Electronic skins (e-skins), composed of various flexible sensors, mimic the sensing functions of human skin aiming for both healthcare monitoring and prosthetics development applications. So far ...different multi-component e-skin devices aimed to fulfill different requirements (biocompatibility, skin adhesion, flexibility, conductivity, sensitivity towards biological stimuli and stretchability) have been reported. However, the obtaining of such devices combining all the above requirements within a single material that simplifies not only cost but specially functioning still remains a challenge. For this, catechol-based materials have attracted special attention due to their adhesive properties, compatibility and melanin-like electrical conduction. In this work, 2,3,6,7,10,11 – hexahydroxy triphenylene (HHTP) was used as catechol moiety in a typical melanin-like polymerization, resulting in a free-standing melanin-inspired film (MN-film). The obtained MN-film showcased good conductivities with dual charge carriers (electrons and ions) under different environments, i.e. pure water and buffers simulating sweat. Large biocompatibility, adhesion and conformability to skin were obtained as well, allowing to implement the film in wearable electronic on-skin devices on porcine skin. Measurements in wearable devices indicated large sensitivity towards different stimuli (strain, motion and temperature) under sweat-like conditions.
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•Melanin-like free-standing films have been successfully designed and synthesized.•Films showcase large conductivities and adhesion to ex-vivo and human skin.•E-skin devices with the films show sensitivity to sweat, motion and temperature.
The performance of organic field‐effect transistors is still severely limited by factors such as contact resistance and charge trapping. Chemical doping is considered to be a promising key enabler ...for improving device performance, although there is a limited number of established doping protocols as well as a lack of understanding of the doping mechanisms. Here, a very simple doping methodology based on exposing an organic semiconductor thin film to an aqueous iodine solution is reported. The doped devices exhibit enhanced device mobility, which becomes channel‐length independent, a decreased threshold voltage and a reduction in the density of interfacial traps. The device OFF current is not altered, which is in agreement with the spectroscopic data that points out that no charge transfer processes are occurring. Kelvin probe force microscopy characterization of the devices under operando conditions unambiguously proves that an important reduction of the contact resistance takes place after their exposition to the iodine solution, reaching almost ohmic contact.
Thin films of the organic semiconductor C8‐BTBT‐C8 are doped following a very simple methology based on the exposure of the semiconductor to an aqueous iodine solution. This results in organic field‐effect transistors exhibiting a lower threshold voltage and a significantly improved mobility, which is caused by a dramatic decrease of the contact resistance.
In polymeric composite thin films it is possible to translate elastic elongations of the film into reversible nanoscale deformations of the soft organic‐crystal components, leading to films with ...extreme sensitivity to strain changes with durable, fast, and completely reversible responses. Simple prototypes (see image), demonstrate that these sensors are highly promising for a wide range of applications.
A compact and planar donor–acceptor molecule 1 comprising tetrathiafulvalene (TTF) and benzothiadiazole (BTD) units has been synthesised and experimentally characterised by structural, optical, and ...electrochemical methods. Solution‐processed and thermally evaporated thin films of 1 have also been explored as active materials in organic field‐effect transistors (OFETs). For these devices, hole field‐effect mobilities of μFE=(1.3±0.5)×10−3 and (2.7±0.4)×10−3 cm2 V s−1 were determined for the solution‐processed and thermally evaporated thin films, respectively. An intense intramolecular charge‐transfer (ICT) transition at around 495 nm dominates the optical absorption spectrum of the neutral dyad, which also shows a weak emission from its ICT state. The iodine‐induced oxidation of 1 leads to a partially oxidised crystalline charge‐transfer (CT) salt {(1)2I3}, and eventually also to a fully oxidised compound {1I3}⋅1/2I2. Single crystals of the former CT compound, exhibiting a highly symmetrical crystal structure, reveal a fairly good room temperature electrical conductivity of the order of 2 S cm−1. The one‐dimensional spin system bears compactly bonded BTD acceptors (spatial localisation of the LUMO) along its ridge.
Compact donor–acceptor dyad: A compact and planar donor–acceptor molecule 1 comprising tetrathiafulvalene (TTF) and benzothiadiazole (BTD) units has been prepared for investigation of its photoinduced intramolecular charge‐transfer process. Chemical oxidation of 1 affords a partially oxidised crystalline charge‐transfer (CT) salt {(1)2I3}, and eventually also a fully oxidised compound {1I3}⋅1/2I2. The former CT salt exhibits a highly symmetrical crystal structure, forming a wire of TTF+0.5 π‐stacks with compactly bonded BTD acceptors along its ridge (see graphic). This unique structural feature accounts for its good electrical conductivity of 2 S cm−1 at room temperature.
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