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Metal–halide perovskite nanocrystals (NCs) have emerged as suitable light‐emitting materials for light‐emitting diodes (LEDs) and other practical applications. However, LEDs with perovskite NCs undergo environment‐induced and ion‐migration‐induced structural degradation during operation; therefore, novel NC design concepts, such as hermetic sealing of the perovskite NCs, are required. Thus far, viable synthetic conditions to form a robust and hermetic semiconducting shell on perovskite NCs have been rarely reported for LED applications because of the difficulties in the delicate engineering of encapsulation techniques. Herein, a highly bright and durable deep‐blue perovskite LED (PeLED) formed by hermetically sealing perovskite NCs with epitaxial ZnS shells is reported. This shell protects the perovskite NCs from the environment, facilitates charge injection/transport, and effectively suppresses interparticle ion migration during the LED operation, resulting in exceptional brightness (2916 cd m−2) at 451 nm and a high external quantum efficiency of 1.32%. Furthermore, even in the unencapsulated state, the LED shows a long operational lifetime (T50) of 1192 s (≈20 min) in the air. These results demonstrate that the epitaxial and hermetic encapsulation of perovskite NCs is a powerful strategy for fabricating high‐performance deep‐blue‐emitting PeLEDs. [ABSTRACT FROM AUTHOR]

Multimaterial emission layer (EML) with host and dopant is known for its advantages in efficiency and lifetime for organic light‐emitting diodes (OLEDs). However, as the compositions and the mixing ratio in the EML diversify, complex device physics and photophysics and complicated fabrication processes become challenging issues. Herein, a new concept to integrate exciton donor (host) and acceptor (dopant) into a single emitting molecule is suggested. 9‐(8,9,10,11‐Tetradeuterospiro[benzo[de]anthracene‐7,9′‐fluoren]‐2'‐yl)‐9H‐carbazole (SBAF‐Cz) and 8,9,10,11‐tetradeutero‐N‐(9,9‐dimethyl‐9H‐fluoren‐2‐yl)‐N‐phenylspiro[benzo[de]anthracene‐7,9′‐fluoren]‐3‐amine (FPA‐SBAF) are used as host and dopant, respectively. By integrating two units, 8,9,10,11‐tetradeutero‐2′‐(9H‐carbazol‐9‐yl)‐N‐(9,9‐dimethyl‐9H‐fluoren‐2‐yl)‐N‐phenylspiro[benzo[de]anthracene‐7,9′‐fluoren]‐3‐amine (FPA‐SBAF‐Cz) is synthesized, and photophysical and electrical properties are characterized. Density functional theory and experimental results consistently reveal that SBAF‐Cz and FPA‐SBAF are photophysically and electrically independent. The electrical properties of FPA‐SBAF‐Cz behave independently, while the photophysical properties are the sum of those of SBAF‐Cz and FPA‐SBAF, which is attributed to the zero radius of intramolecular energy transfer (ZRIET) between donor and acceptor in FPA‐SBAF‐Cz. The single‐component blue OLED with FPA‐SBAF‐Cz exhibits a maximum external quantum efficiency of 4.18%, which is higher than those of OLEDs with SBAF‐CZ:FPA‐SBAF multicomponent EMLs. Surprisingly, the device lifetime to 50% decrease from initial luminance is 114 h in FPA‐SBAF‐Cz OLED, which is 2.2 times longer than that of SBAF‐Cz:FPA‐SBAF OLEDs. [ABSTRACT FROM AUTHOR]

A highly efficient anthracene‐based 5‐(4‐(10‐phenylanthracen‐9‐yl)phenyl)‐5H‐benzofuro[3,2‐c]carbazole (ATDBF) with nearly 100% exciton utilization efficiency is developed for highly efficient nondoped blue organic light‐emitting diodes (OLEDs) through inter‐ and intramolecular triplet exciton up‐converting mechanisms. The ATDBF emitter opens hybridized hot excitons, triplet–triplet fusion (TTF), and mixed TTF/hot exciton channels for triplet exciton to singlet exciton conversion. The molecular design adopting a benzofuro[3,2‐c]carbazole (BFCz) donor manages the singlet and triplet excited states for hybridized triplet exciton up‐conversion mechanisms, which enable a high external quantum efficiency (EQE) of 7.93% in the ATDBF blue device with color coordinates of (0.15, 0.06). This is one of the best efficiencies of the nondoped blue OLEDs with a y color coordinate below 0.06. [ABSTRACT FROM AUTHOR]

We analyzed the change of electrical characteristics of hyper‐fluorescence OLED according to the doping concentration using Modulus spectroscopy. As the concentration of the thermally activated delayed fluorescence (TADF) sensitizer increased, the turn‐on voltage was reduced by forming a conductive path by the sensitizer. However, it was not related to the external quantum efficiency (EQE). The difference between the two trends can be understood from the electrical and photophysical perspectives such as Modulus spectroscopy, EL spectrum and capacitance‐voltage (C‐V) curve. The ratio of 5:1 device with the most suitable doping ratio showed the highest 14.86% of EQE and 46.82 cd/A of current efficiency (CE). The reason for this result is that the distance between the sensitizer and the dopant is most suitable considering the Förster energy transfer (FRET) radius. This contributed to the closest match between the point at which the maximum value of capacitance and the turn‐on voltage of the device in the C‐V curve. [ABSTRACT FROM AUTHOR]

A high triplet energy host is developed using a silane moiety, 9‐(4‐(triphenylsilyl)dibenzo[b,d]furan‐2‐yl)‐9H‐carbazole (SiDBFCz), is designed through extensive density functional theory (DFT) calculations to obtain appropriate hole and electron injection barriers. The chemical hardness and the charge transport characteristics are comprehensively investigated to realize a bipolar host with high triplet energy over 2.9 eV for deep blue phosphorescent organic light‐emitting diodes (PHOLEDs). The synthesized SiDBFCz clearly exhibits the bipolar characteristics especially with emitter molecules doped. An external quantum efficiency over 19 % without any microcavity optimization is achieved thanks to the good charge balance in the SiDBFCz PHOLED. The device lifetime of the SiDBFCz PHOLED is improved more than 1000 %, compared to the unipolar control devices at an initial luminance of 500 cd m−2. The dramatic enhancement of the operational stability of the deep blue PHOLED is also thoroughly investigated in terms of electrochemical stability of host molecules in charged or excited states. The results clearly indicate that the device lifetime is strongly correlated with the bond dissociation energy and the activation energy for the bond dissociation reaction in triplet excited state. [ABSTRACT FROM AUTHOR]

High triplet energy exciplex hosts are developed using new electron transport type hosts with triphenylsilyl blocking groups to obtain high solid state triplet energy and exciplex triplet energy. Two triphenyltriazine derived hosts, 2‐phenyl‐4,6‐bis(4‐(triphenylsilyl)phenyl)‐1,3,5‐triazine (pSiTrz) and 2‐phenyl‐4,6‐bis(3‐(triphenylsilyl)phenyl)‐1,3,5‐triazine (mSiTrz), are synthesized as the high triplet energy hosts with electron transport properties. The two hosts show high triplet energy over 2.90 eV both in solution and solid film, and afford high triplet energy over 2.90 eV in the mixed hosts with a hole transport type 2,2′‐di(9H‐carbazol‐9‐yl)‐1,1′‐biphenyl (oCBP) host. The doping of a deep blue phosphorescent emitter in the mixed host oCBP:mSiTrz achieves high external quantum efficiency over 20% with a color coordinate of (0.14, 0.16) and device lifetime of longer than 1000 h at 100 cd m‐2. This is the first demonstration of simultaneous achievement over 20% external quantum efficiency (EQE) and 1000 h lifetime in the deep blue organic light‐emitting diodes with a x+y color coordinate value below 0.30. [ABSTRACT FROM AUTHOR]

• p-host and fluorescent dopant was seamlessly integrated into a single molecule. • Non-conventional exciplex formed between fused p-host and n-host. • ZETPLEX, an extremely efficient energy transfer within fused p-host and n-host. A multi-component emissive layer (EML) composed of a mixture of p- and n-type hosts and a dopant is a widely used structure in organic light-emitting diodes (OLEDs) due to its high efficiency and operational stability. However, multi-component EML devices impose limitations such as difficulty in accurately controlling the mixing ratio and profiles in the manufacturing process, high costs, and complexity in the photophysical properties of the components. In this paper, a p-type host fused with a blue fluorescent dopant, 5,9-di([1,1′-biphenyl]-2-yl)-2′-(9H-carbazole-9-yl)3,7-dimethyl-5,5a,5a1,9,9a,16a-hexahydrospiro[5,9-diaza-16b-boraindeno[2,1-b]naphtho[1,2,3-fg]anthracene-11,9′-fluorene] (DABNA-Spiro-Cz), was designed and successfully synthesized to construct a novel EML structure. Completely fused within DABNA-Spiro-Cz, the p-type host and blue fluorescent dopant can independently perform their respective roles. An exciplex is formed between n-type host and p-type host unit in the DABNA-Spiro-Cz molecule and its energy is effectively transferred to the blue fluorescent dopant unit in DABNA-Spiro-Cz. In other words, a degree of freedom is earned from a conventional 3-component exciplex-dopant system. A high external quantum efficiency of 14.9 % was achieved thanks to " z ero-radius of intramolecular e nergy t ransfer in exci plex (ZETPLEX)" system, which is completely non-conventional and novel. We believe the ZETPLEX mechanism opens a new era of designing emissive materials and paves a new way of constructing a novel EML and device architecture for highly efficient OLEDs. [ABSTRACT FROM AUTHOR]

• Intermolecular interaction between host and deep blue Pt complex utilized in WOLEDs. • By varying the ratio of n-type host, a wide range of colors was achieved. • Highly efficient WOLEDs were realized with a single deep blue Pt(II) complex. Previous studies on white organic light-emitting diodes (WOLEDs) using a single Pt dopant relied on square-planar Pt complexes, exhibiting various emission characteristics due to ligand-centered π-π interactions. However, this approach limits the range of the materials selections to those with excimer or aggregation-induced emission (AIE) properties. In this study, a new method for creating WOLEDs with a single Pt dopant is proposed. We observed the emergence of an intermolecular interaction, specifically the formation of an exciplex due to π-π interaction between the n-host (ET) and the Pt complex, leading to a low-energy yellow emission. By varying the mixing ratio of ET and Pt complex, a spectrum of emissions ranging from pure blue to yellow was achievable. Consequently, we constructed 3-stack tandem devices, leveraging color variations based on the ET:Pt ratio. As a result, we successfully achieved a cool white emission with a Color Rendering Index (CRI) of 66.7, International Commission on Illumination (CIE) coordinates of (0.294, 0.380). Additionally, through optimization of the device structure, external quantum efficiency (EQE) was enhanced from 18.3% to 21.9%. This novel and simple device architecture adjusting intermolecular interaction based on molecular geometry between ET and Pt(II) complex provides a solution to materials limitations in WOLEDs. [ABSTRACT FROM AUTHOR]

The pursuit of hybridized local and charge transfer (HLCT) excited state-based emitters is a promising strategy to achieve high external quantum efficiency in blue organic light-emitting diodes (OLEDs). Two isomeric dimethyl-dihydroindenocarbazole-anthracene-phenanthroimidazole-based emissive molecules (PhAnsIn and PhAnoIn) were designed and explored based on the HLCT scheme. All molecules possessed the HLCT excited-state characters, according to the photophysical investigation and density functional theory calculations. Consequently, PhAnsIn and PhAnoIn showed good blue emission with peaks at 457 and 464 nm and photoluminescence quantum yield of 80.6% and 56.5% in neat films, respectively. The fabricated blue OLEDs with PhAnsIn and PhAnoIn as emitters also realized the corresponding blue emission with electroluminescence peaks at 458 and 457 nm, respectively. The nondoped devices based on PhAnsIn and PhAnoIn exhibited maximum external quantum efficiencies of 8.2% and 8.5% with CIE coordinates of (0.14, 0.12) and (0.14, 0.11), respectively. • Hybridized local and charge transfer excited state based blue fluorescence emitter. • High photoluminescence quantum yield of 80.6% in a neat film. • Non-doped blue fluorescence organic light-emitting diodes with external quantum efficiency of 8.2%. [ABSTRACT FROM AUTHOR]

"Hot-exciton" materials exhibiting high-lying reverse intersystem crossing (hRISC) are promising candidates for organic light-emitting diode (OLED) materials owing to their improved exciton utilization efficiency and efficiency roll-off. To investigate the excited-state structure–property relationship in anthracene/benzophenone-based materials, we designed and prepared three anthracene-benzophenone derivatives by varying substituents at peripheral benzophenone units, namely, AnBP-F , AnBP-H , and AnBP-OMe. Systematic investigation of the excited-state properties of these compounds and DFT calculations showed that they have hybridized local and charge-transfer (HLCT) characteristics in their emissive transitions. All prepared compounds were adapted in a non-doped OLED device, which exhibited an external quantum efficiency (EQE) of up to 2.88%. To further study the exciton dynamics in the device, magnetoelectroluminescence was measured, which exhibits the combined characteristics of triplet–triplet annihilation (TTA) and HLCT mechanisms. [Display omitted] • Anthracene/benzophenone-based HLCT emitters were prepared by varying substituents at peripheral benzophenone units. • Substituents help to tune the nature of the excited state. • Non-doped OLEDs achieved EQE max of 2.88%. • Studies on the exciton dynamics of the device indicate that the TTA and HLCT mechanisms concurrently exist. [ABSTRACT FROM AUTHOR]