Advanced flexible strain sensors for human motion detection and other potential use have attracted great attention in recent years. However, the preparation of strain sensor with both high sensitivity and large workable strain range remains a challenge. In this work, the carbon nanotube (CNT) suspensions with the assistance of cellulose nanocrystals (CNC) were directly pumped into the porous electrospun thermoplastic polyurethanes (TPU) membranes through a simple filtration process to prepare the flexible strain sensors in one step. The sensitivity and workable strain range of the strain sensors are tunable by changing the mass ratios of CNTs/CNC and the total amount of hybrid fillers. With increase in the total amount of fillers, a change of filler layer from droplet to completely continuous film was observed, resulting in a sharp increase of strain sensitivity. By combining the ultraelasticity of the TPU material and the high sensitivity of hybrid fillers, the strain sensor with large workable strain range (>500%) and high sensitivity (gauge factor = 321) was successfully prepared. Its applications in visual control and full-range human body motion detection were demonstrated, showing its tremendous potential applications in future intelligent electronics.
Stretchable and wearable sensors with active response to various environmental stimuli possess numerous potential applications in stretchable electronics, motion sensors, environmental monitoring, and so on. Herein, we report a new method to realize control on the local conductive networks of strain sensors, thus, their sensing behavior. These multifunctional crack-based sensors were prepared via spray coating a mixture of carbon nanotube (CNT) and 3-aminopropyltriethoxysilane (KH550) with various ratios onto polydimethylsiloxane (PDMS). The conductive CNT/KH550 layer exhibits brittle mechanical behavior which triggers the formation of cracks upon stretching. This is thought to be responsible for the observed electromechanical behavior. These sensors exhibit adjustable gauge factors of 5-1000, stretchability (ε) of 2-250%, linearity (nonlinearity-linearity) and high durability over 1000 stretching-releasing cycles for mechanical deformation. Washable, wearable, and water-repellent sensors were prepared through such a method to successfully detect human physiological activities. Moreover, the variation in temperature or the presence of solvent can also be detected due to the thermal expansion and swelling of the PDMS layer. It is expected that such a concept could be used to prepare sensors for multiple applications, thanks to its multifunctionality, adjustable and robust performance, simple and low-cost fabrication strategy.
While 2D Ruddlesden-Popper (RP) perovskites exhibit attractive opto-electronic properties and stability for use in perovskite solar cells (PSCs), their complicated film-forming processes often induce a non-negligible level of defects that significantly undermine the power conversion efficiency (PCE) and stability of PSCs. Here, the use of two organic ammonium salts with the same chain length, namely monoammonium (butylammonium iodide, BAI) and diammonium (1,4-butanediamine dihydroiodide, BDAI 2 ) for surface defect passivation of RP-2D perovskite films of (AA) 2 MA 4 Pb 5 I 16 (n = 5) are reported. It is found that the diammonium BDAI 2 not only effectively reduces the defect density (similarly to using monoammonium BAI) but forms a Dion-Jacobson (DJ) 2D structure to enhance interfacial charge extraction and suppress surface charge recombination. As a result, a boosted PCE of 18.34% has been obtained with a high open-circuit voltage of 1.24 V. Owing to the enhanced structural integrity of the DJ phase, the RP-2D/DJ-2D perovskite heterojunction films exhibit supreme material robustness, which translates to the impressive environmental stability of devices, showing nearly zero-degradation of the efficiency after 800 h of continuous thermal aging (60 °C) for 800 h. This work enriches the fundamental understanding of the impacts of the DJ-2D structure on the surface properties of 2D perovskites.
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