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Abstract This paper investigates the electrical, morphological, and mechanical behavior of ultrathin layer-by-layer polyaniline/poly(vinyl sulfonic acid) (PANI/PVS) ultrathin films for ammonia gas sensing. Atomic force microscopy shows that the PANI/PVS surface's roughness increases almost linearly with the number of PANI/PVS bilayers, while the surface morphology varies from a rod-like structure to a film-like architecture. Impedance measurements and their representation by a Cole-Cole model confirm this transition at ~15 bilayers. The designed sensor shows low response time (< 1 min), an optimal operating frequency range (1–100 Hz), high stability and sensibility to ammonia (~ 98 kΩ/ppm), and low sensibility to strain (~ 3.6 kΩ/%). This study suggests that hopping carriers' concentration remains constant, and hopping carriers' mobility changes with the number of bilayers. The simultaneous analysis of morphology with complex impedance measurements is a strategy for enhancing the electrical performance of low-cost and flexible organic sensing devices.

Recent advances in materials and manufacturing processes pave the way for the establishment of piezoelectric materials via printing techniques as flexible sensors, actuators, and generators. Such flexible devices are key building blocks for future advanced robotic skin and conformable medical devices. Herein special focus is given to printed devices for its lightweight, flexibility, and manufacturing by high throughput techniques, offering a disruptive advantage in integration technologies and a wide range of opportunities for industrialization routes, where cost‐effective applications are required. In this Progress Report, the different system parameters are discussed, pinpointing the ones that affect the production of reliable flexible printed piezoelectric devices and limit this technology to achieve higher technological maturity. Focus is made on screen and inkjet printing as fabrication techniques and the well‐established piezoelectric polymer poly(vinylidene fluoride‐co‐trifluoroethylene). Key limiting factors found for the manufacturing of robust scalable all‐printed piezoelectric devices stems mainly from the piezoelectric ink production and processing. Finally, the integration of these materials, via printing technologies, into soft, flexible, and even stretchable substrates is analyzed and insights are gathered on the manufacturing trends to achieve low‐cost production of flexible piezoelectric devices embedded in electronic skin and smart wearables. [ABSTRACT FROM AUTHOR]

Flexible quantum dotlight‐emitting diodes (QLEDs) are demonstrated by using hot‐pressing AgNWs as the transparent conductive electrode and EGaIn as the back electrode. Both AgNWs and EGaIn are printable, and thus the whole device can be fabricated via vacuum‐free processes. The hot‐pressing AgNWs electrode exhibits excellent physical characteristics such as high transparency of 96.7% in the visible spectral region, and low sheet resistance of 28 Ω/sq. With the AgNWs and EGaIn, vacuum‐free‐fabricated QLEDs are successfully achieved with efficiency 13.2cd/A. Because of the elimination of the costly vacuum processes, the proposed fabrication processes are low cost and allow rapid fabrication of flexible QLEDs with high performance. [ABSTRACT FROM AUTHOR]

Recent findings demonstrate that cellulose, a highly abundant, versatile, sustainable, and inexpensive material, can be used in the preparation of very stable and flexible electrochemical energy storage devices with high energy and power densities by using electrodes with high mass loadings, composed of conducting composites with high surface areas and thin layers of electroactive material, as well as cellulose-based current collectors and functional separators. Close attention should, however, be paid to the properties of the cellulose (e.g., porosity, pore distribution, pore-size distribution, and crystallinity). The manufacturing of cellulose-based electrodes and all-cellulose devices is also well-suited for large-scale production since it can be made using straightforward filtration-based techniques or paper-making approaches, as well as utilizing various printing techniques. Herein, the recent development and possibilities associated with the use of cellulose are discussed, regarding the manufacturing of electrochemical energy storage devices comprising electrodes with high energy and power densities and lightweight current collectors and functional separators., (© 2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Integrating thermoelectric generators (TEGs) into textiles is attractive for body heat harvesting to power wearable electronics. Textile‐integrated TEGs have the advantage of conformity to the body that ensures efficient heat transfer and does not impede movement. Additive printing techniques and solution processable polymer‐based thermoelectric (TE) materials can be used for this purpose. However, a number of fabrication challenges limit the realization of a printed polymer‐based textile TEG using a low cost, scalable, and textile compatible process. In this work, stencil and transfer printing techniques are successfully employed to fabricate a 32‐leg device with a modest fill factor (≈30%) on a commercial sports fabric substrate. PEDOT:PSS and Poly[Na(NiETT)] are formulated into inks and used as the p‐type and the n‐type polymer materials, respectively. The textile‐integrated TE device yields an open circuit voltage of ≈3 mV at ΔT = 3 K. The fabrication process is scaled up to demonstrate an 864‐leg device that yields a voltage output of ≈47 mV. This work is the first demonstration of a textile TEG based on p‐ and n‐type conducting polymers capable of through‐plane body heat harvesting. It serves as a proof‐of‐concept for integrating TE devices into mainstream fabrics and clothing. [ABSTRACT FROM AUTHOR]