Exciton Loss Research Articles

2‐Ethylhexyl‐4,6‐Dibromo‐3‐Cyano‐3‐Thieno[3,4‐b]Thiophene Enables Low HOMO Energy Level Polymer Donor

AbstractThe new halogen‐free donor polymer PCN6 is constructed using 2‐ethylhexyl‐4,6‐dibromo‐3‐cyano‐thieno[3,4‐b]thiophene as acceptor (A) block, and is compared in detail with the commercially available PTB7‐Th. It is found that PCN6 has a wider film absorption (300–700 nm) and lower highest occupied molecular orbital (HOMO) energy levels (−5.52 eV) than PTB7‐Th (−5.34 eV), suggesting a great advantage of the monocyano‐functionalized modification strategy in terms of molecular absorption and energy level tuning. The performance difference between PCN6:Y6‐ and PTB7‐Th:Y6‐based organic solar cells (OSCs) is compared by a series of studies including light intensity dependence, carrier mobility, AFM, TEM, and GIWAXS. The results show that PCN6:Y6‐based OSCs have stronger crystallinity, better charge transport, higher and more balanced carrier mobility, and less exciton complex loss. Therefore, the power conversion efficiency (PCE) of PCN6:Y6‐based OSCs reaches 11.34%, while the PCE of PTB7‐Th:Y6‐based OSCs is only 9.02%. These results suggest that 2‐ethylhexyl‐4,6‐dibromo‐3‐cyano‐thieno[3,4‐b]thiophene is an excellent A block for the construction of halogen‐free donor polymers with low HOMO energy levels, and also demonstrate that the introduction of cyano in the conjugated backbone of polymers is a good strategy to achieve high‐performance OSCs.

Efficient Polycrystalline Single-Cation Perovskite Light-Emitting Diodes by Simultaneous Intracrystal and Interfacial Defect Passivation.

Polycrystalline perovskite light-emitting diodes (PeLEDs) have shown great promise with high efficiency and easy processability. However, PeLEDs using single-cation polycrystalline perovskite emitters have demonstrated low efficiency due to defects within the grains and at the interfaces between the perovskite layer and the charge injection contact. Thus, simultaneous defect engineering of perovskites to suppress exciton loss within the grains and at the interfaces is crucial for achieving high efficiency in PeLEDs. Here, 1,8-octanedithiol which is a strong nucleophile, is used to increase the luminescence efficiency of a single-cation perovskite by suppressing non-radiative recombination within the grains of their polycrystalline emitter film as well as at their interface with an anode. The dithiol additive performs a multifunctional role in defect passivation, spatial confinement of excitons, and prevention of exciton quenching at the interface between the perovskite layer and the underlying hole-injection layer. Photoluminescence studies demonstrate that incorporating the dithiol additive significantly enhances the charge carrier dynamics in perovskites, resulting in an external quantum efficiency (EQE) of up to 23.46% even in a simplified PeLED that does not use a hole-injection layer. This represents the highest level of EQE achieved among devices utilizing polycrystalline single-cation perovskites.

Construction of Binary Matrix for Efficient Room Temperature Phosphorescence Emission

AbstractDespite the extensive research on room temperature phosphorescent (RTP) materials, it remains a great challenge to further improve the photophysical properties of RTP materials. In this study, the RTP emission of guest molecule is significantly enhanced by constructing binary matrices containing cyanuric acid (CA) and amino‐containing compounds. Systematic studies show that the strong interaction between the two components of binary matrix induced variations in the guest molecular configuration and excited state electron distribution, thus facilitating the production of more triplet excitons. Furthermore, the binary matrix also exhibits stronger domain‐limiting effect compared to the CA mono‐matrix, effectively inhibits the energy loss of triplet excitons due to quenching and non‐radiative transitions. The prepared binary matrix RTP materials present ultralong phosphorescence lifetime and high phosphorescence quantum yield (up to 3.21 s and 7.31%, respectively), and even achieve bright RTP emission in a variety of organic solvents and aqueous media. Moreover, the RTP emission intensity of the best binary matrix composite can reach more than 28 times that of the CA mono‐matrix composite, and the RTP lifetime can be extended by 1.51 s.

External Electric Field Control of Exciton Motion in Porphyrin-Based Metal Organic Frameworks.

Porphyrins are excellent light-harvesting complexes. Presently they are unsuitable for photovoltaic applications, as their excellent light absorbance is compensated to a large extent by their poor transport properties, where most excitons are lost by recombination. Arranging porphyrins in regular, strongly bound, lattices of surface-anchored metal-organic frameworks (PP-SURMOFs) may facilitate charge carrier dissociation, but does not significantly enhance the conductive properties. In most cases, photogenerated excitons traverse undirected, Brownian motion through a hopping process, resulting in a substantial diffusion length to reach electrodes, leading to significant exciton loss through recombination. Here, we propose to guide exciton diffusion indirectly by an external electric field. We show that electric fields, even as strong as 1 V nm-1, do not affect the HOMO-LUMO gap of the porphyrins. However, fields of 0.1 V nm-1 and even less demonstrate a notable Stark effect, with slight band gap reductions, for some PP-SURMOFs. When applied as an electric field gradient, for instance, via the substrate, it creates a unidirectional hopping pathway for the excitons. Consequently, we expect a significant reduction of exciton diffusion length leading to increased utilization of photogenerated excitons as they reach the electrodes. This strategy holds promise for integrating photoactive molecules in photovoltaic and photocatalytic applications.

Enhancing efficiency and stability of non-fullerene organic solar cells via volatilizable solid-liquid-mixed additive system

While traditional high-boiling-point liquid additives like 1,8-diiodooctane (DIO) and 1-chloronaphthalene (CN) et al. are commonly used, here we explore the potential of solid additives to optimize organic solar cells (OSCs) performance. Thieno[3,2-b]thiophene (TT), a volatilizable solid additive (VSA), is introduced into the PM6:Y6 OSCs system. TT's similarity to the Y6 backbone allows it high miscibility with Y6 molecules. In light of the fully volatile property, TT induces more uniform and condensed intermolecular packing of the active layer. This refinement increases the power conversion efficiency (PCE) from 14.45% to 15.31%. To further optimize morphology, TT is combined with the liquid additive CN, creating a binary liquid-solid additive system. This combination promotes favorable nanoscale phase separation within the PM6:Y6 active layer. Overall, the OSCs processed with TT+CN achieve an impressive efficiency of 16.43%, attributed to improved charge transport and reduced exciton recombination losses from the dual additives' synergistic effects. Importantly, the OSCs processed with TT demonstrate enhanced long-term stability, retaining 89.5% of their initial performance after 30 days, outperforming devices without additives (87.3%) and those processed with CN alone (80.5%). In summary, this research introduces TT as a promising volatilizable solid additive and a rational additive strategy to manipulate active layer film morphology. These advances hold significant potential for developing high-efficiency and stable OSCs, contributing to sustainable energy solutions.

TADF polymer enables over 20% EQE in solution‐processed green fluorescent OLEDs

AbstractSolution‐processed fluorescent organic light‐emitting diodes (OLEDs) are believed to be favorable for low‐cost, large‐area, and flexible displays but still suffer from the limited external quantum efficiency (EQE) below 5%. Herein, we demonstrate the EQE breakthrough by introducing a donor–acceptor type thermally activated delayed fluorescence (TADF) polymer as the sensitizer for the typical green‐emitting fluorescent dopants. Benefitting from their matched energy alignment, the unwanted trap‐assisted recombination directly on fluorescent dopant is prevented to avoid the additional loss of triplet excitons. Indeed, triplet excitons are mainly formed on the polymeric TADF sensitizer via a Langevin recombination and then spin‐flipped to singlet excitons due to the good upconversion capability. Followed by an efficient Förster energy transfer, both singlet and triplet excitons can be harvested by fluorescent dopants, leading to a promising solution‐processed green hyperfluorescence with a record‐high EQE of 21.2% (72.2 cd/A, 59.7 lm/W) and Commission Internationale de L'Eclairage coordinates of (0.32, 0.59). The results clearly highlight the great potential of solution‐processed fluorescent OLEDs based on TADF polymers as the sensitizer.

Blue ZnSeTe quantum dot light-emitting diodes with low efficiency roll-off enabled by an in situ hybridization of ZnMgO nanoparticles and amino alcohol molecules.

ZnSeTe quantum dots (QDs) have been employed as promising emitters for blue QD-based light-emitting diodes (QLEDs) due to their unique optoelectronic properties and environmental friendliness. However, such QLEDs usually suffer from serious efficiency roll-off primarily stemming from exciton loss at the interface of the QD layer and the ZnMgO (ZMO) electron transport layer (ETL), which remarkably hinders their application in flat-panel displays. Herein, we propose an in situ hybridization strategy that involves the pre-introduction of amino alcohols into the reaction solution. This strategy effectively suppresses the nucleophilic condensation process by facilitating the coordination of ammonium and hydroxyl groups with metal cations (M2+, i.e. Zn2+ and Mg2+). It slows down the growth rate of ZMO nanoparticles (NPs) while simultaneously facilitating M-O coordination, resulting in the synthesis of small-sized and low-defect ZMO NPs. Notably, this in situ hybridization approach not only alleviates emission quenching at the QDs/ETL interface but also elevates the energy level of the ETL for enhancing carrier injection. We further investigated the impact of amino alcohols with varying carbon-chain lengths on the performance of ZMO NPs and the corresponding LED devices. The optimal blue ZnSeTe QLED demonstrates an impressive EQE of 8.6% with only an ∼11% drop when the current density is increased to 200 mA cm-2, and the device operating lifetime extends to over 1300 h. Conversely, the device utilizing traditionally post-treated ZMO NPs as the ETL exhibits 45% efficiency roll-off and device lifetime of merely 190 h.

Achieving 9% EQE in light-emitting electrochemical cells via a TADF-sensitized fluorescence strategy.

Light-emitting electrochemical cells (LECs) are appealing for cost-effective, large-area emission applications; however, their luminescence efficiency is significantly limited by exciton annihilation caused by high concentration polarons. Here, we present thermally activated delayed fluorescence (TADF) sensitized fluorescence LECs (TSF-LECs) that achieve a record 9% EQE. The TADF sensitizers with rapid reverse intersystem crossing (RISC) rates can effectively convert triplet excitons to singlet excitons in LECs, thereby establishing a more efficient overall energy transfer pathway. Importantly, magneto-electroluminescence measurements indicate that the additional RISC route in TSF-LECs significantly suppresses the annihilation of triplet excitons and thus reduces exciton loss under high concentration polaron conditions. Compared to LECs without a sensitizer, TSF-LECs exhibit improved EQE and luminance, extended operational lifetimes, and suppressed efficiency roll-off. A flexible display prototype based on TSF-LECs was further fabricated, capable of stably displaying high-brightness preset patterns for extended periods. The exploration of the exciton dynamics in high concentration polaron environments offers valuable insights for future developments in high-efficiency LEC technology.

Effect of 1‐Fluoro‐2‐iodobenzene Solvent Additive on the Crystallization of Donors and Acceptors, and Ultrafast Carrier Dynamics in Polymer Solar Cells

AbstractControlled sequential crystallization of donors and acceptors is a critical factor for achieving enhanced phase separation and efficient charge transfer performance in polymer solar cells (PSCs). In this study, a comprehensive investigation of a structurally simple solvent additive, 1‐fluoro‐2‐iodobenzene (OFIB) is conducted, which efficiently controls the morphology of the active layer, resulting in fibrous assembly and significantly enhancing the power conversion efficiency from 16.34% to 18.38% based on the PM6:L8‐BO system. Density functional theory, molecular dynamics simulations, and grazing incidence small‐ and wide‐angle X‐ray scattering techniques reveal that the addition of OFIB to the processed blend aligns the orientation of the acceptor molecules, thereby enhancing the overall π–π stacking in the active layer. OFIB establishes nearly equal‐strength π–π interactions with the conjugated frameworks of both the donor and acceptor materials, benefiting from the multiple electron conjugation between its iodine atom and the conjugated framework in the active layer. Femtosecond‐timescale photophysical studies demonstrate that the OFIB‐optimized active layer shows reduced exciton losses at the donor–acceptor interface. This study offers a new perspective on the mechanism underlying the function of solvent additives and presents a comprehensive research methodology that will guide the development of next‐generation non‐fullerene acceptors for efficient PSCs.

Thermally Activated Delayed Fluorescence Triplet State Excitons for High‐Performance Organic Photodetectors: A Novel Strategy

AbstractPhotoinduced charge‐trapping is a promising strategy for boosting the photosensitivity of organic photodetectors at the expense of their response time. In addition, they have a low carrier extraction yield due to the formation of low‐energy triplet excitons through the recombination of a photogenerated hole–electron pair. Materials with thermally activated delayed fluorescence (TADF) exhibit a long‐lived (≈µs) excited spin‐triplet nearly iso‐energetically aligned with that of an excited spin‐singlet, which results in suppressed exciton losses and is widely used in organic light‐emitting diodes. The extraction and population of triplet state excitons in TADFs is a sought‐after but underexplored aspect of photoinduced gating in photodetectors. A 1,2,3,5‐tetrakis(carbazol‐9‐yl)4,6‐Dicyanobenzene (4CzIPN) TADF blend with a high‐mobility Poly[2,5‐bis(3‐tetradecylthiophen‐2‐yl)thieno[3,2‐b]thiophene] (PBTTT‐C14) polymer via bulk type‐II offset can increase free carrier extraction yield (fast response) and retain trapped electrons in TADF triplet states (high gain). The PBTTT‐C14/4CzIPN ultraviolet photodetector device maintains a trade‐off between high photogain (≈103) and fast response time (79 ms) at 300 nm while operating at a shallow dark current (≈pA). Furthermore, the device shows high external quantum efficiency (≈104 %) and detectivity (≈1011 Jones) for low light power (<pW). The innovative application of TADF material can lead to exciting new developments in organic‐based high‐performance photodetection.

Simultaneously Realizing High Efficiency and High Color Rendering Index for Hybrid White Organic Light-Emitting Diodes by Ultra-Thin Design of Delayed Fluorescence Sensitized Phosphorescent Layers.

In consideration of energy economization and light quality, concurrently attaining high external quantum efficiency (ηext ) and high color rendering index (CRI) is of high significance for the commercialization of hybrid white organic light-emitting diodes (WOLEDs) but is challenging. Herein, a blue luminescent molecule (2PCz-XT) consisting of a xanthone acceptor and two 3,6-diphenylcarbazole donors is prepared, which exhibits strong delayed fluorescence, short delayed fluorescence lifetime, and excellent electroluminescence property, and can sensitize green, orange, and red phosphorescent emitters efficiently. By employing 2PCz-XT as sensitizer and phosphorescent emitters as dopants, efficient two-color and three-color WOLED architectures with ultra-thin phosphorescent emitting layers (EMLs) are proposed and constructed. By incorporating a thin interlayer to modulate exciton recombination zone and reduce exciton loss, high-performance three-color hybrid WOLEDs are finally achieved, providing a high ηext of 26.8% and a high CRI value 83 simultaneously. Further configuration optimization realizes a long device operational lifetime. These WOLEDs with ultra-thin phosphorescent EMLs are among the state-of-the-art hybrid WOLEDs in the literature, demonstrating the success and applicability of the proposed device design for developing robust hybrid WOLEDs with superb efficiency and color quality.

Non‐Doped Blue AIEgen‐Based OLED with EQE Approaching 10.3 %

AbstractAggregation‐induced emission (AIE) luminogens (AIEgens) are attractive for the construction of non‐doped blue organic light‐emitting diodes (OLEDs) owning to their high emission efficiency in the film state. However, the large internal inversion rate (kIC(Tn)) between high‐lying triplet levels (Tn) and Tn‐1 causes a huge loss of triplet excitons, resulting in dissatisfied device performance of these AIEgens‐based non‐doped OLEDs. Herein, we designed and synthesized a blue luminogen of DPDPB‐AC by fusing an AIEgen of TPB‐AC and a DMPPP, which feature hot exciton and triplet‐triplet annihilation (TTA) up‐conversion process, respectively. DPDPB‐AC successfully inherits the AIE feature and excellent horizontal dipole orientation of TPB‐AC. Furthermore, it owes smaller kIC(Tn) than TPB‐AC. When DPDPB‐AC was applied in OLED as non‐doped emitting layer, an outstanding external quantum efficiency of 10.3 % and an exceptional brightness of 69311 cd m−2 were achieved. The transient electroluminescent measurements and steady‐state dynamic analysis confirm that both TTA and hot exciton processes contribute to such excellent device performance. This work provides a new insight into the design of efficient organic fluorophores by managing high‐lying triplet excitons.

Non-Doped Blue AIEgen-Based OLED with EQE Approaching 10.3 .

Aggregation-induced emission (AIE) luminogens (AIEgens) are attractive for the construction of non-doped blue organic light-emitting diodes (OLEDs) owning to their high emission efficiency in the film state. However, the large internal inversion rate (kIC (Tn) ) between high-lying triplet levels (Tn ) and Tn-1 causes a huge loss of triplet excitons, resulting in dissatisfied device performance of these AIEgens-based non-doped OLEDs. Herein, we designed and synthesized a blue luminogen of DPDPB-AC by fusing an AIEgen of TPB-AC and a DMPPP, which feature hot exciton and triplet-triplet annihilation (TTA) up-conversion process, respectively. DPDPB-AC successfully inherits the AIE feature and excellent horizontal dipole orientation of TPB-AC. Furthermore, it owes smaller kIC (Tn) than TPB-AC. When DPDPB-AC was applied in OLED as non-doped emitting layer, an outstanding external quantum efficiency of 10.3 % and an exceptional brightness of 69311 cd m-2 were achieved. The transient electroluminescent measurements and steady-state dynamic analysis confirm that both TTA and hot exciton processes contribute to such excellent device performance. This work provides a new insight into the design of efficient organic fluorophores by managing high-lying triplet excitons.

Realizing High Efficiency and High Color Quality for All‐Fluorescence White Organic Light‐Emitting Diodes by Interlayer‐Sensitizing Configuration with Electron‐Capturing Agent

AbstractAs a promising next‐generation lighting technology, all‐fluorescence white organic light‐emitting diodes (WOLEDs) have advanced rapidly but still face the formidable challenge of achieving high efficiencies and high color quality simultaneously. Herein, an interlayer sensitization strategy assisted by electron‐capturing agent with thermally activated delayed fluorescence (TADF) is proposed for the fabrication of high‐performance all‐fluorescence WOLEDs. The proof‐of‐concept three‐color devices with an interlayer‐sensitizing configuration are designed, and a low concentration of TADF electron‐capturing agent is codoped with a red conventional fluorescence (CF) emitter to reduce exciton loss. The major energy transfer from TADF sensitizing layer to red CF emitter combined with the supplementary energy transfer from TADF electron‐capturing agent to CF emitter can successfully increase exciton utilization. The synergistic effect endows the three‐color all‐fluorescence WOLEDs with high efficiencies, high color quality, and improved efficiency stability and operational stability, simultaneously. The resultant WOLEDs successfully attain remarkable external quantum efficiency of 31.0%, outstanding color rendering index of 93 and long operational lifetime. The record‐beating comprehensive performances of these WOLEDs strongly demonstrate the great potential of the proposed strategy for the exploration of high‐performance all‐fluorescence WOLEDs.

Robust perovskite formation via vacuum thermal annealing for indoor perovskite solar cells

Perovskite materials are fascinating candidates for the next-generation solar devices. With long charge carrier lifetime, metal-halide perovskites are known to be good candidates for low-light harvesting. To match the irradiance spectra of indoor light, we configured a triple-cation perovskite material with appropriate content of bromide and chloride (FA0.45MA0.49Cs0.06Pb(I0.62Br0.32Cl0.06)3) to achieve an optimum band gap (Eg) of sim1.80 eV. With low photon flux at indoor condition, minimal recombination is highly desirable. To achieve such goal, we, for the first time, combined dual usage of antisolvent deposition and vacuum thermal annealing, namely VTA, to fabricate a high-quality perovskite film. VTA leads to compact, dense, and hard morphology while suppressing trap states at surfaces and grain boundaries, which are key culprits for exciton losses. With low-cost carbon electrode architecture, VTA devices exhibited average power conversion efficiency (PCE) of 27.7 ± 2.7% with peak PCE of 32.0% (Shockley–Queisser limit of 50–60%) and average open-circuit voltage (Voc) of 0.93 ± 0.02 V with peak Voc of 0.96 V, significantly more than those of control and the vacuum treatment prior to heat.

Multi-Sensitization Strategy for High Efficiency and Low Efficiency Roll-off Solution-Processed Single-Emission-Layer All-Fluorescence White Organic Light-Emitting Diodes

Limited by the inefficient energy transfer from blue thermally activated delayed fluorescence (TADF) material to the complementary color fluorescent dopant and unwanted charge trapping effect, it is challenging to achieve a spectrally stable, high efficiency and low efficiency roll-off solution-processed single-emission-layer (SEL) white organic light-emitting diodes (WOLEDs). Herein, a highly efficient solution-processed all-fluorescence SEL-WOLED with suppressed efficiency roll-off and stable electroluminescence spectra is achieved by introducing a hybridized local and charge-transfer (HLCT) orange-red emitter (BDP-C-Cz) and a TADF sensitizer (4CziPN) into an optimized blue TADF OLED. Specially, the adopted BDP-C-Cz emitter has a high molar absorption coefficient, whose absorption spectrum has a significant overlap with the emission spectra of 4CziPN and blue emitter. By additionally introducing 4CziPN as an assistant sensitizer of blue emitter, Förster energy transfer can be enhanced to give favorable exciton allocation and thus effectively blocks triplet exciton loss. Accordingly, a recorded external quantum efficiency of 22.8% and current efficiency of 60.0 cd/A were realized for the solution-processed SEL-WOLEDs, with color coordinates of (0.33, 0.44) and good color stability, providing a valuable guidance for the future development of simplified, high-efficiency and low-cost WOLEDs.

Quantifying the Energy Loss of Triplet Excitons on High‐Lying Triplet States to Develop High Efficiency Blue Fluorescence OLEDs Based on AIE Emitter

Abstract“Hot exciton” molecules that allow the transition of excitons from a high‐lying triplet state (Tn, n≥ 2) to singlet states (Sm, m≥1) by a reverse intersystem crossing (hRISC) process have become an effective strategy to achieve high efficiency fluorescence organic light emitting diodes (OLEDs). However, the understanding of the dynamic behavior of the “hot exciton” process is still very lacking. Herein, the exciton dynamics of an aggregation‐induced emission (AIE) molecule TPA‐An‐mPhCz with the “hot exciton” property are deeply investigated, and the proportion between hRISC and internal inversion (IC) of excitons on Tn is successfully quantified by in situ transient electroluminescent measurements and theoretical calculation. It is found that the IC process increases severe energy loss of Tn excitons. By introducing a triplet–triplet annihilation up‐conversion layer in the emissive layer to efficiently recapture the IC excitons and further doping a blue fluorescent emitter in the TPA‐An‐mPhCz layer to achieve high photoluminescence quantum yield (PLQY), the resulting OLED achieves a maximum external quantum efficiency of 12.5% with negligible efficiency roll‐off. More impressively, the operational lifetime LT75 (lifetime to 75% of the initial luminance) of the device with efficient triplets utilization performs a remarkable 116 h under 1000 cd m−2. This work provides the fundamentals for the design of hot exciton materials with efficient exciton utilization to develop efficient blue fluorescence OLEDs.

Strategic Management of High‐Lying Triplet Excitons to Realize the Breakthrough in Efficiency of Blue Fluorescence OLEDs Based on AIE Emitter

AbstractAggregation‐induced emission (AIE) materials are attractive for the fabrication of high‐efficiency organic light‐emitting diodes (OLEDs) owing to the “hot exciton” process by reverse intersystem crossing (hRISC) and high photoluminescence quantum yields (PLQY). However, the internal conversion (IC) from the high‐lying triplet excitation states (Tn, n≥2) to the lower excited triplet state (Tn‐1) is inevitable, resulting in severe exciton losses. Herein, an effective device structure is designed that reuses the lost triplet excitons caused by IC and realizes the breakthrough in the efficiency of blue fluorescence OLEDs based on AIE molecule as an emitter. The maximum external quantum efficiency reached as high as 14.8% and is kept at 14.4% at the luminance of 1000 cd m−2. In the designed device, a triplet–triplet annihilation (TTA) up‐conversion material 1‐[2,5‐dimethyl‐4‐(1‐pyrenyl)phenyl]pyrene (DMPPP) is introduced into the AIE emitter as a triplet sensitizer to receive the lost triplet excitons, and a thin TTA up‐conversion layer 9‐[4‐(10‐phenyl‐9‐anthryl)phenyl]‐9H‐carbazole (CzPA) is introduced in the middle of the doped layer to form the emissive layer (EML). It is found that the hRISC process of iTPB‐2AC greatly enhances the utilization efficiency of TTA intermediate state ([TT]*) excitons on CzPA to iTPB‐2AC so that the utilization of the lost excitons is maximized. This work establishes physical insights into the AIE emission materials and device fabrication of high‐efficiency blue fluorescence OLEDs.

Enhanced Förster Energy Transfer Through Horizontal Orientation of Sensitizer Molecules in Hyperfluorescent Organic Light‐Emitting Diodes

AbstractFörster resonance energy transfer (FRET) in sensitized fluorescent (SF) organic light‐emitting diodes (OLEDs) is an important process for suppressing triplet exciton loss during energy transfer toward the fluorescent dopant. Herein, the contribution of the relative orientation between the sensitizer and emitting dopant to the FRET in state‐of‐the‐art SF OLEDs is explained using experimental and theoretical approaches. The enhanced relative orientation factor (κ2) from 0.375 to 1.250 is theoretically demonstrated in the FRET theory depending on the orientation of the sensitizer and emitting dopant. On comparing two SF OLED systems with different sensitizers, the sensitizer with a higher horizontal dipole orientation exhibits a higher FRET rate, resulting in the enhanced κ2. The exciton dynamics under device operation are explored to quantitatively verify the contribution of the enhanced FRET rate to the exciton transfer processes; the triplet consumption rate of the sensitizer improves by 2.2 times, demonstrating an efficient exciton transfer.

Multiexciton Generation from a 2D Organic-Inorganic Hybrid Perovskite with Nearly 200% Quantum Yield of Red Phosphorescence.

2D organic-inorganic hybrid perovskites (OIHPs) show obvious advantages in the field of optoelectronics due to their high luminescent stability and good solution processability. However, the thermal quenching and self-absorption of excitons caused by the strong interaction between the inorganic metal ions lead to a low luminescence efficiency of 2D perovskites. Herein, a 2D Cd-based OIHP phenylammonium cadmium chloride(PACC) with a weak red phosphorescence (ΦP < 6%) at 620nm and a blue afterglow is reported. Interestingly, the Mn-doped PACC exhibits very strong red emission with nearly 200% quantum yield and 15ms lifetime, thus resulting in a red afterglow. The experimental data prove that the doping of Mn2+ not only induces the multiexciton generation (MEG) process of the perovskite, avoiding the energy loss of inorganic excitons, but also promotes the Dexter energy transfer from organic triplet excitons to inorganic excitons, thus realizing the superefficient red-light emission of Cd2+ . This work suggests that guest metal ions can induce host metal ions to realize MEG in 2D bulk OIHPs, which provides a new idea for the development of optoelectronic materials and devices with ultrahigh energy utilization.