With 1-methyl-2-pyrrolidinone (NMP) as the solvent, the biodegradable gel polymer electrolyte films are prepared based on poly(vinyl alcohol) (PVA), lithium bis(trifluoromethane)sulfonimide (LiTFSI), and 1-ethyl-3 methylimidazoliumbis(trifluoromethylsulfonyl)imide (EMITFSI) by means of solution casting. The films are characterized to evaluate their structural and electrochemical performance. The 60PVA-40LiTFSI + 10 wt.% EMITFSI system exhibits excellent mechanical properties and a high ionic transference number (0.995), indicating primary ionic conduction in the film. In addition, because of the flexibility of polymer chain segments, its relaxation time is as low as 5.30 × 10−7 s. Accordingly, a high ionic conductivity (3.6 × 10−3 S cm−1) and a wide electrochemical stability window (~5 V) are obtained. The electric double-layer capacitor (EDLC) based on this electrolyte system shows a specific capacitance of 101 F g−1 and an energy density of 10.3 W h kg−1, even after 1000 charge-discharge cycles at a current density of 0.4 A g−1 under a charging voltage of 2 V. All these excellent properties imply that the NMP-soluble 60PVA-40LiTFSI + 10 wt.% EMITFSI gel polymer electrolyte could be a promising electrolyte candidate for electrochemical device applications.
Thick ͑800 m͒ polyvinylidene fluoride/trifluoroethylene ͑P͑VDF-TrFE͒͒ copolymer films for transducer applications are poled under applied voltage at elevated temperatures. By using different heat treatments, poling temperatures, and poling time, we are able to prepare a uniformly poled film with a single resonance peak at 1.3 MHz, or a nonuniformly poled film with two resonances ͑1.3 and 2.6 MHz͒, or a film with bimorph structure with a single resonance at 2.6 MHz. The nonuniform polarization which arises from charge injection from the cathode is checked by the pressure wave propagation method. The polarization mechanisms in these thick films are expected to be similar to those previously reported for thin films. The results obtained in this work may lead to practical applications because they suggest a means for controlling transducer frequency by poling.
Charge transfer at the hetero‐interface is at the center of van der Waals (vdWs) heterostructure devices for multi‐functional applications. Compared with the extensively investigated photogenerated carrier transfer driven by the built‐in electric field from the conduction or valence band offset, the charge transfer due to the Fermi level difference of the two adjacent constitutes, and its influence on the opto‐/electronic performance of vdWs heterostructure devices are not clarified. Herein, by taking an example of WSe2/InSe heterostructure, it is demonstrated that the charge transfer at the hetero‐interface is an efficient “doping” strategy to dramatically modulate the carrier densities of atomically thin counterparts due to the extension of “band bending” across the entire heterostructure, paving the way for the creation of lateral WSe2 p‐n and n‐n+ homo‐junctions with multi‐functionalities, including promising rectification, photovoltaic, and photodetection abilities. Moreover, the device physics of lateral homo‐junctions, including potential distribution, band diagram, and photocurrent generation mechanisms, is revealed by gate‐dependent Kelvin probe force microscopy and scanning photocurrent measurements. This work not only provides a general avenue to build 2D lateral homo‐junctions, but also give deeper insights into the device physics of the junctions by coupling scanning probe and scanning photocurrent techniques.
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