Conducting hydrogels have attracted much attention for the emerging field of hydrogel bioelectronics, especially poly(3,4‐ethylenedioxythiophene): poly(styrene sulfonate) (PEDOT:PSS) based hydrogels, because of their great biocompatibility and stability. However, the electrical conductivities of hydrogels are often lower than 1 S cm−1 which are not suitable for digital circuits or applications in bioelectronics. Introducing conductive inorganic fillers into the hydrogels can improve their electrical conductivities. However, it may lead to compromises in compliance, biocompatibility, deformability, biodegradability, etc. Herein, a series of highly conductive ionic liquid (IL) doped PEDOT:PSS hydrogels without any conductive fillers is reported. These hydrogels exhibit high conductivities up to ≈305 S cm−1, which is ≈8 times higher than the record of polymeric hydrogels without conductive fillers in literature. The high electrical conductivity results in enhanced areal thermoelectric output power for hydrogel‐based thermoelectric devices, and high specific electromagnetic interference (EMI) shielding efficiency which is about an order in magnitude higher than that of state‐of‐the‐art conductive hydrogels in literature. Furthermore, these stretchable (strain >30%) hydrogels exhibit fast self‐healing, and shape/size‐tunable properties, which are desirable for hydrogel bioelectronics and wearable organic devices. The results indicate that these highly conductive hydrogels are promising in applications such as sensing, thermoelectrics, EMI shielding, etc.

Lightweight and low-cost flexible thermoelectric (TE) materials improve the heat-to-electricity conversion efficiency compared to rigid materials by minimizing the heat loss between TE devices and heat sources in waste heat recovery. Multi-walled carbon nanotube (MWCNT) has excellent mechanical and electrical properties. However, the TE power factor (PF) of MWCNTs is much lower than single/double-walled carbon nanotube (S/DWCNT), which is often lower than 40 µW m −1 -K −2 . Herein an effective way to achieve high PFs of ≈1800 µW m −1 -K −2 for p-type and ≈1000 µW m −1 -K −2 for n-type in flexible MWCNT films is reported. The high power factor is achieved by taking advantage of the anisotropic electrical conductivity and isotropic Seebeck coefficient feature of 1D CNTs as well as the following doping and cold-pressing to improve the electrical conductivity of MWCNT films. The PF values are comparable to that of state-of-the-art S/DWCNT films and most inorganic TE materials. A Lego-like TE generator (TEG) with an assembling structure is fabricated to show the heat-to-electricity ability of the materials, which exhibits the highest areal output power of ≈27 W m −2 among CNT-based flexible TEGs. This method may be extended to other 1D-material based composites to boost the development of high PF flexible TE materials.

Joints widely exist in traditional organic electronic devices that are composed of p−n modules, including organic thermoelectric (TE) devices. They often harm the performance of the devices by increasing their electrical resistance and thermal resistance. Recently, a few joint-free approaches have been reported to fabricate TE devices with a single carbon nanotube (CNT) composite film. However, the resolution of p−n patterns is low, e.g., >100 μm, with a conventional printing/dropcasting method. Herein, a plasma treatment method was reported to fabricate joint-free TE devices with a single-piece flexible CNT composite film whose performance was higher than that of traditional devices in energy harvesting and solid-state cooling. In addition, this method provided p−n patterns with a high resolution of ∼1−2 μm which is promising for making future high integration level TE devices. This method can be extended to fabricate a broad range of high integration level organic electronic devices composed of p−n modules.

Conducting polymers typically transfer either electrons or holes. It is rare to see high bipolar (p-and n-type) electrical conductivities within a single bulk doped organic polymer without the assistant of gate voltage. Here, we report that FeCl 3 doped solution-processable D-A copolymer poly (2,5-bis(2octyldodecyl)-3,6-di(thiophen-2-yl)diketopyrrolo [3,4-c] pyrrole-1,4-dione-altthieno[3,2-b]thiophen) (DPPTTT) could exhibit a high p-type electrical conductivity of 130.6 S/cm and a good n-type electrical conductivity of 14.2 S/cm when engineering the doping level. Both the p-and n-type electrical conductivities are superior to that of most of the solution-processable D-A copolymers including monopolar polymers. The high electrical conductivity results in high thermoelectric performance of DPPTTT in both p-and n-type, which also leads to a high current density of 3 A/cm 2 for a fully organic planar p-n junction created with only one material. Structural and spectroscopic tests have been performed to provide a fundamental understanding of the polarity switching mechanism. The results open the opportunity of making p-and n-type modules with a single conducting polymer for future modern organic electronics.This study may arouse the interest of researchers in exploring novel conducting polymers and enrich the knowledge of charge transport in organic materials.

P–N junctions exist in many solid‐state organic devices, such as light‐emitting diodes, solar cells, and thermoelectric devices. Creating P–N junctions by bulk chemical doping in a single organic material (like silicon doped by boron and phosphorus) may capitalize the vast scientific and technological groundwork established in the inorganic semiconducting field. However, high‐performance single‐organic‐material P–N junctions are seldom reported, because the diffusion of the dopant counterions often leads to transient rectification properties. Herein, a new type of lateral fully organic diodes created in single donor–acceptor (D–A) copolymer films with only one P‐type dopant is reported. The achieved lateral devices exhibit high current densities of ≈3.83 A cm−2 and a high rectification ratio of ≈2100, which are beyond the requirements for high‐frequency identification tags. The P‐ to N‐type polarity switching mechanism is proposed after spectroscopic and structural tests. Decent stability of the organic diode is obtained, which is due to the long channel length and low diffusion speed of the large size of dopants. This work opens the opportunities to create P–N junctions in ways of silicon‐based inorganic semiconductors and promises new opportunities for integrating organic materials for flexible and printable organic devices.

No abstract

No abstract

No abstract