ABSTRACT Simultaneously achieving high sensitivity and ultrafast response is a challenge for photodetectors, a bottleneck further compounded by the environmental toxicity of lead‐based halide perovskite photodetectors. Herein, we overcome these limitations via a lead‐free, quasi‐2D germanium‐based halide perovskite, PEA 2 MA 3 Ge 4 I 13 . Distinguished by its non‐centrosymmetric structure, this material exhibits robust ferroelectricity, pyroelectricity, and second‐order nonlinear optical susceptibility. By coupling the pyroelectric effect and photovoltaic effect, we successfully decouple the conventional sensitivity‐speed trade‐off, achieving a very high specific detectivity of 6.3 × 10 14 Jones alongside a remarkable response time in ns scale. The practical viability of these devices is demonstrated through advanced applications in tens of centimeter‐level (1 ns light travelling time) light detection and ranging (LiDAR) and fast visible light communication (VLC). This work establishes a compelling strategy for realizing next‐generation, environmentally benign, and high‐performance optoelectronics.

Herein, we propose a synthetic approach for triazine-based donor–acceptor systems and efficient OLED devices when doped into a wide-bandgap host.

Abstract Fabricating high-performance 2D nanosheet-based semiconductor devices faces challenges due to the structural damage caused by traditional metal electrode deposition processes. This study introduces a novel polycarbonate (PC) assisted metal electrode transfer technique that effectively preserves the structural and electronic properties of MoS 2 nanosheets. Using the proposed method, metal electrodes are successfully transferred onto MoS 2 nanosheets via the shadow mask process (20 μm channel) and photolithography (8 μm and 3 μm channels) for photodetector and field-effect transistor (FET) fabrication, respectively. Photodetectors fabricated with transferred electrodes exhibit stable current-voltage characteristics, with the shadow mask-based photodetector achieving a maximum photoresponsivity of 0.73 µA/W under a 450 nm laser at 10 V bias. The photolithography-based photodetector demonstrates higher photoresponsivity of 3.62 mA/W due to enhanced light absorption. Additionally, the FETs fabricated using the PC transfer process show NMOS behavior with electron mobility values of up to 0.17 cm 2 /V s during reverse sweeps. PC covered FETs further improve performance under ambient conditions, achieving electron mobility up to 0.517 cm 2 /V s and stable switching current ratios. These findings underscore the PC assisted electrode transfer method’s advantages in maintaining material integrity, achieving stable device performance, and offering scalability for large-scale applications.

Interfacial ferroelectricity, recently discovered in van der Waals (vdW) materials, exhibits switchable dipoles at the interface. Most experiments are realized by stacking high-symmetry two-dimensional (2D) lattices in specific stacking configurations. A prototype based on a synthetic and low-symmetry 2D lattice is robust for switchable dipoles with broken symmetry at the interface. Here, we show that interfacial ferroelectricity can be spatially tunable by controlling the odd-even layer number in the synthetic low-symmetry lattice of 1T'-WTe2. A high ferroelectric transition temperature (TC) of >550 K is confirmed. The density functional theory (DFT) calculations indicate that interlayer sliding along the b-axis enables polarization switching of the interfacial dipoles. This study moves a significant step toward spatially tunable interfacial ferroelectricity.

Triplet-triplet fusion (TTF) is one of the efficient methods to harvest low-energy triplet excitons to become high-energy singlet emission and achieve excellent performances in blue organic light-emitting diodes (OLEDs). Further progress, an advanced approach is Hyper-TTF OLED by utilizing bi-emitting-layers (bi-EMLs) to separate the charge recombination zone and TTF zone to prevent triplet exciton and polaron quenching. The bi-EML mainly involves pyrene and anthracene derivatives. The novel pyrene derivatives, PPCbz and PPtCbz, constructed with pyrene and carbazole, are successfully synthesized. In the bi-emitting-layer structure, the PPCbz and PPtCbz are respectively employed as the host for the carrier recombination and exciton generation layer, in which singlet excitons can be rapidly transported to the emitters, and the triplet excitons can be triaged to the adjacent TTF layer for luminescence. The blue Hyper-TTF OLED of PPCbz achieves an exceptionally high external quantum efficiency (eta EQE) of 16.3%, representing the record-high eta EQE value among the reported blue TTF OLEDs. It can also be applied to deep blue emission by incorporating a blue MR-TADF emitter, achieving a device performance with a narrow emission bandwidth of 22 nm, CIE coordinates of (0.131, 0.084), and an eta EQE of 12.1%.

The second‐harmonic generation (SHG) susceptibilities of few‐layer SnSe with ferroelectric stacking are investigated using both experimental and theoretical approaches. Theoretical calculations predict a maximum bulk SHG susceptibility of 2444 pm V −1 at 1.2 eV, which is three orders of magnitude larger than that of typical nonlinear crystals. Experimentally, a maximum value of 1424 pm V −1 at 1.19 eV in close agreement with the theoretical prediction is measured. The anisotropic SHG patterns observed experimentally align with theoretical predictions based on the material's point group symmetry. The photon‐energy dependence of SHG patterns is also measured within the range of 1.19 to 1.55 eV to explore the relative strengths of various SHG susceptibilities. Notably, the measured is significantly larger than the theoretical value of bulk AC‐SnSe, likely due to the strain effects and the mixing of ferroelectric and antiferroelectric stacking configurations in the practical SnSe few‐layer samples.

Artificial intelligence (AI) models remain an emerging strategy to accelerate materials design and development. We demonstrate that CNN models can characterize DNA origami nanostructures employed in programmable self-assembly, which is important in many applications such as in biomedicine. Specifically, we benchmark the performance of 9 CNN models, namely, AlexNet, GoogLeNet, VGG16, VGG19, ResNet18, ResNet34, ResNet50, ResNet101, and ResNet152 to characterize the ligation number of DNA origami nanostructures in transmission electron microscopy (TEM) images. We first pretrain CNN models using a large image data set of 720 images from our coarse-grained (CG) molecular dynamics (MD) simulations. Then, we fine-tune the pretrained CNN models, using a small experimental TEM data set with 146 TEM images. All CNN models were found to have similar computational time requirements, although their model sizes and performances are different. We use 20 test MD images to demonstrate that among all of the pretrained CNN models, ResNet50 and VGG16 have the highest and second-highest accuracies. Among the fine-tuned models, VGG16 was found to have the highest agreement with the test TEM images. Thus, we conclude that fine-tuned VGG16 models can quickly characterize the number of ligation sites of nanostructures in large TEM images.

Anti‐counterfeiting technology is crucial for ensuring the authenticity of currency, identification documents, and high‐value products. To address the growing sophistication of counterfeit techniques, a multi‐layered anti‐counterfeiting platform is developed based on an azopolymer (PAzo) system that integrates challenge‐response authentication and physically unclonable function (PUF)‐like characteristics within a unified framework. By leveraging the molecular orientation control of PAzo under linearly polarized light (LPL), encrypted patterns are fabricated that remain invisible under standard conditions and require polarized optical microscopy (POM) for decryption. The fabrication process involves sequential LPL exposures with patterned masks, inducing spatially defined anisotropic molecular alignment, potentially enabling PUF‐like authentication through unique structural variations. To further enhance security, two dynamic anti‐counterfeiting strategies are introduced: 1) dynamic dual pattern anti‐counterfeiting, which encodes multiple polarization‐dependent patterns that appear sequentially under POM as the analyzer is rotated, 2) Moiré pattern animation anti‐counterfeiting, which encodes multiple patterns into a single composite structure that requires a predefined scan pattern for decryption. These multi‐dimensional decryption conditions significantly increase security by introducing both physical and optical constraints. This PAzo‐based approach offers a scalable and adaptive authentication solution, providing enhanced protection against increasingly sophisticated counterfeiting threats.

Blue TADF OLED with EQE= 35.8% and CIE= (0.14, 0.25) was demonstrated by using 4TCzBN emitter in a host consisting of electron donor and acceptor moieties which showed high PLQY= 98.6% and higg light extraction ratio of 36.3%.

2D monolayered transition-metal dichalcogenides (TMDCs) are promising materials for realizing ultracompact, low-threshold semiconductor lasers. And the development of the electrical-driven TMDC devices is crucial for enhancing the integration potential of practical optoelectronic systems. However, at the current stage, the electrically-driven 2-D TMDC laser has never been realized. Herein, the first electrically-driven 2-D TMDC microcavity laser have been developed. In this device, an alternating current (AC) generates electroluminescence lasing in suspended monolayered WSe2 integrated on a microdisk cavity. The input-output curve, bandwidth narrowing, and second-order coherence is analyzed to confirm the lasing characteristics at room temperature. The realization of the room-temperature AC-driven 2-D TMDC laser establishes a new area of research on electrically pumped compact lasers and is likely to assist with the implementation of diverse TMDC-based practical photonic devices in the future.

We present hetero-epitaxial thin films of a single crystal gallium nitride on fluorophlogopite mica (F-mica) without buffer layers. It employs quasi-van der Waals epitaxy to directly grow GaN thin films on flexible substrates, thus integrating 2D layered materials with conventional semiconductor to achieve highly flexible van der Waals thin films. The nitridation and annealing atmosphere are critical on the direct growth of GaN films on substrates via quasi-van der Waals epitaxy. Specifically, we demonstrate that surface modification of F-mica through annealing under NH3 atmosphere to form a nanoscale nitride layer, which supports the hetero-epitaxy without buffer layers. Our research highlights that this modified F-mica substrate provides superior nucleation sites and smoother surface characteristics, leading to the growth of GaN thin films with lower dislocation densities and improved structural integrity. This innovative approach not only simplifies the hetero-epitaxial growth process but yields GaN crystals suitable for high-performance flexible electronic and optoelectronic devices. Our findings generalize a substantial pathway in the fabrication of highly flexible semiconductor thin films on 2D materials, leveraging the unique properties of 2D materials and quasi-van der Waals epitaxy to achieve superior material performance. It supports the advancements of next-generation 2D materials formation and flexible devices.

Deterministic incorporation of colloidal quantum emitters into silicon-based photonic devices would enable major advances in quantum optics and nanophotonics. However, precisely positioning sub-10 nm particles onto micron-sized photonic structures with nanometer-scale accuracy remains an outstanding challenge. Here, we introduce Cavity-Shape Modulated Origami Placement (CSMOP) that leverages the shape programmability of DNA origami to selectively deposit colloidal nanomaterials within lithographically defined resist cavities patterned onto arbitrary photonic devices with high yield and orientation control. Soft-silicification-passivation stabilizes the deposited origami, while preserving their spatially programmable DNA hybridization sites, which enable site-specific attachment of plasmonic gold nanorods (AuNRs) and semiconductor quantum rods (QRs). This offers control over light scattering and emission polarization, respectively, with deterministic integration of individual QRs within silicon nitride waveguides, micro-ring resonators, and bullseye cavities. CSMOP thereby offers a general platform for the integration of colloidal nanomaterials into photonic circuits, with broad potential to empower quantum information science and technology. ### Competing Interest Statement The authors have declared no competing interest.

Artificial intelligence (AI) models remain an emerging strategy to accelerate materials design and development. We demonstrate that convolutional neural network (CNN) models can characterize DNA origami nanostructures employed in programmable self-assembling, which is important in many applications such as in biomedicine. Specifically, we benchmark the performance of 9 CNN models – viz. AlexNet, GoogLeNet, VGG16, VGG19, ResNet18, ResNet34, ResNet50, ResNet101, and ResNet152 – to characterize the ligation number of DNA origami nanostructures in transmission electron microscopy (TEM) images. We first pre-train CNN models using a large image dataset of 720 images from our coarse-grained (CG) molecular dynamics (MD) simulations. Then, we fine-tune the pre-trained CNN models, using a small experimental TEM dataset with 146 TEM images. All CNN models were found to have similar computational time requirements, while their model sizes and performances are different. We use 20 test MD images to demonstrate that among all of the pre-trained CNN models ResNet50 and VGG16 have the highest and second highest accuracies. Among the fine-tuned models, VGG16 was found to have the highest agreement on the test TEM images. Thus, we conclude that fine-tuned VGG16 models can quickly characterize the ligation number of nanostructures in large TEM images.

High-energy metal deposition significantly impacts the performance and reliability of two-dimensional (2D) semiconductors and nanodevices. This study investigates the localized annealing effect in atomically thin In2O3 induced during high-energy metal deposition. The localized heating effect alters the electronic performance of In2O3 devices, especially in shorter channel devices, where heat dissipation is further constrained. This effect creates a conductivity gradient along the In2O3 device with higher conductivity near the metal contact, as observed by conductive atomic force microscopy (C-AFM). This gradient leads to a pronounced threshold voltage (Vth) shift as the channel length (Lch) decreases, resembling a short-channel effect but one driven by thermal mechanisms rather than conventional mechanisms. Furthermore, metals with higher latent heats can exacerbate these effects. We also show that reversing the deposition sequence and postdeposition oxygen annealing effectively suppress Vth shifts across different Lch. This work offers key insights into controlling thermal effects during fabrication to improve ultrathin oxide transistor performance.

Two-dimensional (2-D) monolayer transition-metal dichalcogenides (TMDCs) are promising materials for realizing ultracompact, low-threshold semiconductor lasers. And the development of the electrical-driven TMDC devices is crucial for enhancing the integration potential of practical optoelectronic systems. However, at current stage, the electrically-driven 2-D TMDC laser has never been realized. Herein, we have developed the first electrically-driven 2-D TMDC microcavity laser.

An appropriate host featuring a wide band gap (E-g) and high triplet energy (T-1) is crucial for facilitating highly efficient blue-light emitting devices. In this study, 4Ac26CzBz, a new host comprising acridan and carbazole moieties linked to a benzimidazole core, has been synthesized and characterized. Notedly, 4Ac26CzBz exhibits a wide optical gap (E-g) and high triplet energy (T-1) of 3.3 and 3.0 eV, respectively, and has been proven a suitable host for blue thermally activated delayed fluorescence (TADF) OLED. By adopting 4TCzBN as a blue-light dopant, a remarkably high device external quantum efficiency of 35.8 % (59.8 cd/A and 62.8 lm/W) and a low turn-on voltage (<3 eV) have been demonstrated, with significant suppression of the efficiency roll-off, maintaining a high efficiency of 29.7 % as luminance at 1000 cd/m(2). This excellent performance is deduced from the host's ambipolar carrier transporting properties, which refer to its ability to transport both electrons and holes effectively, high photoluminescence quantum yield (PLQY) of 98.6 %, and highly horizontal orientation of transition dipole, as determined through diverse analytical measurements. The good material properties of 4Ac26CzBz and the high OLED performance reveal its potential for the next generation's advanced display and lighting applications.

We employ ultrafast optical pump-probe spectroscopy to reveal the energy transfer (ET) mechanism between organic Alq 3 molecules and Si. Inserting ultrathin SiO 2 layers between Alq 3 and Si exposes SiO 2 -thickness-dependent relaxation dynamics of photoexcited carriers and discloses ET from Alq 3 to Si, comparable with a dipole-dipole interaction model.

A transfer-free graphene with high magnetoresistance (MR) and air stability has been synthesized using nickel-catalyzed atmospheric pressure chemical vapor deposition. The Raman spectrum and Raman mapping reveal the monolayer structure of the transfer-free graphene, which has low defect density, high uniformity, and high coverage (>90%). The temperature-dependent (from 5 to 300 K) current-voltage (I-V) and resistance measurements are performed, showing the semiconductor properties of the transfer-free graphene. Moreover, the MR of the transfer-free graphene has been measured over a wide temperature range (5-300 K) under a magnetic field of 0 to 1 T. As a result of the Lorentz force dominating above 30 K, the transfer-free graphene exhibits positive MR values, reaching similar to 8.7% at 300 K under a magnetic field (1 Tesla). On the other hand, MR values are negative below 30 K due to the predominance of the weak localization effect. Furthermore, the temperature-dependent MR values of transfer-free graphene are almost identical with and without a vacuum annealing process, indicating that there are low density of defects and impurities after graphene fabrication processes so as to apply in air-stable sensor applications. This study opens avenues to develop 2D nanomaterial-based sensors for commercial applications in future devices.

The energy transfer (ET) between organic molecules and semiconductors is a crucial mechanism for enhancing the performance of semiconductor-based optoelectronic devices, but it remains undiscovered. Here, ultrafast optical pump-probe spectroscopy was utilized to directly reveal the ET between organic Alq3 molecules and Si semiconductors. Ultrathin SiO2 dielectric layers with a thickness of 3.2-10.8 nm were inserted between Alq3 and Si to prevent charge transfer. By means of the ET from Alq3 to Si, the SiO2 thickness-dependent relaxation dynamics of photoexcited carriers in Si have been unambiguously observed on the transient reflectivity change (ΔR/R) spectra, especially for the relaxation process on a time scale of 200-350 ps. In addition, these findings also agree with the results of our calculation in a model of long-range dipole-dipole interactions, which provides critical information for developing future optoelectronic devices.

Based on the classic 1,1′:4′,1″‐terphenyl fluorophore, a novel near‐ultraviolet (NUV) fluorescent BB4Ph (4,4″′‐bis(2,3,4,5‐tetraphenylphen‐1‐yl)(1,1′:4′,1″‐terphenyl) is designed, synthesized, and characterized. BB4Ph exhibits a NUV fluorescence with a λ max of 373 and 380 nm in solution and as a thin film, respectively. The grazing incidence wide‐angle X‐ray scattering (GIWAXS) reveals BB4Ph having a high value of order parameter ( S GIWAXS ) of 0.59 for a molecular layer array normal to the substrate; the angle‐dependent photoluminescence (ADPL) measurement shows Θ (horizontal–dipole ratios) as high as 95% with the neat film. The non‐doped BB4Ph organic light‐emitting diodes (OLEDs) show external quantum efficiency (EQE) up to 5.24% with 1931 Commission Internationale de l’ Eclairage coordinates (CIE x,y ) of (0.16, 0.04), a NUV electroluminescence. With 4P‐Cz (9,9′‐(1,1′:4′,1″:4″,1′″‐quaterphenyl‐4,4′″‐diyl)dicarbazole) as a dopant emitter, doped BB4Ph OLEDs show the highest EQE of 6.99% and a NUV 1931 CIE x,y (0.16, 0.04). The photoluminescence quantum yield is measured for the thin film of BB4Ph and 4P‐Cz:BB4Ph as 68% and 96%, respectively. Hence, the low limits of light outcoupling efficiency (η out ) of the two individual OLEDs are estimated as 31% and 29%, respectively.