Air‐Stable Cesium Lead Iodide Perovskite for Ultra‐Low Operating Voltage Resistive Switching

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.     

Flexible Piezoelectric Nanocomposite Generators Based on Formamidinium Lead Halide Perovskite Nanoparticles

Organic–inorganic lead halide perovskite materials have recently attracted much attention in the field of optoelectronic devices. Here, a hybrid piezoelectric nanogenerator based on a composite of piezoelectric formamidinium lead halide perovskite (FAPbBr₃) nanoparticles and polydimethylsiloxane polymer is fabricated. Piezoresponse force spectroscopy measurements reveal that the FAPbBr₃ nanoparticles contain well‐developed ferroelectric properties with high piezoelectric charge coefficient (d₃₃) of 25 pmV⁻¹. The flexible device exhibits high performance with a maximum recordable piezoelectric output voltage of 8.5 V and current density of 3.8 μA cm⁻² under periodically vertical compression and release operations. The alternating energy generated from nanogenerators can be used to charge a capacitor and light up a red light‐emitting diode through a bridge rectifier. This result innovatively expands the feasibility of organic–inorganic lead halide perovskite materials for application in a wide variety of high‐performance energy harvesting devices.     

Epitaxial Growth of Large‐Scale Orthorhombic CsPbBr3 Perovskite Thin Films with Anisotropic Photoresponse Property

Inorganic cesium lead halide perovskite (CsPbX₃, X = Cl, Br, I) is a promising material for developing novel electronic and optoelectronic devices. Despite the substantial progress that has been made in the development of large perovskite single crystals, the fabrication of high‐quality 2D perovskite single‐crystal films, especially perovskite with a low symmetry, still remains a challenge. Herein, large‐scale orthorhombic CsPbBr₃ single‐crystal thin films on zinc‐blende ZnSe crystals are synthesized via vapor‐phase epitaxy. Structural characterizations reveal a “CsPbBr₃(110)//ZnSe(100), CsPbBr₃[?110]//ZnSe[001] and CsPbBr₃[001]//ZnSe[010]” heteroepitaxial relationship between the covering CsPbBr₃ layer and the ZnSe growth substrate. It is exciting that the epitaxial film presents an in‐plane anisotropic absorption property from 350 to 535 nm and polarization‐dependent photoluminescence. Photodetectors based on the epitaxial film exhibit a high photoresponsivity of 200 A W^?1, a large on/off current ratio exceeding 10⁴, a fast photoresponse time of about 20 ms, and good repeatability at room temperature. Importantly, a strong polarization‐dependent photoresponse is also found on the device fabricated using the epitaxial CsPbBr₃ film, making the orthorhombic perovskite promising building blocks for optoelectronic devices featured with anisotropy.     

Structural and optoelectronic properties of hybrid halide perovskites for solar cells

Trihalide perovskites are an emerging class of materials, which have shown excellent performance so far in solution-processed optoelectronic devices such as perovskite solar cells (PSCs) and light emitting diodes (LEDs). The energy band gap (E_gap) of this class of materials is tunable and can be varied from 1.5 eV to 2.3 eV by changing its chemical composition, exhibiting a promising character to design versatile optoelectronic devices. It is thus, imperative to understand the relation between structural and optoelectronic properties of the perovskite-based materials offering intrinsic complexity. Hence, different interactions, defects as well as structural disorder have a defining role in the material properties. The intrinsic properties have been shown to have a significant impact on the performance of these perovskite materials. These properties include high dielectric constants, ambipolar transport features of long range, low exciton binding energies, and ferroelectric polarizations. In the current review, we briefly explore the crystal structure of the perovskite materials at atomistic-level and draw a comparison of the basic optical and electrical properties originating from particular atomic compositions together with their arrangements therein, and moreover, their applications in future optoelectronic devices are elaborated upon.     

Single‐Crystal Hybrid Perovskite Platelets on Graphene: A Mixed‐Dimensional Van Der Waals Heterostructure with Strong Interface Coupling

Van der Waals (vdW) heterostructures open up excellent prospects in electronic and optoelectronic applications. In this work, mixed‐dimensional metal‐halide perovskite/graphene heterostructures are prepared through selective growth of CH₃NH₃PbBr₃ platelets on patterned single‐layer graphene using chemical vapor deposition. Preferred growth of single‐crystal CH₃NH₃PbBr₃ platelets on graphene surfaces is achieved, which is accompanied by significant photoluminescence quenching. Raman spectra reveal that perovskite platelets cause p‐type doping in the graphene layer. A significant Fermi level decrease of 272 meV in graphene is estimated, which corresponds to a high doping density of 7.5 × 10¹² cm^?2. Surface potentials measured by Kelvin probe force microscopy indicate a negatively charged perovskite surface under illumination, which is consistent with the upward band bending deduced from conducting atomic force microscopy measurements. Moreover, a field‐effect phototransistor is fabricated using the perovskite/graphene heterostructure channel, and the increased Dirac voltage under illumination confirms an enhanced p‐type character in graphene. These findings enrich the understanding of strong interface coupling in such mixed‐dimensional vdW heterostructures and pave the way toward novel perovskite‐based optoelectronic devices.     

Laser‐Induced Localized Growth of Methylammonium Lead Halide Perovskite Nano‐ and Microcrystals on Substrates

Perovskite‐based optoelectronic devices have shown remarkable performances, especially in the field of photovoltaics. Still, a rapid solution‐processing approach able to produce localized stable perovskite crystals remains a general challenge, and is a key step toward the miniaturization of such materials in on‐chip components. This study presents the confined growth of methylammonium (MA) lead halide perovskite crystals that is thermally induced through localized laser irradiation. Importantly, such structures remain stable over time; that is, they neither dissolve back into the surrounding liquid nor detach from the substrate. This is attributed to a chemical reaction locally triggered by the induced heat on the substrate surface that is transferred to the perovskite precursors (liquid) layer, thus generating “on‐demand” MA ions from the N‐methylformamide solvent. By tuning the laser parameters, such as power density or irradiation time, variations in shape and size of the crystals, from microcrystals of ≈50 µm to nanocuboids of ≈500 nm, are observed. This study also demonstrates that with an optimized distance between the irradiated regions and by controlling the relative laser displacement speed, luminescent and photoconductive MAPbBr₃ wires and microplates can be generated.     

Light‐Responsive Ion‐Redistribution‐Induced Resistive Switching in Hybrid Perovskite Schottky Junctions

Hybrid Perovskites have emerged as a class of highly versatile functional materials with applications in solar cells, photodetectors, transistors, and lasers. Recently, there have also been reports on perovskite‐based resistive switching (RS) memories, but there remain open questions regarding device stability and switching mechanism. Here, an RS memory based on a high‐quality capacitor structure made of an MAPbBr₃ (CH₃NH₃PbBr₃) perovskite layer sandwiched between Au and indium tin oxide (ITO) electrodes is reported. Such perovskite devices exhibit reliable RS with an ON/OFF ratio greater than 10³, endurance over 10³ cycles, and a retention time of 10⁴ s. The analysis suggests that the RS operation hinges on the migration of charged ions, most likely MA vacancies, which reversibly modifies the perovskite bulk transport and the Schottky barrier at the MAPbBr₃/ITO interface. Such perovskite memory devices can also be fabricated on flexible polyethylene terephthalate substrates with high bendability and reliability. Furthermore, it is found that reference devices made of another hybrid perovskite MAPbI₃ consistently exhibit filament‐type switching behavior. This work elucidates the important role of processing‐dependent defects in the charge transport of hybrid perovskites and provides insights on the ion‐redistribution‐based RS in perovskite memory devices.     

Dual-Phase Stabilized Perovskite Nanowires for Reduced Defects and Longer Carrier Lifetime

1D perovskite materials are of significant interest to build a new class of nanostructures for electronic and optoelectronic applications. However, the study of colloidal perovskite nanowires (PNWs) lags far behind those of other established perovskite materials such as perovskite quantum dots and perovskite thin films. Herein, a dual-phase passivation strategy to synthesize all-inorganic PNWs with minimized surface defects is reported. The local phase transition from CsPbBr₃ to CsPb₂Br₅ in PNWs increases the photoluminescence quantum yield, carrier lifetime, and water-resistivity, owing to the energetic and chemical passivation effect. In addition, these dual-phase PNWs are employed as an interfacial layer in perovskite solar cells (PSCs). The enhanced surface passivation results in an efficient carrier transfer in PSCs, which is a critical enabler to increase the power conversion efficiency (PCE) to 22.87%, while the device without PNWs exhibits a PCE of 20.74%. The proposed strategy provides a surface passivation platform in 1D perovskites, which can lead to the development of novel nanostructures for future optoelectronic devices.     

Bidirectional All‐Optical Synapses Based on a 2D Bi2O2Se/Graphene Hybrid Structure for Multifunctional Optoelectronics

Neuromorphic computing has been extensively studied to mimic the brain functions of perception, learning, and memory because it may overcome the von Neumann bottleneck. Here, with the light‐induced bidirectional photoresponse of the proposed Bi₂O₂Se/graphene hybrid structure, its potential use in next‐generation neuromorphic hardware is examined with three distinct optoelectronic applications. First, a photodetector based on a Bi₂O₂Se/graphene hybrid structure presents positive and negative photoresponsibility of 88 and ?110 A W^?1 achieved by the excitation of visible wavelength and ultraviolet wavelength light at intensities of 1.2 and 0.3 mW cm^?2, respectively. Second, this unique photoresponse contributes to the realization of all optically stimulated long‐term potentiation or long‐term depression to mimic synaptic short‐term plasticity and long‐term plasticity, which are attributed to the combined effect of photoconductivity, bolometric, and photoinduced desorption. Third, the devices are applied to perform digital logic functions, such as “AND” and “OR,” using full light modulation. The proposed Bi₂O₂Se/graphene‐based optoelectronic device represents an innovative and efficient building block for the development of future multifunctional artificial neuromorphic systems.     

Controlled Growth and Reliable Thickness‐Dependent Properties of Organic–Inorganic Perovskite Platelet Crystal

Organolead halide perovskites (e.g., CH₃NH₃PbI₃) have caught tremendous attention for their excellent optoelectronic properties and applications, especially as the active material for solar cells. Perovskite crystal quality and dimension is crucial for the fabrication of high‐performance optoelectronic and photovoltaic devices. Herein the controlled synthesis of organolead halide perovskite CH₃NH₃PbI₃ nanoplatelets on SiO₂/Si substrates is investigated via a convenient two‐step vapor transport deposition technique. The thickness and size of the perovskite can be well‐controlled from few‐layers to hundred nanometers by altering the synthesis time and temperature. Raman characterizations reveal that the evolutions of Raman peaks are sensitive to the thickness. Furthermore, from the time‐resolved photoluminescence measurements, the best optoelectronic performance of the perovskite platelet is attributed with thickness of ≈30 nm to its dominant longest lifetime (≈4.5 ns) of perovskite excitons, which means lower surface traps or defects. This work supplies an alternative to the synthesis of high‐quality organic perovskite and their possible optoelectronic applications with the most suitable materials.     

Inch‐Size Single Crystal of a Lead‐Free Organic–Inorganic Hybrid Perovskite for High‐Performance Photodetector

Large‐size crystals of organic–inorganic hybrid perovskites (e.g., CH₃NH₃PbX₃, X = Cl, Br, I) have gained wide attention since their spectacular progress on optoelectronic technologies. Although presenting brilliant semiconducting properties, a serious concern of the toxicity in these lead‐based hybrids has become a stumbling block that limits their wide‐scale applications. Exploring lead‐free hybrid perovskite is thus highly urgent for high‐performance optoelectronic devices. Here, a new lead‐free perovskite hybrid (TMHD)BiBr₅ (TMHD = N,N,N,N‐tetramethyl‐1,6‐hexanediammonium) is prepared from facile solution process. Emphatically, inch‐size high‐quality single crystals are successfully grown, the dimensions of which reach up to 32 × 24 × 12 mm³. Furthermore, the planar arrays of photodetectors based on bulk lead‐free (TMHD)BiBr₅ single crystals are first fabricated, which shows sizeable on/off current ratios (≈10³) and rapid response speed (τ_rise = 8.9 ms and τ_decay = 10.2 ms). The prominent device performance of (TMHD)BiBr₅ strongly underscores the lead‐free hybrid perovskite single crystals as promising material candidates for optoelectronic applications.     

Enhanced Photoluminescence and Photoresponsiveness of Eu3+ Ions-Doped CsPbCl3 Perovskite Quantum Dots under High Pressure

Metal halide perovskite quantum dots (QDs) have garnered tremendous attention in optoelectronic devices owing to their excellent optical and electrical properties. However, these perovskite QDs are plagued by pressure-induced photoluminescence (PL) quenching, which greatly restricts their potential applications. Herein, the unique optical and electrical properties of Eu³⁺-doped CsPbCl₃ QDs under high pressure are reported. Intriguingly, the PL of Eu³⁺ ions displays an enhancement with pressure up to 10.1 GPa and still preserves a relatively high intensity at 22 GPa. The optical and structural analysis indicates that the sample experiences an isostructural phase transition at approximately 1.53 GPa, followed by an amorphous state evolution, which is simulated and confirmed through density functional theory calculations. The pressure-induced PL enhancement of Eu³⁺ ions can be associated with the enhanced energy transfer rate from excitonic state to Eu³⁺ ions. The photoelectric performance is enhanced by compression and can be preserved upon the release of pressure, which is attributed to the decreased defect density and increased carrier mobility induced by the high pressure. This work enriches the understanding of the high-pressure behavior of rare-earth-doped luminescent materials and proves that high pressure technique is a promising way to design and realize superior optoelectronic materials.     

High‐Order Shift Current Induced Terahertz Emission from Inorganic Cesium Bromine Lead Perovskite Engendered by Two‐Photon Absorption

High‐order nonlinear optical phenomena are interesting from a fundamental point of view as they reveal intrinsic symmetries of the materials. Potentially they can also be used for practical optoelectronic applications. High‐order shift current is one of these phenomena, and yet it has never been detected in experiments, primarily due to the difficulty in conventional contact detection. In this work, the shift current due to the two‐photon absorption (TPA) from all‐inorganic perovskite CsPbBr₃ is first observed by a contactless and nondestructive terahertz (THz) emission method. The results reveal that the THz emission is dominated by a high‐order shift current (fourth‐order nonlinear optical effect) with the below‐bandgap photon energy of femtosecond laser excitation. The high‐order shift current origins from the broken inversion symmetry induced by the dynamic stereochemical activity of the Pb²⁺ lone pair. A microscopic TPA‐assisted nonlinear optical model is presented to describe the photophysical process of the THz emission. The model matches well with the quadratic pump fluence and angular dependence of the THz emission. This work can not only open a new venue for the all‐inorganic perovskite‐based nonlinear optoelectronics and THz devices, but also afford a THz technology for the high‐order nonlinear effect analysis.     

High‐Sensitivity Floating‐Gate Phototransistors Based on WS2 and MoS2

In recent years, 2D layered materials have been considered as promising photon absorption channel media for next‐generation phototransistors due to their atomic thickness, easily tailored single‐crystal van der Waals heterostructures, ultrafast optoelectronic characteristics, and broadband photon absorption. However, the photosensitivity obtained from such devices, even under a large bias voltage, is still unsatisfactory until now. In this paper, high‐sensitivity phototransistors based on WS₂ and MoS₂ are proposed, designed, and fabricated with gold nanoparticles (AuNPs) embedded in the gate dielectric. These AuNPs, located between the tunneling and blocking dielectric, are found to enable efficient electron trapping in order to strongly suppress dark current. Ultralow dark current (10^?11 A), high photoresponsivity (1090 A W^?1), and high detectivity (3.5 × 10¹¹ Jones) are obtained for the WS₂ devices under a low source/drain and a zero gate voltage at a wavelength of 520 nm. These results demonstrate that the floating‐gate memory structure is an effective configuration to achieve high‐performance 2D electronic/optoelectronic devices.     

Engineering the Exciton Dissociation in Quantum‐Confined 2D CsPbBr3 Nanosheet Films

Recent years have witnessed a rapid development of all‐inorganic halide perovskite in optoelectronic devices. Ultrathin 2D CsPbBr₃ nanosheets (NSs) with large lateral dimensions have demonstrated exceptional photophysical properties because of their analogous exciton electronic structure to quantum wells. Despite the incredible progress on device performance, the photophysics and carrier transportation parameters of quantum‐confined CsPbBr₃ NSs are lacking, and the fundamental understanding of the exciton dissociation mechanism is far less developed. Here, a ligands rearrangement mechanism is proposed to explain why annealed NS films have an increased charge transfer rate and a decreased exciton binding energy and lifetime, prompting tunneling as a dominant way of exciton dissociation to separate photogenerated excitons between neighboring NSs. This facile but efficient method provides a new insight to manipulate perovskite nanocrystals coupling. Moreover, ultrathin 2D CsPbBr₃ NS film is demonstrated to have a enhanced absorption cross section and high carrier mobility of 77.9 cm² V^?1 s^?1, contributing to its high responsivity of 0.53 A W^?1. The photodetector has a long‐term stability up to three months, which are responsible for reliable perovskite‐based device performance.     

The Relationship between Chemical Flexibility and Nanoscale Charge Collection in Hybrid Halide Perovskites

Hybrid organometal halide perovskites are known for their excellent optoelectronic functionality as well as their wide‐ranging chemical flexibility. The composition of hybrid perovskite devices has trended toward increasing complexity as fine‐tuned properties are pursued, including multielement mixing on the constituents A and B and halide sites. However, this tunability presents potential challenges for charge extraction in functional devices. Poor consistency and repeatability between devices may arise due to variations in composition and microstructure. Within a single device, spatial heterogeneity in composition and phase segregation may limit the device from achieving its performance potential. This review details how the nanoscale elemental distribution and charge collection in hybrid perovskite materials evolve as chemical complexity increases, highlighting recent results using nondestructive operando synchrotron‐based X‐ray nanoprobe techniques. The results reveal a strong link between local chemistry and charge collection that must be controlled to develop robust, high‐performance hybrid perovskite materials for optoelectronic devices.     

High‐Performance Near‐IR Photodetector Using Low‐Bandgap MA0.5FA0.5Pb0.5Sn0.5I3 Perovskite

Photodetectors with ultrafast response are explored using inorganic/organic hybrid perovskites. High responsivity and fast optoelectronic response are achieved due to the exceptional semiconducting properties of perovskite materials. However, most of the perovskite‐based photodetectors exploited to date are centered on Pb‐based perovskites, which only afford spectral response across the visible spectrum. This study demonstrates a high‐performance near‐IR (NIR) photodetector using a stable low‐bandgap Sn‐containing perovskite, (CH₃NH₃)_0.5(NH₂CHNH₂)_0.5Pb_0.5Sn_0.5I₃ (MA_0.5FA_0.5Pb_0.5Sn_0.5I₃), which is processed with an antioxidant additive, ascorbic acid (AA). The addition of AA effectively strengthens the stability of Sn‐containing perovskite against oxygen, thereby significantly inhibiting the leakage current. Consequently, the derived photodetector shows high responsivity with a detectivity of over 10¹² Jones ranging from 800 to 970 nm. Such low‐cost, solution processable NIR photodetectors with high performance show promising potential for future optoelectronic applications.     

Enhanced Performance of Planar Perovskite Solar Cells Induced by Van Der Waals Epitaxial Growth of Mixed Perovskite Films on WS2 Flakes

Organic–inorganic metal halide perovskite solar cells (PSCs) have attracted much research interest owing to their high power conversion efficiency (PCE), solution processability, and the great potential for commercialization. However, the device performance is closely related to the quality of the perovskite film and the interface properties, which cannot be easily controlled by solution processes. Here, 2D WS₂ flakes with defect‐free surfaces are introduced as a template for van der Waals epitaxial growth of mixed perovskite films by solution process for the first time. The mixed perovskite films demonstrate a preferable growth along (001) direction on WS₂ surfaces. In addition, the WS₂/perovskite heterojunction forms a cascade energy alignment for efficient charge extraction and reduced interfacial recombination. The inverted PSCs with WS₂ interlayers show high PCEs up to 21.1%, which is among the highest efficiency of inverted planar PSCs. This work demonstrates that high‐mobility 2D materials can find important applications in PSCs as well as other perovskite‐based optoelectronic devices.     

Metallo‐Hydrogel‐Assisted Synthesis and Direct Writing of Transition Metal Dichalcogenides

Two dimensional (2D) transition metal dichalcogenides (TMDCs) have attracted interest for their compelling nanoscale new properties and numerous potential applications including fast optoelectronic devices, ultrathin photovoltaics, and high‐performance catalysts. Large‐scale growth of uniform TMDC materials is essential for investigating their physics and for their integration into devices. However, the wafer scale deposition of TMDCs on arbitrary nonselective substrates is still beyond the current state‐of‐the‐art. In this article, a method to synthesize layered TMDCs (MoS₂ and WS₂) at the wafer‐scale by sulfurization of transition metal ions (Mo⁵⁺ and W⁶⁺) in a gelatin template (metallo‐hydrogel) is reported. This process is adaptable to versatile substrates, including amorphous silicon oxide, high‐temperature quartz, and silicon. Although the products are nominally few layer materials, direct band photoluminescent (≈1.8 eV), similar to single‐ or decoupled multilayer MoS₂ is observed. Finally, the solution‐based deposition enables contact printing of TMDC channels to be useable for device applications including thin film transistors with printed silver contacts using the same process.     

Formamidinium‐Based Dion‐Jacobson Layered Hybrid Perovskites: Structural Complexity and Optoelectronic Properties

Layered hybrid perovskites have emerged as a promising alternative to stabilizing hybrid organic–inorganic perovskite materials, which are predominantly based on Ruddlesden‐Popper structures. Formamidinium (FA)‐based Dion‐Jacobson perovskite analogs are developed that feature bifunctional organic spacers separating the hybrid perovskite slabs by introducing 1,4‐phenylenedimethanammonium (PDMA) organic moieties. While these materials demonstrate competitive performances as compared to other FA‐based low‐dimensional perovskite solar cells, the underlying mechanisms for this behavior remain elusive. Here, the structural complexity and optoelectronic properties of materials featuring (PDMA)FA_n–1Pb_nI_3n+1 (n = 1–3) formulations are unraveled using a combination of techniques, including X‐ray scattering measurements in conjunction with molecular dynamics simulations and density functional theory calculations. While theoretical calculations suggest that layered Dion‐Jacobson perovskite structures are more prominent with the increasing number of inorganic layers (n), this is accompanied with an increase in formation energies that render n > 2 compositions difficult to obtain, in accordance with the experimental evidence. Moreover, the underlying intermolecular interactions and their templating effects on the Dion‐Jacobson structure are elucidated, defining the optoelectronic properties. Consequently, despite the challenge to obtain phase‐pure n > 1 compositions, time‐resolved microwave conductivity measurements reveal high photoconductivities and long charge carrier lifetimes. This comprehensive analysis thereby reveals critical features for advancing layered hybrid perovskite optoelectronics.