Over the past years, the application potential of ferroelectric nanomaterials with unique physical properties for modern electronics is highlighted to a large extent. However, it is relatively challenging to fabricate inorganic ferroelectric nanomaterials, which is a process depending on a vacuum atmosphere at high temperatures. As significant complements to inorganic ferroelectric nanomaterials, the nanomaterials of molecular ferroelectrics are rarely reported. Here a low-cost room-temperature antisolvent method is used to synthesize free-standing 2D organic-inorganic hybrid perovskite (OIHP) ferroelectric nanosheets (NSs), that is, (CHA)2PbBr4 NSs (CHA = cyclohexylammonium), with an average lateral size of 357.59 nm and a thickness ranging from 10 to 70 nm. This method shows high repeatability and produces NSs with excellent crystallinity. Moreover, ferroelectric domains in single NSs can be clearly visualized and manipulated using piezoresponse force microscopy (PFM). The domain switching and PFM-switching spectroscopy indicate the robust in-plane ferroelectricity of the NSs. This work not only introduces a feasible, low-cost, and scalable method for preparing molecular ferroelectric NSs but also promotes the research on molecular ferroelectric nanomaterials.
Realizing room-temperature magnetic skyrmions in two-dimensional van der Waals ferromagnets offers unparalleled prospects for future spintronic applications. However, due to the intrinsic spin fluctuations that suppress atomic long-range magnetic order and the inherent inversion crystal symmetry that excludes the presence of the Dzyaloshinskii-Moriya interaction, achieving room-temperature skyrmions in 2D magnets remains a formidable challenge. In this study, we target room-temperature 2D magnet Fe3GaTe2 and unveil that the introduction of iron-deficient into this compound enables spatial inversion symmetry breaking, thus inducing a significant Dzyaloshinskii-Moriya interaction that brings about room-temperature Néel-type skyrmions with unprecedentedly small size. To further enhance the practical applications of this finding, we employ a homemade in-situ optical Lorentz transmission electron microscopy to demonstrate ultrafast writing of skyrmions in Fe3-xGaTe2 using a single femtosecond laser pulse. Our results manifest the Fe3-xGaTe2 as a promising building block for realizing skyrmion-based magneto-optical functionalities.
Serious open-circuit voltage (Voc) loss originating from nonradiative recombination and mismatch energy level at TiO2/perovskite buried interface dramatically limits the photovoltaic performance of all-inorganic CsPbIxBr3-x (x = 1, 2) perovskite solar cells (PSCs) fabricated through low-temperature methods. Here, an ionic liquid (IL) bridge is constructed by introducing 1-butyl-3-methylimidazolium acetate (BMIMAc) IL to treat the TiO2/perovskite buried interface, bilaterally passivate defects and modulate energy alignment. Therefore, the Voc of all-inorganic CsPbIBr2 PSCs modified by BMIMAc (Target-1) significantly increases by 148 mV (from 1.213 to 1.361 V), resulting in the efficiency increasing to 10.30% from 7.87%. Unsealed Target-1 PSCs show outstanding long-term and thermal stability. During the accelerated degradation process (85 °C, RH: 50â¼60%), the Target-1 PSCs achieve a champion PCE of 11.94% with a remarkable Voc of 1.403 V, while the control PSC yields a promising PCE of 10.18% with a Voc of 1.319 V. In particular, the Voc of 1.403 V is the highest Voc reported so far in carbon-electrode-based CsPbIBr2 PSCs. Moreover, this strategy enables the modified all-inorganic CsPbI2Br PSCs to achieve a Voc of 1.295 V and a champion efficiency of 15.20%, which is close to the reported highest PCE of 15.48% for all-inorganic CsPbI2Br PSCs prepared by a low-temperature process. This study provides a simple BMIMAc IL bridge to assist bifacial defect passivation and elevate the photovoltaic performance of all-inorganic CsPbIxBr3-x (x = 1, 2) PSCs.
Flexible perovskite solar cells (F-PSCs) have emerged as promising alternatives to conventional silicon solar cells for applications in portable and wearable electronics. However, the mechanical stability of inherently brittle perovskite, due to residual lattice stress and ductile fracture formation, poses significant challenges to the long-term photovoltaic performance and device lifetime. In this paper, to address this issue, a dynamic "ligament" composed of supramolecular poly(dimethylsiloxane) polyurethane (DSSP-PPU) is introduced into the grain boundaries of the PSCs, facilitating the release of residual stress and softening of the grain boundaries. Remarkably, this dynamic "ligament" exhibits excellent self-healing properties and enables the healing of cracks in perovskite films at room temperature. The obtained PSCs have achieved power conversion efficiencies of 23.73% and 22.24% for rigid substrates and flexible substrates, respectively, also 17.32% for flexible mini-modules. Notably, the F-PSCs retain nearly 80% of their initial efficiency even after subjecting the F-PSCs to 8000 bending cycles (r = 2 mm), which can further recover to almost 90% of the initial efficiency through the self-healing process. This remarkable improvement in device stability and longevity holds great promise for extending the overall lifetime of F-PSCs.
Magnetic skyrmions are topologically protected swirling spin textures with great potential for future spintronic applications. The ability to induce skyrmion motion using mechanical strain not only stimulates the exploration of exotic physics but also affords the opportunity to develop energy-efficient spintronic devices. However, the experimental realization of strain-driven skyrmion motion remains a formidable challenge. Herein, we demonstrate that the inhomogeneous uniaxial compressive strain can induce the movement of isolated skyrmions from regions of high strain to regions of low strain at room temperature, which was directly observed using an in situ Lorentz transmission electron microscope with a specially designed nanoindentation holder. We discover that the uniaxial compressive strain can transform skyrmions into a single domain with in-plane magnetization, resulting in the coexistence of skyrmions with a single domain along the direction of the strain gradient. Through comprehensive micromagnetic simulations, we reveal that the repulsive interactions between skyrmions and the single domain serve as the driving force behind the skyrmion motion. The precise control of skyrmion motion through strain provides exciting opportunities for designing advanced spintronic devices that leverage the intricate interplay between strain and magnetism.
The deterministic creation and modification of domain walls in ferroelectric films have attracted broad interest due to their unprecedented potential as the active element in non-volatile memory, logic computation and energy-harvesting technologies. However, the correlation between charged and antiphase states, and their hybridization into a single domain wall still remain elusive. Here we demonstrate the facile fabrication of antiphase boundaries in BiFeO3 thin films using a He-ion implantation process. Cross-sectional electron microscopy, spectroscopy and piezoresponse force measurement reveal the creation of a continuous in-plane charged antiphase boundaries around the implanted depth and a variety of atomic bonding configurations at the antiphase interface, showing the atomically sharp 180° polarization reversal across the boundary. Therefore, this work not only inspires a domain-wall fabrication strategy using He-ion implantation, which is compatible with the wafer-scale patterning, but also provides atomic-scale structural insights for its future utilization in domain-wall nanoelectronics.
Rhenium disulfide (ReS2) is a promising piezoelectric catalyst due to its excellent electron transfer ability and abundant unsaturated sites. The 1T' phase structure leads to the evolution of ReS2 into a centrosymmetric spatial structure, which restricts its application in piezoelectric catalysis. Herein, we propose a controllable defect engineering strategy to trigger the piezoelectric response of ReS2. The introduction of vacancy defects disrupts the initial centrosymmetric structure, which breaks the piezoelectric polarization bond and generates piezoelectric properties. By using transmission electron microscopy, we characterized it at the atomic scale and determined that vacancy defects contribute to an excellent piezoelectric property through first-principles calculations. Notably, the piezoelectric coefficient of the catalyst with 40 s-etching (ReS2@C-40) is 23.07 pm/V, an order of magnitude greater than other transition metal dichalcogenides. It demonstrated the feasibility of optimizing piezoelectric properties by increasing the conformational asymmetry. Based on its remarkable piezoelectric activity, ReS2@C-40 exhibits highly efficient piezo-photocatalytic synergistic sterilization performance with 99.99% eradication of Escherichia coli and 96.67% of Staphylococcus aureus within 30 min. This pioneering research on the coupling effect of ReS2 in piezoelectric catalysis and photocatalysis provides ideas for the development of piezo-photocatalysts and efficient water purification technologies.
Tin-based perovskite solar cells (T-PSCs) have become the star photovoltaic products in recent years due to their low environmental toxicity and superior photovoltaic performance. However, the easy oxidation of Sn2+ and the energy level mismatch between the perovskite film and charge transport layer limit its efficiency. In order to regulate the microstructure and photoelectric properties of tin-based perovskite films to enhance the efficiency and stability of T-PSCs, guanidinium bromide (GABr) and organic Lewis-based additive methylamine cyanate (MAOCN) are introduced into the FA0.9PEA0.1SnI3-based perovskite precursor. A series of characterizations show that the interactions between additive molecules and perovskite mutually reconcile to improve the photovoltaic performance of T-PSCs. The introduction of GABr can adjust the band gap of the perovskite film and energy level alignment of T-PSCs. They significantly increase the open-circuit voltage (Voc). The MAOCN material can form hydrogen bonds with SnI2 in the precursor, which can inhibit the oxidation of Sn2+ and significantly improve the short-circuit current density (Jsc). The synergistic modulation of the dual additives reduces the trap-state density and improves photovoltaic performance, resulting in an increased champion efficiency of 9.34 for 5.22% of the control PSCs. The unencapsulated T-PSCs with GABr and MAOCN dual additives prepared in the optimized process can retain more than 110% of their initial efficiency after aging for 1750 h in a nitrogen glovebox, but the control PSCs maintain only 50% of their initial efficiency kept in the same conditions. This work provides a new perspective to further improve the efficiency and stability of T-PSCs.
The van der Waals (vdW) ferromagnet Fe3-δ GeTe2 has garnered significant research interest as a platform for skyrmionic spin configurations, that is, skyrmions and skyrmionic bubbles. However, despite extensive efforts, the origin of the Dzyaloshinskii-Moriya interaction (DMI) in Fe3-δ GeTe2 remains elusive, making it challenging to acquire these skyrmionic phases in a controlled manner. In this study, it is demonstrated that the Fe content in Fe3-δ GeTe2 has a profound effect on the crystal structure, DMI, and skyrmionic phase. For the first time, a marked increase in Fe atom displacement with decreasing Fe content is observed, transforming the original centrosymmetric crystal structure into a non-centrosymmetric symmetry, leading to a considerable DMI. Additionally, by varying the Fe content and sample thickness, a controllable transition between Néel-type skyrmions and Bloch-type skyrmionic bubbles is achieved, governed by a delicate interplay between dipole-dipole interaction and the DMI. The findings offer novel insights into the variable skyrmionic phases in Fe3-δ GeTe2 and provide the impetus for developing vdW ferromagnet-based spintronic devices.
Tin-based perovskite solar cells (TPSCs) have become one of the most prospective photovoltaic materials due to their remarkable optoelectronic properties and relatively low toxicity. Nevertheless, the rapid crystallization of perovskites and the easy oxidization of Sn2+ to Sn4+ make it challenging to fabricate efficient TPSCs. In this work, a piperazine iodide (PI) material with -NH- and -NH2+- bifunctional groups is synthesized and introduced into the PEA0.1FA0.9SnI3-based precursor solution to tune the microstructure, charge transport, and stability of TPSCs. Compared with piperazine (PZ) containing only the -NH- group, the PI additive displays better effects on regulating the microstructure and crystallization, inhibiting Sn2+ oxidation and reducing trap states, resulting in an optimal efficiency of 10.33%. This is substantially better than that of the reference device (6.42%). Benefiting from the fact that PI containing -NH- and -NH2+- groups can passivate both positively charged defects and negatively charged halogen defects, unencapsulated TPSCs modified with the PI material can maintain about 90% of their original efficiency after being kept in a N2 atmosphere for 1000 h, much higher than the value of 47% in reference TPSCs without additives. This work provides a practical method to prepare efficient and stable pure TPSCs.
Reservoir computing (RC) offers efficient temporal information processing with low training cost. All-ferroelectric implementation of RC is appealing because it can fully exploit the merits of ferroelectric memristors (e.g., good controllability); however, this has been undemonstrated due to the challenge of developing ferroelectric memristors with distinctly different switching characteristics specific to the reservoir and readout network. Here, we experimentally demonstrate an all-ferroelectric RC system whose reservoir and readout network are implemented with volatile and nonvolatile ferroelectric diodes (FDs), respectively. The volatile and nonvolatile FDs are derived from the same Pt/BiFeO3/SrRuO3 structure via the manipulation of an imprint field (Eimp). It is shown that the volatile FD with Eimp exhibits short-term memory and nonlinearity while the nonvolatile FD with negligible Eimp displays long-term potentiation/depression, fulfilling the functional requirements of the reservoir and readout network, respectively. Hence, the all-ferroelectric RC system is competent for handling various temporal tasks. In particular, it achieves an ultralow normalized root mean square error of 0.017 in the Hénon map time-series prediction. Besides, both the volatile and nonvolatile FDs demonstrate long-term stability in ambient air, high endurance, and low power consumption, promising the all-ferroelectric RC system as a reliable and low-power neuromorphic hardware for temporal information processing.
Cognition , Long-Term Potentiation , Memory, Short-Term , Neuronal Plasticity , Nutritional Status
The construction of type-II or S-scheme heterojunctions can effectively accelerate the directional migration of charge carriers and inhibit the recombination of electron-hole pairs to improve the catalytic performance of the composite catalyst; therefore, the construction and formation mechanism of a heterojunction are worth further investigation. Herein, Cu2O@Cu4(SO4)(OH)6·H2O core-shell polyhedral heterojunctions were fabricated via in situ etching Cu2O with octahedral, cuboctahedral, and cubic shapes by sodium thiosulfate (Na2S2O3). Cu2O@Cu4(SO4)(OH)6·H2O polyhedral heterojunctions demonstrated obviously enhanced sterilization and degradation performance than the corresponding single Cu2O polyhedra and Cu4(SO4)(OH)6·H2O. When Cu2O with a different morphology contacts with Cu4(SO4)(OH)6·H2O, a built-in electric field is established at the interface due to the difference in Fermi level (Ef); meanwhile, the direction of band bending and the band alignment are determined. These lead to the different migration pathways of electrons and holes, and thereby, a type-II or S-scheme heterojunction is constructed. The results showed that octahedral o-Cu2O@Cu4(SO4)(OH)6·H2O is an S-scheme heterojunction; however, cuboctahedral co-Cu2O@Cu4(SO4)(OH)6·H2O and cubic c-Cu2O@Cu4(SO4)(OH)6·H2O are type-II heterojunctions. By means of X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), diffuse reflectance spectra (DRS), and Mott-Schottky analyses, the band alignments, Fermi levels, and band offsets (ΔECB, ΔEVB) of Cu2O@Cu4(SO4)(OH)6·H2O polyhedral heterojunctions were estimated; the results indicated that the catalytic ability of the composite catalyst is determined by the type of heterojunction and the sizes of band offsets. Cubic c-Cu2O@Cu4(SO4)(OH)6·H2O has the strongest driving force (namely, biggest band offsets) to accelerate charge migration and effectively separate charge carriers, so it exhibits the strongest catalytic bactericidal and degrading abilities.
Piezo-electrocatalysis as an emerging mechano-to-chemistry energy conversion technique opens multiple innovative opportunities and draws great interest over the past decade. However, the two potential mechanisms in piezo-electrocatalysis, i.e., screening charge effect and energy band theory, generally coexist in the most piezoelectrics, making the essential mechanism remain controversial. Here, for the first time, the two mechanisms in piezo-electrocatalytic CO2 reduction reaction (PECRR) is distinguished through a narrow-bandgap piezo-electrocatalyst strategy using MoS2 nanoflakes as demo. With conduction band of -0.12 eV, the MoS2 nanoflakes are unsatisfied for CO2 -to-CO redox potential of -0.53 eV, yet they achieve an ultrahigh CO yield of ≈543.1 µmol g-1 h-1 in PECRR. Potential band position shifts under vibration are still unsatisfied with CO2 -to-CO potential verified by theoretical investigation and piezo-photocatalytic experiment, further indicating that the mechanism of piezo-electrocatalysis is independent of band position. Besides, MoS2 nanoflakes exhibit unexpected intense "breathing" effect under vibration and enable the naked-eye-visible inhalation of CO2 gas, independently achieving the complete carbon cycle chain from CO2 capture to conversion. The CO2 inhalation and conversion processes in PECRR are revealed by a self-designed in situ reaction cell. This work brings new insights into the essential mechanism and surface reaction evolution of piezo-electrocatalysis.
Precise manipulation of skyrmion nucleation in microscale or nanoscale areas of thin films is a critical issue in developing high-efficient skyrmionic memories and logic devices. Presently, the mainstream controlling strategies focus on the application of external stimuli to tailor the intrinsic attributes of charge, spin, and lattice. This work reports effective skyrmion manipulation by controllably modifying the lattice defect through ion implantation, which is potentially compatible with large-scale integrated circuit technology. By implanting an appropriate dose of nitrogen ions into a Pt/Co/Ta multilayer film, the defect density was effectively enhanced to induce an apparent modulation of magnetic anisotropy, consequently boosting the skyrmion nucleation. Furthermore, the local control of skyrmions in microscale areas of the macroscopic film was realized by combining the ion implantation with micromachining technology, demonstrating a potential application in both binary storage and multistate storage. These findings provide a new approach to advancing the functionalization and application of skyrmionic devices.
Ferroelectrics with negative capacitance effects can amplify the gate voltage in field-effect transistors to achieve low power operation beyond the limits of Boltzmann's Tyranny. The reduction of power consumption depends on the capacitance matching between the ferroelectric layer and gate dielectrics, which can be well controlled by adjusting the negative capacitance effect in ferroelectrics. However, it is a great challenge to experimentally tune the negative capacitance effect. Here, the observation of the tunable negative capacitance effect in ferroelectric KNbO3 through strain engineering is demonstrated. The magnitude of the voltage reduction and negative slope in polarization-electric field (P-E) curves as the symbol of negative capacitance effects can be controlled by imposing various epitaxial strains. The adjustment of the negative curvature region in the polarization-energy landscape under different strain states is responsible for the tunable negative capacitance. Our work paves the way for fabricating low-power devices and further reducing energy consumption in electronics.
Skyrmions are swirling spin textures with topological characters promising for future spintronic applications. Skyrmionic devices typically rely on the electrical manipulation of skyrmions with a circular shape. However, manipulating elliptically distorted skyrmions can lead to numerous exotic magneto-electrical functions distinct from those of conventional circular skyrmions, significantly broadening the capability to design innovative spintronic devices. Despite the promising potential, its experimental realization so far remains elusive. In this study, the current-driven dynamics of the elliptically distorted skyrmions in geometrically confined magnet Fe3 Sn2 is experimentally explored. This study finds that the elliptical skyrmions can reversibly split into smaller-sized circular skyrmions at a current density of 3.8 × 1010 A m-2 with the current injected along their minor axis. Combined experiments with micromagnetic simulations reveal that this dynamic behavior originates from a delicate interplay of the spin-transfer torque, geometrical confinement, and pinning effect, and strongly depends on the ratio of the major axis to the minor axis of the elliptical skyrmions. The results indicate that the morphology is a new degree of freedom for manipulating the current-driven dynamics of skyrmions, providing a compelling route for the future development of spintronic devices.
Nowadays many semantic segmentation algorithms have achieved satisfactory accuracy on von Neumann platforms (e.g., GPU), but the speed and energy consumption have not meet the high requirements of certain edge applications like autonomous driving. To tackle this issue, it is of necessity to design an efficient lightweight semantic segmentation algorithm and then implement it on emerging hardware platforms with high speed and energy efficiency. Here, we first propose an extremely factorized network (EFNet) which can learn multi-scale context information while preserving rich spatial information with reduced model complexity. Experimental results on the Cityscapes dataset show that EFNet achieves an accuracy of 68.0% mean intersection over union (mIoU) with only 0.18M parameters, at a speed of 99 frames per second (FPS) on a single RTX 3090 GPU. Then, to further improve the speed and energy efficiency, we design a memristor-based computing-in-memory (CIM) accelerator for the hardware implementation of EFNet. It is shown by the simulation in DNN+NeuroSim V2.0 that the memristor-based CIM accelerator is â¼63× (â¼4.6×) smaller in area, at most â¼9.2× (â¼1000×) faster, and â¼470× (â¼2400×) more energy-efficient than the RTX 3090 GPU (the Jetson Nano embedded development board), although its accuracy slightly decreases by 1.7% mIoU. Therefore, the memristor-based CIM accelerator has great potential to be deployed at the edge to implement lightweight semantic segmentation models like EFNet. This study showcases an algorithm-hardware co-design to realize real-time and low-power semantic segmentation at the edge.
Automobile Driving , Semantics , Algorithms , Computer Simulation , Learning
The poor interfacial contact and imperfections between the charge transport layer and perovskite film often result in carrier recombination, inefficient charge collection, and inferior stability of perovskite solar cells (PSCs). Therefore, interface engineering is quite crucial to achieve high-performance and stable PSCs. Here, we introduced a cinnamate-functionalized cellulose nanocrystals (Cin-CNCs) interfacial layer between SnO2 and perovskite active layer for enhancing carrier transport ability and crystal growth of perovskite, meanwhile endowing additional functional of long-term device stability against ultraviolet light. The enhancement of interfacial contact between SnO2 and perovskite layer and cascade energy alignment are realized, which is beneficial for obtaining the desirable perovskite film morphology, passivating the interfacial defects, and restraining charge recombination in the SnO2/perovskite interface. An efficiency as high as 23.18%, with an open-circuit voltage of 1.15 V and a significantly enhanced fill factor of 81.07%, is achieved. In addition, the unencapsulated PSCs maintain 75% of the initial PCE after aging for over 1500 h under 25 °C and 30% relative humidity, with better light-soaking stability. These results exhibit the vital role for Cin-CNCs in interfacial modification and constructing high-performance perovskite solar cells.
Poly (3-hexylthiophene) (P3HT) is one of the most attractive hole transport materials (HTMs) for the pursuit of stable, low-cost, and high-efficiency perovskite solar cells (PSCs). However, the poor contact and the severe recombination at P3HT/perovskite interface lead to a low power conversion efficiency (PCE). Thus, we construct a molecular bridge, 2-((7-(4-(bis(4-methoxyphenyl)amino)phenyl)-10-(2-(2-ethoxyethoxy)ethyl)-10H-phenoxazin-3-yl)methylene)malononitrile (MDN), whose malononitrile group can anchor the perovskite surface while the triphenylamine group can form π-π stacking with P3HT, to form a charge transport channel. In addition, MDN is also found effectively passivate the defects and reduce the recombination to a large extent. Finally, a PCE of 22.87% has been achieved with MDN-doped P3HT (M-P3HT) as HTM, much higher than the efficiency of PSCs with pristine P3HT. Furthermore, MDN gives the un-encapsulated device enhanced long-term stability that 92% of its initial efficiency maintain even after two months of aging at 75% relative humidity (RH) follow by one month of aging at 85% RH in the atmosphere, and the PCE does not change after operating at the maximum power point (MPP) under 1 sun illumination (~45 oC in N2) over 500 hours.
BiFeO3-BaTiO3 (BF-BT) dielectric ceramics are receiving more and more concern for advanced energy storage devices owing to their excellent ferroelectric properties and environmental sustainability. However, the energy density and efficiency are limited in spite of the large remanent polarization. Herein, we proposed a multiscale optimization strategy via a local compositional disorder with a Birich content and nanodomain engineering by introducing the Sr0.7Bi0.2Ca0.1TiO3 (SBCT) into BF-BT ceramics. Interestingly, an extraordinary energy storage property (ESP) with a high reversible energy storage density (Wrec) of â¼3.79 J/cm3 and an ultrahigh polarization discrepancy (ΔP) of â¼58.5 µC/cm2 were obtained in the SBCT-modified BF-BT ceramics under 160 kV/cm. The boosted ESP should be attributed to the fact that the replacement of A/B-sites cations could transform the long-range ferroelectric order of the BF-BT system into polar nanoregions (PNRs) along with the refined grain size, decreased leakage current, and broadened energy band gap. Moreover, good frequency (1-103 Hz) and temperature (25-125 °C) stabilities, high fatigue resistance (× 105), large power density (â¼31.1 MW/cm3), and fast discharge time (â¼97 ns) were also observed for the optimized ceramics. These results illustrate a potentially effective method for creating high ESP lead-free ceramics at a low electric field.
