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A bendable Ag-coated hollow waveguide (HWG) based on the acrylonitrile-butadiene-styrene (ABS) tube is fabricated for low-loss transmission and imaging of low-frequency terahertz (THz) waves. ABS plastic tubing is selected since it allows growing a smooth silver (Ag) reflective film with good adhesion to the inner wall and contributes to constructing a bendable THz HWG structure. The low-loss transmission window of the ABS/Ag-coated HWG is at 0.2–1.0 THz. The attenuation characteristics of the as-prepared waveguide samples with different bore sizes (2.3, 3.2, and 4.2 mm) at 100 and 300 GHz are investigated. The 3.2-mm-bore THz waveguide exhibits good bendability and transmission performance. Its measured straight transmission loss is 1.02 dB/m at 300 GHz, and the bending loss reaches 1.56 dB/m at 150° (the curvature radius is 10 cm). Moreover, a far-field confocal waveguide-based THz imaging system is established based on the ABS/Ag-coated HWG. High-quality imaging with a super-resolution of 1.12 mm was achieved using the 3.2-mm-bore waveguide samples at 100 GHz.

Antimony selenide (Sb2Se3) thin film solar cells have gained worldwide intense research owing to their suitable bandgap, high absorption coefficient, benign grain boundaries, earth-abundant element constituents and low fabrication cost. It is extremely important to investigate the interface passivation and minimize the carrier recombination to realize high-efficiency Sb2Se3solar cells. Very little is known, however, about the carrier recombination mechanisms at the interfaces of Sb2Se3solar cells. Herein, we show that a novel solution-processed SnO2layer (∼12 nm) incorporated into Sb2Se3thin film solar cells results in high power conversion efficiency of 7.5%, namely, an improvement of 39% relative to that of the solar cell without SnO2interfacial layer. Furthermore, the open-circuit voltage (Voc) is the highest ever reported for Sb2Se3solar cells. These improvements benefit from the better preferred [221] orientation, less bulk and interfacial defects in the Sb2Se3absorbers, and relatively ideal heterointerfaces due to the SnO2passivation. This work opens up new routes for the critical importance of interfacial control in Sb2Se3solar cells, which could be extended to other emerging low-dimensional thin film solar cells.

The triple-cation mixed halide perovskite Cs0.05(MA0.17FA0.83)0.95Pb(I0.83Br0.17)3emerges as one of the most promising candidates for photovoltaics due to superior optoelectronic properties, but the thermal stability is still a major challenge for the viability of perovskite solar cells towards commercialization. Herein, we firstly explore the thermal response of the photovoltaic performances to access device physical changes. It is shown that the efficiency loss originates from decreased charge mobility, increased trap density and generation of PbI2charge recombination centers near the interface. In-depth analysis of evolutions in morphology, chemical composition, dynamic and electronic structure of the perovskite layer at the nanometer scales indicates that it is initial dangling bonds and vacancies on the imperfect surfaces decrease the activation energy and cause the perovskite decomposition in a layer-by-layer pathway sequentially from the film surface to bulk. Based on the results, a strategy of surface passivation to improve the thermal stability is demonstrated and discussed. This work for the first time provides insights into the physical and chemical change of such triple-cation perovskite and indicates that more effort should be invested in surface treatment for enhancing perovskite device stability.

The authors demonstrate a robust memcapacitor by stacking a ferroelectric capacitor on a metal‐insulator‐semiconductor structure. In‐memory vector‐matrix multiplication is achieved using a ferroelectric memcapacitor array. During the in‐memory computing, it intrinsically consumes zero energy in memcapacitors themselves. It sheds light on an ultralow‐power neuromorphic hardware based on ferroelectric memcapacitors.

Analog storage through synaptic weights using conductance in resistive neuromorphic systems and devices inevitably generates harmful heat dissipation. This thermal issue not only limits the energy efficiency but also hampers the very‐large‐scale and highly complicated hardware integration as in the human brain. Here we demonstrate that the synaptic weights can be simulated by reconfigurable non‐volatile capacitances of a ferroelectric‐based memcapacitor with ultralow‐power consumption. The as‐designed metal/ferroelectric/metal/insulator/semiconductor memcapacitor shows distinct 3‐bit capacitance states controlled by the ferroelectric domain dynamics. These robust memcapacitive states exhibit uniform maintenance of more than 104s and well endurance of 109cycles. In a wired memcapacitor crossbar network hardware, analog vector‐matrix multiplication is successfully implemented to classify 9‐pixel images by collecting the sum of displacement currents (I= C× dV/dt) in each column, which intrinsically consumes zero energy in memcapacitors themselves. Our work sheds light on an ultralow‐power neural hardware based on ferroelectric memcapacitors. We demonstrate a robust memcapacitor by stacking ferroelectric capacitor on the metal‐insulator‐semiconductor structure. It possesses a long retention time of more than 104s and well endurance of 109cycles. Ultralow‐power in‐memory computing based on ferroelectric memcapacitor array intrinsically consumes zero energy in memcapacitors themselves. It sheds light on an ultralow‐power neural hardware based on ferroelectric memcapacitors.

Imitating the associative intelligence of the biological brain is attractive but is poorly achieved in hardware because the complex tunable connection in neural networks is difficult to reproduce. We develop a circuit composed of a three-terminal memristor network to reproduce the biological conditioning process artificially. The synaptic weight between co-firing neurons is strengthened simultaneously by generating a feedback signal from the integrate-and-fire neuron to the gate of the synaptic memristor. The network allows the multi-associative capacity of recalling more than one digit in one circuit. Both single and multi-associative learning for recalling digital images are achieved. Furthermore, all 10 digital images from “0” to “9” are successfully recalled in an associative network with such paralleling circuits. Assisted by this associative layer, a typical classification network effectively improves the recognition rate for fragmentary digital images. Our work sheds light on brain-inspired artificial associative memory and provides a strategy for applications, such as object recognition with partial features and similar scenes.

Stainless steel (SUS) capillary tubes were examined as a category of structural tube for establishing a metallic attenuated total reflection (ATR) GeO_2 hollow waveguide. GeO_2 films were grown on the inner wall of SUS tubes by different liquid phase deposition (LPD) cycles. Fourier transform infrared (FTIR) spectra, scanning electronic microscope (SEM) image, and transmission loss for a CO_2 laser were measured to investigate the effects of the LPD cycles on the transmission behavior of the hollow waveguide samples. The film thickness and surface roughness increase with every LPD cycle. The two LPD cycle sample has a film thickness equivalent to the CO_2 laser wavelength, while the surface roughness is acceptable. This sample has the lowest transmission loss (0.27  dB/m) among these samples. The bending loss, output beam profile, and full divergence angle (FDA) were further studied. Higher-order modes are excited by bending the sample, inducing additional loss, decentralized beam profile, and larger FDA.

Searching van der Waals ferroic materials that can work under ambient conditions is of critical importance for developing ferroic devices at the two-dimensional limit. Here we report the experimental discovery of electric-field-induced reversible antiferroelectric (AFE) to ferroelectric (FE) transition at room temperature in van der Waals layered α-GeSe, employing Raman spectroscopy, transmission electron microscopy, second-harmonic generation, and piezoelectric force microscopy consolidated by first-principles calculations. An orientation-dependent AFE–FE transition provides strong evidence that the in-plane (IP) polarization vector aligns along the armchair rather than zigzag direction in α-GeSe. In addition, temperature-dependent Raman spectra showed that the IP polarization could sustain up to higher than 700 K. Our findings suggest that α-GeSe, which is also a potential ferrovalley material, could be a robust building block for creating artificial 2D multiferroics at room temperature.