Fushan Li

Highly reproducible memory effect of organic multilevel resistive-switch device utilizing graphene oxide sheets/polyimide hybrid nanocomposite

The functionalization of graphene oxide (GO) sheets with polyimide (PI) enables the layer-by-layer fabrication of a GO-PI hybrid resistive-switch device and leads to high reproducibility of the memory effect. The current-voltage curves for the as-fabricated device exhibit multilevel resistive-switch properties under various reset voltages. The capacitance-voltage characteristics for a capacitor based on GO-PI nanocomposite indicate that the electrical switching may originate from the charge trapping in GO sheets. The high device-to-device uniformity and unique memory properties of the device make it an attractive candidate for applications in next-generation high-density nonvolatile flash memories.

Organic bistable devices based on core/shell CdSe∕ZnS nanoparticles embedded in a conducting poly(N-vinylcarbazole) polymer layer

Current-voltage measurements on the Al/[CdSe∕ZnS nanoparticles embedded in a hole-transporting poly(N-vinylcarbazole) (PVK) layer]/indium tin oxide (ITO)/glass structures at 300K showed a nonvolatile electrical bistability behavior. Capacitance-voltage (C-V) measurements on the Al/[CdSe∕ZnS nanoparticles embedded in a PVK layer]/ITO/glass structures at 300K showed a metal-insulator-semiconductor behavior with a flatband voltage shift due to the existence of the CdSe∕ZnS nanoparticles, indicative of trapping, storing, and emission of charges in the electronic states of the CdSe nanoparticles. Operating mechanisms for the Al/[CdSe∕ZnS nanoparticles embedded in the PVK layer]/ITO/glass devices are described on the basis of the C-V results.

Wearable Electricity Generators Fabricated Utilizing Transparent Electronic Textiles Based on Polyester/Ag Nanowires/Graphene Core–Shell Nanocomposites

The technological realization of wearable triboelectric generators is attractive because of their promising applications in wearable self-powered intelligent systems. However, the low electrical conductivity, the low electrical stability, and the low compatibility of current electronic textiles (e-textiles) and clothing restrict the comfortable and aesthetic integration of wearable generators into human clothing. Here, we present high-performance, transparent, smart e-textiles that employ commercial textiles coated with silver nanowire/graphene sheets fabricated by using a scalable, environmentally friendly, full-solution process. The smart e-textiles show superb and stable conduction of below 20 Ω/square as well as excellent flexibility, stretchability, foldability, and washability. In addition, wearable electricity-generating textiles, in which the e-textiles act as electrodes as well as wearable substrates, are presented. Because of the high compatibility of smart e-textiles and clothing, the electricity-generating textiles can be easily integrated into a glove to harvest the mechanical energy induced by the motion of the fingers. The effective output power generated by a single generator due to that motion reached as high as 7 nW/cm(2). The successful demonstration of the electricity-generating glove suggests a promising future for polyester/Ag nanowire/graphene core-shell nanocomposite-based smart e-textiles for real wearable electronic systems and self-powered clothing.

Memory effect of CdSe∕ZnS nanoparticles embedded in a conducting poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene-vinylene] polymer layer

Capacitance-voltage (C-V) measurements on Au/a conducting poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene-vinylene] polymer layer containing core/shell CdSe∕ZnS nanoparticles (hybrid layer)/indium tin oxide (ITO) coated glass and Al/hybrid layer/ITO coated glass capacitors at 300K showed metal-insulator-semiconductor behavior with a large flatband voltage shift. This shift was due to the existence of the CdSe∕ZnS nanoparticles, indicative of trapping, storing, and emission of charge carriers in the CdSe∕ZnS nanoparticles. Symmetric and asymmetric C-V characteristics appeared in the Al/hybrid layer/ITO coated glass and Au/hybrid layer/ITO coated glass capacitors, respectively. A dipolar carrier trapping model is proposed to explain the symmetric behavior in the C-V curve.Capacitance-voltage (C-V) measurements on Au/a conducting poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene-vinylene] polymer layer containing core/shell CdSe∕ZnS nanoparticles (hybrid layer)/indium tin oxide (ITO) coated glass and Al/hybrid layer/ITO coated glass capacitors at 300K showed metal-insulator-semiconductor behavior with a large flatband voltage shift. This shift was due to the existence of the CdSe∕ZnS nanoparticles, indicative of trapping, storing, and emission of charge carriers in the CdSe∕ZnS nanoparticles. Symmetric and asymmetric C-V characteristics appeared in the Al/hybrid layer/ITO coated glass and Au/hybrid layer/ITO coated glass capacitors, respectively. A dipolar carrier trapping model is proposed to explain the symmetric behavior in the C-V curve.

UV photovoltaic cells based on conjugated ZnO quantum dot/multiwalled carbon nanotube heterostructures

In situ growth of ZnO quantum dots (QDs) on the surface of multiwalled carbon nanotubes (MWCNTs) was realized via a mild solution-process method, which resulted in an improvement in photoinduced charge separation and transport of carriers to the collecting electrode. The charge transfer efficiency was significantly increased by more than 90% due to the conjugation of ZnO QDs with MWCNTs, as confirmed by photoluminescence measurements. Ultraviolet photovoltaic cells based on the charge transfer at the ZnO QD-MWCNT heterostructures were fabricated, and their power conversion efficiency was measured to be above 1%.

Memory effect of nonvolatile bistable devices based on CdSe∕ZnS nanoparticles sandwiched between C60 layers

Current-voltage and conductance-voltage (G-V) measurements on three-layer Al∕C60∕CdSe nanoparticles∕C60∕indium tin oxide (ITO) structures fabricated by using a spin-coating method showed a nonvolatile electrical bistable behavior. Capacitance-voltage (C-V) measurements on Al∕C60∕CdSe nanoparticles∕C60∕ITO structures showed a clockwise hysteresis with a flatband voltage shift due to the existence of the CdSe nanoparticles, indicative of memory effects in the devices. Current-time measurements showed that the devices exhibited excellent memory retention ability at ambient conditions. Possible operating mechanisms for the memory effects in the Al∕C60∕CdSe nanoparticles∕C60∕ITO devices are described on the basis of the G-V and the C-V results.

Formation and electrical bistability properties of ZnO nanoparticles embedded in polyimide nanocomposites sandwiched between two C60 layers

The electrical bistability of the memory device based on ZnO nanoparticles embedded in a polyimide (PI) layer was investigated. Transmission electron microscopy and selected area electron diffraction pattern measurements showed that ZnO nanocrystals were formed inside the PI layer. Current-voltage measurements on Al∕C60∕ZnO nanoparticles embedded in PI layer/C60/indium tin oxide structures at 300K showed a current bistability with a large on/off ratio of 104. The current-voltage hysteresis characteristics at negative voltages could be modified by varying the applied positive erasing voltage. The memory device fabricated utilizing ZnO nanoparticles embedded in a PI layer exhibited excellent environmental stability at ambient conditions.

All-solution processed semi-transparent perovskite solar cells with silver nanowires electrode.

In this work, we report an all-solution route to produce semi-transparent high efficiency perovskite solar cells (PSCs). Instead of an energy-consuming vacuum process with metal deposition, the top electrode is simply deposited by spray-coating silver nanowires (AgNWs) under room temperature using fabrication conditions and solvents that do not damage or dissolve the underlying PSC. The as-fabricated semi-transparent perovskite solar cell shows a photovoltaic output with dual side illuminations due to the transparency of the AgNWs. With a back cover electrode, the open circuit voltage increases significantly from 1.01 to 1.16 V, yielding high power conversion efficiency from 7.98 to 10.64%.

Mimicking Classical Conditioning Based on a Single Flexible Memristor

The mimicking of classical conditioning, including acquisition, extinction, recovery, and generalization, can be efficiently achieved by using a single flexible memristor. In particular, the experiment of Pavlovs dog is successfully demonstrated. This demonstration paves the way for reproducing advanced neural processes and provides a frontier approach to the design of artificial-intelligence systems with dramatically reduced complexity.

Efficient tristable resistive memory based on single layer graphene/insulating polymer multi-stacking layer

Tristable resistive memories based on single layer graphene (SLG)/insulating polymer multi-stacking layer were fabricated. By using the traditional transfer method, the chemical vapor deposition-synthesized SLG serving as charging layers were combined with poly(methyl methacrylate) (PMMA) layers and polystyrene (PS) layers to form charge traps with various depth. Based on the PS/SLG/PMMA/SLG/PMMA multi-stacking layer, the devices exhibited efficient tristable memory performances. The ratios as large as 104 between different resistive states were maintained for a retention time of more than 104 s. The operation mechanisms of stepping-charging in the multi-stacking layer for the tristable resistive switching were proposed on the basis of the current-voltage analysis.