Centimeter-Sized Single Crystals of Two-Dimensional Hybrid Iodide Double Perovskite (4,4-Difluoropiperidinium)4AgBiI8 for High-Temperature Ferroelectricity and Efficient X-Ray Detection

Ferroelectricity and X-ray detection property have been recently implemented for the first time in hybrid bromide double perovskites. It sheds a light on achieving photosensitive and ferroelectric multifunctional materials based on 2D lead-free hybrid halide double perovskites. However, the low T_c, small P_s, and relatively low X-ray sensitivity in the reported bromide double perovskites hinder practical applications. Herein, the authors demonstrate a novel 2D lead-free iodide double perovskite (4,4-difluoropiperidinium)₄AgBiI₈ (1) for high-performance X-ray sensitive ferroelectric devices. Centimeter-sized single crystal of 1 is obtained and exhibits an excellent ferroelectricity including a high T_c up to 422 K and a large P_s of 10.5 μC cm⁻². Moreover, due to a large X-ray attenuation and efficient charge carrier mobility (μ)–charge carrier lifetime (τ) product, the crystal 1 also exhibits promising X-ray response with a high sensitivity up to 188 μC·Gy_air⁻¹ cm⁻² and a detection limit below 3.13 μGy_air·s⁻¹. Therefore, this finding is a step further toward practical applications of lead-free halide perovskite in high-performance photoelectronic devices. It will afford a promising platform for exploring novel photosensitive ferroelectric multifunctional materials based on lead-free double perovskites.     

Exciton Dynamics and Optically Pumped Lasing in 1-Naphthylmethylamine-Based Quasi-2D Perovskite Films

Films of the quasi-2D perovskite based on 1-naphthylmethylamine (NMA) are promising as the gain medium for optically pumped lasing and future electrically pumped lasing because of its low lasing threshold and small electroluminescence efficiency rolloff. However, reasons for the low threshold and small efficiency rolloff are still unclear. Therefore, exciton dynamics are investigated in NMA-based quasi-2D perovskite films. It is found that quenching of bright excitons by other excitons or charge carriers is unlikely in NMA-based quasi-2D perovskite films, which is one reason for the low lasing threshold and small efficiency rolloff. Moreover, thermally stimulated current measurements reveal that the defect levels inside the band gap of the NMA-based quasi-2D perovskite are shallow, with a depth of ≈0.3 eV, causing a decrease in nonradiative exciton recombination through the defects. Therefore, population inversion can be easily achieved, leading to the low lasing threshold as well. For fabrication of NMA-based quasi-2D perovskite laser devices with even lower lasing thresholds, a circular-shaped optical resonator, and small-molecule-based defect passivation are used. Optically pumped lasing can be obtained from these devices, with a threshold of ≈1 µJ cm⁻², which is one of the lowest values ever reported in any perovskite lasers.     

Fluorinated Organic A-Cation Enabling High-Performance Hysteresis-Free 2D/3D Hybrid Tin Perovskite Transistors

2D tin-based perovskites have gained considerable attention for use in diverse optoelectronic applications, such as solar cells, lasers, and thin-film transistors (TFTs), owing to their good stability and optoelectronic properties. However, their intrinsic charge-transport properties are limited, and the insulating bulky organic ligands hinder the achievement of high-mobility electronics. Blending 3D counterparts into 2D perovskites to form 2D/3D hybrid structures is a synergistic approach that combine the high mobility and stability of 3D and 2D perovskites, respectively. In this study, reliable p-channel 2D/3D tin-based hybrid perovskite TFTs comprising 3D formamidinium tin iodide (FASnI₃) and 2D fluorinated 4-fluoro-phenethylammonium tin iodide ((4-FPEA)₂SnI₄) are reported. The optimized FPEA-incorporated TFTs show a high hole mobility of 12 cm² V⁻¹ s⁻¹, an on/off current ratio of over 10⁸, and a subthreshold swing of 0.09 V dec⁻¹ with negligible hysteresis. This excellent p-type characteristic is compatible with n-type metal-oxide TFT for constructing complementary electronics. Two procedures of antisolvent engineering and device patterning are further proposed to address the key concern of low-performance reproducibility of perovskite TFTs. This study provides an alternative A-cation engineering method for achieving high-performance and reliable tin-halide perovskite electronics.     

Self-Healing Lithographic Patterning of Perovskite Nanocrystals for Large-Area Single-Mode Laser Array

Lead halide perovskites exhibit extraordinary optoelectronic performances and are being considered as a promising medium for high-quality photonic devices such as single-mode lasers. However, for perovskite-based single-mode lasers to become practical, fabrication and integration on a chip via the standard top-down lithography process are strongly desired. The chief bottleneck to achieving lithography of perovskites lies in their reactivity to chemicals used for lithography as illustrated by issues of instability, surface roughness, and internal defects with the fabricated structures. The realization of lithographic perovskite single-mode lasers in large areas remains a challenge. In this work, a self-healing lithographic patterning technique using perovskite CsPbBr₃ nanocrystals is demonstrated to realize high-quality and high-crystallinity single-mode laser arrays. The self-healing process is compatible with the standard lithography process and greatly improves the quality of lithographic laser cavities. A single-mode microdisk laser array is demonstrated with a low threshold of 3.8 µJ cm⁻². Moreover, the control of the lasing wavelength is made possible over a range of up to 6.4 nm by precise fabrication of the laser cavities. This work presents a general and promising strategy for standard top-down lithography fabrication of high-quality perovskite devices and enables research on large-area perovskite-based integrated optoelectronic circuits.     

Rapid 2D Patterning of High-Performance Perovskites Using Large Area Flexography

Solution processing of metal halide perovskites offers the potential for efficient, high-speed roll-based manufacturing of emerging optoelectronic devices such as lightweight photovoltaics and light emitting diodes at lower cost than achievable with incumbent technologies (e.g., Silicon). However, current perovskite fabrication methods are limited in their speed, uniformity, and patterning resolution, relying on subtractive postdeposition scribing for integration of modules and device arrays. Here, a method for flexographic printing of MA_0.6FA_0.4PbI₃ at 60 m min⁻¹, the fastest reported perovskite absorber deposition and the first report of inline drying integrated with roll-based printing, is presented. This process delivers high-resolution patterning (< 3 µm line edge roughness) and precise thickness control through rheological design of precursor inks, allowing scalably printed 50 µm features over large areas (140 cm²), while obviating damaging scribing steps. 2D scanning photoluminescence (PL) is applied to resolve correlations between ink leveling dynamics and optoelectronic quality. Integrating these highly uniform printed perovskite absorbers into n-i-p planar perovskite solar cells, photovoltaic conversion efficiency up to 20.4% (0.134 cm²), the highest performance yet reported for any roll-printed perovskite cells is achieved. This study, thus, establishes flexography as a scalable approach to deposit precisely-patterned high-quality perovskites extensible to applications in emitter and detector arrays.     

Role of Schottky barrier height at source/drain contact for electrical improvement in high carrier concentration amorphous InGaZnO thin film transistors

We report the fabrication of bottom-gate thin film transistors (TFTs) at various carrier concentrations of an amorphous InGaZnO (a-IGZO) active layer from ~10¹⁶ to ~10¹⁹ cm⁻³, which exceeds the limit of the concentration range for a conventional active layer in a TFT. Using the Schottky TFTs configuration yielded high TFT performance with saturation mobility (μ_sat), threshold voltage (V_TH), and on off current ratio (I_ON/I_OFF) of 16.1 cm²/V s, −1.22 V, and 1.3×10⁸, respectively, at the highest carrier concentration active layer of 10¹⁹ cm⁻³. Other carrier concentrations (<10¹⁹ cm⁻³) of IGZO resulted in a decrease of its work function and increase in activation energy, which changes the source/drain (S/D) contact with the active layer behavior from Schottky to quasi Ohmic, resulting in achieving conventional TFT. Hence, we successfully manipulate the barrier height between the active layer and the S/D contact by changing the carrier concentration of the active layer. Since the performance of this Schottky type TFT yielded favorable results, it is feasible to explore other high carrier concentration ternary and quaternary materials as active layers.     

A Spacer Cation Assisted Nucleation and Growth Strategy Enables Efficient and High-Luminance Quasi-2D Perovskite LEDs

Quasi-2D Ruddlesden-Popper perovskites receive tremendous attention for application in light-emitting diodes (LEDs). However, the role of organic ammonium spacers on perovskite film has not been fully-understood. Herein, a spacer cation assisted perovskite nucleation and growth strategy, where guanidinium (GA⁺) spacer is introduced into the perovskite precursor and at the interface between the hole transport layer (HTL) and the perovskite, to achieve dense and uniform perovskite films with enhanced optical and electrical performance is developed. A thin GABr interface pre-formed on HTL provides more nucleation sites for perovskite crystal; while the added GA⁺ in perovskite reduces the crystallization rate due to strong hydrogen bonding interacts with intermediates, which promotes the growth of enhanced-quality quasi-2D perovskite films. The ionized ammonium group ( NH₃⁺) of GA⁺ also favors formation of polydisperse domain distribution, and amine or imine ( NH₂ or NH) group interact with perovskite defects through coordination bonding. The spacer cation assisted nucleation and growth strategy is advantageous for producing efficient and high-luminance perovskite LEDs, with a peak external quantum efficiency of over 20% and a luminance up to 100 000 cd m⁻². This work can inform and underpin future development of high-performance perovskite LEDs with concurrent high efficiency and brightness.     

Highly Sensitive Self-Powered 2D Perovskite Photodiodes with Dual Interface Passivations

2D perovskites have attracted intensive attention by virtue of their excellent optical and electrical properties along with good stabilities. Herein, a highly sensitive self-powered photodiode based on (PEA)₂(MA)₄Pb₅I₁₆ (PEA=C₆H₅(CH₂)NH₃, MA=CH₃NH₃) 2D perovskite is demonstrated by dual interface passivations. The Al₂O₃ bottom passivation can reduce the pinhole defects in the 2D perovskite film and suppress the trap-related recombination loss, bringing forward much reduced dark current and increased photocurrent. The poly (methyl methacrylate) (PMMA) top passivation can encapsulate the 2D perovskite film and thus improve the stability of the device. These results show that the 2D perovskite-based photodiode with dual interface passivations exhibits a large photo-to-dark current ratio of 10⁷, a fast response speed of 597 ns and a linear dynamic range of 160 dB without bias. Responsivity (R) and detectivity (D*) respectively reach 0.36 A W⁻¹ and 5.4 × 10¹² Jones under 532 nm laser illumination at a power density of 1.5 nW cm⁻². Moreover, the dual interface passivated device exhibits good stabilities. This study paves the road for developing low-cost, low-power, solution processed image sensors.     

Cyano‐Substituted Oligo(p‐phenylene vinylene) Single Crystals: A Promising Laser Material

Organic crystals that combine high charge‐carrier mobility and excellent light‐emission characteristics are expected to be of interest for light‐emitting transistors and diodes, and may offer renewed hope for electrically pumped laser action. High‐luminescence‐efficiency cyano‐substituted oligo(p‐ phenylene vinylene) (CN‐DPDSB) crystals (η ≈ 95%) grown by the physical vapor transport method is reported here, with high mobilities (at ≈10^?2 cm² V^?1 s^?1 order of magnitude) as measured by time‐of‐flight. The CN‐DPDSB crystals have well‐balanced bipolar carrier‐transport characteristics (μ_hole≈ 2.5–5.5 × 10^?2 cm² V^?1 s^?1; μ_electron ≈ 0.9–1.3 × 10^?2 cm² V^?1 s^?1) and excellent optically pumped laser properties. The threshold for amplified spontaneous emission (ASE) is about 4.6 μJ per pulse (23 KW cm^?2), while the gain coefficient at the peak wavelength of ASE and the loss coefficient caused by scattering are ≈35 and ≈1.7 cm^?1, respectively. This indicates that CN‐DPDSB crystals are promising candidates for organic laser diodes.     

Highly efficient quasi-two dimensional perovskite light-emitting diodes by phase tuning

Tetraphenylphosphonium chloride (TPPCl) is used as an additive in the antisolvent for preparing the quasi-two Dimensional (quasi-2D) perovskite film. This strategy is not only beneficial for the morphology formation but also the phase tuning of the quasi-2D perovskite film. Highly efficient and stable perovskite light-emitting diodes (PeLEDs) were achieved with the maximum luminance of 35,000 cd/m², the maximum current efficiency of 48.0 cd/A and the maximum external quantum efficiency (EQE) of 12.42%. Due to the reduced exciton quenching rate, improved charge carrier injection and transport ability, the electroluminescent performance of the TPPCl-based PeLEDs has been enhanced.     

Stereo-Active Lone Pairs Induced Giant Polarization in a 2D Ge-Based Halide Perovskite Antiferroelectric

Antiferroelectrics, characterized by electrically controlled antipolar-polar phase transformation, have attracted tremendous attention as a class of promising electroactive materials for assembling electronic devices. The emerging two-dimensional (2D) halide perovskites with superior compositional diversity offer an ideal platform for exploring electroactive materials, whereas lead-free antiferroelectric counterparts are still scarcely reported. Herein, for the first time, a new lead-free 2D germanium iodide perovskite antiferroelectric (i-BA)₂CsGe₂I₇ ( 1 , i-BA is iso-butylammonium) has been presented, which exhibits a high Curie temperature (T_c) up to 403 K. Remarkably, benefiting from the lone pair stereochemical activity in Ge²⁺ induced large structural distortion and Cs⁺ ion off-center displacement, 1 shows well-defined double P–E hysteresis loops in a wide temperature range with a giant maximum polarization up to 18.8 µC cm⁻², which achieves a new high record among molecular antiferroelectrics. Moreover, under a low external electric field of 22.5 kV cm⁻¹, the antipolar-polar phase transformation in 1 affords a recoverable energy storage density W_rec of 0.27 J cm⁻³ and high storage efficiency up to 79.76%. Such lead-free halide perovskite antiferroelectric with intriguing antiferroelectric behaviors, including high T_c, large polarization and remarkable energy storage properties, is exciting, which provides an alternative candidate for high-performance antiferroelectrics for environmentally friendly electronic devices.     

Patterning Liquid Crystalline Organic Semiconductors via Inkjet Printing for High-Performance Transistor Arrays and Circuits

Liquid crystalline (LC) organic semiconductors having long-range-ordered LC phases hold great application potential in organic field-effect transistors (OFETs). However, to meet real device application requirements, it is a prerequisite to precisely pattern the LC film at desired positions. Here, a facile method that combines the technique of inkjet printing and melt processing to fabricate patterned LC film for achieving high-performance organic integrated circuits is demonstrated. Inkjet printing controls the deposition locations of the LC materials, while the melt processing implements phase transition of the LC materials to form high-quality LC films with large grain sizes. This approach enables to achieve patterned growth of high-quality 2,7-dioctyl[1]-benzothieno[3,2-b][1]benzothiophene (C₈-BTBT) LC films. The patterned C₈-BTBT LC film-based 7 × 7 OFET array has 100% die yield and shows high average mobility of 6.31 cm² V⁻¹ s⁻¹, along with maximum mobility up to 9.33 cm² V⁻¹ s⁻¹. As a result, the inverters based on the patterned LC films reach a high gain up to 23.75 as well as an ultrahigh noise margin over 81.3%. Given the good generality of the patterning process and the high quality of the resulting films, the proposed method paves the way for high-performance organic integrated devices.     

Vertical-type 3D/Quasi-2D n-p Heterojunction Perovskite Photodetector

This research demonstrates a state-of-the-art vertical-transport photodetector with an n-type 3D MAPbI₃/p-type quasi-2D (Q-2D) BA₂MA₂Pb₃I₁₀ perovskite heterojunction. This structure introduces a ≈0.6 V built-in electric field at the n-p junction that greatly improves the characteristics of the perovskite photodetector, and the presence of Q-2D perovskite on the surface improves the life. The electrical polarities of the 3D and the Q-2D perovskite layers are simply controlled by self-constituent doping, making clearly defined n-p characteristics. Doctor-blade coating is used to fabricate the photodetector with a large area. The Q-2D materials with highly oriented (040) Q-2D (n = 2,3) planes are near the surface, and the (111) preferred planes mixed with high index Q-2D materials (n = 4,5) are found near the 3D/Q-2D interface. The stacking and interface are beneficial for carrier extraction and transport, yielding an external quantum efficiency of 77.9%, a carrier lifetime long as 295.7 ns, and a responsibility of 0.41 A W⁻¹. A low dark current density of 6.2 × 10⁻⁷ mA cm⁻² and a high detectivity of 2.82 × 10¹³ Jones are obtained. Rise time and fall time are fast as 1.33 and 10.1 µs, respectively. The results show the application potential of 3D/Q-2D n-p junction perovskite photodetectors.     

Efficient and Stable Quasi-2D Perovskite Solar Cells Enabled by Thermal-Aged Precursor Solution

Quasi-2D perovskites have received wide attention in photovoltaics owing to their excellent materials robustness and merits in the device stability. However, the highest power conversion efficiency (PCE) reported on quasi-2D perovskite solar cells (PSCs) still lags those of the 3D counterparts, mainly caused by the relatively high voltage loss. Here, a study is presented on the mitigation of voltage loss in quasi-2D PSCs via usage of thermal-aged precursor solutions (TAPSs). Based on the (AA)₂MA₄Pb₅I₁₆ (n = 5) quasi-2D perovskite absorber with a bandgap of ≈1.60 eV, a record-high open-circuit voltage of 1.24 V is obtained, resulting in boosting the PCE to 18.68%. The enhanced photovoltaic performance afforded by TAPS is attributed to the thermal-aged solution processing that triggers colloidal aggregations to reduce the nucleation sites inside the solution. As a result, formation of high-quality perovskite films featuring compact morphology, preferential crystal orientation, and lowered trap density is allowed. Of importance, with the improved film quality, the corrosion of Ag electrode induced by ion migrations is effectively restrained, which leads to a satisfactory storage stability with <2% degradation after 1200 h under nitrogen environment without encapsulation.     

High-Performance Photodetector and Angular-Dependent Random Lasing from Long-Chain Organic Diammonium Sandwiched 2D Hybrid Perovskite Non-Linear Optical Single Crystal

3D organic-inorganic metal halide perovskites are excellent materials for optoelectronic applications due to their exceptional properties, solution processability, and cost-effectiveness. However, the lack of environmental stability highly restricts them from practical applications. Herein, a stable centimeter-long 2D hybrid perovskite (N-MPDA)[PbBr₄] single crystal using divalent N1-methylpropane-1,3-diammonium (N-MPDA) cation as an organic spacer, is reported. The as-grown single crystal exhibits stable optoelectronic performance, low threshold random lasing, and multi-photon luminescence/multi-harmonic generation. A photoconductive device fabricated using (N-MPDA)[PbBr₄] single crystal exhibits an excellent photoresponsivity (≈124 AW⁻¹ at 405 nm) that is ≈4 orders of magnitudes higher than that of monovalent organic spacer-assisted 2D perovskites, such as (BA)₂PbBr₄ and (PEA)₂PbBr₄, and large specific detectivity (≈10¹² Jones). As an optical gain media, the (N-MPDA)[PbBr₄] single crystal exhibits a low threshold random lasing (≈6.5 µJ cm⁻²) with angular dependent narrow linewidth (≈0.1 nm) and high-quality factor (Q ≈ 2673). Based on these results, the outstanding optoelectronic merits of (N-MPDA)[PbBr₄] single crystal will offer a high-performance device and act as a dynamic material to construct stable future electronics and optoelectronic-based applications.     

Confinement-Induced Phonon Softening and Hardening in Sb2Te3 Thin Films

Scaling effects in Sesqui-chalcogenides are of major interest to understand and optimize their performance in heavily scaled applications, including topological insulators and phase-change devices. A combined experimental and theoretical study is presented for molecular beam epitaxy-grown films of antimony-telluride  (Sb₂Te₃). Structural,vibrational, optical, and bonding properties upon varying confinement are studied for thicknesses ranging from 1.3 to 56 nm. In ultrathin films, the low-frequency coherent phonons of A_1g¹ symmetry are softened compared to the bulk (64.5 cm⁻¹ at 1.3 nm compared to 68 cm⁻¹ at 55.8 nm). A concomitant increase of the high-frequency A_1g² Raman mode is seen. X-ray diffraction analyses unravel an accompanying out of plane stretch by 5%, mainly stemming from an increase in the Te-Te gap. This conclusion is supported by density functional theory slab models, which reveal a significant dependency of chemical bonding on film thickness. Changes in atomic arrangement, vibrational frequencies, and bonding extend over a thickness range much larger than observed for other material classes. The finding of these unexpectedly pronounced thickness-dependent effects in quasi-2D material Sb₂Te₃ allows tuning of the film properties with thickness. The results are discussed in the context of a novel bond-type, characterized by a competition between electron localization and delocalization.     

Enabling Efficient Blue-Emissive Circularly Polarized Luminescence by In Situ Crafting of Chiral Quasi-2D Perovskite Nanosheets within Polymer Nanofibers

Chiral perovskite materials have intrigued enormous interests because of their appealing chiroptical properties and tailorable non-centrosymmetric structures. However, it remains challenging to realize high-efficiency blue emissive circularly polarized luminescence (CPL) of intrinsic chiral perovskite nanomaterials at room temperature. Herein, a robust and versatile electrospinning strategy is reported for in situ construction of chiral 2D and quasi-2D perovskite nanosheets (PNSs) protected in polymer hybrid nanofibers. It is found that quasi-2D chiral PNS/polymer possesses inherent chirality and enhanced CPL properties at room temperature compared to 2D counterparts. Notably, CPL emission color of chiral quasi-2D PNS/polymer can be tuned from deep blue to sky blue, and a high luminescence dissymmetry values up to −8.0 × 10⁻³ can be achieved. Different perovskites, polymers, and nanofibrous structures are expanded to explore the universality of polymer protected PNSs. Significantly, compared to spin-coated film, the stabilities of quasi-2D PNS/polymer film are greatly improved due to the effective protection of polymer. The obtained PNS/polymer hybrid nanofiber films can be conveniently implemented for circularly polarized light emitting diode devices. This study may open up a new avenue for the scalable fabrication of chiral perovskite nanomaterials of interest and their applications in the CPL related fields.     

Deconvoluting Energy Transport Mechanisms in Metal Halide Perovskites Using CsPbBr3 Nanowires as a Model System

Understanding energy transport in metal halide perovskites is essential to effectively guide further optimization of materials and device designs. However, difficulties to disentangle charge carrier diffusion, photon recycling, and photon transport have led to contradicting reports and uncertainty regarding which mechanism dominates. In this study, monocrystalline CsPbBr₃ nanowires serve as 1D model systems to help unravel the respective contribution of energy transport processes in metal-halide perovskites. Spatially, temporally, and spectrally resolved photoluminescence (PL) microscopy reveals characteristic signatures of each transport mechanism from which a robust model describing the PL signal accounting for carrier diffusion, photon propagation, and photon recycling is developed. For the investigated CsPbBr₃ nanowires, an ambipolar carrier mobility of μ = 35 cm² V⁻¹ s⁻¹ is determined, and is found that charge carrier diffusion dominates the energy transport process over photon recycling. Moreover, the general applicability of the developed model is demonstrated on different perovskite compounds by applying it to data provided in previous related reports, from which clarity is gained as to why conflicting reports exist. These findings, therefore, serve as a useful tool to assist future studies aimed at characterizing energy transport mechanisms in semiconductor nanowires using PL.     

Double-Side Crystallization Tuning to Achieve over 1 µm Thick and Well-Aligned Block-Like Narrow-Bandgap Perovskites for High-Efficiency Near-Infrared Photodetectors

Solution-processed narrow-bandgap Sn–Pb perovskites have shown their potential in near-infrared (NIR) photodetection as a promising alternative to traditional silicon and inorganic compounds. To achieve efficient NIR photodetection, high-quality Sn–Pb perovskite thick films with well-packed, smooth, and pinhole/void-free features are highly desirable for boosting the spectral absorption. Understanding the crystallization kinetics and tuning the crystallization are fundamentally important to reach such high-quality thick Sn–Pb perovskite films, and have been limitedly explored. Herein, an approach of double-side crystallization tuning through low-temperature space-restricted annealing in methylammonium-free Sn–Pb perovskite films with over 1 µm thickness is proposed. More specifically, through simultaneously retarding the crystallization in the top of precursor films and promoting the crystal growth of the bottom of precursor films, high-quality and block-like thick FA_0.85Cs_0.15Sn_0.5Pb_0.5I₃ perovskite films with improved crystallinity, preferred out-of-plane orientation, and reduced trap density are achieved. Finally, photovoltaic-mode Sn–Pb perovskite NIR photodetectors show a high external quantum efficiency of ≈80% at 760–900 nm, a recorded responsivity of 0.53 A W⁻¹, and a high specific detectivity of 6 × 10¹² Jones at 940 nm. This study offers the fundamental understanding of the crystallization kinetics of thick perovskite films and paves the way for perovskite-based emerging NIR photodetection and imaging applications.     

Electrical Interrogation of Thickness-Dependent Multiferroic Phase Transitions in the 2D Antiferromagnetic Semiconductor NiI2

2D magnetic materials hold promise for quantum and spintronic applications. 2D antiferromagnetic materials are of particular interest due to their relative insensitivity to external magnetic fields and higher switching speeds compared to 2D ferromagnets. However, their lack of macroscopic magnetization impedes detection and control of antiferromagnetic order, thus motivating magneto-electrical measurements for these purposes. Additionally, many 2D magnetic materials are ambient-reactive and electrically insulating or highly resistive below their magnetic ordering temperatures, which imposes severe constraints on electronic device fabrication and characterization. Herein, these issues are overcome via a fabrication protocol that achieves electrically conductive devices from the ambient-reactive 2D antiferromagnetic semiconductor NiI₂. The resulting gate-tunable transistors show band-like electronic transport below the antiferromagnetic and multiferroic transition temperatures of NiI₂, revealing a Hall mobility of 15 cm² V⁻¹ s⁻¹ at 1.7 K. These devices also allow direct electrical probing of the thickness-dependent multiferroic phase transition temperature of NiI₂ from 59 K (bulk) to 28 K (monolayer).