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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)2Cs3Pb4I13, to those based on 3D CsPbI3. Astonishingly, the ON/OFF ratio of the (PEA)2Cs3Pb4I13-based memory devices (109) is three orders of magnitude higher than that of the CsPbI3 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 CsPbI3 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. Memory technology: Organic tricks improve stability A type of computer memory that stores data by changing the resistance of insulating crystals can be made more durable with organic chemical additives. Resistive memory devices constructed from inorganic crystals known as halide perovskites are inexpensive and have minimal power requirements. However, they can degrade quickly in humid conditions. Hyojung Kim from Seoul National University in South Korea and colleagues now report that these stability issues can be improved by sandwiching thin layers of aromatic hydrocarbons between halide perovskite crystals. The water-repelling nature of the organic molecules helps double the lifespan of the new hybrid compared to an unmodified halide perovskite device. In addition, the organic layers augment the differences between 'ON' and 'OFF' resistive memory states, making device operation more reliable. ReRAM devices based on halide perovskites have recently emerged as a new class of data storage device, where the switching materials used in these devices have attracted huge attention in recent years. In this study, we compare the resistive switching characteristics of ReRAM devices based on a quasi-2D halide perovskite, (PEA)2Cs3Pb4I13, to those based on 3D CsPbI3. Astonishingly, the ON/OFF ratio of the (PEA)2Cs3Pb4I13-based memory devices was much higher than that of the CsPbI3 device. Also this device retained a high ON/OFF current ratio for two weeks under ambient conditions, whereas the CsPbI3 device degraded rapidly and showed unreliable memory properties after five days. We strongly believe that quasi-2D halide perovskites have potential in resistive switching memory based on their high ON/OFF ratio and long-term stability. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) perovskites have gained much attention lately owing to their excellent optoelectronic properties, chemical tunability, and environmental stability. Multiple methods have been devised to synthesize high quality 2D perovskite single crystals, and recent progress in fabricating its heterostructures is notable as well. In particular, with growing interest in 2D van der Waals heterostructures, 2D perovskites have become a strong candidate as a new building block for heterostructures to reveal unique physical properties across different interfaces. Until now, various heterostructure devices of 2D perovskite single crystals with other types of 2D materials such as transition metal dichalcogenides (TMDs) and graphene have been studied, which have shown intriguing results including interlayer excitons and enhanced electronic properties. Here, we introduce various synthetic approaches to realize 2D perovskite single crystals and unique characteristics of their single crystal heterostructures fabricated with precision, possessing sharp interfaces. Moreover, recent studies of semiconductor devices based on 2D perovskite single crystal heterostructures are discussed in-depth. New perspectives to further the horizon in the field of 2D perovskite heterostructures are suggested in this work including the consideration of metal–2D material van der Waals contact, application of dry transfer techniques, electric bias driven ion diffusion studies, and nanocrystal array fabrication. 2D perovskite heterostructure single crystal devices factoring in these novel perspectives will further uncover the true potential of these materials for highly efficient and stable semiconductor devices. [ABSTRACT FROM AUTHOR]

Resistive switching (RS) memory devices are gaining recognition as data storage devices due to the significant interest in their switching material, Halide perovskite (HP). The electrical characteristics include hysteresis in its current–voltage (I–V) relationship. It can be attributed to the production and migration of defects. This property allows HPs to be used as RS materials in memory devices. However, 3D HPs are vulnerable to moisture and the surrounding environment, making their devices more susceptible to deterioration. The potential of two-dimensional (2D)/quasi-2D HPs for optoelectronic applications has been recognized, making them a viable alternative to address current restrictions. Two-dimensional/quasi-2D HPs are created by including extended organic cations into the ABX3 frameworks. By adjusting the number of HP layers, it is possible to control the optoelectronic properties to achieve specific features for certain applications. This article presents an overview of 2D/quasi-2D HPs, including their structures, binding energies, and charge transport, compared to 3D HPs. Next, we discuss the operational principles, RS modes (bipolar and unipolar switching), in RS memory devices. Finally, there have been notable and recent breakthroughs in developing RS memory systems using 2D/quasi-2D HPs. [ABSTRACT FROM AUTHOR]

Perovskite solar cells (PSCs) have been significantly improved by utilizing an inorganic hole-transporting layer (HTL), such as nickel oxide. Despite the promising properties, there are still limitations due to defects. Recently, research on self-assembled monolayers (SAMs) is being actively conducted, which shows promise in reducing defects and enhancing device performance. In this study, we successfully engineered a p-i-n perovskite solar cell structure utilizing HC-A1 and HC-A4 molecules. These SAM molecules were found to enhance the grain morphology and uniformity of the perovskite film, which are critical factors in determining optical properties and device performance. Notably, HC-A4 demonstrated superior performance due to its distinct hydrophilic properties with a contact angle of 50.3°, attributable to its unique functional groups. Overall, the HC-A4-applied film exhibited efficient carrier extraction properties, attaining a carrier lifetime of 117.33 ns. Furthermore, HC-A4 contributed to superior device performance, achieving the highest device efficiency of 20% and demonstrating outstanding thermal stability over 300 h. [ABSTRACT FROM AUTHOR]

Although past years have witnessed tremendous promises of cesium lead halide perovskite nanocrystals (CsPbX3 NCs), realization of high performance devices based on CsPbX3 NCs with sufficient reliability is still seriously hampered due to their instability. The representative consequence of instability in CsPbX3 NCs is merging occurring under air conditions. When the CsPbX3 NCs are exposed to air, their bright photoluminescence is rapidly diminished because charge carrier radiative recombination is hindered in enlarged domains. Because CsPbX3 NCs merge along a specific direction (surface), merging-free CsPbX3 NCs can be synthesized by controlling the surface chemistry. In this study, we developed an effective post-synthetic strategy to completely redesign the surface of CsPbX3 NCs. The post-synthetically modified surfaces of CsPbX3 NCs after treatment with oleylammonium halides exhibited significantly enhanced stability, whose morphology showed nearly no evidence of merging in air. Electron microscopy and quantitative spectroscopy studies revealed that controllable atomic layer etching, which results in the removal of the merging-vulnerable (110) surface, occurs on the surface of CsPbX3 NCs by our post-synthetic treatment with oleylammonium halides. Finally, we proposed a mechanism derived from our effective post-synthetic chemistry, thus realizing high stability of CsPbX3 NCs. [ABSTRACT FROM AUTHOR]

Recently perovskites-based inorganic compounds have been researched incredibly for their photocatalytic applications. In this work, rubidium tin chloride [Rb2SnCl6] and caesium-incorporated rubidium [(RbXCs1-X)2SnCl6]-defect perovskites were synthesized for photocatalytic applications. This material is very useful for the degradation of dyes under UV irradiation among other photocatalysts, because of its superior properties such as nontoxicity, low cost, simple preparation methods and long-term thermal stability. The crystal structure, morphology and elemental composition of synthesized defect perovskite materials have been analysed using XRD, FESEM and EDAX mapping analysis. The UV studies reveal that the band-gap values were tuned (from 2.71 eV in Rb2SnCl6 to 3.78 eV in (Rb0.5Cs0.5)2SnCl6), resulting in a blue shift of the PL emission peak (from 458 to 328 nm) due to the incorporation of caesium in rubidium site. The thermal stability of (Rb0.5Cs0.5)2SnCl6 is enhanced over other synthesized defect perovskite materials because 76% of samples remained at the highest temperature of 750 °C. Synthesized defect perovskite materials were used in the photocatalytic degradation of methylene blue dye under UV light radiation. Furthermore, an excellent photocatalytic degradation is observed for (Rb0.5Cs0.5)2SnCl6 (78% to 85%) compared to other defect perovskite materials even after 120 min irradiation. The increase in photocatalytic efficiency of (Rb0.5Cs0.5)2SnCl6 is due to strong absorption of light, large separation of electron–holes pairs and the size of the nanoparticles. Also, the radical trapping experiment showed that the super oxide radicals (.O2−) and photo-generated holes (h+) were the predominant active species in the photocatalytic degradation of methylene blue dye process. This study concludes that the defect perovskites are the potential materials for photocatalytic application. [ABSTRACT FROM AUTHOR]

Abstract: CsPbX3 (X = halide, Cl, Br, or I) all‐inorganic halide perovskites (IHPs) are regarded as promising functional materials because of their tunable optoelectronic characteristics and superior stability to organic–inorganic hybrid halide perovskites. Herein, nonvolatile resistive switching (RS) memory devices based on all‐inorganic CsPbI3 perovskite are reported. An air‐stable CsPbI3 perovskite film with a thickness of only 200 nm is successfully synthesized on a platinum‐coated silicon substrate using low temperature all‐solution process. The RS memory devices of Ag/polymethylmethacrylate (PMMA)/CsPbI3/Pt/Ti/SiO2/Si structure exhibit reproducible and reliable bipolar switching characteristics with an ultralow operating voltage (<+0.2 V), high on/off ratio (>106), reversible RS by pulse voltage operation (pulse duration < 1 ms), and multilevel data storage. The mechanical flexibility of the CsPbI3 perovskite RS memory device on a flexible substrate is also successfully confirmed. With analyzing the influence of phase transition in CsPbI3 on RS characteristics, a mechanism involving conducting filaments formed by metal cation migration is proposed to explain the RS behavior of the memory device. This study will contribute to the understanding of the intrinsic characteristics of IHPs for low‐voltage resistive switching and demonstrate the huge potential of them for use in low‐power consumption nonvolatile memory devices on next‐generation computing systems. [ABSTRACT FROM AUTHOR]

We demonstrated an effective poly(p-chloro-xylylene) (Parylene-C) encapsulation method for MAPbI3 solar cells. By structural and optical analysis, we confirmed that Parylene-C efficiently slowed the decomposition reaction in MAPbI3. From a water permeability test with different encapsulating materials, we found that Parylene-C-coated MAPbI3 perovskite was successfully passivated from reaction with water, owing to the hydrophobic behavior of Parylene-C. As a result, the Parylene-C-coated MAPbI3 solar cells showed better device stability than uncoated cells, virtually maintaining the initial power conversion efficiency value (15.5 ± 0.3%) for 196 h. [ABSTRACT FROM AUTHOR]