High Exciton Utilization Efficiency Research Articles

Pure room temperature phosphorescence emission in nondoped OLEDs: adjustable oxidation states and excited-state modulation.

Purely organic room temperature phosphorescence (RTP) materials are a new kind of triplet emitter, which can harvest both singlet and triplet excitons in theory, thus showing great application potential for organic light-emitting diodes (OLEDs). However, nondoped OLEDs based on RTP emitters have been rarely explored owing to challenges in realizing efficient phosphorescence in single-component systems. Herein, three donor-acceptor-type luminogens were designed and synthesized in which phenothiazine, with different oxidation degrees, acted as the electron donor and acetophenone as the acceptor. The adjustable oxidation states of phenothiazine enabled the modulation of excited states, facilitating the transition from dual RTP and thermally activated delayed fluorescence emissions to pure RTP. A nondoped OLED device was then fabricated based on the pure RTP emitter, achieving a high exciton utilization efficiency of 86%, clearly demonstrating the enhancement of electroluminescence performance through RTP properties.

Constructing Organic Phosphorescent Scintillators with Enhanced Triplet Exciton Utilization Through Multi-Mode Radioluminescence for Efficient X-Ray Imaging.

The development of organic phosphorescent scintillators with high exciton utilization efficiency has attracted significant attention but remains a difficult challenge because of the inherent spin-forbidden feature of X-ray-induced triplet excitons. Herein, a design strategy is proposed to develop organic phosphorescent scintillators through thermally activated exciton release to convert stabilized spin-forbidden triplet excitons to spin-allowed singlet excitons, which enables singlet exciton-dominated multi-mode emission simultaneously from the lowest singlet, triplet, and stabilized triplet states. The resultant scintillators demonstrate a maximum photoluminescence efficiency of 65.8% and a minimum X-ray radiation detection limit of 110nGys-1; this allows efficient radiography imaging with a spatial resolution of ≈10.0 lp mm-1. This study advances the fundamental understanding of exciton dynamics under X-ray excitation, significantly broadening the practical use of phosphorescent materials for safety-critical industries and medical diagnostics.

Efficient and ultra-high luminance orange-red organic light emitting diode (OLED) based on triphenylamine-benzothiadiazole-phenoxazine hybrid molecule with hybrid local and charge-transfer (HLCT) characteristic

Due to the energy gap law, red emission needs relatively narrow energy gap, thus the nonradiative transition rate (knr) grows exponentially and eventually impacts the materials fluorescent efficiency. Here, an orange-red emission donor-acceptor-π-donor (D-A-π-D’) material N, N-diphenyl-4-(7-(4-(10-phenyl-10 H-phenoxazin-3-yl) phenyl) benzo [c] (Huang et al., 2019; Park et al., 2008; Caspar et al., 1982) [1,2,5] thiadiazol-4-yl) aniline (TBphPP) was designed and synthesized. Introducing a benzene π-bridge between the strong donor 10-phenyl-10H-phenoxazin (PPOX) and acceptor 2,1,3-benzothiadiazole (BTZ) not only is able to stretch the molecular conjugation so as to increase the proportion of LE state in hybrid local and charge-transfer (HLCT) state but also increase the overlap area of the electron cloud to improve luminous efficiency. As a result, the non-doped organic light-emitting diode (OLED) of TBphPP exhibited high luminance of 17,886 cd m−2 and relatively high exciton utilization efficiency (EUE) of 44 % with a standard red electroluminescent peak at 620 nm. Importantly, the optimized doped device based on TBphPP achieved high performance that the maximum external quantum efficiency (EQEmax) was up to 9.86 % with a higher EUE of 66.2 % and the efficiency roll-off (ηroll-off) at 100,000 cd m−2 was only 3.55 %. Simultaneously, it has reached ultra-high luminescence of 180,583 cd m−2, high current efficiency of 29.02 cd A−1 and power efficiency of 16.47 l m W−1. To our knowledge, the TBphPP device with such ultra-high luminance and high efficiency is one of the best performance orange-red materials based on HLCT characteristic.

Multifunctional applications of organic light-emitting diodes and room temperature phosphorescence based on benzoyl-fluorene hybrid molecules

Organic light-emitting diodes (OLEDs) and room temperature phosphorescence (RTP) materials have attracted great interests for their wide application in lighting and other fields. How to efficiently utilize triplet excitons to achieve the multifunctionality of OLED and RTP simultaneously is a major challenge. Herein, two blue molecules, 3PCZFB and 3PCZBF were reported. Theoretical calculations indicate that both molecules possess hybrid localized charge transfer (HLCT) characteristic. More importantly, both can simultaneously obtain electro-fluorescence and RTP properties by multiple harvesting of triplet excitons with high spin-orbit coupling matrix element (SOCME). The introduction of benzoyl fluorene increased the contribution of the n-orbital, resulting in a high SOCME, which is beneficial to both high exciton utilization efficiency (EUE) and RTP. The non-doped OLED of 3PCZFB achieved maximum external quantum efficiency (EQEmax) of 4.9 % and EUE of 58.6 % at 459 nm. Besides, 0.1 % 3PCZFB and 3PCZBF doped in PMMA sheets achieve RTP efficiencies of 6.6 % at 524 nm and 25.9 % at 506 nm, as well as lifetimes of 379.8 ms and 204.8 ms. This is the first time Benzoyl fluorene-based molecules achieved dual-function applications in OLED and RTP by utilizing and recycling triplet excitons of T1.

Deep red/near-infrared electro-fluorescence material with nearly 10% external quantum efficiency based on hybridized local and charge-transfer

Although the hot exciton mechanism with hybridized local and charge-transfer (HLCT) characteristics is a promising molecular design strategy, there are few organic deep red (DR) and near-infrared (NIR) HLCT-type emitters with high external quantum efficiency (EQE). Herein, this work reports three DR/NIR emitters with high EQE, TNZ-3PPOXP, TPANZPOXP, and 2PPOXNZ. These emitters show DR/NIR emission in the neat film, 664 nm for TNZ-3PPOXP, 718 nm for TPANZPOXP, and 724 nm for 2PPOXNZ. Interestingly, the emitters all possess hybridized local and charge-transfer (HLCT) characteristics and potential hot exciton channels. The corresponding non-doped OLED achieve high exciton utilization efficiency (EUE) and NIR emission, 55.6 %@694 nm for TNZ-3PPOXP, 82.8 %@736 nm for TPANZPOXP, and 42.3 %@756 nm for 2PPOXNZ. More importantly, with these emitters as the guest, PO-01 as the phosphorescent sensitizer, and CBP as the host, the sensitization device achieved nearly 10 % EQE, 9.55 %@662 nm for TNZ-3PPOXP, 4.20 %@699 nm for TPANZPOXP, and 4.49 %@702 nm for 2PPOXNZ. To our knowledge, this is one of the highest device efficiencies based on HLCT as the guest.

Thermally Activated Delayed Fluorescent Ag(I) Complexes for Highly Efficient Scintillation and High‐Resolution X‐Ray Imaging

AbstractOrganic thermally activated delayed fluorescent (TADF) scintillators hold promising potential for applications in medical radiography and security detection, but the poor X‐ray absorption ability and inferior radioluminescence (RL) hampered their progression. Herein, the study has pioneered the development of high‐performance TADF Ag(I)‐based scintillators from M2X2(dppb)2 (M = Ag, Cu; X = Cl, Br, I) complexes with 1,2‐Bis(diphenylphosphino)benzene (dppb) ligand. In comparison with Cu(I) complexes, the Ag(I) series generally exhibited superior scintillation performance. Notably, Ag2Cl2(dppb)2 (Ag1) stands out with exceptionally high RL intensity (≈125% higher than that of CsI:Tl) and a low detection limit of 59.8 nGy s−1. The outstanding scintillation performance of Ag1 is primarily attributed to the synergistic effect of the high exciton utilization efficiency origin from a small singlet‐triplet energy gap, enhanced X‐ray absorption capacity by heavy atoms, and the high photoluminescence quantum yield (76.47% in ambient atmosphere). By fabricating a flexible film constructed with Ag1 submicron crystalline powders, a high spatial resolution of 25.0 lp mm−1 for X‐ray imaging is obtained. It offers new opportunities for utilizing TADF metal–organic complexes for highly efficient X‐ray scintillation and imaging.

B‒N covalent bond-involved π-extension of multiple resonance emitters enables high-performance narrowband electroluminescence.

Multi-boron-embedded multiple resonance thermally activated delayed fluorescence (MR-TADF) emitters show promise for achieving both high color-purity emission and high exciton utilization efficiency. However, their development is often impeded by a limited synthetic scope and excessive molecular weights, which challenge material acquisition and organic light-emitting diode (OLED) fabrication by vacuum deposition. Herein, we put forward a B‒N covalent bond-involved π-extension strategy via post-functionalization of MR frameworks, leading to the generation of high-order B/N-based motifs. The structurally and electronically extended π-system not only enhances molecular rigidity to narrow emission linewidth but also promotes reverse intersystem crossing to mitigate efficiency roll-off. As illustrated examples, ultra-narrowband sky-blue emitters (full-width at half-maximum as small as 8nm in n-hexane) have been developed with multi-dimensional improvement in photophysical properties compared to their precursor emitters, which enables narrowband OLEDs with external quantum efficiencies (EQEmax) of up to 42.6%, in company with alleviated efficiency decline at high brightness, representing the best efficiency reported for single-host OLEDs. The success of these emitters highlights the effectiveness of our molecular design strategy for advanced MR-TADF emitters and confirms their extensive potential in high-performance optoelectronic devices.

Highly efficient hot exciton deep-blue OLEDs based on triphenyl-phosphine oxide modified anthracene derivatives

The utilization of triplet state excitons is important for the efficiency of organic light-emitting diodes (OLEDs). In this work, two isomers (p-PIAnPO and m-PIAnPO) of anthracene-based derivatives with triphenylphosphine oxide (PO) and phenanthroimidazole (PI) in different positions were designed and synthesized. In particular, PO provides large spatial hindrance and promotes hole transport, and PI has excellent bipolar transport ability, which helps to balance carrier transport. The para-linkage (p-PIAnPO) favors conjugation expansion and achieves high luminescence efficiencies, whereas the meta-linkage (m-PIAnPO) provides a highly twisted molecular conformation, thus effectively interrupting conjugation and leading to deep-blue emission. These molecules exhibit excellent thermal stability and efficient electroluminescence properties. Non-doped OLEDs using p-PIAnPO and m-PIAnPO as the light-emitting layers achieve maximum external quantum efficiencies of 6.0% and 4.2% with the λEL at 466 nm and 448 nm, corresponding to high exciton utilization efficiency (EUE) of 59%–88% and 54%–81%. In addition, p-PIAnPO-based OLEDs achieve an ultra-low efficiency roll-off of 1.7% at 1000 cd m−2. Theoretical calculations and experimental results show that the high EUE is mainly attributed to the high-lying reverse intersystem crossing from T3 to S1 namely hot exciton channel.

Efficient Non-Doped Blue Electroluminescence Based on Phenanthroimidazole–Benzoylfluorene Hybrid Molecules with High Spin-Orbit Coupling and Balanced Charge Mobilities

Developing non-doped blue organic light-emitting diodes (OLEDs) with excellent photoluminescence quantum yield (PLQY), high exciton utilization efficiency (EUE) and balanced carrier mobility is an urgent challenge. Herein, two blue molecules...

Anthracene derivatives with strong spin-orbit coupling and efficient high-lying reverse intersystem crossing beyond the El-Sayed rule.

The attention to materials with hot exciton channel and triplet-triplet fusion (TTF) mediated high-lying reverse intersystem crossing (hRISC) has been raised for their ability to convert non-emissive 'dark' triplets into radiative singlet excitons. This spin conversion process results in high exciton utilization efficiency (EUE) that exceeds the theoretical limits. Notably, it is known that such spin conversion processes from the high-lying excited triplet to the singlet state are facilitated by the orthogonal orbital transition effect governed by the El-Sayed's rule. In this study, an anthracene derivative with indenoquinoline substituent 7,7-dimethyl-9-(10-(4-(naphthalen-1-yl)phenyl)anthracen-9-yl)-7H-indeno[1,2-f]quinoline (2MIQ-NPA) was synthesized and analyzed to investigate whether the hRISC process occurs in these molecules, even when the El-Sayed's rule is not followed. The hRISC channels of the emitter were fully unraveled through DFT calculations and experiments, which were quantitatively subdivided using transient electroluminescence measurements. The results showed that 2MIQ-NPA, which does not follow the El-Sayed's rule and has a relatively strong spin-orbit coupling matrix element of 0.116 cm-1 between the high-lying triplet state of T4 and the lowest singlet state of S1, effectively converted triplet excitons into singlet excitons with an EUE of 64.3%, contributed by a direct hot exciton channel of 19.2% and a TTF-mediated hot exciton channel of 15.1%. Despite the low outcoupling efficiency, the non-doped device with 2MIQ-NPA achieved an excellent device performance with an external quantum efficiency of 7.0%.

Management of Host–Guest Triplet Exciton Distribution for Stable, High‐Efficiency, Low Roll‐Off Solution‐Processed Blue Organic Light‐Emitting Diodes by Employing Triplet‐Energy‐Mediated Hosts

AbstractHigh‐quality hosts are indispensable for simultaneously realizing stable, high efficiency, and low roll‐off blue solution‐processed organic light‐emitting diodes (OLEDs). Herein, three solution processable bipolar hosts with successively reduced triplet energies approaching the T1 state of thermally activated delayed fluorescence (TADF) emitter are developed and evaluated for high‐performance blue OLED devices. The smaller T1 energy gap between host and guest allows the quenching of long‐lived triplet excitons to reduce exciton concentration inside the device, and thus suppresses singlet‐triplet and triplet‐triplet annihilations. Triplet‐energy‐mediated hosts with high enough T1 and better charge balance in device facilitate high exciton utilization efficiency and uniform triplet exciton distribution among host and TADF guest. Benefited from these synergetic factors, a high maximum external quantum efficiency (EQEmax) of 20.8%, long operational lifetime (T50 of 398.3 h @ 500 cd m−2), and negligible efficiency roll‐off (EQE of 20.1% @ 1000 cd m−2) are achieved for bluish‐green TADF OLEDs. Additionally introducing a narrowband emission multiple‐resonance TADF material as terminal emitter to accelerate exciton dynamic and improve exciton utilization, a higher EQEmax of 23.1%, suppressed roll‐off and extended lifetime of 456.3 h are achieved for the sky‐blue sensitized OLEDs at the same brightness.

Realization of Pyreno[4,5-d]imidazole-based HLCT emissions through tuning the energy level of the charge-transfer state

Organic light-emitting diodes (OLEDs) have lately been used in tablet displays, for instance in mobile phones and televisions, and are considered to be the next generation of displays and solid-state lighting due to their light weight, high flexibility, and energy efficiency. Hybridized local and charge-transfer (HLCT) excited state fluorophores, capable of making full use of excitons by reverse intersystem crossing from high-lying triplet states to singlet states, have drawn increasing attention in OLED applications. The HLCT state can be efficiently achieved by constructing D-π-A type molecules, whose characteristics of their excited state are widely influenced by the difference of torsion angles between donor (D) and acceptor (A). Herein, pyreno[4,5-d]imidazole and triphenylamine were selected as the electron acceptor and electron donor, respectively. Based on this molecular design, two D-π-A type molecules, pTPA-PyI and mTPA-PyI were designed and synthesized with different torsion angles between D and A. In addition, the introduction of fluorine atoms in molecules could provide more and stronger charge transfer (CT) state components into the excited states of the molecule, which could facilitate the formation of HLCT states with improving exciton utilization of the molecule. As a result, pTPA-PyI with linear molecular geometry possessed HLCT properties, which could achieve a large yield of singlet exciton formation. The non-doped pTPA-PyI-based OLED demonstrated steady blue emission with a peak at 460 nm and CIE coordinates of (0.15, 0.20). The highest current efficiency was 7.7 cd A−1, the maximum brightness was 48637 cd m−2, and the external quantum efficiency (EQE) was 6.38%. When the brightness was 1000 cd m−2, the efficiency roll-off was incredibly low as 0.6%, yet the EQE of 6.34% was still achievable. Additionally, it possesses a high exciton-utilization efficiency of up to 97%. However, the locally excited (LE) and CT states of mTPA-PyI could not sufficiently hybridize due to its larger torsion angle between D and A with the smaller dipole moment and the interrupted conjugation structure of the molecule which led to high energy level of CT state. As a result, by altering the torsion angle between D and A, it is feasible to change the constituents and levels of the LE and CT states in order to actualize the HLCT feature.

Excited-State Descriptors for High-Throughput Screening of Efficient Electro-Fluorescent Materials

Electro-fluorescent materials with 100% internal quantum efficiency (IQE) and short fluorescence lifetimes (τf, ∼ ns) are desirable and achievable by harvesting high-lying triplet excitons. However, the IQE governed by exciton utilization efficiency (EUE) and photoluminescence quantum yield (PLQY) remains low. Herein, from the electro-fluorescence process involving triplet excitons and energy gap law, we established two excited-state descriptors (triplet–triplet energy gap ΔETT and oscillator strength f) to characterize EUE, PLQY and τf, by taking a series of hot exciton compounds as prototypes. Subsequently, these descriptors were employed to perform high-throughput screening of over 5000 fluorophores, predicting 19 candidate molecules with a high IQE (>90%). We stressed that the large values of these descriptors are conducive to high EUE and PLQY and short τf. This work presents a guideline to design and screen efficient electro-fluorescent materials beyond the spin-statistical limit.

“Exciton Recovery” Strategy in Hot Exciton Emitter toward High‐Performance Non‐Doped Deep‐Blue and Host‐Sensitized Organic Light‐Emitting Diodes

AbstractThe “hot exciton” mechanism based on high‐lying reverse intersystem crossing process has great advantages in achieving high‐performance deep‐blue organic light‐emitting diodes (OLEDs). Nevertheless, how to solve the loss of high‐lying excitons to improve device performance further is a pressing and challenging issue. To break through this shackle, a novel deep‐blue emitter based on “exciton recovery” strategy is successfully design, namely CAT. By combining the transient absorption spectrum, theoretical calculation, magneto‐electroluminescence, and transient‐electroluminescence measurements, the multi‐channeled pathways of excitons utilization via hot exciton and triplet‐triplet annihilation processes is comprehensively demonstrated, and the proportion of singlet excitons by each channel. Finally, a high exciton utilization efficiency is successfully achieved, and the non‐doped OLED based on CAT exhibit an excellent external quantum efficiency of 10.39% with the CIE coordinates of (0.15, 0.087). Furthermore, the sensitized blue fluorescent OLED by CAT as host also achieves excellent performance. More importantly, the operational lifetime of the “multi‐channel” sensitized device is evaluated for the first time, performing the remarkable LT50(lifetime to 50% of the initial luminance) of 320 h at 540 cd m−2. These results fully reveal the significance of the “exciton recovery” strategy and give new inspiration for exploring high‐performance blue OLEDs.

Double-locked narrowband hybrid locally-excited and charge-transfer emitter exhibiting amplified spontaneous emission

<p>Hybrid Locally-excited and Charge-Transfer (HLCT) materials have garnered significant attention for their high exciton utilization efficiency in organic light-emitting diodes (OLEDs). However, conventional HLCT materials suffer from broad emission, which limits their applications. In this study, we report a narrowband HLCT emitter, namely 10-(dimesitylboranyl)-8,8,12,12-tetraphenyl-8,12-dihydrobenzo[9,1]quinolizino[3,4,5,6,7-<i>klmn</i>]phenoxazine (PXZ-DL), incorporated by double-locked intramolecular connection. PXZ-DL exhibits a narrow emission spectrum with a small full width at half-maximum (FWHM) of 35 nm and 47 nm in solution and as an OLED emitter, respectively. Moreover, PXZ-DL demonstrates a high photoluminescence quantum yield of 100% and an external quantum efficiency of 8.0%. Additionally, PXZ-DL demonstrates excellent performance in amplified spontaneous emission with a low threshold of 5.7 ��J cm<sup>-2</sup> and a narrow FWHM of 11 nm. The intramolecular lock strategy offers a promising approach for the development of HLCT materials with high color purity.</p>

Highly efficient deep-blue organic light-emitting diodes (OLEDs) based on hot-exciton materials with multiple triplet exciton conversion channels

High-energy triplet exciton conversion, high exciton utilization efficiency and high device efficiency were achieved through multiple hot-exciton conversion channels.

High-efficiency all fluorescence white OLEDs with high color rendering index by manipulating excitons in co-host recombination layers.

All fluorescence white organic light-emitting diodes (WOLEDs) based on thermally activated delayed fluorescence (TADF) emitters are an attractive route to realize highly efficient and high color quality white light sources. However, harvesting triplet excitons in these devices remains a formidable challenge, particularly for WOLEDs involving conventional fluorescent emitters. Herein, we report a universal design strategy based on a co-host system and a cascaded exciton transfer configuration. The co-host system furnishes a broad and charge-balanced exciton generation zone, which simultaneously endows the devices with low efficiency roll-off and good color stability. A yellow TADF layer is put forward as an intermediate sensitizer layer between the blue TADF light-emitting layer (EML) and the red fluorescence EML, which not only constructs an efficient cascaded Förster energy transfer route but also blocks the triplet exciton loss channel through Dexter energy transfer. With the proposed design strategy, three-color all fluorescence WOLEDs reach a maximum external quantum efficiency (EQE) of 22.4% with a remarkable color rendering index (CRI) of 92 and CIE coordinates of (0.37, 0.40). Detailed optical simulation confirms the high exciton utilization efficiency. Finally, by introducing an efficient blue emitter 5Cz-TRZ, a maximum EQE of 30.1% is achieved with CIE coordinates of (0.42, 0.42) and a CRI of 84 at 1000 cd m-2. These outstanding results demonstrate the great potential of all fluorescence WOLEDs in solid-state lighting and display panels.

Sequential Multiple Borylation Toward an Ultrapure Green Thermally Activated Delayed Fluorescence Material.

Multiple-resonance thermally activated delayed fluorescence (MR-TADF) emitters have emerged as an important component of organic light-emitting diodes (OLEDs) because of their narrowband emission and high exciton utilization efficiency. However, the chemical space of MR-TADF emitters remains mostly unexplored because of the lack of suitable synthetic protocols. Herein, we demonstrate a sequential multiple borylation reaction that provides new synthetically accessible chemical space. ω-DABNA, the proof-of-concept material, exhibited narrowband green TADF with a full width at half-maximum of 22 nm and a small singlet-triplet energy gap of 13 meV. The OLED employing it as an emitter exhibited electroluminescence at 512 nm, with Commission International de l'Éclairage coordinates of (0.13, 0.73) and a high external quantum efficiency (EQE) of 31.1%. Moreover, the device showed minimum efficiency roll-off, with an EQE of 29.4% at 1000 cd m-2.

Deep-Blue Triplet-Triplet Annihilation Organic Light-Emitting Diode (CIEy ≈ 0.05) Using Tetraphenylimidazole and Benzonitrile Functionalized Anthracene/Chrysene Emitters.

Herein, new deep-blue triplet-triplet annihilation (TTA) molecules, namely 4-(10-(4-(1,4,5-triphenyl-1H-imidazol-2-yl)phenyl)anthracen-9-yl)benzonitrile (TPIAnCN) and 4-(12-(4-(1,4,5-triphenyl-1H-imidazol-2-yl)phenyl)chrysen-6-yl)benzonitrile (TPIChCN), are designed, synthesized, and investigated as emitters for organic light-emitting diodes (OLED). TPIAnCN and TPIChCN are composed of polyaromatic hydrocarbons of anthracene (An) and chrysene (Ch) as the cores functionalized with tetraphenylimidazole (TPI) and benzonitrile (CN) moieties, respectively. The experimental and theoretical results verify their excellent thermal properties, photophysical properties, as well as electrochemical properties. Particularly, their emissions are in the deep blue region, with TTA emissions being observed in their thin films. By utilization of these molecules as emitters, deep blue TTA OLEDs with CIE coordinates of (0.15, 0.05), high external quantum efficiency of 6.84%, and high exciton utilization efficiency (ηs) of 48% were fabricated. This result manifests the potential use of chrysene as an alternate building block to formulate new TTA molecules for accomplishing high-performance TTA OLEDs.

High-performance circularly polarized electroluminescence from d-f transition europium(II) complexes

Circularly polarized organic light-emitting diodes (CP-OLEDs) have attracted increasing interest for their advantages in generating circularly polarized light directly and efficiently. To date, chiral luminescent materials with different emission mechanisms have been investigated as emitters in CP-OLEDs, but it is difficult to achieve a high luminescence dissymmetry factor (g) and high efficiency simultaneously. Herein, chiral luminescent europium(II) complexes with d-f transition characteristics are synthesized and used as emitters in CP-OLEDs. The europium(II) complexes show a maximum g value of 6.6 × 10−3 in doped films, and the corresponding CP-OLEDs show a maximum external quantum efficiency up to 15.6%. The performance is attributed to the unique europium(II) complex with a d-f transition mechanism, which results in a theoretically high magnetic transition dipole moment and high exciton utilization efficiency. This study focusing on chiral d-f transition-containing lanthanide complexes opens up an avenue to future exploration of high-performance chiroptical materials.