以昇陳

By incorporating a three-dimensional spiro unit into multiple resonance thermally activated delayed fluorescence emitters, the device efficiency is increased to nearly 1.5 times that of the unhindered emitter. Notably, the linkage pattern with spatial interaction and hindrance can maintain the narrow FWHM and curb unfavorable redshifts at a high doping ratio.

Abstract

A multiple resonance thermally activated delayed fluorescence (MR-TADF) molecule with a fused, planar architecture tends to aggregate at high doping ratios, resulting in broad full width at half maximum (FWHM), redshifting electroluminescence peaks, and low device efficiency. Herein, we propose a mono-substituted design strategy by introducing spiro-9,9′-bifluorene (SBF) units with different substituted sites into the MR-TADF system for the first time. As a classic steric group, SBF can hinder interchromophore interactions, leading to high device efficiency (32.2–35.9 %) and narrow-band emission (≈27 nm). Particularly, the shield-like molecule, SF1BN, seldom exhibits a broadened FWHM as the doping ratio rises, which differs from the C3-substituted isomer and unhindered parent emitter. These results manifest an effective method for constructing highly efficient MR-TADF emitters through a spiro strategy and elucidate the feasibility for steric modulation of the spiro structure in π-framework.

A strategic substitution of the bulky groups effectively suppresses the intermolecular interaction and the formation of isomers in mBP-DABNA-Me. Therefore, the mBP-DABNA-Me based organic light-emitting diode exhibits an efficiency of 24.3% with a pure blue emission, color-coordinate of (0.124, 0.140). Notably, the substituents hinder the bathochromic shift, keeping the pure blue emission even at a high concentration of 25%.

Abstract

Multi-resonance (MR) thermally activated delayed fluorescent (TADF) emitters are highly attractive due to their superior color purity as well as efficient light-harvesting ability from singlets and triplets. However, boron and nitrogen-based MR-TADF emitters suffer from their strong π–π interaction owing to their rigid flat cores. Herein, a boron-based multi-resonance blue TADF emitter with suppressed intermolecular interaction and isomer formation is developed through a simple synthetic process by introducing meta-xylene and meta-phenyphenyl groups to the core. The MR-TADF emitter, mBP-DABNA-Me, shows a narrowband blue emission with a peak at 467 nm, along with full width at half maximum of 28 nm, and photoluminescence quantum yield of 97%. Notably, highly efficient pure blue organic light-emitting diode (OLED) is realized using mBP-DABNA-Me, showing a maximum external quantum efficiency of 24.3% and a stable blue emission with a Commission Internationale de L'Eclairage coordinate of (0.124, 0.140). The color purity of the OLED is maintained at a high doping concentration of over 20%, attributed to the suppressed intermolecular interaction between the MR emitters.

Herein, a hyaluronic acid-based microneedle patch loaded with melanin nanoparticles from cuttlefish ink is constructed to concurrently mediate both tumor photothermal therapy and skin tissue regeneration as a robust supplementary therapy after surgical resection of skin tumors. This biocompatible nanoplatform accompanied with feasible near-infrared irradiation meets almost all demands of tumor eradicating and wound healing in clinically postsurgical treatment.

Abstract

Unhealed wound after malignant skin tumor resection, characterized by full-thickness cutaneous defects, large open cavities, and incomplete tumor tissue resection are the leading cause for long recovery times, poor prognoses, and high recurrence among patients. Herein, a hyaluronic acid (HA)-based microneedle (MN) functionalized with biomineralized melanin nanoparticles is fabricated to concurrently administer tumor photothermal therapy (PTT) and promote skin tissue regeneration. Natural melanin nanoparticles derived from cuttlefish ink (CINP) possessing antioxidative and photothermal functionalities are employed to scavenge ROS and implement PTT. Further, CINPs are encapsulated within an amorphous silica shell that served as a source of bioactive SiO44− to stimulate skin tissue regeneration. Due to the physical penetration characteristics of microneedles, the obtained CINP@SiO2-HA MNs could exert photothermal eradication of the remaining subcutaneous tumor cells to avoid recurrence and inhibit Staphylococcus aureus infection in wound beds. Moreover, benefiting from ROS-scavenging and SiO44− release, inflammatory environment can be well controlled and angiogenic gene expression can be up-regulated for skin tissue regeneration. With requisite biofunctionality, convenient synthesis, and excellent biocompatibility, CINP@SiO₂-HA MNs accompanied with clinically feasible irradiation meet the multiple demands of tumor eradication and wound healing, holding great potential as a supplementary therapy following skin tumor resection.

From a thermodynamic view, intermolecular interactions inside bulk-heterojunctions control the basic exciton/charge behaviors and microstructures. Therefore, manipulating these interactions is of great importance. By the cooperation of phenylalkyl side chains and unilateral π-bridge strategy, this work rationally manipulates the multidimensional interactions in photovoltaic cells, accounting for the most competitive efficiency among acceptors with unilateral or bilateral π-bridges.

Abstract

Thanks to the development of acceptor–donor–acceptor (A–D–A) type electron acceptors, organic solar cells (OSCs) have achieved marvelous progress in recent years. However, a systematic investigation about the structure–efficiency relationship is still highly desired to better understand the working mechanisms inside a bulk heterojunction (BHJ). In this study, new acceptors with the synergistic effect of side chain and unilateral π-bridge strategy are designed, accounting for lower energy loss, expanded absorption, modulated intermolecular interactions and BHJ morphology. As a consequence, the resultant A–D–π–A acceptor ID-C6Ph-ST-4F based binary solar cell receives an impressive efficiency up to 15.36%, much greater than the A–D–A analog ID-C6Ph-4F (10.75%), and ranks the best among all small molecular acceptors with symmetric or asymmetric π-bridges. The results highlight the promising manipulation of phenylalkyl side chain and unilateral π-bridge on intermolecular interactions among acceptor molecules and interactions between donor and acceptor (D/A) molecules. Superior interactions among acceptor molecules are an essential precondition to ensure preferable molecular assembly for charge transport, and meanwhile, moderately enhanced D/A interactions are also crucial for proper phase-separation networks with efficient exciton dissociation and charge generation.

A newly designed and synthesized asymmetric acceptor TIT-2Cl is elaborately introduced into the PM6:Y6 system to inhibit the over-aggregation of Y6. Due to the formation of vertical phase separation and improved carrier transport, the PM6/Y6:TIT-2Cl-based device achieves better stability and high efficiency approaching 18.18% by combining ternary strategy and layer-by-layer method, which is the highest efficiency reported for PM6:Y6-based devices.

Abstract

Although much research on device engineering have brought about significant improvements in PM6:Y6-based polymer solar cell (PSCs) performance, there is still a lack of relevant research to solve the problems caused by the over-aggregation of Y6 and the long-term stability of the device morphology. Herein, a newly designed and synthesized low-bandgap asymmetric small molecule acceptor TIT-2Cl based on thieno[3,2-b]indole core is elaborately introduced into PM6:Y6-based PSCs to suppress the over-aggregation of Y6 molecules with significantly increased efficiency from 15.78% to 17.00%. Moreover, the addition of TIT-2Cl contributes to improved light harvesting, the lowest unoccupied molecular orbital level of Y6:TIT-2Cl, charge separation, transport, and extraction. Simultaneously, the PSCs are further prepared by using the progressive spin-coating method of layer-by-layer (LBL). Due to the formation of vertical phase distribution and the improvement of carrier transport performance, the champion efficiency of LBL-type ternary PSCs reaches 18.18%, which is the highest efficiency reported for PM6:Y6-based PSCs, along with superior stability and compositional insensitivity. Therefore, the results show that the combination of ternary strategy by incorporating appropriate asymmetric molecules and the LBL method is an effective means to fabricate highly efficient stable PSCs.

A photothermal agent (PTA) based on an amphipathic squaraine dye is developed with high photothermal conversion efficiency (PCE, 81.2%). Implementing the strategy of H-aggregation influences nonradiative decay process acceleration, promoting heat generation. In vitro and in vivo investigations confirm its high stability, biocompatibility, tumor accumulation, and efficient tumor ablation in photothermal therapy.

Abstract

Understanding and implementing the ordered supramolecular assembly in organic photothermal materials is challenging, yet significant, for photothermal performance enhancement. Herein, an amphipathic squaraine dye (PSQ) with a poly (ethylene glycol) chain attached as a hydrophilic anchor is synthesized. In aqueous solution, PSQ spontaneously self-assembles into uniform nanospheres (PSQ-NSs) with well-defined H-dimeric substructures. Molecular dynamics simulations are conducted to illustrate the self-assembly process. Reorganization energy calculations show that nonradiative decay is accelerated by H-dimeric PSQ low-frequency out-of-plane vibrational modes, which enables a rapid dissipation of excited-state energy to heat. As such, the resultant H-dimeric PSQ-NSs exhibit ultrahigh photothermal conversion efficiency (81.2%) under laser irradiation (0.3 W cm⁻², 808 nm) in water. In vitro and in vivo evaluations confirm their high stability, biocompatibility, tumor accumulation, and efficient tumor inhibition in photothermal therapy. It is expected that the self-assembling H-dimers will become a unique platform for the precise designing of small-molecule PTAs for future clinical PTT applications.

A rational design principle is proposed to achieve an advanced nanowire nano-architecture from an ultra-deep-blue emissive conjugated molecule (FCz-C8-Am) via the synergistic effect of the hydrogen bonding - and pendant π–π stacking interactions. This nano-architecture presents a stable ultra-deep-blue emission with an efficiency of >75% and a CIE value of (0.16, 0.06), associated with a single-molecular excitonic behavior.

Abstract

Organic conjugated molecules with a rigid rod-like π-backbone structure automatically and easily self-assemble into an anisotropic nanostructure. However, supersecondary structures obtained from the hierarchical secondary self-assembly of nanostructures have rarely been reported for non-amphiphilic conjugated molecules. Here, a nanowire architecture as a supersecondary structure from an ultra-deep-blue fluorene-based conjugated molecule (FCz-C8-Am) to improve the emission efficiency and stability is reported. In significant contrast to the four reference molecules, the FCz-C8-Am molecules grow into soft nanowires and further self-assemble into a series of nanowire architectures in the gelation process. This is associated with the synergistic effect of the hydrogen bonds among the amide units, pendant π–π stacking interactions between pendant Cz units, and appropriate soft steric interaction among side-chains, which are the three design requirements for preparing these nanowire architectures. Interestingly, this supersecondary architecture of FCz-C8-Am has a stable ultra-deep-blue emission, with an efficiency of ≈77% and a Commission Internationale de L'Eclairage (CIE) value of (0.16, 0.06) in the solid state. These findings provide a profound understanding of the relationship between the inherent molecular structure, supramolecular interaction, and supersecondary nano-architecture, offering useful information for the development of new functional optoelectronic materials.

A novel donor-pillar[5]arene-acceptor structure with aggregation-induced emission property shows a twisted conformation and intramolecular through-space charge transfer (TSCT). Balancing of blue locally-excited state emission and yellow TSCT emission via viscosity and polar guest generates the single-molecule white-light emission.

Abstract

The fabrication of single-molecule white-light emission (SMWLE) materials has become a highly studied topic in recent years and through-space charge transfer (TSCT) is emerging as an important concept in this field. However, the preparation of ideal TSCT-based SMWLE materials is still a big challenge. Herein, we report a bifunctional pillar[5]arene (TPCN-P5-TPA) with a linear donor-spacer-acceptor structure and aggregation-induced emission (AIE) property. The bulky pillar[5]arene between the donor and acceptor induces a twisted conformation and a non-conjugated structure, resulting in intramolecular TSCT. In addition, the AIE feature and pillar[5]arene cavity endow TPCN-P5-TPA with responsiveness to viscosity and polar guests, by which the TSCT emission is triggered. The combination of blue locally-excited state emission and yellow TSCT emission of TPCN-P5-TPA generates SMWLE. Therefore, we provide a new and versatile strategy for the construction of TSCT-based SMWLE materials.

Circularly polarized white organic light-emitting diodes that can harvest both singlet and triplet excitons have been developed by combining two pairs of spiro-type circularly polarized delayed fluorescence enantiomers with complementary emissions as chiral emissive layers. Remarkable device performances are observed, with an external quantum efficiency of up to 21.6 % and intense circularly polarized luminescence having a |g _EL| factor of 3.0×10⁻³.

Abstract

In this study, we report the first circularly polarized white organic light-emitting diodes (CP-WOLEDs) based on all thermally activated delayed fluorescence (TADF) materials. Two pairs of spiro-type TADF enantiomers, (R/S)-SPOCN (5,5′-((2,2′,3,3′-tetrahydro-1,1′-spirobi[indene]-7,7′-diyl)bis(oxy))bis(4-(10H-phenoxazin-10-yl)phthalonitrile)) and (R/S)-OSFSO (2′-(trifluoromethyl)-spiro[quinolino[3,2,1-kl]phenoxazine-9,9′-thioxanthene]-10′,10′-dioxide), serve as emitters with complementary emission. The CP-OLEDs exhibit warm white emission with a CIE coordinate of (0.35, 0.46). Besides, decent device performances are observed with an external quantum efficiency of up to 21.6 % at maximum and 11.8 % at 1000 cd m⁻². Obvious circularly polarized electroluminescence signals are detected with a dissymmetry factor |g _EL| of around 3.0×10⁻³. This is the first report of CP-WOLEDs that can harvest both singlet and triplet excitons, which provides a feasible strategy for the development of CP-WOLEDs with remarkable device performances.

The general acceptor reconstruction strategies of acceptor bonding and acceptor fusing for non-red thermally activated delayed fluorescent (TADF) acceptors are developed to expand red TADF emitters. The reconstructed acceptor spatial structures induce the regulable radiative and non-radiative transfer processes of the emitters for high-efficient red TADF emission.

Abstract

The development of high-efficient red thermally activated delayed fluorescent (TADF) materials is crucial to expanding their applications. Here, the acceptor reconstruction strategies of acceptor bonding and acceptor fusing in donor–acceptor-type materials to modulate their nonradiative deactivation process and emission color for expanding high-efficient red TADF emitters are presented. They are applied to design novel red TADF emitters TXO-b-TPA and TXO-f-TPA based on non-red thioxanthone oxide (TXO) acceptor. Compared to TXO-based emitter TXO-TPA, these acceptor reconstruction strategies enable red-shifted (48–88 nm) and efficient red TADF emission (600–640 nm). Their radiative and nonradiative transition processes can be modulated by the different molecular orbital and excited state distributions based on their acceptor structural differences, which results in a dramatic enhancement of their organic light-emitting diode (OLED) device efficiencies from 1.21/3.63% (TXO-f-TPA) to 20.9% (TXO-b-TPA). These results confirm that the acceptor reconstruction strategies provide a viable solution for overcoming the limitations of previous red TADF emitters. Moreover, the retrieval of reported TADF materials can further demonstrate that these acceptor reconstruction strategies can be transferrable to more non-red TADF materials to expand high-efficient red-shift and/or red TADF materials.

A strategy of donor arylmethylation for enhancing horizontal dipole orientation of thermally activated delayed fluorescence emitters is presented. The resulting emitter achieves a higher horizontal dipole ratio of 81% and superior electroluminescence performance with a maximum external quantum efficiency of 37.0% and power efficiency of 124.5 lm W⁻¹.

Abstract

Designing thermally activated delayed fluorescence (TADF) emitters with high horizontal orientation dipole ratios (Θ_//) is regarded as one of the key measures to achieve high light outcoupling efficiency and thus efficient organic light-emitting diodes (OLEDs). Herein, donor arylmethylation is presented to construct horizontally oriented TADF emitters. Two compounds PFDMAC-TRZ and DPFDMAC-TRZ are designed and synthesized through Friedel-Crafts arylmethylation of their parent TADF molecule DMAC-TRZ with 9-phenyl-9-fluorenol. The 9-phenyl-9-fluorene substituents endow PFDMAC-TRZ and DPFDMAC-TRZ with similar excited states and emission characteristics as DMAC-TRZ due to the unique σ–π conjugation. Impressively, with an arylmethylated donor, PFDMAC-TRZ and DPFDMAC-TRZ show an enhanced horizontal orientation dipole ratio of 78% and 81%, respectively. Green TADF OLED based on DPFDMAC-TRZ reaches a maximum external quantum efficiency of 37.0% and power efficiency of 124.5 lm W⁻¹, which represents one of the most efficient green OLEDs reported so far. This work provides a facile yet powerful strategy to design and construct horizontally oriented luminogens for high-performance optical devices.

Two high-efficiency boron-nitrogen (B/N) framework-based multiple-resonance thermally activated delayed fluorescence emitters with π-extended and fused conjugated high-triplet-energy units show small singlet-triplet energy gap and large spin-orbital coupling values with full widths at half maximum of 27 and 29 nm, respectively. The corresponding organic light-emitting diodes display high external quantum efficiencies of up to 26.1% and 28.0% with low-efficiency roll-off.

Abstract

The simultaneous achievement of multiple-resonance thermally activated delayed fluorescence (MR-TADF) materials with strong narrowband emission and efficient reverse intersystem crossing (RISC) process can further promote the advancement of organic light-emitting diodes (OLEDs). Herein, a new strategy is proposed to achieve two π-extended MR-TADF emitters (NBO and NBNP) peaking at 487 and 500 nm via fusing conjugated high-triplet-energy units (carbazole, dibenzofuran) into boron-nitrogen (B/N) framework, aiming to increase charge transfer delocalization of the B/N skeleton and minimize singlet-triplet energy gap (∆E _ST). This strategy endows the two emitters with full width at half maximum of 27 and 29 nm, and high photoluminescence efficiencies above 90% in doped films, respectively. Additionally, considerable rate constants of RISC are obtained due to the small ∆E _ST (0.12 and 0.09 eV) and large spin-orbital coupling values. Consequently, the OLEDs based on NBO and NBNP show the maximum external electroluminescence quantum efficiency of up to 26.1% and 28.0%, respectively, accompanied by low-efficiency roll-off. These results provide a feasible design strategy to construct efficient MR-TADF materials for OLEDs with suppressed efficiency roll-off.

Photoswitchable thermally activated delayed fluorescence polymeric nanoparticles (PDFPNs) with a unique luminescent “double-check” strategy exhibit dual-color fluorescence and variable fluorescence lifetime upon fluorescence resonance energy transfer process through external lights irradiation. The established PDFPNs show promising application in the high-contrast dual-color confocal and time-resolved luminescence bioimaging in oxygenic living cells.

Abstract

Thermally activated delayed fluorescence (TADF) materials have attracted increasing attention due to their great potential in time-resolved luminescence imaging (TRLI) in bioimaging. However, the triplet state (T₁) of delay fluorescence is quenched readily by oxygen and the autofluorescence of biological systems remains inevitable interference in luminescence imaging, which often reduces signal-to-noise ratio during biodetection. To address this issue, the authors design a two-component photoswitchable TADF polymeric nanoparticle (PDFPNs) by covalently incorporating a well-designed TADF molecule (PDC-DA) and a photochromic spiropyran derivative (SPMA). The as-prepared PDFPNs with a unique luminescent “double-check” strategy exhibit dual-color fluorescence and variable fluorescence lifetime upon fluorescence resonance energy transfer (FRET) process through external lights irradiation. The obtained PDFPNs display the advantages of negligible oxygen-sensitivity, high FRET efficiency, rapid photoresponsiveness, outstanding photoreversibility, and prominent long-term fluorescence stability. The established PDFPNs show promising application in the high-contrast dual-color confocal and time-resolved luminescence bioimaging in oxygenic living cells.

A novel force-induced near-infrared emissive mechanophore and the corresponding hydrogels are developed. Evaluation of their mechanofluorochromic performances proves that the mechanophore has sensitive and tunable responsivity, serving as a force meter in hydrogels to characterize different mechanical stresses (tensile stress, compression and friction force) within a broad force range.

Abstract

Mechanofluorochromic polymers, which can indicate damage or excessive stress in highly polarized environments with a clearly perceptible optical signal, are potentially useful in a variety of exciting applications. However, most reported fluorochromic mechanophores exhibit poor color contrast and fluorescence penetration, or are irreversible in polarized phase after mechanical activation. Here, this challenge is tackled by designing and engineering a novel near-infrared (NIR) emissive, rhodanmin derived mechanophore (Rh-Co) in a kind of hydrogel composites. The ring-opened Rh-Co is unique in high molar extinction coefficient and bright NIR emission with such optical transition under force directly corresponding to covalent bond scission and reversibly switchable in an aqueous environment. The hydrogel composites thus can sensitively change their color from yellow to green and emit highly penetrated NIR fluorescence when different types of forces (tension, compression, and friction force) are applied, highlighting the potential applications of Rh-Co in biocompatible environments as a “force meter.”

High-performance circularly polarized electroluminescence with a high external quantum efficiency of 33.2%, large electroluminescence dissymmetry factor of 2.8 × 10⁻³, and narrow full-width at half-maximum of 42 nm, are achieved by Förster resonance energy transfer from a newly developed chiral exciplex host to an achiral MR-TADF emitter.

Abstract

Organic light-emitting diodes (OLEDs) that can simultaneously achieve narrowband emission, high efficiency, and circularly polarized luminescence remain a formidable challenge. In this study, a simple strategy is developed to address this challenge. A chiral exciplex-forming co-host is first designed by employing a chiral donor and an achiral acceptor molecule. The chiral exciplex host enables an achiral green multiple-resonance thermally activated delayed fluorescence emitter to achieve high-performance circularly polarized electroluminescence (CP-EL) with a high external quantum efficiency of 33.2%, large electroluminescence dissymmetry factor of 2.8 × 10⁻³, and a small full-width at half-maximum of 42 nm. This work provides a general approach for realizing CP-EL using easily available achiral emitters and can significantly extend the scope of circularly polarized OLEDs.

An ambipolar self-host multi-resonance (MR) thermally activated delayed fluorescence emitter is constructed with a structure featuring an MR chromophore functionalized with an ambipolar self-host segment, which preserves blue emission at 472 nm with a full width at half maximum of 28 nm and achieves accelerated singlet radiation and suppressed singlet and triplet non-radiations, leading to desired ≈100% photoluminescence and internal electroluminescence quantum yields.

Abstract

Emerging multi-resonance (MR) thermally activated delayed fluorescence (TADF) emitters can combine 100% exciton harvesting and high color purity for their organic light-emitting diodes (OLED). However, the highly planar configurations of MR molecules lead to intermolecular-interaction-induced quenching. A feasible way is integrating host segments into MR molecules, namely a “self-host” strategy, but without involving additional charge transfer and/or vibrational components to excited states. Herein, an ambipolar self-host featured MR emitter, tCBNDADPO, is demonstrated, whose ambipolar host segment (DADPO) significantly and comprehensively improves the TADF properties, especially greatly accelerated singlet radiative rate constant of 2.11 × 10⁸ s⁻¹ and exponentially reduced nonradiative rate constants. Consequently, at the same time as preserving narrowband blue emission with an FWHM of ≈28 nm at a high doping concentration of 30%, tCBNDADPO reveals state-of-the-art photoluminescence and electroluminescence quantum efficiencies of 99% and 30%, respectively. The corresponding 100% internal quantum efficiency of tCBNDADPO supported by an ultrasimple trilayer and heavily doped device demonstrates the feasibility of the ambipolar self-host strategy for constructing practically applicable MR materials.

12.42% monolithic 25.42 cm² flexible organic solar cells (OSCs) are reported based on the nanogrid electrodes modified by amorphous indium tin oxide (ITO) modification layer. The modification of amorphous ITO also ensures excellent air shelf stability, as well as mechanical properties.

Abstract

Printed metal nanogrid electrode exhibits superior characteristics for use in flexible organic solar cells (OSCs). However, the high surface roughness and inhomogeneity between grid and blank region is adverse for performance improvement. In this work, a thin amorphous indium tin oxide (ITO) film (α-ITO) is introduced to fill the blank and to improve the charge transporting. The introduction of α-ITO significantly improves the comprehensive properties of metal grid electrode, which exhibits excellent bending resistance and long-term stability under double 85 condition (under 85 °C and 85% relative humidity) for 200 h. Both experimental and simulation results reveal α-ITO with a sheet resistance of 20 000 Ω □⁻¹ is sufficient to improve the charge transporting within the adjacent grids, leading to a remarkable efficiency of 16.54% for 1 cm² flexible devices. With area increased to 4.00, 9.00, and 25.42 cm², the devices still display a performance of 16.22%, 14.69%, and 12.42%, respectively, showing less efficiency loss during upscaling. And the 25.42 cm² monolithic flexible device exhibits a certificated efficiency of 12.03%. Moreover, the device shows significantly improved air stability relative to conventional high-conductive poly(3,4-ethylenedioxythiophene):polystyrene sulfonate-modified device. All these make the α-ITO-modified Ag/Cu electrode promise to achieve high-efficient and long-term stable large-area flexible OSCs.

A comprehensive optimization strategy, including 2-phenylethylammonium ligand (PEA⁺)-passivated FAPbI₃ quantum dots (QDs), synergistic coverage effects between the QDs and hole-transporting layers, and effective electron-transporting layers for constructing a feasible device structure leads to a high-efficiency near-infrared (NIR) QD-based light-emitting diode (QLED) centered at 772 nm and exhibiting a maximum external quantum efficiency up to 15.4%, the highest external quantum efficiency recorded for perovskite-based NIR QLEDs.

Abstract

In recent years, the performance of perovskite quantum dots (QDs) and QD-based light-emitting diodes (QLEDs) has improved greatly, with electroluminescence (EL) efficiency of green and red emission exceeding 20%. However, the development of perovskite near-infrared (NIR) QLEDs has reached stagnation, where the reported maximum EL efficiency is still below 6%, limiting their further applications. In this work, new NIR-emissive FAPbI₃ QDs are developed by post-treating long alkyl-encapsulated QDs with 2-phenylethylammonium iodide (PEAI). The incorporation of PEAI reduces the QD surface defects for giving a high photoluminescence quantum yield up to 61.6%. The n-octane solution of PEAI-passivated FAPbI₃ QDs is spin coated on top of the PEDOT:PSS-treated ITO electrode modified with a thermally crosslinked hole-transporting layer to give a full-coverage, smooth, and dense QD film. Incorporating with an effective electron-transporting material, CN-T2T, which has deep lowest unoccupied molecular orbital and good electron mobility, the optimal device with EL λ_max at 772 nm achieves an external quantum efficiency up to 15.4% at a current density of 0.54 mA cm⁻² (2.6 V), which is the highest efficiency ever reported for perovskite-based NIR QLEDs. This study provides a facile strategy to prepare high-quality perovskite QD films suitable for highly efficient NIR QLED applications.

Through the rational design of organic luminogens with strong intramolecular charge transfer and optimized molecular geometry, the mobile phone flashlight-excited red afterglow imaging of lymph nodes in living mice is realized for the first time, offering a safe and conventional approach to realize the afterglow imaging of living mice with deep issue penetration and high signal-to-noise ratio.

Abstract

Organic room temperature phosphorescence (RTP) materials with ultralong lifetime possess the remarkable advantage in bioimaging for elimination of background noise by characteristic time scale. However, most of RTP luminogens need to be excited by the harmful ultraviolet (UV) lamp, and exhibit green or yellow emission with shallow tissue penetration, constraining the in vivo bioimaging for further application in clinical diagnosis and pathological study. In this text, the much safer excitation process by sunlight and mobile phone flashlight is realized by organic luminogens with various electronic pull–push systems. Moreover, the bright red RTP emission with lifetime up to 344 ms is achieved by optimizing molecular geometry and electronic property. Especially, the mobile phone flashlight-excited red afterglow imaging of lymph nodes in living mice has been realized for the first time, affording a safe and conventional approach to achieve the afterglow imaging of living mice with deep issue penetration and high signal-to-noise ratios.

High-performance circularly polarized electroluminescence with a high external quantum efficiency of 33.2%, large electroluminescence dissymmetry factor of 2.8 × 10⁻³, and narrow full-width at half-maximum of 42 nm, are achieved by Förster resonance energy transfer from a newly developed chiral exciplex host to an achiral MR-TADF emitter.

Abstract

Organic light-emitting diodes (OLEDs) that can simultaneously achieve narrowband emission, high efficiency, and circularly polarized luminescence remain a formidable challenge. In this study, a simple strategy is developed to address this challenge. A chiral exciplex-forming co-host is first designed by employing a chiral donor and an achiral acceptor molecule. The chiral exciplex host enables an achiral green multiple-resonance thermally activated delayed fluorescence emitter to achieve high-performance circularly polarized electroluminescence (CP-EL) with a high external quantum efficiency of 33.2%, large electroluminescence dissymmetry factor of 2.8 × 10⁻³, and a small full-width at half-maximum of 42 nm. This work provides a general approach for realizing CP-EL using easily available achiral emitters and can significantly extend the scope of circularly polarized OLEDs.

Publication date: 15 June 2022

Source: Chemical Engineering Journal, Volume 438

Author(s): Wei Yang, Weimin Ning, Hsin Jungchi, Tengxiao Liu, Xiaojun Yin, Changqing Ye, Shaolong Gong, Chuluo Yang

A comprehensive optimization strategy, including 2-phenylethylammonium ligand (PEA⁺)-passivated FAPbI₃ quantum dots (QDs), synergistic coverage effects between the QDs and hole-transporting layers, and effective electron-transporting layers for constructing a feasible device structure leads to a high-efficiency near-infrared (NIR) QD-based light-emitting diode (QLED) centered at 772 nm and exhibiting a maximum external quantum efficiency up to 15.4%, the highest external quantum efficiency recorded for perovskite-based NIR QLEDs.

Abstract

In recent years, the performance of perovskite quantum dots (QDs) and QD-based light-emitting diodes (QLEDs) has improved greatly, with electroluminescence (EL) efficiency of green and red emission exceeding 20%. However, the development of perovskite near-infrared (NIR) QLEDs has reached stagnation, where the reported maximum EL efficiency is still below 6%, limiting their further applications. In this work, new NIR-emissive FAPbI₃ QDs are developed by post-treating long alkyl-encapsulated QDs with 2-phenylethylammonium iodide (PEAI). The incorporation of PEAI reduces the QD surface defects for giving a high photoluminescence quantum yield up to 61.6%. The n-octane solution of PEAI-passivated FAPbI₃ QDs is spin coated on top of the PEDOT:PSS-treated ITO electrode modified with a thermally crosslinked hole-transporting layer to give a full-coverage, smooth, and dense QD film. Incorporating with an effective electron-transporting material, CN-T2T, which has deep lowest unoccupied molecular orbital and good electron mobility, the optimal device with EL λ_max at 772 nm achieves an external quantum efficiency up to 15.4% at a current density of 0.54 mA cm⁻² (2.6 V), which is the highest efficiency ever reported for perovskite-based NIR QLEDs. This study provides a facile strategy to prepare high-quality perovskite QD films suitable for highly efficient NIR QLED applications.