Ultrastretchable, Highly Conductive, Rapid Self-Recovery, and Antiswelling Hydrogels as Multifunctional Wearable Electronic Devices

The development of wearable electronic devices requires stretchable, highly conductive, self-recovery, and ideally environmentally resistant sensors. Hydrogels are ideal candidates for fabricating flexible sensors due to their stretchability and unique ionic conduction pathways. However, the intrinsic incompatibility of the conductive and elastic networks in hydrogels and the high hydrophilicity of the hydrogel network led to difficulties in obtaining hydrogels with strong mechanical properties, high conductivity, rapid self-recovery ability, and antiswelling properties. Based on the single-core multidentate coordination strategy, single-core multidentate coordinated chitosan/poly(acrylic acid)/Al3+ (CPAL) hydrogels were prepared with Al3+ as a metal coordination center and the amino group of chitosan (CS) and the carboxyl group of poly(acrylic acid) (PAA) as coordination atoms. The obtained hydrogels exhibit excellent tensile stress/strain: 1.11 ± 0.04 MPa/2472.79 ± 99.27%, rapid self-recovery capability (mechanical properties were fully recovered in 10 min), antifatigue property, good conductivity (1.09 ± 0.02 S/m), and antiswelling property. Furthermore, flexible sensors based on CPAL hydrogels demonstrated multiplex mode sensing. It was worth noting that the flexible devices based on CPAL hydrogel could not only use Morse code table to realize mechanical-information visualization but also detect the human condition in multiple dimensions, including temperature, electromyographic (EMG), and electrocardiogram (ECG). In this work, we reported a single-core multidentate coordination strategy that provided a pathway for fabricating the ideal hydrogel-based flexible sensors, showing great potential for wearable electronic devices

Energy Level Alignment of N‑Doping Fullerenes and Fullerene Derivatives Using Air-Stable Dopant

Doping has been proved to be one of the powerful technologies to achieve significant improvement in the performance of organic electronic devices. Herein, we systematically map out the interface properties of solution-processed air-stable n-type (4-(1,3-dimethyl-2,3-dihydro-1<i>H</i>-benzoimidazol-2-yl)­phenyl) doping fullerenes and fullerene derivatives and establish a universal energy level alignment scheme for this class of n-doped system. At low doping levels at which the charge-transfer doping induces mainly bound charges, the energy level alignment of the n-doping organic semiconductor can be described by combining integer charger transfer-induced shifts with a so-called double-dipole step. At high doping levels, significant densities of free charges are generated and the charge flows between the organic film and the conducting electrodes equilibrating the Fermi level in a classic “depletion layer” scheme. Moreover, we demonstrate that the model holds for both n- and p-doping of π-backbone molecules and polymers. With the results, we provide wide guidance for identifying the application of the current organic n-type doping technology in organic electronics

Direct Intertube Cross-Linking of Carbon Nanotubes at Room Temperature

Carbon nanotubes (CNTs) have long been regarded as an efficient free radical scavenger because of the large-conjugation system in their electronic structures. Hence, despite abundant reports on CNT reacting with incoming free radical species, current research has not seen CNT itself displaying the chemical reactivity of free radicals. Here we show that reactive free radicals can in fact be generated on carbon nanotubes via reductive defluorination of highly fluorinated single-walled carbon nanotubes (FSWNTs). This finding not only enriches the current understanding of carbon nanotube chemical reactivity but also opens up new opportunities in CNT-based material design. For example, spacer-free direct intertube cross-linking of carbon nanotubes was previously achieved only under extremely high temperature and pressure or electron/ion beam irradiation. With the free radicals on defluorinated FSWNTs, the nanotubes containing multiple radicals on the sidewall can directly cross-link with each other under ambient temperature through intertube radical recombination. It is demonstrated that carbon nanotube fibers reinforced via direct cross-linking displays much improved mechanical properties

The Effect of Oxygen Uptake on Charge Injection Barriers in Conjugated Polymer Films

The energy offset between the electrode Fermi level and organic semiconductor transport levels is a key parameter controlling the charge injection barrier and hence efficiency of organic electronic devices. Here, we systematically explore the effect of in situ oxygen exposure on energetics in n-type conjugated polymer P­(NDI2OD-T2) films. The analysis reveals that an interfacial potential step is introduced for a series of P­(NDI2OD-T2) electrode contacts, causing a nearly constant downshift of the vacuum level, while the ionization energies versus vacuum level remain constant. These findings are attributed to the establishment of a so-called double-dipole step via motion of charged molecules and will modify the charge injection barriers at electrode contact. We further demonstrate that the same behavior occurs when oxygen interacts with p-type polymer TQ1 films, indicating it is possible to be a universal effect for organic semiconductors

(<i>Z</i>)‑(Thienylmethylene)oxindole-Based Polymers for High-Performance Solar Cells

An oxindole-based monomer, (<i>Z</i>)-3-(thiophen-2-yl-methylene)­indolin-2-one (TEI) has been synthesized. The hemi-isoindigo, TEI was polymerized separately with bis­(trimethylstannyl) functionalized thiophene, bis­(alkoxy)­benzodithiophene, and bis­(alkylthienyl)­benzodithiophene to form polymers <b>PTEI-T</b>, <b>PTEI-BDTO</b>, and <b>PTEI-BDTT</b>, respectively. These new conjugated polymers showed low-lying HOMO energy levels (−5.26 to −5.42 eV), suitable LUMO energy levels (−3.63 to −3.66 eV), strong absorption in visible region and extended to near-IR. The inverted bulk heterojunction (BHJ) polymer solar cells based on the new polymers were fabricated and tested. The solar cell devices based on the blend of <b>PTEI-T</b>:[6,6]-phenyl-C₆₁-butyric acid methyl ester (PC₆₁BM) achieved a short-circuit current density (<i>J</i>_sc) value of 13.4 mA cm^–2, a fill factor (FF) of 0.65, an open circuit voltage (<i>V</i>_oc) of 0.85 V, and a power conversion efficiency (PCE) of 7.32%. The high performance solar cell devices were realized with the polymer which had a relatively simple structure

Light Extraction of Trapped Optical Modes in Polymer Light-Emitting Diodes with Nanoimprinted Double-Pattern Gratings

Despite the rapid development of polymer light-emitting diodes (PLEDs), the overall device efficiency is still limited because ∼80% of the generated light is trapped in a conventional device architecture by the high refractive index of organic materials and the optical confinement and internal reflection. The implementation of the energy dissipation compensation techniques is urgently required for further enhancement in the efficiency of PLEDs. Here, we demonstrate that incorporating the double-pattern Bragg gratings in the organic layers with soft nanoimprinting lithography can dramatically enhance the light extraction of trapped optical modes in PLEDs. The resulting efficiency is 1.35 times that of a conventional device with a flat architecture used as a comparison. The experimental and theoretical analyses indicate that the enhanced out-coupling efficiency is attributed to the combination of the ordinary Bragg scattering, the guided-mode resonance (GMR), surface plasmon polariton (SPP) modes, and the hybrid anticross coupling between GMR and SPP, leading to the extraordinary efficient photo flux that can transfer in direction of the leaky modes. We anticipate that our method provides a new pathway for precisely manipulating nanoscale optical fields and could enable the integration of different optical modes in PLEDs for the viable applications

0.7% Roll-off for Solution-Processed Blue Phosphorescent OLEDs with a Novel Electron Transport Material

A novel cross-linkable electron transport material, 1,3,5-tris­(5-(4-vinylphenyl)­pyridin-3-yl)­benzene (TV-TmPY), for solution-processing as well as a small molecule, 1,3,5-tris­(5-phenylpyridin-3-yl)­benzene (TmPY), for vacuum deposition were designed and synthesized for OLEDs. TV-TmPY and TmPY with identical core structures are fully characterized to systematically investigate the impact of solution processing and vacuum deposition on the performance of phosphorescent OLEDs. Over 90% EQE (external quantum efficiency) was achieved for the solution-processed TV-TmPY-based device compared to that of the vacuum-deposited TmPY at a luminance of 1000 cd m^–2. An EQE deviation of 0.7% was observed ranging from 100 to 1000 cd m^–2 with TV-TmPY, which is the smallest value to date for solution-processed OLEDs, and over 12% EQEs were achieved for the trilayered solution-processed green and blue phosphorescent OLEDs