Dielectric Design of High Dielectric Constant Poly(Urea-Urethane) Elastomer for Low-Voltage High-Mobility Intrinsically Stretchable All-Solution-Processed Organic Transistors.

Stretchable organic transistors for skin-like biomedical applications require low-voltage operation to accommodate limited power supply and safe concerns. However, most of the currently reported stretchable organic transistors operate at relatively high voltages. Decreasing their operational voltage while keeping the high mobility still remains a key challenge. Here, the study presents a new dielectric design to achieve high-dielectric constant poly(urea-urethane) (PUU) elastomer, by incorporating a flexible small-molecular diamine crosslinking agent 4-aminophenyl disulfide (APDS) into the main chain of (poly (propylene glycol), tolylene 2,4-diiso-cyanate terminated) (PPG-TDI). Compared with commercial elastomers, the PUU elastomer as dielectric of the stretchable organic transistors shows the outstanding advantages including lower surface roughness (0.33 nm), higher adhesion (45.18 nN), higher dielectric constant (13.5), as well as higher stretchability (896%). The PUU dielectric enables the intrinsically stretchable, all-solution-processed organic transistor to operate at a low operational voltage down to -10 V, while preserving a substantial mobility of 1.39 cm2 V-1 s-1. Impressively, the transistor also demonstrates excellent electrical stability under repeated switching of 10 000 cycles, and remarkable mechanical robustness when stretched up to 100%. The work opens up a new molecular engineering strategy to successfully realize low-voltage high-mobility stretchable all-solution-processed organic transistors.

Solution-Processed 1D Wurtzite ZnS Nanostructures with Controlled Crystallographic Orientation and Tunable Band-Edge Emission.

1D compound semiconductor nanomaterials possess unique physicochemical properties that strongly depend on their size, composition, and structures. ZnS has been widely investigated as one of the most important semiconductors, and the control of crystallographic orientation of 1D ZnS nanostructures is still challenging and crucial to exploring their anisotropic properties. Herein, a solution-processed strategy is developed to synthesize 1D wurtzite (w-)ZnS nanostructures with the specific <002> and <210> orientations by co-decomposing the copper dibutyldithiocarbamate {[(C4 H9 )2 NCS2 ]2 Cu, i.e., R2 Cu} and zinc dibutyldithiocarbamate (R2 Zn) precursors in the mixed solvents of oleylamine and 1-dodecanethoil. A solution-solid-solid (SSS)-Oriented growth mechanism is proposed, which includes oriented nucleation dominated and SSS growth dominated stages. The crystallographic orientation mainly depends on the interfacial energy and ligand effect. The 1D w-ZnS nanostructures with controlled crystallographic orientation display unique morphologies, i.e., <002>-oriented w-ZnS nanorod enclosed with {110} facets while <210>-oriented w-ZnS nanobelt enclosed with wide (002) and narrow (110) facets. The bandgap of 1D w-ZnS nanostructures can be tuned from 3.94 to 3.82 eV with the crystallographic growth direction varied from <002> to <210>, thus leading to the tunable band-edge emission from ≈338 to ≈345 nm.

Solution-processed bilayer InGaZnO/In2O3thin film transistors at low temperature by lightwave annealing.

At low temperatures about 230 °C, bilayer InGaZnO/In2O3thin film transistors (TFTs) were prepared by a solution process with lightwave annealing. The InGaZnO/In2O3bilayer TFTs with SiO2as dielectric layer show high electrical performances, such as a mobility of 7.63 cm2V-1s-1, a threshold voltage (Vth) of 3.8 V, and an on/off ratio higher than 107, which are superior to single-layer InGaZnO TFTs or In2O3TFTs. Moreover, bilayer InGaZnO/In2O3TFTs demonstrated a great bias stability enhancement due to the introduction of top InGaZnO film act as a passivation layer, which could prevent the interaction of ambient air with the bottom In2O3layer. By using high dielectric constant AlOxfilm, the InGaZnO/In2O3TFTs exhibit an improved mobility of 47.7 cm2V-1s-1. The excellent electrical performance of the solution-based InGaZnO/In2O3TFTs shows great application potential for low-cost flexible printed electronics.

Mesoporous Metal Fluoride Nanocomposite Films with Tunable Optical Properties Derived from Precursor Instability.

The precisely tailored refractive index of optical materials is the key to utilizing and manipulating light during its propagation through the matrix, thereby improving their application performances. In this paper, mesoporous metal fluoride films with engineered composition (MgF2 :LaF3 ) are demonstrated to achieve finely tunable refractive indices. These films are prepared using a precursor-derived one-step assembly approach via the simple mixing of precursor solutions (Mg(CF3 OO)2 and La(CF3 OO)3 ); then pores are formed simultaneously during solidification owing to the inherent instability of La(CF3 OO)3 . The mesoporous structures are realized through Mg(CF3 OO)2 and La(CF3 OO)3 ions, which interacted with each other based on their electrostatic forces, providing a wide range of refractive indices (from 1.37 to 1.16 at 633 nm). Furthermore, it is systematically several MgF2(1-x) -LaF3(x) layers with different compositions (x = 0.0, 0.3, and 0.5) to form the graded refractive index coating that is optically consecutive between the substrate and the air for broadband and omnidirectional antireflection. An average transmittance of ≈98.03% (400-1100 nm) is achieved with a peak transmittance of ≈99.04% (at 571 nm), and the average antireflectivity is maintained at ≈15.75% even at an incidence of light of 65° (400-850 nm).

Boost of Gas Adsorption Kinetics of Covalent Organic Frameworks via Ionic Liquid Solution Process.

Adsorption, storage, and conversion of gases (e.g., carbon dioxide, hydrogen, and iodine) are the three critical topics in the field of clean energy and environmental mediation. Exploring new methods to prepare high-performance materials to improve gas adsorption is one of the most concerning topics in recent years. In this work, an ionic liquid solution process (ILSP), which can greatly improve the adsorption kinetic performance of covalent organic framework (COF) materials for gaseous iodine, is explored. Anionic COF TpPaSO3 H is modified by amino-triazolium cation through the ILSP method, which successfully makes the iodine adsorption kinetic performance (K80% rate) of ionic liquid (IL) modified COF AC4 tirmTpPaSO3 quintuple compared with the original COF. A series of experimental characterization and theoretical calculation results show that the improvement of adsorption kinetics is benefited from the increased weak interaction between the COF and iodine, due to the local charge separation of the COF skeleton caused by the substitution of protons by the bulky cations of ILs. This ILSP strategy has competitive help for COF materials in the field of gas adsorption, separation, or conversion, and is expected to expand and improve the application of COF materials in energy and environmental science.

Sodium Incorporation for Performance Improvement of Solution-Processed Submicron CuIn(S,Se)2 Thin Film Solar Cells.

Low-cost solution-processed CuIn(S,Se)2 (CISSe) has great potential for large-scale production of photovoltaics (PV). However, low power conversion efficiency caused by poor crystallinity is one of the main drawbacks compared to vacuum-processed CISSe solar cells. In this work, three strategies for sodium (Na) incorporation into solution-processed CISSe by soaking in sodium chloride (NaCl) aqueous-ethanol solution [1 molarity (M) for 10 minutes (min)], either prior to absorber deposition (pre-deposition treatment, Pre-DT), before selenization (pre-selenization treatment, Pre-ST), or after selenization (post-selenization treatment, PST) are researched. The Pre-ST CISSe solar cells achieve a better PV performance than those from the other two strategies of Na incorporation. For optimization, soaking times (5, 10, and 15 min) and NaCl concentrations (from 0.2 to 1.2 m) of the Pre-ST are researched. The highest efficiency achieved is 9.6% with an open-circuit voltage (Voc ) of 464.5 mV, a short-circuit current density (jsc ) of 33.4 mA cm-2 , and a fill factor (FF) of 62.0%. Compared to the reference CISSe solar cell, Voc , jsc , FF, and efficiency of the champion Pre-ST CISSe device are improved absolutely by 61.0 mV, 6.5 mA cm-2 , 9%, and 3.8%, respectively. Simultaneously, the open-circuit voltage deficit, the back contact barrier, and the bulk recombination are found to be reduced for Pre-ST CISSe.

Carbazole-Decorated Organoboron Emitters with Low-Lying HOMO Levels for Solution-Processed Narrowband Blue Hyperfluorescence OLED Devices.

The hyperfluorescence has drawn great attention in achieving efficient narrowband emitting devices based on multiple resonance thermally activated delayed fluorescence (MR-TADF) emitters. However, achieving efficient solution-processed pure blue hyperfluorescence devices is still a challenge, due to the unbalanced charge transport and serious exciton quenching caused by that the holes are easily trapped on the high-lying HOMO (the highest occupied molecular orbital) level of traditional diphenylamine-decorated emitters. Here, we developed two narrowband blue organoboron emitters with low-lying HOMO levels by decorating the MR-TADF core with weakly electron-donating carbazoles, which could suppress the hole trapping effect by reducing the hole traps between host and MR-TADF emitter from deep (0.40 eV) to shallow (0.14/0.20 eV) ones for facilitating hole transport and exciton formation, as well as avoiding exciton quenching. And the large dihedral angle between the carbazole and MR-TADF core makes the carbazole act as a steric hindrance to inhibit molecular aggregation. Accordingly, the optimized solution-processed pure blue hyperfluorescence devices simultaneously realize record external quantum efficiency of 29.2 %, narrowband emission with a full-width at half-maximum of 16.6 nm, and pure blue color with CIE coordinates of (0.139, 0.189), which is the best result for the solution-processed organic light-emitting diodes based on MR-TADF emitters.

Over 16% Efficient Solution-Processed Cu(In,Ga)Se2 Solar Cells via Incorporation of Copper-Rich Precursor Film.

Solution processing of Cu(In,Ga)Se2 (CIGS) absorber is a highly promising strategy for a cost-effective CIGS photovoltaic device. However, the device performance of solution-processed CIGS solar cells is still hindered by the severe non-radiative recombination resulting from deep defects and poor crystal quality. Here, a simple and effective precursor film engineering strategy is reported, where Cu-rich (CGI >1) CIGS layer is incorporated into the bottom of the CIGS precursor film. It has been discovered that the incorporation of the Cu-rich CIGS layer greatly improves the absorber crystallinity and reduces the trap state density. Accordingly, more efficient charge generation and charge transfer are realized. As a result of systematic processing optimization, the champion solution-processed CIGS device delivers an improved open-circuit voltage of 656 mV, current density of 33.15 mA cm-2 , and fill factor of 73.78%, leading to the high efficiency of 16.05%.

Cibalackrot Dendrimers for Hyperfluorescent Organic Light-Emitting Diodes.

Hyperfluorescent organic light-emitting diodes (HF-OLEDs) enable a cascading Förster resonance energy transfer (FRET) from a suitable thermally activated delayed fluorescent (TADF) assistant host to a fluorescent end-emitter to give efficient OLEDs with relatively narrowed electroluminescence compared to TADF-OLEDs. Efficient HF-OLEDs require optimal FRET with minimum triplet diffusion via Dexter-type energy transfer (DET) from the TADF assistant host to the fluorescent end-emitter. To hinder DET, steric protection of the end-emitters has been proposed to disrupt triplet energy transfer. In this work, the first HF-OLEDs based on structurally well-defined macromolecules, dendrimers is reported. The dendrimers contain new highly twisted dendrons attached to a Cibalackrot core, resulting in high solubility in organic solvents. HF-OLEDs based on dendrimer blend films are fabricated to show external quantum efficiencies of >10% at 100 cd m-2 . Importantly, dendronization with the bulky dendrons is found to have no negative impact to the FRET efficiency, indicating the excellent potential of the dendritic macromolecular motifs for HF-OLEDs. To fully prevent the undesired triplet diffusion, Cibalackrot dendrimers HF-OLEDs are expected to be further improved by adding additional dendrons to the Cibalackrot core and/or increasing dendrimer generations.

Expeditious, scalable solution growth of metal oxide films by combustion blade coating for flexible electronics.

Metal oxide (MO) semiconductor thin films prepared from solution typically require multiple hours of thermal annealing to achieve optimal lattice densification, efficient charge transport, and stable device operation, presenting a major barrier to roll-to-roll manufacturing. Here, we report a highly efficient, cofuel-assisted scalable combustion blade-coating (CBC) process for MO film growth, which involves introducing both a fluorinated fuel and a preannealing step to remove deleterious organic contaminants and promote complete combustion. Ultrafast reaction and metal-oxygen-metal (M-O-M) lattice condensation then occur within 10-60 s at 200-350 °C for representative MO semiconductor [indium oxide (In2O3), indium-zinc oxide (IZO), indium-gallium-zinc oxide (IGZO)] and dielectric [aluminum oxide (Al2O3)] films. Thus, wafer-scale CBC fabrication of IGZO-Al2O3 thin-film transistors (TFTs) (60-s annealing) with field-effect mobilities as high as ∼25 cm2 V-1 s-1 and negligible threshold voltage deterioration in a demanding 4,000-s bias stress test are realized. Combined with polymer dielectrics, the CBC-derived IGZO TFTs on polyimide substrates exhibit high flexibility when bent to a 3-mm radius, with performance bending stability over 1,000 cycles.

Solution-Processed Two-Dimensional Metal Oxide Anticorrosion Nanocoating.

Molecularly thin two-dimensional (2D) nanomaterials are attractive building blocks for constructing anticorrosion nanocoatings as an ultimate pursuit in the metal-related industry. However, the nanocoating of prefocused graphene is far from industrial demands due to its high cost, low scalability, and insufficient quality. We propose all requirements to realize rational anticorrosion nanocoating of metal oxide nanosheets. The proof-of-concept study with Ti0.87O2 and Ca2Nb3O10 nanosheets demonstrates that the 10 and 20 nm thick coatings fabricated by a facile layer-by-layer (LbL) self-assembly on stainless steel (SUS) give perfect inhibition efficiency (IE) values of 99.92% and 99.89%, respectively. A driving test with a nanosheet-coated car-baffle demonstrated suitable corrosion resistance and mechanical and thermal robustness for industrial applications. The revealed and controlled thermal oxidation mechanisms are critical toward high-temperature application of the 2D oxide anticorrosion nanocoating. The advantages of nanosheet coating and extensible materials design will open a solid but exciting route to anticorrosion nanotechnology.

Solution-Processed Yellow Organic Light-Emitting Diodes Based on Two New Ionic Ir (III) Complexes.

Two new and efficient cationic yellow-emissive Ir (III) complexes (Ir1 and Ir2) are rationally designed by using 2-(4-chloro-3-(trifluoromethyl)phenyl)-4-methylquinoline as the main ligand, and, respectively, 4,4'-dimethyl-2,2'-bipyridyl and 4,4'-dimethoxy-2,2'-bipyridyl as the ancillary ligands. Both complexes show enhanced phosphorescence (546 nm with 572 nm as shoulder and high phosphorescent quantum efficiency in solution, which is in favor of efficient solution-processed phosphorescent organic light-emitting diodes. Compared with Ir2, the Ir1-based device displays excellent device performance, with maximum external quantum efficiency, current efficiency, and power efficiency of up to 7.92%, 26.32 cd/A and 15.31 lm/W, respectively, thus proving that the two new ionic Ir (III) complexes exhibit great potential for future solution-processed electroluminescence.

Recent Progresses in Solution-Processed Tandem Organic and Quantum Dots Light-Emitting Diodes.

Solution processes have promising advantages of low manufacturing cost and large-scale production, potentially applied for the fabrication of organic and quantum dot light-emitting diodes (OLEDs and QLEDs). To meet the expected lifespan of OLEDs/QLEDs in practical display and lighting applications, tandem architecture by connecting multiple light-emitting units (LEUs) through a feasible intermediate connection layer (ICL) is preferred. However, the combination of tandem architecture with solution processes is still limited by the choices of obtainable ICLs due to the unsettled challenges, such as orthogonal solubility, surface wettability, interfacial corrosion, and charge injection. This review focuses on the recent progresses of solution-processed tandem OLEDs and tandem QLEDs, covers the design and fabrication of various ICLs by solution process, and provides suggestions on the future challenges of corresponding materials and devices, which are anticipated to stimulate the exploitation of the emerging light technologies.

Highly Efficient Solution-Processed Blue Phosphorescent Organic Light-Emitting Diodes Based on Co-Dopant and Co-Host System.

The low-lying HOMO level of the blue emitter and the interfacial miscibility of organic materials result in inferior hole injection, and long exciton lifetime leads to triplet-triplet annihilation (TTA) and triplet-polaron annihilation (TPA), so the efficiencies of blue phosphorescent organic light-emitting diodes (PhOLEDs) are still unsatisfactory. Herein, we design co-host and co-dopant structures to improve the efficiency of blue PhOLEDs by means of solution processing. TcTa acts as hole transport ladder due to its high-lying HOMO level, and bipolar mCPPO1 helps to balance carriers' distribution and weaken TPA. Besides the efficient FIr6, which acts as the dominant blue dopant, FCNIrPic was introduced as the second dopant, whose higher HOMO level accelerates hole injection and high triplet energy facilitates energy transfer. An interesting phenomenon caused by microcavity effect between anode and cathode was observed. With increasing thickness of ETL, peak position of electroluminescence (EL) spectrum red shifts gradually. Once the thickness of ETL exceeded 140 nm, emission peak blue-shifts went back to its original position. Finally, the maximum current efficiency (CE), power efficiency (PE), and external quantum efficiency (EQE) of blue phosphorescent organic light-emitting diode (PhOLED) went up to 20.47 cd/A, 11.96 lm/W, and 11.62%, respectively.

Solution-processed AIEgen NIR OLEDs with EQE Approaching 15 .

Organic near-infrared (NIR) luminogens have attracted intensive attention considering their vast potential applications in areas like bioimaging, organic light-emitting diodes (OLEDs) and night-vision telecommunication. However, organic NIR luminogens with high solid quantum efficiencies are scarce, limiting their applications. Here, we reported an electron-deficient acceptor, BSM, based on dithiafulvalene and benzothiadiazole, which could work as a strong acceptor to produce highly efficient NIR emitters with aggregation-induced emission (AIE) property. One of the AIEgens, TBSMCN emitted at 820 nm with a solid quantum yield of 10.7 %. When applied to solution-processed OLEDs, an outstanding external quantum efficiency (EQE) of 9.4 % was achieved with a peak wavelength at 728 nm. Moreover, its non-doped device could achieve an extraordinary EQE of 2.2 % peaking at 804 nm. In the further optimized configuration, when an extra sensitizer was added to harvest triplet excitons, the EQE unprecedentedly soared up to 14.3 % with a peak wavelength of 750 nm.

Self-Powered Low-Cost UVC Sensor Based on Organic-Inorganic Heterojunction for Partial Discharge Detection.

Power outages caused by the aging of high-voltage power facilities can cause significant economic and social damage. To prevent such problems, it is necessary to implement a widespread and sustainable monitoring system. Partial discharge (PD) is a preliminary symptom of power equipment aging accompanying the light, typically in the UV range. UVC (200-280 nm) is more useful than UVA and UVB because of low interference from the environment owing to its solar-blindness by the stratosphere. Therefore, to realize a wide-range and durable diagnosis system, it is necessary to develop sensors that can selectively detect UVC, while enabling mass production at low-cost and low power consumption. Here, a solution-processable photodiode sensor that is inexpensive, mass-producible, and self-powered with selective UVC detection is developed. The optoelectronic characteristics of photodiode consisting of organic p-polymer and inorganic n-ZnO nanoparticles are systematically studied to determine the optimum p-type polymer and its thickness. The device shows high-performance: fast response time (rise/fall time: 36.6/37.0 ms) and high spectral response in the UVC region (maximum responsivity of 20 mA W-1 ) under self-powered operation. Furthermore, the practical application of the device to detect PD signals with a visual alarm system under UVC release conditions is demonstrated.

Performance improvements in all-solution processed inverted QLEDs realized by inserting an electron blocking layer.

Highly efficient, all-solution processed inverted quantum dot light-emitting diodes (QLEDs) are demonstrated by employing 1,3,5-tri(m-pyrid-3-yl-phenyl)benzene (TmPyPB) layer as electron blocking layer. Electron injection from ZnO electron transport layer to quantum dots (QDs) emission layer (EML) can be adjusted by thickness of TmPyPB layer, enabling the balanced charge carriers in QDs EML. With optimal thickness of this TmPyPB adjuster, 59.7% increment in the device current efficiency (from 8.2 to 13.1 cd A-1) and 46.2% improvement in the maximum luminance (from 31916 to 46674 cd m-2) are achieved, compared with those of the control QLED which has double hole transport layer structure. On the other hand, we find luminescence quenching process, which often happens at the interface of ZnO nanoparticles and QDs, is not obvious in our QLEDs, in which the ZnO layer is fabricated in precursor method, and this conclusion is verified through Time Resolution Photoluminescence test. In a word, this strategy provides a direction for optimizing charge carrier balance in all-solution processed inverted QLED.

Tailoring Solution-Processable Li Argyrodites Li6+xP1-xMxS5I (M = Ge, Sn) and Their Microstructural Evolution Revealed by Cryo-TEM for All-Solid-State Batteries.

Owing to their high Li+ conductivities, mechanical sinterability, and solution processability, sulfide Li argyrodites have attracted much attention as enablers in the development of high-performance all-solid-state batteries with practicability. However, solution-processable Li argyrodites have been developed only for a composition of Li6PS5X (X = Cl, Br, I) with insufficiently high Li+ conductivities (∼10-4 S cm-1). Herein, we report the highest Li+ conductivity of 0.54 mS cm-1 at 30 °C (Li6.5P0.5Ge0.5S5I) for solution-processable iodine-based Li argyrodites. A comparative investigation of three iodine-based argyrodites of unsubstituted and Ge- and Sn-substituted solution-processed Li6PS5I with varied heat-treatment temperature elucidates the effect of microstructural evolution on Li+ conductivity. Notably, local nanostructures consisting of argyrodite nanocrystallites in solution-processed Li6.5P0.5Ge0.5S5I have been directly captured by cryogenic transmission electron microscopy, which is a first for sulfide solid electrolyte materials. Specifically, the promising electrochemical performances of all-solid-state batteries at 30 °C employing LiCoO2 electrodes tailored by the infiltration of Li6.5P0.5Ge0.5S5I-ethanol solutions are successfully demonstrated.

Perovskite Light-Emitting Devices with Doped Hole Transporting Layer.

Perovskite quantum dots (PQDs) have drawn global attention in recent years and have been used in a range of semiconductor devices, especially for light-emitting diodes (LEDs). However, because of the nature of low-conductive ligands of PQDs and surface and bulk defects in the devices, charge injection and transport should be carefully managed in order to maximize the electroluminescent performances. In this study, we employed three p-dopants, i.e., 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ), 1,3,4,5,7,8-hexafluoro-11,11,12,12-tetracyanonaphtho-2,6-quinodimethane (F6-TCNNQ), and 11,11,12,12-tetracyanonaphtho-2,6-quinodimethane (TCNH14), respectively doped into the commonly used hole transporting layer (HTL) poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA). Compared with the devices with the neat PTAA, those with the doped PTAA as the HTLs achieved the improved electroluminescent performances. In particular, the device with the strong oxidant F4-TCNQ exhibited an improvement factor of 27% in the peak external quantum efficiency compared with the control device with the neat PTAA. The capacitance and transient electroluminescent measurements were carried out to identify the imperceptible interactions in the doped HTL and at the interface between the HTL and PQDs.

Solution-Processed OLEDs Based on Thermally Activated Delayed Fluorescence Copper(I) Complexes with Intraligand Charge-Transfer Excited State.

A new series of tetrahedral heteroleptic copper(I) complexes exhibiting efficient thermally-activated delayed fluorescence (TADF) in green to orange electromagnetic spectral regions has been developed by using D-A type N^N ligand and P^P ligands. Their structures, electrochemical, photophysical, and electroluminescence properties have been characterized. The complexes exhibit high photoluminescence quantum yields (PLQYs) of up to 0.71 at room temperature in doped film and the lifetimes are in a wide range of 4.3-24.1 µs. Density functional theory (DFT) calculations on the complexes reveal the lowest-lying intraligand charge-transfer excited states that are localized on the N^N ligands. Solution-processed organic light emitting diodes (OLEDs) based on one of the new emitters show a maximum external quantum efficiency (EQE) of 7.96%.