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Quasi‐two‐dimensional (quasi‐2D) perovskites are emerging as efficient emitters in blue perovskite light‐emitting diodes (PeLEDs), while the imbalanced crystallization of the halide‐mixed system limits further improvements in device performance. The rapid crystallization caused by Cl doping produces massive defects at the interface, leading to aggravated non‐radiative recombination. Meanwhile, unmanageable perovskite crystallization is prone to facilitate the formation of nonuniform low‐dimensional phases, which results in energy loss during the exciton transfer process. Here, we propose a multifunctional interface engineering for nucleation and phase regulation by incorporating the zwitterionic additive potassium sulfamate into the hole transport layer. By using potassium ions (K+) as heterogeneous nucleation seeds, finely controlled growth of interfacial K+‐guided grains is achieved. The sulfamate ions can simultaneously regulate the phase distribution and passivate defects through coordination interactions with undercoordinated lead atoms. Consequently, such synergistic effect constructs quasi‐2D blue perovskite films with smooth energy landscape and reduced trap states, leading to pure‐blue PeLEDs with a maximum external quantum efficiency (EQE) of 17.32 %, spectrally stable emission at 478 nm and the prolonged operational lifetime. This work provides a unique guide to comprehensively regulate the halide‐mixed blue perovskite crystallization by manipulating the characteristics of grain‐growth substrate. [ABSTRACT FROM AUTHOR]

Organic light‐emitting diodes (OLEDs) based on thermally activated delayed fluorescence (TADF) materials are promising for the realization of highly efficient emitters. However, severe efficiency roll‐off at high brightness still remains as a huge challenge for TADF‐based OLEDs. Herein, rod‐like orange‐red TADF emitters of 2BNCz‐PZ and 2BNtCz‐PZ with acceptor‐donor‐acceptor (A‐D‐A) configuration are developed by bearing dihydrophenazine donor and discoidal rigid boron, nitrogen‐contained polycyclic aromatic hydrocarbons acceptors. Both emitters exhibit hybrid long‐range/short‐range charge‐transfer excitation for small singlet‐triplet energy splitting, short delayed lifetime, and high photoluminescence quantum yield, leading to fast singlet radiation rate over 107 s−1 and fast reverse intersystem crossing rate over 106 s−1. Furthermore, a horizontal emitting dipole orientation factor over 90% is realized. The optimized orange‐red OLED based on 2BNtCz‐PZ presents a maximum external quantum efficiency (EQE) of 31.0% and a slight EQE roll‐off to 22.2% at 1 000 cd m−2 with emission peak over 600 nm. In addition, the single‐emitting layer white OLEDs achieve a maximum EQE of 30.6% due to the use of these orange‐red dopants with intense charge‐transfer absorption band. This work reveals the potential of the rod‐like A‐D‐A configuration for constructing highly efficient orange‐red TADF emitters with low‐efficiency roll‐off. [ABSTRACT FROM AUTHOR]

White organic light-emitting diodes (OLEDs) hold great promise for applications in displays and lighting due to high efficiency and superior white color balance. However, further improvement in efficiency remains a continuous and urgent demand due to limited energy flow extraction. A powerful method for drastically releasing the trapped energy flow in conventional white OLEDs is demonstrated by implementing unique quasi-periodic subwavelength nanofunnel arrays (NFAs) via soft nanoimprinting lithography, which is ideal for enhancing light extraction without any spectral distortion or angular dependence. The resulting efficiency is over 2 times that of a conventional OLED used as a comparison. The external quantum efficiency and power efficiency are raised to 32.4% and 56.9 lm W−1, respectively. Besides, the substantial increase in efficiency over a broad bandwidth with angular color stability, the experimental proofs show that the NFA-based extraction structure affords the enticing capacity against scrubbing and the self-cleaning feature, which are critical to the commercial viability in practical applications. [ABSTRACT FROM AUTHOR]

Highly power-efficient white organic light-emitting diodes (OLEDs) are still challenging to make for applications in high-quality displays and general lighting due to optical confinement and energy loss during electron-photon conversion. Here, an efficient white OLED structure is shown that combines deterministic aperiodic nanostructures for broadband quasi-omnidirectional light extraction and a multilayer energy cascade structure for energy-efficient photon generation. The external quantum efficiency and power efficiency are raised to 54.6% and 123.4 lm W−1 at 1000 cd m−2. An extremely small roll-off in efficiency at high luminance is also obtained, yielding a striking value of 106.5 lm W−1 at 5000 cd m−2. In addition to a substantial increase in efficiency, this device structure simultaneously offers the superiority of angular color stability over the visible wavelength range compared to conventional OLEDs. It is anticipated that these findings could open up new opportunities to promote white OLEDs for commercial applications. [ABSTRACT FROM AUTHOR]

Highlights: [•] The doping effects of cesium compounds on device characteristics of OLEDs are studied. [•] The charge transport property is highly dependent on doping constituent materials. [•] The operational stability of OLEDs replies on the doping mechanism. [Copyright &y& Elsevier]

The effect of cesium carbonate (Cs2CO3) doping on the electron transport properties of 4,7-diphenyl-1, 10-phenanthroline (BPhen) layer has been investigated in organic light-emitting diodes (OLEDs). Temperature-dependent admittance spectroscopy studies show that the incorporation of Cs2CO3 from 0 to 42 wt. % can decrease the activation energy of the BPhen layer from 1.3 to 0.18 eV, resulting in the enhanced electron injection and transport with respect to reduced injection barrier and increased conductivity of the BPhen layer. This is consistent with the performance improvement in OLEDs, which yields better electrical characteristics and enhanced luminance efficiency. [ABSTRACT FROM AUTHOR]

Organic Light-Emitting Diodes: The Strategies for High-Performance Single-Emissive-Layer White Organic Light-Emitting Diodes (Laser Photonics Rev. 15(3)/2021) The strategies focus on the molecular design methods of single-molecule devices, the energy transfer mechanisms in various multiple-molecule devices with all-fluorescence, all-phosphorescence, and fluorescence-phosphorescence hybrid structures, and the combination of exciplex emitters and complementary fluorescent/delayed fluorescent/phosphorescent emitters. In article number 2000474, Yan-Qing Li, Jian-Xin Tang, and co-workers review the recent developments for constructing single-emissive-layer white organic light-emitting diodes (SEL-WOLEDs). [Extracted from the article]

Flexible organic light‐emitting diodes (OLEDs) are attracting tremendous attention due to their promise as a key element in bendable display and curved lighting applications. However, their performance in terms of efficiency and bendability is limited, since flexible transparent electrodes with superior electrical, optical, and mechanical properties are rare. Here, a multifunctional electrode architecture that is based on flexible plastic, and consists of electrically conductive silver nanowires, a nanopatterned ZnO outcoupling layer, and a hole‐injection polymer layer, is proposed for the actualization of high‐performance flexible OLEDs. The trapped light in the waveguide and substrate modes is effectively released by integrating aperiodic nanostructures into high‐refractive‐index ZnO layers on both sides of the plastic substrate. A maximum external quantum efficiency of 61.7% and a power efficiency of 126.6 lm W−1 are achieved for the white‐emission flexible OLEDs with broadband and angle‐independent outcoupling enhancement. In addition, the proposed approach allows for high‐level mechanical flexibility, retaining over 80% of the initial efficiency after 3000 cycles of repeated bending. [ABSTRACT FROM AUTHOR]

On page 2660, J. X. Tang and co‐workers demonstrate a powerful method for drastically releasing the trapped energy flow in conventional white organic light‐emitting diodes by implementing a unique quasi‐periodic subwavelength nanofunnel array via soft nanoimprinting litho‐graphy. Besides the substantial increase in efficiency over a broad bandwidth without any spectral distortion or angular dependence, this array affords an enticing capacity against scrubbing and the self‐cleaning feature, which are critical to the commercial viability in practical applications. [ABSTRACT FROM AUTHOR]

Organic light-emitting diodes (OLEDs) using a tandem structure offer a highly attractive option for the applications of next-generation flat panel displays and solid-state lighting due to the extremely high brightness and efficiency along with the long operational lifetime. In general, reliable information about interface energetics of the charge generation layers (CGLs), which plays the central role in charge generation and carrier injection into the stacked emission units, is highly desirable and advantageous for interface engineering and the performance optimization of tandem OLEDs. In this review, our recent studies on tandem OLEDs are overviewed, especially from interface energetics perspective via photoemission spectroscopy. The electronic structures of various transition metal oxide (TMO)-based CGLs and their role in charge generation process are reviewed, addressing the n-type doping impact of organic layers in CGLs, thermal annealing-induced oxygen vacancy in TMOs, and the interfacial stability of CGLs on the device operational lifetime. The resulting energy level alignments are summarized in correspondence with tandem OLED performance. [ABSTRACT FROM AUTHOR]

[Display omitted] • The emitters show through-space charge transfer and aggregation-induced delayed-fluorescence. • The exciton quenching in aggregate state is mitigated by disrupting intermolecular π-π stacking. • Non-doped OLEDs with non-doped emitters show an EQE over 20% and minimal roll-off. The development of non-doped through-space charge transfer thermally activated delayed fluorescent (TSCT-TADF) materials remains a significant challenge, with only limited examples reported to date. Herein, we present an innovative approach to enhance the efficiency of non-doped organic light-emitting diodes (OLEDs) by integrating a bulky neutral m -terphenyl or tetraphenylsilicon unit into the TSCT-TADF core. The installation of a rigid bulky group not only disturbs the intermolecular π-π stacking but also alleviates exciton quenching in the aggregate state. These materials show distinct aggregation-induced emission characteristics and achieve a high photoluminescence quantum yield in neat films. These properties enable the realization of highly efficient doped OLEDs with an external quantum efficiency (EQE) exceeding 30%. Importantly, non-doped devices achieve a record-high EQE of 21.4% with minimal efficiency roll-off. The design strategy employing rigid bulky shielding demonstrated in this study proves to be a promising approach for the development of efficient non-doped TSCT-TADF emitters. [ABSTRACT FROM AUTHOR]

We report computational and experimental studies (i) on the Fermi level (E F ) pinning phenomena in weakly interacting electrode-organic semiconductor systems with pentacene, N, N-Di(naphthalene-l-yl)-N, N’-diphenyl-benzidine (α-NPD) and Poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT)], and (ii) to elucidate a common reason of the pinning phenomena which have been widely observed for various organic materials on inert electrode surfaces. For (i), the computed results on the electrode-dependence of E F -HOMO and E F -LUMO distance agreed excellently with UPS and Kelvin-probe results. For (ii) we found theoretically that the pinning phenomena occur at systems even without any electronic states in the HOMO-LUMO gap, and thereby indicate that this is a universal Fermi-level pinning-like phenomena for various band gap materials, even if specific interface states do not exist upon contact. We further obtained for Gaussian-distributed HOMO and LUMO that the minimal hole and electron injection barriers are quantitatively determined by degree of standard deviations of HOMO and LUMO bands, which are in excellent agreement with the experimental results. Furthermore, our results provide a guideline for approaching the “zero” injection barriers. [ABSTRACT FROM AUTHOR]

The role of transition metal oxides (TMOs) based intermediate connectors in tandem organic light emitting diodes (OLEDs) has been studied via capacitance-voltage and current-voltage characteristics, in order to elucidate the dynamic processes of charges generation and transport within externally applied voltages. The TMO-based intermediate connectors are composed of molybdenum trioxide (MoO 3 ) and cesium azide (CsN 3 )-doped-4, 7–diphenyl-1, 10-phenanthroline (BPhen) layers, where MoO 3 and CsN 3 are used due to low deposition temperatures. From the obtained results of capacitance and current density, charges generation in CsN 3 :BPhen/MoO 3 /NPB is proposed to the defect states in thermally evaporated MoO 3 , which offers a minimal energy offset for charges generation. Moreover, our results clearly indicate that charges generation efficiency is not only relying on the MoO 3 -NPB interface, but also influenced by CsN 3 :BPhen-MoO 3 interface. CsN 3 doped BPhen layer further improves charges separation efficiency, which finally results in favorable charges transport into the adjacent layers and ensure to function efficiently for tandem OLEDs. [ABSTRACT FROM AUTHOR]

Through-bond charge transfer (TBCT) and through-space charge transfer (TSCT) are simultaneously demonstrated in SFO-SPAC-based TADF emitters, leading to high EQEs of 23.5% and 22.3% in evaporation- and solution-processed non-doped OLEDs along with low efficiency roll-off. [Display omitted] • TBCT and TSCT channels are simultaneously realized in TADF emitters. • Spiral donor–acceptor framework of SFO-SPAC shows nearly 100% PLQY in neat films. • The evaporated non-doped OLEDs achieve an EQE of 23.5% with low roll-off. • The solution-processed non-doped TADF OLEDs achieve an EQE of 22.3%. The development of thermally activated delayed fluorescence (TADF) emitters with fast reverse intersystem crossing rate (RISC) remains huge challenge. In this work, donor–acceptor-type TADF material SFO-SPAC is designed and synthesized, which contains methyl and F-atom shells along with dual-spiral segments. The SFO-SPAC emitter features through-bond and through-space charge transfer due to the distorted donor–acceptor structures and the induced effects of F-atoms. The neat film of SFO-SPAC exhibits a photoluminescence quantum yield of 96%, a fast RISC rate of 1.04 × 106 s−1, and a fast radiative decay rate of 1.90 × 107 s−1. Consequently, the evaporation-processed non-doped green organic light emitting diode (OLED) achieves a maximum external quantum efficiency (EQE) of 23.5% and low efficiency roll-off with an EQE of 20.1% at 5000 cd m−2. In addition, the solution-processed non-doped device shows high EQE up to 22.3%. [ABSTRACT FROM AUTHOR]

Highlights: [•] Solution-processed Au nanoparticles (NPs):MoO X was used as an inter-layer in OLEDs. [•] The interface properties and good device stability were investigated. [•] The improved electrical properties were achieved due to modification of interface. [•] Localized surface plasmon induced efficiency enhancement was realized due to Au NPs. [Copyright &y& Elsevier]

Abstract: We report on the role of cesium fluoride (CsF) doping on the enhanced electron transport properties of tris-(8-hydroxyquinolin) aluminum (Alq3) for organic light-emitting diodes. The electronic structures of CsF-doped Alq3 layers with various doping concentration are characterized by in situ ultraviolet and X-ray photoelectron spectroscopies, showing an n-type electrical doping effect with Fermi level shift towards unoccupied molecular orbital and the formation of chemistry-induced gap-states. The increase in conductivity and reduction in electron injection barrier in CsF-doped Alq3 layer with optimal doping concentration lead to the enhanced electron injection and transport, which are consistent with the improved electrical characteristics of OLEDs. [Copyright &y& Elsevier]

Abstract: We report on a high-quality hybrid intermediate connector (IC) used in tandem organic light-emitting diodes (OLEDs), which is composed of an ultrathin MoO3 interlayer sandwiched between a n-type Cs2CO3-doped 4,7-diphenyl-1,10-phenanthroline (BPhen) layer and a p-type MoO3-doped N,N′-diphenyl-N,N′-bis(1-naphthyl)-(1,1′-biphenyl)-4,4′-diamine (NPB) layer. The charge generation characteristics for light emission in tandem OLEDs have been identified by studying the interfaces and the corresponding devices. The hybrid IC structure exhibits superior charge generation capability, and its interfacial electronic structures are beneficial to the generation and injection of electrons and holes into bottom and top emission units, respectively. Compared to the organic-TMO bilayer and doped p–n junction structures, the hybrid IC structure combining MoO3-based interlayer and p-type doping can effectively decrease the driving voltage and improve the current efficiency of tandem devices due to the increased bulk heterojunction-like charge generation interfaces. Our results indicate that the TMO-based hybrid IC structure can be a good structure in the fabrication of high-efficiency tandem OLEDs. [Copyright &y& Elsevier]

Three D-σ-A type thermally activated delayed fluorescent materials (TADF), AQ-S-Cz, AQ-S-DPA and AQ-S-DMAC, with sulfur atom connect donors and acceptor, were designed and synthesized. All of the emitters exhibit small ΔE ST (<0.2 eV) and the limited overlap of the molecular frontier orbitals because of the C–S σ bond and the distorted molecular structure. AQ-S-Cz and AQ-S-DMAC with rigid donor obtained higher photoluminescence quantum yields than AQ-S-DPA. The three emitters have excellent TADF performance and short delayed fluorescence lifetimes (0.32 μs for AQ-S-Cz, 0.15 μs for AQ-S-DPA, 0.28 μs for AQ-S-DMAC). The experiment results show that the three emitters have intra-molecular charge transition (intra-CT), especially inter-molecular charge transition (inter-CT) effect. The luminescence of these emitters can be efficiently regulated by intra-CT, especially inter-CT and realize prominent red shift from yellow (556 nm) to red emission (657 nm). Compared with that of AQ-S-Cz and AQ-S-DPA, the device based on AQ-S-DMAC obtained maximum external quantum efficiencies of 7.17% with turn-on voltage of 3.5 V. This work enriches the D-σ-A type orange-red TADF materials and provides a perspective approach of developing long wavelength TADF emitters. [Display omitted] • Three D-σ-A type TADF materials with C–S σ bond were designed and synthesized. • The luminescence of three emitters can be efficiently adjusted by intra-CT, especially inter-CT, and realize obvious red shift from yellow to red emission. • The smaller ΔE ST s can be obtained by C–S bond blocking the conjugate between donor and acceptor, meanwhile the rigid donor suppress the non-radiation process to achieve higher PLQYs. • The AQ-S-DMAC-based TADF-OLED emits orange-red fluorescence and obtains EQE max of 7.17%. [ABSTRACT FROM AUTHOR]

An novel acceptor PSP was designed to construct two TADF materials, PSPP and PSPBP, with rigid PXZ as donor in 3-position or 3,5-position of PSP. Both TADF emitters successfully achieve small ΔE ST (≈ 0.2 eV) and high PLQYs as well as good device performance. Compared with the PSPBP-based OLED, the OLED based on PSPP with one donor PXZ achieves higher the maximum external quantum efficiency and lower turn-on voltage. [Display omitted] • An novel acceptor PSP was designed to construct two TADF materials, PSPP and PSPBP. • Both PSPP and PSPBP exhibit high PLQYs as well as good device performance. • The OLED based on PSPP achieves higher EQE max and lower turn-on voltage. 3-(Phenylsulfonyl)pyridine (PSP), an unreported acceptor, is used to construct two thermally activated delayed fluorescent materials (TADF), PSPP and PSPBP, with rigid PXZ as donor in 3-position or 3, 5-position of PSP. Both PSPP and PSPBP have large twisted structure due to highly steric hindrance, resulting in small ΔE ST. Simultaneously, the frontier molecular orbitals of PSPP and PSPBP show limited spatial overlap, which improve photoluminescence quantum yields. Both emitters have distinct TADF performance. The OLEDs based on these emitters exhibit good photoelectric properties. This work enriches the acceptor selection scope and possesses crucial significance to developing new TADF molecules. [ABSTRACT FROM AUTHOR]