Resistive random-access memory (ReRAM) devices based on halide perovskites have recently emerged as a new class of data storage devices, where the switching materials used in these devices have attracted extensive attention in recent years. Thus far, three-dimensional (3D) halide perovskites have been the most investigated materials for resistive switching memory devices. However, 3D-based memory devices display ON/OFF ratios comparable to those of oxide or chalcogenide ReRAM devices. In addition, perovskite materials are susceptible to exposure to air. Herein, we compare the resistive switching characteristics of ReRAM devices based on a quasi-two-dimensional (2D) halide perovskite, (PEA) 2 Cs 3 Pb 4 I 13 , to those based on 3D CsPbI 3. Astonishingly, the ON/OFF ratio of the (PEA) 2 Cs 3 Pb 4 I 13-based memory devices (10 9) is three orders of magnitude higher than that of the CsPbI 3 device, which is attributed to a decrease in the high-resistance state (HRS) current of the former. This device also retained a high ON/OFF current ratio for 2 weeks under ambient conditions, whereas the CsPbI 3 device degraded rapidly and showed unreliable memory properties after 5 days. These results strongly suggest that quasi-2D halide perovskites have potential in resistive switching memory based on their desirable ON/OFF ratio and long-term stability.

Converting solar energy by photoelectrochemical water splitting has been regarded as a promising way to resolve the global energy crisis and alleviate environmental pollution. Silicon, which is earth-abundant and has a narrow band gap, is an attractive material for photoelectrochemical water splitting. However, Si-based photoelectrodes suffer from photocorrosion, which leads to instability in electrolytes and high overpotential. Herein, we have fabricated a metal–insulator–semiconductor structure of NiO x /Ni/n-Si photoanodes for highly efficient water splitting. NiO x /Ni nanoparticles, which act as well-known oxygen evolution catalysts, are deposited on the surface of silicon by facile pulsed electrodeposition. Light absorption and catalytic activity are greatly affected by the coverage of Ni nanoparticles, and the highly efficient NiO x /Ni catalyst structure is induced by simple annealing. The NiO x /Ni nanoparticles show highly enhanced charge separation and transport efficiency, which are vital factors for photoelectrochemical water splitting, leading to ∼100% Faradaic efficiency and incident photon-to-current efficiency. A low onset potential of 1.08 V versus a reversible hydrogen electrode for 1 mA/cm2 and a high photocurrent density of 14.7 mA/cm2 at 1.23 V are obtained.

Ferroelectric field effect transistors (FeFETs) have attracted attention as next-generation devices as they can serve as a synaptic device for neuromorphic implementation and a one-transistor (1T) for achieving high integration. Since the discovery of hafnium–zirconium oxide (HZO) with high ferroelectricity (even at a thickness of several nanometers) that can be fabricated by a complementary metal–oxide–semiconductor-compatible process, FeFETs have emerged as devices with great potential. In this article, the basic principles of the FeFET and the design strategies for state-of-the-art FeFETs will be discussed. FeFETs using Pb(ZrxTi1−x)O3, polyvinylidene fluoride, HZO, and two-dimensional materials are emphasized. FeFETs, ferroelectric semiconductor field effect transistors, and metal–ferroelectric–insulator–semiconductor structures to which those materials can be applied are introduced, and their exotic performances are investigated. Finally, the limitations of these devices’ current performance and the potential of these materials are presented.

Transition metal dichalcogenides (TMDs) have attracted enormous attention in diverse research fields. Especially, gas sensors are considered in a promising application exploiting TMDs. However, the studies are confined to only major TMDs such as MoS 2 and WS 2 . Particularly, the chemoresistive sensing properties of two-dimensional (2D) NbS 2 have never been explored. For the first time, we report room temperature NO 2 sensing characteristics of 2D NbS 2 nanosheets and the sensing mechanisms using first-principles calculations based on density functional theory. The results demonstrate that the NbS 2 edges possessing different configurations depending on synthetic conditions differ in the sensing ability of the TMD nanosheets. This study not only broadens the potential of 2D NbS 2 for gas sensing applications, but also presents the important role of edge configuration of TMDs depending on synthetic conditions for further studies.

Neuromorphic computing, which mimics biological neural networks, can overcome the high-power and large-throughput problems of current von Neumann computing. Two-terminal memristors are regarded as promising candidates for artificial synapses, which are the fundamental functional units of neuromorphic computing systems. All-inorganic CsPbI 3 perovskite-based memristors are feasible to use in resistive switching memory and artificial synapses due to their fast ion migration. However, the ideal perovskite phase α-CsPbI 3 is structurally unstable at ambient temperature and rapidly degrades to a non-perovskite δ-CsPbI 3 phase. Here, dual-phase (Cs 3 Bi 2 I 9 ) 0.4 −(CsPbI 3 ) 0.6 is successfully fabricated to achieve improved air stability and surface morphology compared to each single phase. Notably, the Ag/polymethylmethacrylate/(Cs 3 Bi 2 I 9 ) 0.4 −(CsPbI 3 ) 0.6 /Pt device exhibits non-volatile memory functions with an endurance of ≈10 3 cycles and retention of ≈10 4 s with low operation voltages. Moreover, the device successfully emulates synaptic behavior such as long-term potentiation/depression and spike timing/widthdependent plasticity. This study will contribute to improving the structural and mechanical stability of all-inorganic halide perovskites (IHPs) via the formation of dual phase. In addition, it proves the great potential of IHPs for use in low-power non-volatile memory devices and electronic synapses.The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adfm.201906686.femto-Joule scale. [1,2] Neuromorphic computing systems that emulate the human brain are considered promising candidates for overcoming the energy and throughput limitations of conventional von Neumann computing systems. Inspired by the human brain, neuromorphic computing systems are composed of electronic neurons and synapses, and achieve a high degree of parallelism with the physically united memory and information processing unit. Artificial synapses are fundamental functional units of neuromorphic architectures, where electrical stimuli from a pre-neuron are transmitted to a post-neuron, thereby generating updated synaptic weight (i.e., causing a conductance change in an electronic device). Notably, resistive switching (RS) memory has been actively investigated for synaptic devices due to its scalability, simple structure, fast operation speed, and low-energy consumption, which are the most important requirements for neuromorphic computing. [3,4] In the last few years, halide perovskites (HPs) with the chemical formula ABX 3 [where A is an organic or inorganic (Cs or Rb) cation, B is a divalent metal cation (Pb or Sn), and X is a halide anion (I, Cl, or Br)] have been widely investigated for RS memory and artificial synapses because of their tunable bandgaps and fast ion migration. [5][6][7] To date, organolead HPs (OHPs, A = methylammonium (MA), B = Pb, and X = I, Cl, or Br) have been successfully utilized as the active layer of memristor-based artificial synapses, emulat...