Ionic liquids are increasingly employed as dielectrics to generate high charge densities and enable low‐voltage operation with organic semiconductors. However, effects on structure and morphology of ...the active material are not fully known, particularly for permeable semiconductors such as conjugated polymers, in which ions from the ionic liquid can enter and electrochemically dope the semicrystalline film. To understand when ions enter, where they go, and how they affect the film, thin films of the archetypal semiconducting polymer, poly(3‐hexylthiophene), are electrochemically doped with 1‐ethyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide, the archetypal ionic liquid. High‐resolution, ex situ X‐ray diffraction measurements and complete pole figures reveal changes with applied voltage, cycling, and frequency in lattice spacing, crystallite orientation, and crystallinity in the bulk and at the buried interface. Dopant ions penetrate the film and enter the crystallites at sufficiently high voltages and low frequencies. Upon infiltrating crystallites, ions permanently expand lamellar stacking and contract pi‐stacking. Cycling amplifies these effects, but higher frequencies mitigate the expansion of bulk crystallites as ions are hindered from entering crystallites. This mechanistic understanding of the structural effects of ion penetration will help develop models of the frequency and voltage impedance response of electrochemically doped conjugated polymers and advance electronic applications.
X‐ray characterization reveals two regimes of structural change in thin films of polymer poly(3‐hexylthiophene) gated through 1‐ethyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide. Tracking how ion penetration affects lattice spacing, crystalline orientation, and crystallinity elucidates mechanisms of the structural changes induced. Ions penetrate the film and enter crystallites at sufficiently high voltages and low frequencies. Cycling amplifies changes, though some effects are mitigated at higher frequencies.
Brain-inspired computing paradigms have led to substantial advances in the automation of visual and linguistic tasks by emulating the distributed information processing of biological systems
. The ...similarity between artificial neural networks (ANNs) and biological systems has inspired ANN implementation in biomedical interfaces including prosthetics
and brain-machine interfaces
. While promising, these implementations rely on software to run ANN algorithms. Ultimately, it is desirable to build hardware ANNs
that can both directly interface with living tissue and adapt based on biofeedback
. The first essential step towards biologically integrated neuromorphic systems is to achieve synaptic conditioning based on biochemical signalling activity. Here, we directly couple an organic neuromorphic device with dopaminergic cells to constitute a biohybrid synapse with neurotransmitter-mediated synaptic plasticity. By mimicking the dopamine recycling machinery of the synaptic cleft, we demonstrate both long-term conditioning and recovery of the synaptic weight, paving the way towards combining artificial neuromorphic systems with biological neural networks.
Efficiency, current throughput, and speed of electronic devices are to a great extent dictated by charge carrier mobility. The classic approach to impart high carrier mobility to polymeric ...semiconductors has often relied on the assumption that extensive order and crystallinity are needed. Recently, however, this assumption has been challenged, because high mobility has been reported for semiconducting polymers that exhibit a surprisingly low degree of order. Here, we show that semiconducting polymers can be confined into weakly ordered fibers within an inert polymer matrix without affecting their charge transport properties. In these conditions, the semiconducting polymer chains are inhibited from attaining long-range order in the π-stacking or alkyl-stacking directions, as demonstrated from the absence of significant X-ray diffraction intensity corresponding to these crystallographic directions, yet still remain extended along the backbone direction and aggregate on a local length scale. As a result, the polymer films maintain high mobility even at very low concentrations. Our findings provide a simple picture that clarifies the role of local order and connectivity of domains.
Wearable biosensors have emerged as an alternative evolutionary development in the field of healthcare technology due to their potential to change conventional medical diagnostics and health ...monitoring. However, a number of critical technological challenges including selectivity, stability of (bio)recognition, efficient sample handling, invasiveness, and mechanical compliance to increase user comfort must still be overcome to successfully bring devices closer to commercial applications. We introduce the integration of an electrochemical transistor and a tailor-made synthetic and biomimetic polymeric membrane, which acts as a molecular memory layer facilitating the stable and selective molecular recognition of the human stress hormone cortisol. The sensor and a laser-patterned microcapillary channel array are integrated in a wearable sweat diagnostics platform, providing accurate sweat acquisition and precise sample delivery to the sensor interface. The integrated devices were successfully used with both ex situ methods using skin-like microfluidics and on human subjects with on-body real-sample analysis using a wearable sensor assembly.
Charge transport in conjugated polymer semiconductors has traditionally been thought to be limited to a low-mobility regime by pronounced energetic disorder. Much progress has recently been made in ...advancing carrier mobilities in field-effect transistors through developing low-disorder conjugated polymers. However, in diodes these polymers have to date not shown much improved mobilities, presumably reflecting the fact that in diodes lower carrier concentrations are available to fill up residual tail states in the density of states. Here, we show that the bulk charge transport in low-disorder polymers is limited by water-induced trap states and that their concentration can be dramatically reduced through incorporating small molecular additives into the polymer film. Upon incorporation of the additives we achieve space-charge limited current characteristics that resemble molecular single crystals such as rubrene with high, trap-free SCLC mobilities up to 0.2 cm
/Vs and a width of the residual tail state distribution comparable to k
T.
Organic mixed conductors are increasingly employed in electrochemical devices operating in aqueous solutions that leverage simultaneous transport of ions and electrons. Indeed, their mode of ...operation relies on changing their doping (oxidation) state by the migration of ions to compensate for electronic charges. Nevertheless, the structural and morphological changes that organic mixed conductors experience when ions and water penetrate the material are not fully understood. Through a combination of electrochemical, gravimetric, and structural characterization, the effects of water and anions with a hydrophilic conjugated polymer are elucidated. Using a series of sodium‐ion aqueous salts of varying anion size, hydration shells, and acidity, the links between the nature of the anion and the transport and structural properties of the polymer are systematically studied. Upon doping, ions intercalate in the crystallites, permanently modifying the lattice spacings, and residual water swells the film. The polymer, however, maintains electrochemical reversibility. The performance of electrochemical transistors reveals that doping with larger, less hydrated, anions increases their transconductance but decreases switching speed. This study highlights the complexity of electrolyte‐mixed conductor interactions and advances materials design, emphasizing the coupled role of polymer and electrolyte (solvent and ion) in device performance.
Electrochemical, gravimetric, and X‐ray characterization of organic mixed conductors reveals that structure and transport properties depend on the nature of the electrolyte's ions. Morphological and microstructural changes in the polymer upon swelling and doping are investigated. Anions and water penetrate the bulk of the polymer and can intercalate in the crystallites. Smaller anions exhibit faster transistor switching but lower transconductance.
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