2D Ferroionics: Conductive Switching Mechanisms and Transition Boundaries in Van der Waals Layered Material CuInP2 S6.

The recently unfolded ferroionic phenomena in 2D van der Waals (vdW) copper-indium-thiophosphate (CuInP2 S6 or CIPS) have received widespread interest as they allow for dynamic control of conductive switching properties, which are appealing in the paradigm-shift computing. The intricate couplings between ferroelectric polarization and ionic conduction in 2D vdW CIPS facilitate the manipulation and dynamic control of conductive behaviors. However, the complex interplays and underlying mechanisms are not yet fully explored and understood. Here, by investigating polarization switching and ionic conduction in the temperature and applied electric field domains, it is discovered that the conducting mechanisms of CIPS can be divided into four distinctive states (or modes) with transitional boundaries, depending on the dynamics of Cu ions in the material. Further, it demonstrates that dynamically-tunable synaptic responsive behavior can be well implemented by governing the working-state transition. This research provides an in-depth, quantitative understanding of the complex phenomena of conductive switching in 2D vdW CIPS with coexisting ferroelectric order and ionic disorder. The developed insights in this work lay the ground for implementing high-performance, function-enriched devices for information processing, data storage, and neuromorphic computing based on the 2D ferroionic material systems.

Photosensitive Dielectric 2D Perovskite Based Photodetector for Dual Wavelength Demultiplexing.

Stacked 2D perovskites provide more possibilities for next generation photodetector with more new features. Compared with its excellent optoelectronic properties, the good dielectric performance of metal halide perovskite rarely comes into notice. Here, a bifunctional perovskite based photovoltaic detector capable of two wavelength demultiplexing is demonstrated. In the Black Phosphorus/Perovskite/MoS2 structured photodetector, the comprehensive utilization of the photosensitive and dielectric properties of 2D perovskite allows the device to work in different modes. The device shows normal continuous photoresponse under 405 nm, while it shows a transient spike response to visible light with longer wavelengths. The linear dynamic range, rise/decay time, and self-powered responsivity under 405 nm can reach 100, 38 µs/50 µs, and 17.7 mA W-1 , respectively. It is demonstrated that the transient spike photocurrent with long wavelength exposure is related to the illumination intensity and can coexist with normal photoresponse. Two waveband-dependent signals can be identified and used to reflect more information simultaneously. This work provides a new strategy for multispectral detection and demultiplexing, which can be used to improve data transfer rates and encrypted communications. This work mode can inspire more multispectral photodetectors with different stacked 2D materials, especially to the optoelectronic application of the wide bandgap, high dielectric photosensitive materials.

Ultraviolet photodetector based on RbCu2I3microwire.

Copper-based halide perovskites have shown great potential in lighting and photodetection due to their excellent photoelectric properties, good stability and lead-free nature. However, as an important piece of copper-based perovskites, the synthesis and application of RbCu2I3have never been reported. Here, we demonstrate the synthesis of high-quality RbCu2I3microwires (MWs) by a fast-cooling hot saturated solution method. The prepared MWs exhibit an orthorhombic structure with a smooth surface. Optical measurements show the RbCu2I3MWs have a sharp ultraviolet absorption edge with 3.63 eV optical band gap and ultra-large stokes shift (300 nm) in photoluminescence. The subsequent photodetector based on a single RbCu2I3MW shows excellent ultraviolet detection performance. Under the 340 nm illumination, the device shows a specific detectivity of 5.0 × 109Jones and a responsivity of 380 mA·W-1. The synthesis method and physical properties of RbCu2I3could be a guide to the future optoelectronic application of the new material.

High-performance flexible UV photodetector based on self-supporting ZnO nano-networks fabricated by substrate-free chemical vapor deposition.

Self-supporting ZnO nano-networks have been demonstrated by a substrate-free chemical vapor deposition process for the application as flexible ultraviolet (UV) photodetector. The device shows a responsivity of ∼300 mA W-1over a wide wavelength range from 254 to 365 nm and a high UV/visible rejection ratio of more than 104. More interestingly, a short 90%-10% decay time of <0.12 s can be observed in the air atmosphere, and the current can fully recover to its original dark value within 1 s after switching off the light. The quick response speed should be associated with the wire-wire junction barriers and the adsorption/desorption process of oxygen molecules on the oxygen vacancies near the surface of the ZnO. In addition, the photocurrent, the dark current and the response speed of the ZnO nano-networks flexible UV photodetector nearly stay the same under different bending conditions, suggesting the excellent photoelectric stability and repeatability. Such a simple and cheap way for fabricating self-supporting ZnO-based devices has broad application prospects in the fields of flexible and wearable electronic devices.