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Nature Energy, Published online: 16 November 2023; doi:10.1038/s41560-023-01406-5

Wide-bandgap perovskite solar cells are limited by losses in open-circuit voltage. Wang et al. show that diammonium halide salts promote a homogeneous distribution of halides in the perovskite, improving the performance of single- and triple-junction solar cells.

Uniform area-emissive white OLET device with an efficiency of 13.9% is realized by incorporating phosphorescent blue emissive and fluorescent yellow emissive guests in the active layer based on a unique lateral-integrated device configuration, which is the highest value in the field and demonstrates great potential for full-color display as backlight source for the first time.

Abstract

The construction of high-performance white organic light-emitting transistor (OLET) with uniform area emission is crucial for smart display technologies but remains greatly challenging. Herein, high-efficiency uniform area-emissive OLETs based on a unique lateral-integrated device configuration which incorporates efficient energy transfer of phosphorescent and fluorescent guests, enabling color-tunable and white emission, are demonstrated. Through precisely regulating the energy transfer between host and guests, high external quantum efficiency of 13.9% for white-emission OLETs is achieved due to the improved high exciton utilization and light outcoupling efficiency which is the highest value reported so far for OLETs and prevents exciton-charge annihilation and electrode photon losses. Moreover, good loop stability is also achieved, along with effective gate tunability and ultralow driving voltage of below 5 V. Finally, a 4 × 6 white-emission OLET array for full-color display is demonstrated for the first time, suggesting its great potential applications for advanced display technologies.

Two novel rod-like acceptor-donor-acceptor-configured thermally activated delayed fluorescence emitters with disk boron, nitrogen-contained polycyclic aromatic hydrocarbons (B,N-PAHs) fragments have been designed and synthesized. The orange-red and single-emission-layer white organic light-emitting diodes employing these dopants exhibit external quantum efficiency over 30% and low roll-off.

Abstract

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.

Minimizing non-radiative recombination losses in the state-of-the-art non-fullerene solar cells is of utmost importance in order to achieve power conversion efficiencies over 20% in the future. This review discusses methods to accurately quantify non-radiative voltage losses as well as the current understanding of their origin and empirical strategies for reducing them.

Abstract

Organic solar cells benefit from non-fullerene acceptors (NFA) due to their high absorption coefficients, tunable frontier energy levels, and optical gaps, as well as their relatively high luminescence quantum efficiencies as compared to fullerenes. Those merits result in high yields of charge generation at a low or negligible energetic offset at the donor/NFA heterojunction, with efficiencies over 19% achieved for single-junction devices. Pushing this value significantly over 20% requires an increase in open-circuit voltage, which is currently still well below the thermodynamic limit. This can only be achieved by reducing non-radiative recombination, and hereby increasing the electroluminescence quantum efficiency of the photo-active layer. Here, current understanding of the origin of non-radiative decay, as well as an accurate quantification of the associated voltage losses are summarized. Promising strategies for suppressing these losses are highlighted, with focus on new material design, optimization of donor–acceptor combination, and blend morphology. This review aims at guiding researchers in their quest to find future solar harvesting donor–acceptor blends, which combine a high yield of exciton dissociation with a high yield of radiative free carrier recombination and low voltage losses, hereby closing the efficiency gap with inorganic and perovskite photovoltaics.

Two acceptor–donor–acceptor′–donor–acceptor type organic emitters named NTQ and BTQ with narrow optical gaps of 1.23 and 1.13 eV are employed as short-wavelength infrared (SWIR) emitters for organic light-emitting diodes (OLEDs) applications. The resultant SWIR OLEDs based on NTQ show good SWIR radiation properties, with a maximal radiant exitance of 1.12 mW cm^-2 at 1140 nm, one of the highest values for OLEDs emitting at SWIR region.

Abstract

Short-wavelength infrared (SWIR) organic light-emitting diodes (OLEDs) have attracted great interest due to their potential applications in biological imaging, infrared lighting, optical communication, environmental monitoring, and surveillance. Due to an intrinsic limitation posed by the energy-gap law, achieving high-brightness in SWIR OLEDs remains a challenge. Herein, the study reports the use of novel A–D–A′–D–A type small molecules NTQ and BTQ for high-performance SWIR OLEDs. Benefiting from multiple D–A effect in conjugated skeleton, the small molecules NTQ and BTQ exhibit narrow optical gaps of 1.23 and 1.13 eV, respectively. SWIR electroluminescence (EL) emission from OLEDs based on NTQ and BTQ is achieved, with emission peaks at 1140 and 1175 nm, respectively. Not only owing to a negligible efficiency roll-off across the full range of applied current density but also the ability to afford a high operation current density of 5200 mA cm⁻², the resultant SWIR OLEDs based on NTQ exhibit a maximal radiant exitance of =1.12 mW cm⁻². Furthermore, the NTQ-based OLEDs also possess sub-gap turn-on voltage of 0.85 V, which is close to the physical limits derived from the generalized Kirchhoff and Planck equation. This work demonstrates that A–D–A′–D–A type small molecules offer significant promise for NIR/SWIR emitting material innovations.

Two novel NIR TADF organic emitters, namely OPDC-DTPA and OPDC-DBBPA, were first designed and compared in parallel. Neat films of OPDC-DTPA and OPDC-DBBPA present real NIR emission with peaks at 962 and 1003 nm, respectively. Encouragingly, the solution processable doped NIR OLEDs based on OPDC-DBBPA exhibits a maximum of 0.103 % with an emission at a peak wavelength of 906 nm.

Abstract

Near-infrared (NIR) organic light-emitting diodes (OLEDs) suffer from the low external electroluminescence (EL) quantum efficiency (EQE), which is a critical obstacle for potential applications. Herein, 1-oxo-1-phenalene-2,3-dicarbonitrile (OPDC) is employed as an electron-withdrawing aromatic ring, and by incorporating with triphenylamine (TPA) and biphenylphenylamine (BBPA) donors, two novel NIR emitters with thermally activated delayed fluorescence (TADF) characteristics, namely OPDC-DTPA and OPDC-DBBPA, are first developed and compared in parallel. Intense NIR emission peaks at 962 and 1003 nm are observed in their pure films, respectively. Contributed by the local excited (LE) characteristics in the triplet (T₁) state in synergy with the charge transfer (CT) characteristics for the singlet (S₁) state to activate TADF emission, the solution processable doped NIR OLEDs based on OPDC-DTPA and OPDC-DBBPA yield EL peaks at 834 and 906 nm, accompanied with maximum EQEs of 0.457 and 0.103 %, respectively, representing the state-of-the-art EL performances in the TADF emitter-based NIR-OLEDs in the similar EL emission regions so far. This work manifests a simple and effective strategy for the development of NIR TADF emitters with long wavelength and efficiency synchronously.

Publication date: 15 July 2023

Source: Chemical Engineering Journal, Volume 468

Author(s): Hao-Yu Yang, Heng-Yuan Zhang, Ming Zhang, Hao Zhuo, Hui Wang, Hui Lin, Si-Lu Tao, Cai-Jun Zheng, Xiao-Hong Zhang

Publication date: 1 July 2023

Source: Chemical Engineering Journal, Volume 467

Author(s): Xiangan Song, Shaogang Shen, Shengnan Zou, Fengyun Guo, Ying Wang, Shiyong Gao, Yong Zhang

A class of delayed fluorescent macrocycles is successfully synthesized via a modular strategy. Among them, MC-XT and MC-X show perfect photoluminescence quantum yields (≈100%) due to more ideal macrocyclic structure and larger oscillator strength. Therefore, organic light-emitting diodes (OLEDs) based on MC-XT and MC-X achieve record-high maximum external quantum efficiencies of 26.9% and 31.6%, respectively.

Abstract

Several thermally activated delayed fluorescence (TADF) materials have been studied and developed to realize high-performance organic light-emitting diodes (OLEDs). However, TADF macrocycles have not been sufficiently investigated owing to the synthetic challenges, resulting in limited exploration of their luminescent properties and the corresponding highly efficient OLEDs. In this study, a series of TADF macrocycles is synthesized using a modularly tunable strategy by introducing xanthones as acceptors and phenylamine derivatives as donors. A detailed analysis of their photophysical properties combined with fragment molecules reveals characteristics of high-performance macrocycles. The results indicate that: a) the ideal structure decreases the energy loss, which in turn reduces the non-radiative transitions; b) reasonable building blocks increase the oscillator strength providing a higher radiation transition rate; c) the horizontal dipole orientation (Θ) of the extended macrocyclic emitters is increased. Owing to the high photoluminescence quantum yields of ≈100% and 92% and excellent Θ of 80 and 79% for macrocycles MC-X and MC-XT in 5 wt% doped films, the corresponding devices exhibit record-high external quantum efficiencies of 31.6% and 26.9%, respectively, in the field of TADF macrocycles.

Transformation of a deep-blue MR-TADF emitter, DIDOBNA-N, to a narrowband near-UV emitter, MesB-DIDOBNA-N is demonstrated. Efficient deep-blue OLEDs with EQE_max and CIE _y coordinate of 15.3% and 0.073 with DIDOBNA-N and 16.2% and 0.049 with MesB-DIDOBNA-N illustrate the promise of the molecular design of these emitters.

Abstract

Two multiresonant thermally activated delayed fluorescence (MR-TADF) emitters are presented and it is shown how further borylation of a deep-blue MR-TADF emitter, DIDOBNA-N, both blueshifts and narrows the emission producing a new near-UV MR-TADF emitter, MesB-DIDOBNA-N, are shown. DIDOBNA-N emits bright blue light (Φ_PL = 444 nm, FWHM = 64 nm, Φ _PL = 81%, τ _d = 23 ms, 1.5 wt% in TSPO1). The deep-blue organic light-emitting diode (OLED) based on this twisted MR-TADF compound shows a very high maximum external quantum efficiency (EQE_max) of 15.3% for a device with CIE _y of 0.073. The fused planar MR-TADF emitter, MesB-DIDOBNA-N shows efficient and narrowband near-UV emission (λ _PL = 402 nm, FWHM = 19 nm, Φ _PL = 74.7%, τ _d = 133 ms, 1.5 wt% in TSPO1). The best OLED with MesB-DIDOBNA-N, doped in a co-host, shows the highest efficiency reported for a near-UV OLED at 16.2%. With a CIE _y coordinate of 0.049, this device also shows the bluest EL reported for a MR-TADF OLED to date.

An anion exchange process using HBr is developed and used to achieve pure-red emitting CsPbI_3-xBr_x quantum dots, with 1-dodecanethiol ligands used to suppress halide ion migration. The light-emitting diodes based on the quantum dos show a stable electroluminescence peak at 637 nm, and a maximum external quantum efficiency of 21.8% with an average value of 20.4%.

Abstract

Perovskite-based light-emitting diodes (PeLEDs) with a mixed halide composition can be used to obtain the “pure red” emission, i.e., in the 620–650 nm range, required for high-definition displays. However, fast halide ion migration induces phase separation in these materials under electric fields, resulting in poor spectral stability and low efficiency. Herein, a method for producing mixed halide CsPbI_3-xBr_x quantum dots (QDs) is reported in which ion migration is suppressed. The mixed halide composition is first achieved by anion exchange between CsPbI₃ QDs and hydrobromic acid (HBr), during that the bromine ions efficiently passivate the iodine vacancies of the QDs. The original oleic acid ligands are then exchanged for 1-dodecanethiol (1-DT), which suppresses halide ion migration via the strong binding of the sulfhydryl group with the QD surface. PeLEDs based on these QDs exhibit a pure-red electroluminescence (EL) peak at 637 nm, a maximum external quantum efficiency (EQE) of 21.8% with an average value of 20.4%, a peak luminance of 2653 cd m⁻², and low EQE decease with increasing luminance. The EL spectrum of these devices is stable even at 6.7 V and they have an EQE half-life of 70 min at an initial luminance of 150 cd m⁻².

Nature Materials, Published online: 06 April 2023; doi:10.1038/s41563-023-01529-w

We synthesized stretchable electroluminescent polymers capable of reaching a near-unity theoretical quantum yield through thermally activated delayed fluorescence. Their polymers show 125% stretchability with 10% external quantum efficiency and demonstrate a fully stretchable organic light-emitting diode.

Two thermally actived delayed fluorescence (TADF) materials with subtle chemical modification exhibit different luminescent behavior in aggregation state. Rigid X-aggregation maintains TADF emission with aggregation-induced emission (AIE) feature and efficient intramolecular intersystem crossing (ISC) and reverse ISC(RISC) process, whereas compact H-aggregation disables TADF emission channel with active intermolecular ISC, enhanced phosphorescence, and inhibited RISC process, which leads to aggregation-caused quenching (ACQ) character.

Abstract

The understanding of the excited state dynamics of thermally activated delayed fluorescence (TADF) materials is crucial. In this study, two donor–acceptor-type TADF emitters with highly twisted conformation are synthesized. The emitters with subtle chemical modification of donor unit exhibit opposite aggregation luminescent behaviors: aggregation-induced emission (AIE) and aggregation-caused quenching (ACQ). Through the photophysical properties study, crystallographic analysis, and theory simulations, it is discovered that X-aggregation supports AIE behavior by restricting the intramolecular motions and preserving TADF emission via an efficient reverse intersystem crossing (RISC) process, but on the other hand, H-aggregation leads to ACQ behavior due to inhibited RISC, disabled TADF channel, and weak phosphorescence from radiative low-lying triplet state. The findings shed light on the excited-state dynamic behaviors of TADF emitters, which are dependent on aggregation.

Nature Photonics, Published online: 16 March 2023; doi:10.1038/s41566-023-01164-6

The addition of a strong coupling layer allows polariton-based emission from red and green organic light-emitting diodes with high external quantum efficiency up to 10%, linewidth smaller than 20 nm and angle-independent emission, with spectral shifts smaller than 10 nm over a 60° angular tilt.