transport layers, maximum radiative recombination in the EML can be obtained. The varying highest occupied molecular orbital (HOMO) levels of the HTLs used in the device are in alignment with the work function of the fluorine‐doped tin oxide and HOMO of the EML. The poly(3,4‐ethylenedioxythiophene)‐poly(styrenesulfonate)/N,N′‐bis(naphthalen‐1‐yl)‐N,N′‐bis(phenyl)‐2,2′‐dimethylbenzidine (PEDOT:PSS/NPD)‐based PeLED device shows outstanding performance with a maximum brightness of 19625 cd m−2, highest current efficiency of 19.2 cd A−1, and turn‐on voltage of 3.8 V among the all HTL combinations. These improvements are attributed to the well‐matched HOMO of NPD and PEDOT:PSS, with both the anode and EML allowing improved hole injection and charge balance. Electroluminescence supports the coordinates (0.22, 0.74) for pure green emission provided by the Commission Internationale de I’Eclairage. Perovskite films fabricated on top of PEDOT:PSS/NPD have the best film morphology and crystallinity with the fewest pinholes enabling improved charge transport.

Highly flexible and stable green perovskite light-emitting diodes based on IL-modified PEDOT:PSS film

Flexible light-emitting diodes (LEDs) are highly sought-after for various applications, such as wearable medical devices, decorative lighting, and flexible displays. Perovskite-based LEDs, due to their low cost, ease of fabrication, and high color purity, have attracted significant attention as promising candidates for modern display technology. However, a primary challenge remains in selecting a bottom anode that provides both high electrical conductivity and optical transmittance while maintaining mechanical robustness to endure rigorous bending. To address this issue, a highly flexible and stable ionic liquid (IL)-modified poly(3,4-ethylene dioxythiophene) polystyrene sulfonate (PEDOT:PSS) bottom anode was developed for high-performance flexible perovskite LEDs (PeLEDs). The addition of 1-ethyl-3-methylimidazolium tetracyanoborate (EMIM TCB) IL initiates a depth-dependent rearrangement of the PEDOT and PSS moieties within the PEDOT:PSS film and improves its conductivity by orders of magnitude. Additionally, the IL increases the work function of the PEDOT:PSS layer, leading to a reduced barrier for hole injection. The fabricated flexible green PeLEDs exhibited pure green emission at 520 nm with a maximum external quantum efficiency (EQE) of 11.6% and maximum luminance of 25566.8 cd/m2. Remarkably, the device retained 85% of its initial luminance after 5000 bending cycles at a 5 mm bending radius.

Constructing Highly Efficient Circularly Polarized Multiple Resonance Thermally Activated Delayed Fluorescence Materials with Intrinsically Helical Chirality.

Advanced circularly polarized multiple resonance thermally activated delayed fluorescence (CP-MR-TADF) materials synergize the advantages of circularly polarized luminescence (CPL), narrowband emission and TADF characteristic, which can be fabricated into highly efficient circularly polarized organic light-emitting diodes (CP-OLEDs) with high color purity, directly facing the urgent market strategic demand of ultra-high-definition and 3D displays. In this contribution, based on edge topology molecular engineering (ETME) strategy, a pair of high-performance CP-MR-TADF enantiomers, (P and M)-BN-Py, has been developed, which merges the intrinsically helical chirality into MR framework. The optimized CP-OLEDs with emitters (P and M)-BN-Py and the newly developed ambipolar transport host PhCbBCz exhibit pure green emission with sharp peaks of 532nm, full-width at half-maximums (FWHMs) of 37nm, and Commission Internationale de L'Eclairage (CIE) coordinates of (0.29, 0.68). Importantly, they achieve remarkable maximum external quantum efficiencies (EQEs) of 30.6% and 29.2%, and clear circularly polarized electroluminescence (CPEL) signals with electroluminescence dissymmetry factors (gEL s) of -4.37 × 10-4 and +4.35 × 10-4 for (P)-BN-Py and (M)-BN-Py, respectively. This article is protected by copyright. All rights reserved.

Vacuum-deposited perovskite CsPbBr3 thin-films for temperature-stable Si based pure-green all-inorganic light-emitting diodes

Metal halide perovskite light-emitting diodes (PeLEDs) are excellent candidates in the field of lighting and display due to their outstanding optical-electrical properties. However, the solution-processed technology of perovskite films and the organic electron/hole transport layers of PeLEDs make it still challenging to improve the operational stability of devices. Herein, we successfully prepared highly luminescent CsPbBr3 perovskite films via vacuum-deposited method and then fabricated all-inorganic PeLEDs with the heterostructure of p-NiO/CsPbBr3/n-Si. Our device exhibits pure-green emission with a wavelength of 527 nm, a narrow full width at half-maximum of 18 nm, and a maximum luminance of 51933 cd/m2, representing one of the best brightness pure-green PeLEDs. Most importantly, the PeLEDs exhibited great thermal stability with a heat resistance up to 80 °C. The electroluminescence peak position of the PeLEDs remains consistent when the ambient temperature increases from 40 °C to 110 °C. Moreover, the all-inorganic PeLEDs can maintain their good luminescence performance after seven thermal cycling tests (30 °C–100 °C). This work not only demonstrated a facile strategy to prepare high-quality pure-green CsPbBr3 perovskite films, but also provided an important all-inorganic device structure for high thermal stability of PeLED.

Peripherally non-planar multiple resonance induced thermally activated delayed fluorescence materials containing silyl units

<p>The rigid planar structure of multiple resonance thermally activated delayed fluorescence (MR-TADF) molecules based on boron/nitrogen (B/N) frameworks always causes a substantial roll-off in organic light-emitting diodes (OLEDs) due to intermolecular aggregation. Herein, four MR-TADF emitters (tCzMe3Si, tCzPh3Si, tPhCzMe3Si, and tPhCzPh3Si) were synthesized by introducing non-planar trimethyl/triphenyl silyl (Me3Si and Ph3Si) units at the <i>para</i>-carbon position of a B-substituted phenyl ring to reduce the intermolecular interaction. We further modified the peripheral electron donors of the B/N core, replacing 3,6-di-tert-butyl-9<i>H</i>-carbazole with 3,6-bis(4-(tert-butyl)phenyl)-9<i>H</i>-carbazole, resulting in a pure green emission with high photoluminescence quantum yields (up to 96%). Specifically, OLED based on tPhCzPh3Si exhibited a high external quantum efficiency of 34.6% and a pure green light peaking at 512 nm, with Commission Internationale de l��Eclairage coordinates of (0.14, 0.70).</p>

Dibenzo[b,d]furan/thiophene-fused double boron-based multiresonance emitters with narrowband ultrapure green electroluminescence.

Herein, double boron (DB)-based narrowband pure-green multiresonance (MR) emitters DBF-DBN and DBT-DBN have been designed and synthesized. Dibenzo[b,d]furan and dibenzo[b,d]thiophene as linkages between two B-N skeletons endow target DB-MR-emitters with a rigid and symmetric molecular structure, which efficiently extends the π-conjugation length and suppresses vibrational relaxation, resulting in a narrowband pure-green emission. DBT-DBN exhibits a remarkably higher reverse intersystem crossing (RISC) rate (kRISC = 7.4 × 105 s-1) than DBF-DBN (kRISC = 1.1 × 105 s-1) due to the heavy-atom effect of sulfur. The organic light-emitting diode (OLEDs) based on DBT-DBN shows an ultrapure green emission with maximum external quantum efficiencies (EQEs) up to 31.3%, an emission peak at 520 nm, and a narrow full-width at half-maximum (FWHM) of 24 nm, meeting the BT.2020 green standard.

High-Performance Perovskite Light-Emitting Diodes Enabled by Passivating Defect and Constructing Dual Energy-Transfer Pathway through Functional Perovskite Nanocrystals.

Quasi-2D perovskites have emerged as a promising luminescent material for perovskite light-emitting diodes (Pe-LEDs). However, efficiency and stability are still obstacles to practical application due to numerous defects and inefficient energy transfer of perovskite films. Herein, functional phenethylammonium bromine-modified CsPbBr3 nanocrystals (PEA-CsPbBr3 NCs) are first introduced as multifunctional additive to simultaneously improve abovementioned problems. PEA-CsPbBr3 NCs not only serve as heteronuclear seeds and trigger growth, thus greatly reducing leakage current, but also deliver Cs+ and Br- to passivate the intrinsic defects inside film. More importantly, the PEA-CsPbBr3 construct a new carrier-transfer pathway from the small-n phase of the quasi-2D perovskite to the PEA-CsPbBr3 , which not only accelerates the energy-transfer process but also promotes radiation recombination of carriers due to stronger quantum confinement effect. Afterward, the poly(3,4-ethylenedioxythiophene):polystyrene sulfonate/poly[9,9-dioctylfluoreneco-N-[4-(3-methylpropyl)]diphenylamine]:black phosphorus quantum dot double hole-transport layer is successfully constructed to enhance its carrier-injection and charge-transport abilities. Consequently, a champion external quantum efficiency of 25.32% and maximal brightness of 128 842cd m-2 are achieved, which is the record efficiency of the quasi-2D Pe-LED with pure green emission at 530nm. Moreover, an impressive 174min lifetime is obtained at T50 , which is about five times longer than the control device.

Development of Multifunctional Materials Based on Heavy Concentration Er3+‐Activated Lead‐free Double Perovskite Cs2NaBiCl6

AbstractLead halide perovskites have been very promising for versatile optoelectronic applications, whereas the inherent toxicity and instability of lead halide restrict its wide application. Herein, a kind of high‐performance multifunctional phosphor is designed based on heavy concentration Er3+‐activated lead‐free double perovskite Cs2NaBiCl6 (CNBC), which realizes the self‐sensitization of Er3+ ions and emits high‐brightness pure green emission upon dual near‐infrared (dual‐NIR) excitation. The luminescence properties can be further optimized by adding sensitizers (Yb3+/Nd3+). Interestingly, the emission intensity of the green region is heightened by 212‐fold after Yb3+ ions doping, which is 40 times higher than that of the current popular phosphors (α‐NaYF4:2%Er3+,18%Yb3+). Meanwhile, the temperature sensing properties of the thermally coupled levels (Er3+:2H11/2,4S3/2) in Cs2NaBiCl6:40%Er3+ are also investigated systematically based on the luminescence intensity ratio principle, and the maximum relative sensitivity is calculated to be as high as 1.27% K‐1 (980 nm) and 1.57% K‐1 (808 nm). Fortunately, the thermal stability and the performance for temperature readout of the studied phosphors are still maintaining a high level after doping sensitizers. The insights provided by this work will broaden the scope of lead‐free halide double perovskites in the fields of luminescence and thermometry.

Nonbonding/Bonding Molecular Orbital Regulation of Nitrogen-Boron-Oxygen-embedded Blue/Green Multiresonant TADF Emitters with High Efficiency and Color Purity.

In this study, we synthesized and characterized multiresonant thermally activated delayed fluorescent (TADF) materials embedded with nitrogen-boron-oxygen (N-B-O), exhibiting color-tunability between blue and green, namely NBO, m-DiNBO, and p-DiNBO. The three emitter materials showed a high photoluminescence quantum yield (PLQY) and a state-of-the-art narrow full width at half maximum (FWHM) of 96 %/25 nm, 87 %/17 nm, and 99 %/19 nm, respectively. For m-DiNBO and p-DiNBO, the emission color could be tuned from blue to green by regulating the nonbonding/bonding molecular orbital characters. Owing to the expanded planar molecular structure, m-DiNBO and p-DiNBO showed high horizontal dipole ratio (Θ) of 88 % and 92 %, respectively. OLEDs were prepared with NBO, m-DiNBO, and p-DiNBO, exhibiting high external quantum efficiencies of 16.8 %, 24.2 %, and 21.6 %, respectively. NBO and m-DiNBO exhibited pure-blue emission with CIE coordinates of (0.137, 0.142) and (0.126, 0.098), respectively. p-DiNBO showed pure-green emission with a CIE coordinate of (0.258, 0.665).

Fluorescence intensity ratio technique and its reliability

The present article reports the optical absorption and upconversion (UC) studies of 1.0 mol% Er3+/2.0 mol% Yb3+ doped/codoped glasses prepared by melt-quenching technique. The elements present and the composition of the prepared glass have been confirmed from XPS and XRF analysis respectively. Judd-Ofelt intensity parameters have been calculated using the absorption spectrum which is further utilized to predict the nature of Er_O bond, the transition probabilities, branching ratios and radiative lifetimes. The CIE study shows non-colour tunable and highly pure green emission (94.2%). The temperature-dependent UC emission spectra of the 2.0 mol% Yb3+ sensitized glass have been recorded at three different pump power densities to establish a reliable FIR based temperature scale. Furthermore, the Arrhenius fitting of the temperature-dependent spectra reveals low thermal quenching of green luminescence in the codoped glass.

Simple Double Hetero[5]helicenes Realize Highly Efficient and Narrowband Circularly Polarized Organic Light-Emitting Diodes

Simple Double Hetero[5]helicenes Realize Highly Efficient and Narrowband Circularly Polarized Organic Light-Emitting Diodes