Highly Stable Nonhydroxyl Antisolvent Polymer Dielectric: A New Strategy towards High-Performance Low-Temperature Solution-Processed Ultraflexible Organic Transistors for Skin-Inspired Electronics

Scarcity of the antisolvent polymer dielectrics and their poor stability have significantly prevented solution-processed ultraflexible organic transistors from low-temperature, large-scale production for applications in low-cost skin-inspired electronics. Here, we present a novel low-temperature solution-processed PEI-EP polymer dielectric with dramatically enhanced thermal stability, humidity stability, and frequency stability compared with the conventional PVA/c-PVA and c-PVP dielectrics, by incorporating polyethyleneimine PEI as crosslinking sites in nonhydroxyl epoxy EP. The PEI-EP dielectric requires a very low process temperature as low as 70°C and simultaneously possesses the high initial decomposition temperature (340°C) and glass transition temperature (230°C), humidity-resistant dielectric properties, and frequency-independent capacitance. Integrated into the solution-processed C8-BTBT thin-film transistors, the PEI-EP dielectric enables the device stable operation in air within 2 months and in high-humidity environment from 20 to 100% without significant performance degradation. The PEI-EP dielectric transistor array also presents weak hysteresis transfer characteristics, excellent electrical performance with 100% operation rate, high mobility up to 7.98 cm2 V-1 s-1 (1 Hz) and average mobility as high as 5.3 cm2 V-1 s-1 (1 Hz), excellent flexibility with the normal operation at the bending radius down to 0.003 mm, and foldable and crumpling-resistant capability. These results reveal the great potential of PEI-EP polymer as dielectric of low-temperature solution-processed ultraflexible organic transistors and open a new strategy for the development and applications of next-generation low-cost skin electronics.

Chitosan-Based Flexible Memristors with Embedded Carbon Nanotubes for Neuromorphic Electronics

In this study, we propose high-performance chitosan-based flexible memristors with embedded single-walled carbon nanotubes (SWCNTs) for neuromorphic electronics. These flexible transparent memristors were applied to a polyethylene naphthalate (PEN) substrate using low-temperature solution processing. The chitosan-based flexible memristors have a bipolar resistive switching (BRS) behavior due to the cation-based electrochemical reaction between a polymeric chitosan electrolyte and mobile ions. The effect of SWCNT addition on the BRS characteristics was analyzed. It was observed that the embedded SWCNTs absorb more metal ions and trigger the conductive filament in the chitosan electrolyte, resulting in a more stable and wider BRS window compared to the device with no SWCNTs. The memory window of the chitosan nanocomposite memristors with SWCNTs was 14.98, which was approximately double that of devices without SWCNTs (6.39). Furthermore, the proposed SWCNT-embedded chitosan-based memristors had memristive properties, such as short-term and long-term plasticity via paired-pulse facilitation and spike-timing-dependent plasticity, respectively. In addition, the conductivity modulation was evaluated with 300 synaptic pulses. These findings suggest that memristors featuring SWCNT-embedded chitosan are a promising building block for future artificial synaptic electronics applications.

Numerical Model for Heat Transfer Processes in Dry Ash Conveyors

The dry handling of bottom ash from coal-fired power plants has become more and more important in recent years, e.g. due to a lack of water availability at the location of power plants, or for environmental reasons. Thereby it is crucial that a sufficient cooling of the bottom ash can be ensured by the dry cooling air. Within this work, a numerical model for the assessment of heat transfer processes in dry ash conveyors is developed and implemented into Wolfram Mathematica. The model uses a newly introduced representative geometric quantity for the ash particle geometry. Moreover, in addition to the ash, the cooling air is considered as an own phase, for which a temperature solution is obtained. A numerical example, considering geometrical and operational data of an existing facility, shows that the main heat transfer between the ash and the cooling air takes place in the ash hopper, whereby convective heat transfer from ash to cooling air outweighs the effects from coke combustion and radiation from the boiler outlet area. The convective heat transfer in the ash hopper predominantly depends on the geometrical appearance, i.e. size and shape, of the particles, as well as on the grain density, and on the falling time/velocity. Conservatism of the calculation approach is indicated based on comparison of computed temperatures with measured data and literature values. The derived model can be used in future designs and projections of dry ash handling systems.