The functionalization of semiconducting single-walled carbon nanotubes (SWNTs) with sp 3 defects that act as luminescent exciton traps is a powerful means to enhance their photoluminescence quantum yield (PLQY) and to add optical properties. However, the synthetic methods employed to introduce these defects are currently limited to aqueous dispersions of surfactant-coated SWNTs, often with short tube lengths, residual metallic nanotubes, and poor film-formation properties. In contrast to that, dispersions of polymer-wrapped SWNTs in organic solvents feature unrivaled purity, higher PLQY, and are easily processed into thin films for device applications. Here, we introduce a simple and scalable phase-transfer method to solubilize diazonium salts in organic nonhalogenated solvents for the controlled reaction with polymer-wrapped SWNTs to create luminescent aryl defects. Absolute PLQY measurements are applied to reliably quantify the defect-induced brightening. The optimization of defect density and trap depth results in PLQYs of up to 4% with 90% of photons emitted through the defect channel. We further reveal the strong impact of initial SWNT quality and length on the relative brightening by sp 3 defects. The efficient and simple production of large quantities of defect-tailored polymer-sorted SWNTs enables aerosol-jet printing and spin-coating of thin films with bright and nearly reabsorption-free defect emission, which are desired for carbon nanotube-based near-infrared light-emitting devices.
Entirely photopatternable solid organic electrochemical transistors were fabricated and their excellent performance and pronounced hysteretic behavior studied in detail.
Neural interfaces that directly measure brain activity are increasingly employed to elucidate large-scale brain networks and treat intractable neurological disorders. Considering the softness of brain tissue, current efforts to study chronic disorders aim to minimize invasiveness. We discuss recent progress on flexible neural interfaces with high durability under bending and stretching achieved by using organic materials. Multichannel microelectrodes are usually fabricated on thin polymer substrates as sheets and needles to reach superficial and deep brain structures, respectively. An interesting recent trend is the integration of high-density microelectrodes to measure detailed brain functions. The use of numerous measurement points (the current highest values achieved are 62 500 electrodes cm -2 and 3072 channels) can increase the accuracy of brain state estimation. However, further improvement should be devised for integration in plane considering the density of 250 000 neurons cm -2 in approximate intervals of 20 µm. Meanwhile, the ultimate goal of improving flexibility in neural interfaces is long-term implantation. Widely used approaches for thinning polymers (∼1 µm) and reducing the rigidity of neural interfaces compromise robustness due to high gas permeability and water uptake. We quantitatively analyze the technical proficiency of flexible neural interfaces in vivo regarding microelectrode integration and robustness. The solution contact impedance, which is a crucial factor in microelectrode miniaturization, is exhaustively surveyed and compared across PEDOT:PSS, Au, Pt, Pt black, IrOx, gels, and other components that should be designed within the permissible source impedance for the measurement device to ensure high-accuracy and low-noise measurements of brain activity in the order of microvolts. Furthermore, we detail a multifunctional neural interface with stretchability, optical transparency, easy intraoperative handling, and flexible transistor implementation for building an active electrode array, providing a new approach for flexible interfaces in neuroscience and neuroengineering.
Despite their increasing usefulness in a wide variety of applications, organic electrochemical transistors still lack a comprehensive and unifying physical framework able to describe the current-voltage characteristics and the polymer/electrolyte interactions simultaneously. Building upon thermodynamic axioms, we present a quantitative analysis of the operation of organic electrochemical transistors. We reveal that the entropy of mixing is the main driving force behind the redox mechanism that rules the transfer properties of such devices in electrolytic environments. In the light of these findings, we show that traditional models used for organic electrochemical transistors, based on the theory of field-effect transistors, fall short as they treat the active material as a simple capacitor while ignoring the material properties and energetic interactions. Finally, by analyzing a large spectrum of solvents and device regimes, we quantify the entropic and enthalpic contributions and put forward an approach for targeted material design and device applications.
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