Synergistic Effect and Electrical Properties of Microporous Liquid Metal/Carbon Nanotube Polymer Sponge.

Sensing sponge materials with light weight, high elasticity, and electrical sensing properties are in enormous demand in electronic fields, but there is an imminent need to develop a scalable and facile method for the manufacture of the sensing material. Herein, an efficient in situ polymerization and convenient preparation process is reported to manufacture the microporous liquid metal/carbon nanotube-polysulfide rubber (LM/CNT-PSR) sponges with excellent mechanical and electrical properties, based on fluidic LMs and rigid CNTs with unique synergistic effect for sponge composites. Excellent mechanical properties of LM/CNT-PSR sponges, such as low density, excellent elasticity, remarkable mechanical recoverability, and self-healing property, are endowed by the interconnected microporous structure of sponge and flexible polysulfide rubber matrix with disulfide bonds. In addition, the synergistic effect of LMs and CNTs leads to excellent conductivity and unique electrical sensing property under mechanical pressure. Microporous LM/CNT-PSR sponges with high performance and simple fabrication process are promising sensing materials for various electronic devices, such as human motion monitoring, and weighing sensing.

Unveiling the In Situ and Solvent Polymerization Engineering for Highly Efficient and Flexible Thermally Activated Delayed Fluorescence Organic Light-Emitting Diodes.

Thermally activated delayed fluorescence (TADF) polymer has great potential for the construction of flexible solution-processed organic light-emitting diodes (OLEDs). However, the relationship between polymerization engineering and device functions has rarely been reported. Here, two novel TADF polymers, P-Ph4CzCN and P-Ph5CzCN, with a small energy gap between the first excited singlet and triplet states (ΔEST; <0.16 eV) were newly developed by both solvent and in situ polymerization of a styrene component. Detailed device performance testing indicates that both polymerization strategies ensure that the TADF polymer achieves comparable high efficiencies in commonly rigid devices, and the maximum external quantum efficiencies (EQEmax) were 11.9%, 14.1%, and 16.2% for blue, green, and white OLEDs, respectively. Although in situ polymerization provides a simplified device fabrication process, which avoids the complicated synthesis and purification of the polymer, the inevitable high-temperature annealing makes it fail in a plastic substrate device. In contrast, P-Ph5CzCN achieved by solvent polymerization enables the successful fabrication of a flexible device on a poly(ethylene terephthalate) (PET) substrate, which was the first reported flexible OLED based on a TADF polymer. This work provides a strong guideline for the simple fabrication of TADF polymer devices and the application of TADF polymer materials in OLED flexible panels and flexible lighting.

Novel C3N4-Assisted Bilateral Interface Engineering for Efficient and Stable Perovskite Solar Cells.

g-C3N4-assisted interface engineering has been developed as an effective method to improve the efficiency and stability of perovskite solar cells (PSCs). However, most of the reported works used g-C3N4-induced single-interface modification, which is difficult to passivate the bilateral interfaces of the perovskite layer at the same time. In this paper, we fabricated two kinds of C3N4 materials simultaneously (w-CN and y-CN) after the twice calcination of melamine and used them in the bilateral interface modification toward all-inorganic PSCs. The two kinds of C3N4 play different roles in different interface engineering. On the front interface, w-CN could optimize band level arrangement and improve the perovskite film quality, which contributes to the efficiency of the device. On the back interface, y-CN could also improve the film quality of the perovskite layer, accelerating the extraction of charge carriers. The champion efficiency of the CsPbIBr2-based device treated by the bilateral interface is significantly enhanced from 7.8 to 10.1%. Moreover, the modified perovskite film exhibits negligible degradation after 40 min of exposure in the ambient environment with a relative humidity of 70%, while the pristine perovskite film has a rapid degradation within 20 min.

Highly Efficient Quasi-2D Perovskite Light-Emitting Diodes Incorporating a TADF Dendrimer as an Exciton-Retrieving Additive.

Although small organics or polymer additives have been introduced to enhance film formation and radiative recombination of perovskite light-emitting diodes (PeLEDs), the exciton utilization and quantum efficiency need further optimization. Here, we introduce a thermal-activated delayed fluorescence (TADF) dendrimer as an additive to enhance the surface coverage and reduce the trap state of the grain boundary. More importantly, the TADF nature of such an additive can retrieve the exciton dissociated from perovskite or trapped by the grain boundary and then transfer the energy back to emissive perovskite through the Förster energy transfer process. Since the triplets can be reused by reverse intersystem crossing in such a TADF additive, the theoretical exciton utilization is 100%. As a result, the optimized PeLEDs cooperating with a TADF additive achieved a high current efficiency of 39.0 cd A-1 and an ultrabright luminescence of 18,000 cd m-2, which are almost 5 times higher than those of the control device without an additive. Moreover, the device stability monitored by half-lifetime at 1000 cd m-2 enhanced 2 times after introducing the TADF dendrimer as an additive. The parent dendrimer without a TADF feature was also synthesized as an additive to explore the mechanism action, which found that 54% enhancement of device efficiency can be attributed to defect passivating, while 46% was assigned to retrieved energy. This research first demonstrates that the TADF dendrimer is a promising exciton-retrieving additive for enhancing the performance of PeLEDs by passivating defect, filling up grain boundary, and retrieving leakage exciton.

Design of Blue Thermally Activated Delayed Fluorescent Emitter with Efficient Exciton Gathering Property for High-Performance Fully Solution-Processed Hybrid White OLEDs.

The blue thermally activated delay fluorescence (TADF) emitters are highly attractive in the fields of constructing hybrid white organic light-emitting diodes (WOLEDs) due to its high efficiency and color stability. However, few blue TADF emitters can withstand sequential orthogonal solvents, making it impossible to fabricate the fully solution-processed hybrid WOLEDs. Here, two TADF materials, PCz-4CzCN and TPA-4CzCN, were designed and synthesized by equipping the emissive core with nonconjugated bulky units, which can effectively enhance the solvent resistance ability without disturbing the TADF feature. The photophysical investigation indicates that phenylcarbazole unit can efficiently block the electromer formation to enhance the energy transfer and exciton utilization of the emitter. Accordingly, the blue OLEDs of PCz-4CzCN shows higher external quantum efficiency (EQE) of 22.6%, which is the best performance recorded among the fully solution-processed blue OLEDs. Upon further doping, the yellow phosphor PO-01, the fully solution-processed TADF-phosphor (T-P) hybrid WOLEDs was successfully obtained with high performance for the first time. Thanks to the efficient exciplex formation, the turn-on voltage of the white device is only 2.8 V, and the maximum brightness and power efficiency are as high as 53 300 cd m-2 and 38.5 lm W-1, respectively, which are even higher than the previous reported T-P hybrid WOLEDs with a vacuum-deposited electron transfer layer.

Exciplex Formation and Electromer Blocking for Highly Efficient Blue Thermally Activated Delayed Fluorescence OLEDs with All-Solution-Processed Organic Layers.

Highly efficient solution-processable emitters are greatly desired to develop low-cost organic light-emitting diodes (OLEDs). The recently developed thermally activated delayed fluorescence (TADF) materials are promising candidates, but blue TADF materials compatible with the all-solution-process have still not been achieved. Here, a series of TADF materials, named X-4CzCN, are developed by introducing the bulky units through an unconjugated linker, which realizes high molecular weight to enhance the solvent resistance ability without disturbing the blue TADF feature. Meanwhile, the peripheral wrapping groups efficiently inhibit the triplet-triplet and triplet-polaron quenching by isolating the energy-transfer and charge-transporting channels. The photophysical measurements indicate that a small variation in peripheral unit will have a noticeable effect on the luminescence efficiency. The enlarged volume of peripheral units will make the electroluminescent spectra blueshift, while enhancing the energy transfer of exciplex and blocking the energy leakage of electromer can facilitate the exciton utilization. As a result, the fully solution-processed blue OLED achieves a CIE of (0.16, 0.27), a low turn on voltage of 2.9 eV, and a high external quantum efficiency of 20.6 %. As far as we known, this is the first report of all-solution-processed TADF OLEDs with blue emission, which exhibits a high efficiency even comparable to the vacuum-deposited devices.

Achieving 20% External Quantum Efficiency for Fully Solution-Processed Organic Light-Emitting Diodes Based on Thermally Activated Delayed Fluorescence Dendrimers with Flexible Chains.

Actualizing high-efficiency thermally activated delayed fluorescent (TADF) organic light-emitting diodes (OLEDs) with fully wet processes is of great significance to the development of purely organic electroluminescence and the application of large-area OLED displays. Herein, new strategies are proposed to develop the TADF dendrimers with tunable colors by adjusting the way of linking branches to the core and the numbers of peripheral branches. Due to an energy gradient and efficient exciton utilization in the core-dendron system, the solution-processed OLEDs with the four dendrimers 5CzBN-O-Cz, 5CzBN-O-2Cz, 5CzBN-Cz, and 5CzBN-2Cz all give rise to low turn-on voltages and great device efficiency. Notably, 5CzBN-2Cz affords record-high fully solution-processed TADF OLEDs with external quantum efficiency of above 20%, which is significantly comparable to the efficiency of TADF OLEDs based on vacuum deposition. The work offers a guideline for designing solution-processable materials, paving the way toward practical applications of large-area fully solution-processed OLEDs.

Design of efficient thermally activated delayed fluorescence blue host for high performance solution-processed hybrid white organic light emitting diodes.

Developing a solution-processible blue thermally activated delayed fluorescence (TADF) emitter for hybrid white organic light emitting diodes (WOLEDs) is still a challenge. In this work, two TADF blue emitters are designed and synthesized to explore a common strategy to qualify the small molecular TADF material as a solution-processible blue host. Systematic studies find that the molecular encapsulation by introducing unconjugated carbazoles as steric shields not only keeps the intrinsic TADF feature unchanged, but also effectively suppress the intermolecular interaction induced exciton quenching, which makes the material more efficient for solution-processing. The optimized solution-processed hybrid WOLEDs based on the encapsulated TADF blue host realized a highly efficient device performance with a maximum current efficiency (CE), power efficiency (PE) and external quantum efficiency (EQE) of 45.6 cd A-1, 40.9 lm W-1 and 17.0%, respectively, which are three times higher in device efficiency and twenty times higher in device lifetime than the corresponding device with an unencapsulated TADF blue host. Furthermore, the obtained device exhibits a high electroluminescence (EL) above 20 000 cd m-2 and a stable EL spectrum with nearly unchanged Commission International de L'Eclairage (CIE) coordinate at a wide range of applied voltages. These results clearly demonstrate that the molecular encapsulation of the TADF blue host is a superior and promising strategy to achieve high performance and color stable solution-processed hybrid WOLEDs.

Strategy for the Realization of Highly Efficient Solution-Processed All-Fluorescence White OLEDs-Encapsulated Thermally Activated Delayed Fluorescent Yellow Emitters.

Fabrication of highly efficient all thermally activated delayed fluorescence (TADF) white organic light-emitting diodes (WOLEDs) through solution-process still remains a big challenge. Here, two encapsulated TADF molecules with a small singlet-triplet energy gap (Δ EST) and high photoluminescence quantum yield (PLQY) were designed and synthesized as yellow emitters for solution-processed WOLEDs. The high current, power, and external quantum efficiencies of 41.6 cd A-1, 30.4 lm W-1, and 17.3% were achieved for the solution-processed all-fluorescence WOLEDs with a single-emission layer. In contrast, even with the same Δ EST and PLQY, the corresponding unencapsulated parent emitters will account for nearly 50% loss of the potential device efficiency. This is for the first time that the small molecular TADF blue host and TADF yellow guest are used to construct solution-processed all-fluorescence WOLEDs, which exhibit high efficiency comparable with most of the vacuum-deposited all-fluorescence white devices. These results not only demonstrate the great potential of TADF emitters in achieving highly efficient solution-processed WOLEDs, but also testify the key role of molecular encapsulation in reducing polar-exciton quenching and enhancing electroluminescence performance.

Design of encapsulated hosts and guests for highly efficient blue and green thermally activated delayed fluorescence OLEDs based on a solution-process.

The molecular aggregation and exciton-polaron interaction of the host-guest system were successfully restricted by efficient molecular encapsulation. The solution-processed blue and green TADF OLEDs have been realized with external quantum efficiencies above 23% by employing the encapsulated TADF host and guest as emission layers.

Highly Efficient All-Solution-Processed Fluorescent Organic Light-Emitting Diodes Based on a Novel Self-Host Thermally Activated Delayed Fluorescence Emitter.

Here, we conveniently designed and synthesized a self-host thermally activated delayed fluorescence (TADF) emitter, which can not only form a uniform thin film through wet-process, but also allow the subsequently deposition of electron transporting layer (ETL) by orthogonal solvent. By using this self-host material as emitter, the all-solution-processed multilayer TADF organic light emitting diodes (OLEDs) was successfully fabricated. The maximum current, power and external quantum efficiencies of this nondoped device are 46.3 cd A-1, 39.3 lm W1- and 15.5%, respectively, which are much higher than the values of all-solution-processed OLEDs based on tranditional fluorescence and even comparable to the TADF devices with vacuum-deposited ETL. Moreover, the device maintains the high efficiency of 42.9 cd A-1 and 39.0 cd A-1 at the luminance of 100 cd m-2 for display and 1000 cd m-2 for practical lighting. The high efficiency and small efficiency roll-off of the all-solution-processed fluorescent OLEDs can be attributed to the superiority of the newly designed self-host TADF emitter, which possesses the perfect electroluminescent property and sufficient solvent resistance at the same time.

Self-Host Blue Dendrimer Comprised of Thermally Activated Delayed Fluorescence Core and Bipolar Dendrons for Efficient Solution-Processable Nondoped Electroluminescence.

A self-host thermally activated delayed fluorescence (TADF) dendrimer POCz-DPS for solution-processed nondoped blue organic light-emitting diodes (OLEDs) was designed and synthesized, in which the bipolar phosphine oxide carbazole moiety was introduced by alkyl chain to ensure balanced charge transfer. The investigation of physical properties showed that the bipolar dendrons not only improve the morphological stability but also restrain the concentration quenching effect of the TADF emissive core. The spin-coated OLEDs featuring POCz-DPS as the host-free blue emitter achieved the highest external quantum efficiency (7.3%) and color purity compared with those of doped or nondoped devices based on the parent molecule DMOC-DPS, which indicates that incorporating the merits of encapsulation and bipolar dendron is an effective way to improve the electroluminescent performance of the TADF emitter used for a solution-processed nondoped device.

Constructing a Novel Dendron for a Self-Host Blue Emitter with Thermally Activated Delayed Fluorescence: Solution-Processed Nondoped Organic Light-Emitting Diodes with Bipolar Charge Transfer and Stable Color Purity.

Self-host thermally activated delayed fluorescence (TADF) materials have recently been identified as effective emitters for solution-processed nondoped organic light-emitting diodes (OLEDs). However, except for the carbazole unit, few novel dendrons have been developed to build self-host TADF emitters. This study reports two self-host blue materials, tbCz-SO and poCz-SO, with the same TADF emissive core and different dendrons. The influence of the peripheral dendrons on the photophysical properties and electroluminescent performances of the self-host materials were systematically investigated. The transient fluorescence and electroluminescence spectra indicated that the diphenylphosphoryl carbazole units could effectively encapsulate the emissive core to reduce the concentration quenching effect and to enhance reverse intersystem crossing. By using tbCz-SO and poCz-SO as host-free blue emitters, the performance of the solution-processed nondoped OLED device demonstrated that a more balanced charge transfer from the bipolar dendrons would offer a better current efficiency of 10.5 cd A-1 and stable color purity with Commission Internationale de L'Eclairage units of (0.18, 0.27).

Enhanced Electron Affinity and Exciton Confinement in Exciplex-Type Host: Power Efficient Solution-Processed Blue Phosphorescent OLEDs with Low Turn-on Voltage.

A benzimidazole/phosphine oxide hybrid 1,3,5-tris(1-(4-(diphenylphosphoryl)phenyl)-1H-benzo[d]imidazol-2-yl)benzene (TPOB) was newly designed and synthesized as the electron-transporting component to form an exciplex-type host with the conventional hole-transporting material tris(4-carbazoyl-9-ylphenyl)amine (TCTA). Because of the enhanced triplet energy and electron affinity of TPOB, the energy leakage from exciplex-state to the constituting molecule was eliminated. Using energy transfer from exciplex-state, solution-processed blue phosphorescent organic light-emitting diodes (PHOLEDs) achieved an extremely low turn-on voltage of 2.8 V and impressively high power efficiency of 22 lm W(-1). In addition, the efficiency roll-off was very small even at luminance up to 10 000 cd m(-2), which suggested the balanced charge transfer in the emission layer. This study demonstrated that molecular modulation was an effective way to develop efficient exciplex-type host for high performanced PHOLEDs.

High Power Efficiency Solution-Processed Blue Phosphorescent Organic Light-Emitting Diodes Using Exciplex-Type Host with a Turn-on Voltage Approaching the Theoretical Limit.

Three solution-processable exciplex-type host materials were successfully designed and characterized by equal molar blending hole transporting molecules with a newly synthesized electron transporting material, which possesses high thermal stability and good film-forming ability through a spin-coating technique. The excited-state dynamics and the structure-property relationships were systematically investigated. By gradually deepening the highest occupied molecular orbital (HOMO) level of electron-donating components, the triplet energy of exciplex hosts were increased from 2.64 to 3.10 eV. Low temperature phosphorescence spectra demonstrated that the excessively high triplet energy of exciplex would induce a serious energy leakage from the complex state to the constituting molecule. Furthermore, the low energy electromer state, which only exists under the electroexcitation, was found as another possible channel for energy loss in exciplex-based phosphorescent organic light-emitting diodes (OLEDs). In particular, as quenching of the exciplex-state and the triplet exciton were largely eliminated, solution-processed blue phosphorescence OLEDs using the exciplex-type host achieved an extremely low turn-on voltage of 2.7 eV and record-high power efficiency of 22.5 lm W(-1), which were among the highest values in the devices with identical structure.

Bipolar host with multielectron transport benzimidazole units for low operating voltage and high power efficiency solution-processed phosphorescent OLEDs.

Two soluble bipolar host materials (mCP-BPBI and CP-QPBI), comprising different proportions of hole-transporting carbazole and electron-transporting benzimidazole, were synthesized. Their thermal, physical, and electrochemical properties were characterized. The designated bulky star-shaped structures efficiently suppress the direct intramolecular interaction between the donor and acceptor subunits to give high triplet energies. Through computational studies, varying the ratio of hole- and electron-transporting moieties could significantly change the carrier injection/transporting abilities and charge balance properties of the host materials. Indeed, CP-QPBI with more benzimidazole units shows extremely enhanced current density at the same voltage when compared to mCP-BPBI. The operating voltage of solution-processed phosphorescent light-emitting diodes with CP-QPBI as host were dramatically reduced by ∼3 V compared with the similar devices of mCP-BPBI. At the same time, the power efficiencies were improved for 2-2.5 times at the corresponding voltage. Importantly, both blue and green devices maintain their high efficiencies even at brightness up to 1000 cd m(-2), which clearly demonstrates that the new strategy applied to improve electron-transporting ability and charge-balance property of the solution-processable host material by tuning the ratio of donor and acceptor unit is profitable.

Ideal bipolar host materials with bis-benzimidazole unit for highly efficient solution-processed green electrophosphorescent devices.

An ideal host material with high triplet energy, suitable HOMO energy level, excellent thermal and electrochemical stability, and bipolar charge carrier transport ability was synthesized. A high external quantum efficiency of 13.7% and a luminance efficiency of 48.2 cd A(-1) with low efficiency roll-off were achieved in solution-processed green electrophosphorescent devices.

Alcohol-soluble electron-transport small molecule for fully solution-processed multilayer white electrophosphorescent devices.

A novel alcohol-soluble electron-transport material was designed and synthesized. This material not only possesses a high triplet energy and a low HOMO level but also exhibits excellent electron-transport properties and good film-forming ability. Efficient fully solution-processed multilayer white electrophosphorescent devices have been fabricated by using this alcohol-processable material as an orthogonal electron-transport layer.