以昇陳

Nature Energy, Published online: 07 July 2022; doi:10.1038/s41560-022-01059-w

All-perovskite tandem photovoltaics hold technological potential yet their upscaling is not trivial. Here Nejand et al. fabricate mini-modules using scalable methods and laser-scribed interconnections, achieving a 19.1% efficiency over an aperture area of 12.25 cm2.

Nature Photonics, Published online: 19 May 2022; doi:10.1038/s41566-022-00999-9

A new strategy to reduce charge leakage in quantum-dot light-emitting diodes enables high external quantum efficiencies of 28.7% and 21.9% and excellent T95 lifetimes of 580,000 h and 4,400 h for green and blue devices, respectively.

An unreported high-level reverse intersystem-crossing from upper-level triplet to lowest singlet excitons (T₂ → S₁) is observed when T₂ is well confined in the active layer of pure tetra(t-butyl)rubrene (TBRb) by suppressing the energy loss channels of triplet excitons occurring in charge-carrier transport layers from TBRb-doped organic light-emitting diodes.

Abstract

High external quantum efficiency (EQE) up to 25% has recently been reported from tetra(t-butyl)rubrene (TBRb)-based organic light-emitting diodes (OLEDs), but its physical origin is still vague. Herein, using the featured responses of the evolution processes of electron-hole pairs to an external magnetic field, an unreported high-level reverse intersystem-crossing (HL-RISC) from upper-level triplet to lowest singlet excitons (T₂ →S₁) is observed when T₂ is well confined in the active layer of pure TBRb. This HL-RISC channel becomes stronger with lowering operational temperatures because it is not an endothermic process. Due to the larger separation distance of TBRb molecules with four tert-butyl groups, the intersystem-crossing (ISC) process of polaron pairs is stronger than the singlet fission (SF) process existing in pure TBRb, which is markedly different from the behaviors of excited states in pure rubrene (Rb) with negligible ISC and strong SF. More importantly, HL-RISC is stronger in TBRb than in Rb-doped systems, which is consistent with the higher EQE frequently reported from TBRb-doped OLEDs. Thus, this work deepens the physical understanding of microscopic processes in typical organic multi-functional semiconductors of TBRb or Rb and paves the way for fabricating further high-efficiency yellow OLEDs.

A flexible transparent CsPbBr₃ quantum dots (QDs) mixed in graphene oxide (GO) resistive switching memory is prepared. The devices exhibit an ultrahigh ON/OFF ratio of ≈1.4 × 10⁷ under illumination, increasing by 1077 times than that in the dark. As a flexible memory device, the resistances of the Ag/CsPbBr₃ QDs:GO/ITO device are little affected by the bending curvatures and load-cycling.

Abstract

Perovskite resistive random-access memory (RRAM) is a promising candidate for next-generation logic, adaptive and nonvolatile memory devices, because of its high ON/OFF ratio, low-cost fabrication, and good photoelectric regulation performance. In this work, a flexible transparent CsPbBr₃ quantum dots (QDs) mixed in graphene oxide (GO) RRAM device is introduced, which is controllable by both an electric field and illumination. Under illumination, the ON/OFF ratio of the Ag/CsPbBr₃ QDs:GO/ITO device is ≈1.4 × 10⁷, which is 1077 times larger than that in the dark condition (1.3 × 10⁴). The SET/RESET voltages are +2.28/−2.04 V and +1.68/−1.08 V under the dark and illumination conditions, respectively. As a flexible memory device, the resistances are little affected by the bending curvatures and load-cycling. Before and after 10⁴ bending cycles with a radius of 5 mm under illumination, the ON/OFF ratios keep in the same order, which are 2.5 × 10⁷ and 2.3 × 10⁷, respectively. The ratio values are 8.8 × 10⁴ and 2.9 × 10⁴ under the dark condition, respectively. This innovative resistive memory based on the CsPbBr₃ QDs:GO hybrid film supports a huge space for the development of photoelectrical dual-controlled flexible RRAM devices.

The angular fusion mode and electron-deficient core have different effects in the A-DA′D-A acceptors. The angular fusion is beneficial to enhance light absorption and reduce electron-vibration couplings to simultaneously accelerate exciton diffusion, exciton dissociation, and electron transport, while introducing the electron-deficient core will lead to deeper frontier orbitals, bathochromic absorption, and further promote exciton dissociation.

Abstract

The A-DA′D-A fused-ring electron acceptors with an angular fusion mode and electron-deficient core has significantly boosted organic photovoltaic efficiency. Here, the intrinsic role of the peculiar structure is revealed by comparing representative A-DA′D-A acceptor Y6 with its A-D-A counterparts having different fusion modes. Owing to the more delocalized HOMO and deeper LUMO level, Y6 exhibits stronger and red-shifted absorption relative to the linear and angular fused A-D-A acceptors, respectively. Moreover, the change from linear to angular fusion substantially reduces the electron-vibration couplings, which is responsible for the faster exciton diffusion, exciton dissociation, and electron transport for Y6 than the linear fused A-D-A acceptor. Notably, the electron-vibration coupling for exciton dissociation is further decreased by introducing the electron-deficient core, thus contributing to the efficient charge generation under low driving forces in the Y6-based devices.

This work proposes the circularly polarized luminescence molecule based on a hybridized local and charge-transfer (HLCT) chromophore through chiral perturbation, achieving excellent device performances of high exciton utilization and low-efficiency roll-off with a thermally activated delayed fluorescence sensitizer, which could pave the way to develop the novel CP-HLCT materials and highly efficient circularly polarized organic light-emitting diodes.

Abstract

This work describes the first hot exciton fluorescent material based on benzo[c][1,2,5]thiadiazole and chiral binaphthol enabling circularly polarized luminescence (CPL) through a chiral perturbation strategy. The new molecular architecture displays CPL, hybridized local and charge transfer (HLCT) properties concurrently. Utilizing it as the emitter, circularly polarized organic light-emitting diodes (CP-OLEDs) achieve an external quantum efficiency (EQE) of 7.2% with a good exciton utilization (36%) and a moderate circularly polarized electroluminescence (CPEL) dissymmetry factor (g _EL, 2.1 × 10⁻³). In addition, the CP-HLCT molecule is sensitized by a thermally activated delayed fluorescence material, significantly ameliorating the efficiency of HLCT fluorescent CP-OLEDs. Excellent performances of twofold maximum EQE (EQE_max) of 15.3% and 82% exciton utilization are obtained in the sensitized device, regarding an extremely low-efficiency roll-off of 2.6% at 1000 cd m⁻² as well as CPEL with a g _EL value of 2.0 × 10⁻³.

Efficient deep-blue luminescence via thermally activated delayed fluorescence is obtained with a dense manifold of excited-state energies. Fast reverse intersystem crossing rates enable small efficiency roll-off in organic light-emitting diodes (OLEDs). Hyperfluorescence OLEDs using ν-DABNA exhibit high efficiency and a color purity with CIE (Commission Internationale de l'Éclairage) coordinates (0.13,0.15).

Abstract

There is increasing interest in thermally activated delayed fluorescence (TADF) in materials, and to understand its mechanism in the excited state dynamics. Recent challenges include color purity, efficient deep-blue emission, fast exciton decay lifetimes, high reverse intersystem crossing rates (k _RISC), low-efficiency roll-off in organic light-emitting diodes (OLEDs), and long device lifetimes. Here, a series of compounds having benzonitrile and carbazole rings are examined, that provide a detailed understanding of the excited states, and a guideline for high-performance TADF. A dense alignment of the excited states with several different characters within a small energy range results in high k _RISC of >2 × 10⁶ s⁻¹, while maintaining radiative rate constants (k _r) >10⁷ s⁻¹. OLEDs based on the optimum compound exhibit a low-efficiency roll-off and a CIEy (y color coordinate of Commission Internationale de l'Éclairage) <0.4. TADF-assisted fluorescence (TAF) OLED exhibits a maximum external quantum efficiency of 22.4% with CIE coordinates (0.13,0.15). This work also provides insights for device engineering and molecular designs.

A series of narrowband red emitters with superb photophysical properties is developed by way of novel B/N/O-based polycyclic multiple resonance structures. The red OLEDs incorporating these emitters sensitized by the phosphor display state-of-the-art performance with EQE exceeding 36%, ultralow efficiency roll-off, ultrahigh brightness, and good device lifetime.

Abstract

High-color-purity blue and green organic light-emitting diodes (OLEDs) have been resolved thanks to the development of B/N-based polycyclic multiple resonance (MR) emitters. However, due to the derivatization limit of B/N polycyclic structures, the design of red MR emitters remains challenging. Herein, a series of novel red MR emitters is reported by para-positioning N–π–N, O–π–O, B–π–B pairs onto a benzene ring to construct an MR central core. These emitters can be facilely and modularly synthesized, allowing for easy fine-tuning of emission spectra by peripheral groups. Moreover, these red MR emitters display excellent photophysical properties such as near-unity photoluminescence quantum yield (PLQY), fast radiative decay rate (k _r) up to 7.4 × 10⁷ s⁻¹, and most importantly, narrowband emission with full-width at half-maximum (FWHM) of 32 nm. Incorporating these MR emitters, pure red OLEDs sensitized by phosphor realize state-of-the-art device performances with external quantum efficiency (EQE) exceeding 36%, ultralow efficiency roll-off (EQE remains as high as 25.1% at the brightness of 50 000 cd m⁻²), ultrahigh brightness over 130 000 cd m⁻², together with good device lifetime.

Asymmetric substitution of terminal groups is first applied in small-molecule donors. A record efficiency of 16.34% is achieved for binary all-small-molecule organic solar cells. A unique phenomenon of merits integration is reported rather than the balance between V _oc and J _sc, which is generally observed in asymmetric substitution of nonfullerene acceptors.

Abstract

Asymmetric substitution of end-groups is first applied in molecular donors. Three commonly used end-groups of 2-ethylhexyl cyanoacetate (CA), 2-ethylhexyl rhodanine (Reh), and 1H-indene-1,3(2H)-dione (ID) are combined to construct a series of symmetric and asymmetric donors. Correspondingly, the asymmetric donors SM-CA-Reh and SM-CA-ID show largely increased dipole moments (2.14 and 3.39 D, respectively) and enhanced aggregation propensity, as compared to those of symmetric donors of SM-CA, SM-Reh, and SM-ID. Using N3 as acceptor, interestingly, SM-CA-Reh integrates the photovoltaic characteristics of high fill factor (FF) for SM-CA and high short-circuit current density for SM-Reh, and delivers a record power conversion efficiency (PCE) of 16.34% with a high FF of 77.5%, which is much higher than 15.41% for SM-CA and 14.76% for SM-Reh. However, SM-CA-ID and SM-ID give the lower PCE of 8.20% and 2.76%. Characterization results suggest that the π–π interaction mainly dictates the packing morphology of blend films instead of dipole effect or crystallinity. Mono-substitution of Reh facilitates the molecular demixing appropriately but keeps the characteristic of the fine bicontinuous network of SM-CA:N3. SM-CA-Reh:N3 shows more efficient exciton extraction, higher hole transport, and better miscibility. These results well explain the merits integration and improved photovoltaic performance.

A novel staggered stacking covalent organic framework (COF)-based photosensitizer, COF-618-Cu, is reported, which can simultaneously alleviate photobleaching and aggregation-induced quench effects to achieve desirable phototherapy performance and further elicit robust immunogenic cell death to trigger a durable antitumor immune response for boosting cancer immunotherapy.

Abstract

The synergistic efficacy of phototherapy and cancer immunotherapy is severely restricted by both the inherent photobleaching and aggregation-caused quench (ACQ) defects of photosensitizers and the intrinsic antioxidant tumor microenvironment (TME), such as hypoxia and overexpressed glutathione (GSH). To address these issues, a novel porphyrin-based staggered stacking covalent organic framework (COF), COF-618-Cu, is rationally designed as a reactive oxygen species (ROS) amplifier, owing to its excellent catalase-like activity, COF-618-Cu is capable of consuming endogenous hydrogen peroxide to produce sufficient oxygen to alleviate the tumor hypoxia phenomena. Moreover the overexpressed intracellular GSH is also depleted to decrease the scavenging of ROS, due to the glutathione peroxidase mimic activity of COF-618-Cu. Mechanistic studies reveal that the unique staggered stacking mode between COF-618-Cu interlayers can effectively relieve both the photobleaching and ACQ effects that are inaccessible to commonly eclipsed COFs. These, combined with their excellent photothermal therapy performance, make COF-618-Cu favorable for inducing robust immunogenic cell death and remodeling TME to boost antitumor immunity.

An accessible, fast procedure is shown to measure light-emitting diode (LED) emission zones with current density, different device structures, and ageing. The emission zone in an organic LED is shown to be controlled by emitter doping and to have a strong relationship with device degradation and lifetime. Using the resulting insights, record stability for a thermally activated delayed fluorescence (TADF) organic LED is shown.

Abstract

Device optimization of light-emitting diodes (LEDs) targets the most efficient conversion of electrically injected charges into emitted light. The emission zone in an LED is where charges recombine and light is emitted from. It is believed that the emission zone is strongly linked to device efficiency and lifetime. However, the emission zone size is below the optical diffraction limit, so it is difficult to measure. An accessible method based on a single emission spectrum that enables emission zone measurements with sub-second time resolution is shown. A procedure is introduced to study and control the emission zone of an LED system and correlate it with device performance. A thermally activated delayed fluorescence organic LED emission zone is experimentally measured over all luminescing current densities, while varying the device structure and while ageing. The emission zone is shown to be finely controlled by emitter doping because electron transport via the emitter is the charge-transport bottleneck of the system. Suspected quenching/degradation mechanisms are linked with the emission zone changes, device structure variation, and ageing. Using these findings, a device with an ultralong 4500 h T ₉₅ lifetime at 1000 cd m⁻² with 20% external quantum efficiency is shown.

Imaging Agents A general strategy for the development of far-red and near-infrared ultra-fluorogenic tetrazine bioorthogonal probes is reported by Xiaogang Liu, Haoxing Wu et al. in their Communication (e202117386).

Nature Chemistry, Published online: 16 May 2022; doi:10.1038/s41557-022-00944-x

Phytochromes regulate plant growth by sensing far-red light through the photoisomerization of their protein-bound chromophores. In the phytochrome Agp2, it has now been demonstrated that ultrafast proton-transfer occurs from the chromophore to a protein–water network before photoisomerization, inducing protein changes on the ultrafast timescale. These protein changes develop further on longer timescales, resulting in an activated protein conformation.

A simple design tactic for narrowband blue emitter is demonstrated by incorporating sulfone unit into the boron/nitrogen (B/N) embedded polycyclic skeleton. The resulting blue organic light-emitting diodes achieve a high external quantum efficiency of 32.0% and low efficiency roll-off.

Abstract

The blue multi-resonance thermally activated delayed fluorescence materials, simultaneously realizing narrow full-width at half-maximum, high external quantum efficiency (EQE), and low efficiency roll-off, remains a formidable challenge. Herein, three novel emitters, namely PTZBN1, PTZBN2, and PTZBN3, are designed by gradual peripheral modification in boron/nitrogen (B/N) embedded polycyclic skeleton, which exhibit progressively hypsochromic-shifted emission from 490 nm (PTZBN1) to 468 nm (PTZBN3) with photoluminescence quantum yields up to 98%. In particular, the incorporation of sulfone unit in the boron/nitrogen (B/N) embedded polycyclic skeleton provides a simple but effective tactic for narrowband blue emission. The organic light-emitting diodes based on PTZBN2 achieve one of the-state-of-the-art EQEs of 34.8% with electroluminescence (EL) peak at 478 nm. Impressively, PTZBN3-based device exhibits not only a high maximum EQE of 32.0% with EL peak at 468 nm, but also low efficiency roll-off.

The potential of underexplored quinoid-donor-acceptor strategy for developing practical semiconducting polymers and the role of electron acceptors are comprehensively investigated, leading to high-performance transistors with higher mobilities and robust storage and operational stabilities. Polymers with stronger acceptor units tend to deliver edge-on lamellas, high film crystallinity, small effective hole masses, and decent operational stability.

Abstract

The quinoid-donor-acceptor (Q-D-A) strategy has recently emerged as a promising approach for constructing high mobility semiconducting polymers. In order to fully explore the potential of this strategy in improving the charge transport and elucidating the structure-property-performance relationships in Q-D-A polymers, a series of new polymers with different electron acceptor units and backbone coplanarity have been synthesized and characterized. All of the resulting Q-D-A polymers exhibit much more planar backbone conformations in comparison to their donor-acceptor (D-A) counterparts. Moreover, organic field-effect transistors based on Q-D-A polymers exhibit excellent effective hole mobilities in a range of 0.44 to 3.35 cm² V⁻¹ s⁻¹, most of which are orders of magnitude higher than those of their corresponding D-A polymers. Notably, the hole mobility of 3.35 cm² V⁻¹ s⁻¹ is among the highest for the quinoidal-aromatic polymers characterized by conventional spin-coating methods. Furthermore, the role of electron acceptors in Q-D-A polymers has been comprehensively investigated. Polymers with stronger acceptor units are more inclined to deliver edge-on lamellas, high film crystallinity, small effective hole masses, and decent operational stability. The detailed structure-property-device performance relationship will pave the way toward high performance semiconducting polymers using the potent Q-D-A strategy.

An efficient doping strategy is applied to endow bright room-temperature phosphorescence (RTP) of dibenzothiophene derivatives. The isomer dopants bearing close resemblance to host with matched highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels and small energy gap between singlet- and triplet-excited states enable bright RTP.

Abstract

Doping has shown very promising potential in endowing room-temperature phosphorescence (RTP) properties of organic phosphors with minimal effort. Here, a new isomer design and doping strategy is reported that is applicable to dibenzothiophene (DBT) and its derivatives. Three isomers are synthesized to study the dopant effect on enhancing RTP of DBT derivatives. It is found that isomer dopants bearing close resemblance to the host with matched highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels and small energy difference between singlet- and triplet-excited states can yield efficient RTP for the doped system. Meanwhile, phosphorescence color from yellow to red is achieved by varying isomer dopants used for doping the DBT derivatives. This work represents an RTP enhancement strategy based on isomer design and doping to construct luminescent organic phosphors.