Self-Powered Broadband Photodetection of MoS₂/Sb₂Se₃ Heterostructure

Achieving broadband self-powered photoresponse by a single device remains a top priority in the scientific community. Van der Waals (vdW) heterostructures, a lattice-matched structure, have great potential for self-powered broadband optoelectronic devices. Herein, a MoS2/Sb2Se3 heterostructure broadband photodetector is proposed, which can work in spectral range visible (Vis) to infrared–B (IR–B). The built device exhibited a strong built-in potential, resulting in the device displaying excellent responsivity 42 mAW–1, 125 mAW–1, and 60 mAW–1 for Vis (532 nm), IR–A (1064 nm), and IR–B (1405 nm) light illumination, respectively, under self-powered mode at room temperature. Moreover, the performance of the photodetector is also supported by the technology computer-aided design (TCAD) simulation insights. In addition, the fabricated vdW heterostructure-based device exhibited a stable response at high-temperature (125 °C) conditions and displayed peak responsivity 116 mAW–1 for the IR–A illumination. The fabricated detector is also tested in photoconductive mode, where the computed value of peak state-of-art metrics are responsivity (1.3 × 104 mAW–1), detectivity (3.89 × 1010 Jones), and quantum efficiency (1.5 × 103%) at 0.8 V bias and a weak 5 μW optical power. Along with this, the device is able to detect a very faint optical signal of ∼300 femto-watt. Hence, the proposed MoS2/Sb2Se3 van der Waals heterostructure-based device provides an enforceable pathway toward achieving self-powered technology, opening avenues for its application across a broad spectrum of optoelectronics

Self-Driven UVC–NIR Broadband Photodetector with High-Temperature Reliability Based on a Coco Palm-Like MoS₂/GaN Heterostructure

One of the dominant sources of energy production is burning fossil fuels (coal, natural gas, and petroleum), which emit different optical traces (ultraviolet to infrared). A self-driven broadband optical detector is essential for monitoring these optical signals in harsh environments because it is challenging to apply additional bias under high-temperature conditions. However, the existing optical detectors are constrained to operate at room temperature or require additional bias and present practical limitations in high-temperature operating environments. This study introduces a unique coco palm-like MoS2/GaN heterojunction-based self-powered photodetector that operates in the broadband spectral range from ultraviolet-C to near-infrared. The fabricated detector displays the highest responsivity of 379 mA W–1 under no applied bias at room temperature. The photodetector also exhibits consistent performance at high operating temperatures (up to 250 °C). Under self-driven conditions, the device possesses the highest responsivity of 360 mA W–1 at 250 °C. The heterostructure-based device also achieves the best responsivity of 2.8 × 106 mA W–1 at 8 V applied bias and has remarkable low-light detection abilities down to 9 femto-Watts. The high-temperature-operated self-driven broadband photodetector opens up possibilities for in situ monitoring of optical radiations from diverse industrial processes in challenging conditions and for optical signature-generating systems in the automobile, aerospace, and energy production industries

Strain Modulation of Optoelectronic Properties in Nanolayered Black Phosphorus: Implications for Strain-Engineered 2D Material Systems

Strain engineering is an exciting direct approach to control the key intrinsic properties of two-dimensional (2D) materials. However, fabrication complexities arising from weak van der Waals interaction-induced slippage, coupled with mechanical breakdown of metal electrodes, have prevented fundamental investigations into strain effects on electrical and optoelectronic characteristics of these material systems. To overcome this limitation, we report a simple prestretch fabrication technique that allowed us to demonstrate a functional multilayer black phosphorus (BP)-based device on a stretchable elastomeric platform. By applying a uniaxial compressive strain of up to 10%, we reveal that mechanical strain can be effectively used to modulate the electronic and optical properties of nanolayered BP. This simple strategy can be extended well-beyond BP to other 2D materials, creating opportunities for fundamental investigations into strain effects in 2D material systems and potential applications in strain-engineered sensors for optical synapse applications

Helicity-selective Raman scattering from in-plane anisotropic {\alpha}-MoO3_3

Hyperbolic crystals like {\alpha}-MoO$_3$ can support large wavevectors and photon density as compared to the commonly used dielectric crystals, which makes them a highly desirable platform for compact photonic devices. The extreme anisotropy of the dielectric constant in these crystals is intricately linked with the anisotropic character of the phonons, which along with photon confinement leads to the rich physics of phonon polaritons. However, the chiral nature of phonons in these hyperbolic crystals have not been studied in detail. In this study, we report our observations of helicity selective Raman scattering from flakes of {\alpha}-MoO$_3$. Both helicity-preserving and helicity-reversing Raman scattering are observed. We observe that helical selectivity is largely governed by the underlying crystal symmetry. This study shed light on the chiral character of the high symmetry phonons in these hyperbolic crystals. It paves the way for exploiting proposed schemes of coupling chiral phonon modes into propagating surface plasmon polaritons and for compact photonic circuits based on helical polarized light

Solvent Dopant-Regulated Grain Formation for Bismuth Iodide Thin-Film Photodetectors

Simple solution-based processes to generate pinhole-free bismuth iodide (BiI3) thin films with large, interconnected crystal grains have remained elusive. Here, a survey of the solvent systems for BiI3 is conducted. Using a novel binary solvent doping approach to carefully regulate the crystallization kinetics, we generate high-quality BiI3 thin films. Our method circumvents the current requirement for unreliable postprocessing techniques such as solvent vapor annealing or antisolvent dripping. Investigations reveal that 2-methoxyethanol doped with small amounts of N-methyl-2-pyrrolidone (NMP) is the ideal combination of parent and dopant solvent providing high vapor pressure and the intermediate coordination strength necessary to successfully achieve large grain formation in a single step. To evaluate optoelectronic performance, we integrated our optimized thin films into lithographically patterned lateral photodetectors (PDs). Our PD devices show fast millisecond response times, record responsivities of ∼1.61 A/W at moderate device bias (5 V), and excellent sensitivity, with detectivity reaching 1.9 × 1012 cm Hz1/2 W–1 (Jones). The high-quality BiI3 semiconductor thin films outlined here, coupled with their ease of fabrication, enhance the development of BiI3 optoelectronic devices and also serve as excellent template films for the fabrication of related bismuth perovskite materials

Solvent Dopant-Regulated Grain Formation for Bismuth Iodide Thin-Film Photodetectors

Simple solution-based processes to generate pinhole-free bismuth iodide (BiI3) thin films with large, interconnected crystal grains have remained elusive. Here, a survey of the solvent systems for BiI3 is conducted. Using a novel binary solvent doping approach to carefully regulate the crystallization kinetics, we generate high-quality BiI3 thin films. Our method circumvents the current requirement for unreliable postprocessing techniques such as solvent vapor annealing or antisolvent dripping. Investigations reveal that 2-methoxyethanol doped with small amounts of N-methyl-2-pyrrolidone (NMP) is the ideal combination of parent and dopant solvent providing high vapor pressure and the intermediate coordination strength necessary to successfully achieve large grain formation in a single step. To evaluate optoelectronic performance, we integrated our optimized thin films into lithographically patterned lateral photodetectors (PDs). Our PD devices show fast millisecond response times, record responsivities of ∼1.61 A/W at moderate device bias (5 V), and excellent sensitivity, with detectivity reaching 1.9 × 1012 cm Hz1/2 W–1 (Jones). The high-quality BiI3 semiconductor thin films outlined here, coupled with their ease of fabrication, enhance the development of BiI3 optoelectronic devices and also serve as excellent template films for the fabrication of related bismuth perovskite materials

Solution-Processed VO₂ Nanoparticle/Polymer Composite Films for Thermochromic Applications

Thin films composed of vanadium dioxide (VO2), a well-known thermochromic material with reversible insulator-to-metal-transition near room temperature, are intriguing for intelligent and energy-efficient heat-blocking applications. However, the conventional vacuum-based deposition methods often involve a high-temperature annealing process, and oxidation of VO2 under air exposure further limits their practical applications. In this work, we demonstrate a room-temperature solution process to prepare VO2-based thermochromic thin films using a smart ink composed of crystalline VO2 nanoparticles. To enhance their chemical stability against oxidation and assist in the uniform deposition of the VO2 thin films, polymers were used as both capping agents and for surface modification of the VO2 nanocrystals. Specifically, the concentration of VO2 nanocrystals, the type of polymers, and the molar ratio between VO2 and polymers are systematically tailored, and their effects on the thermochromic performance are also explored. It is revealed that the inclusion of optimum polymers enhanced the thermochromic performance with an almost 4-fold increase in IR switching with a visible luminous transmittance of 86% and a solar modulation of 17.61%. In addition, the inks are compatible with an array of scalable manufacturing processes. We demonstrate uniform films on different substrates, both rigid and flexible, by dip coating, drop casting, and screen printing, offering great feasibility for further scaling up

Visible-Active Artificial Synapses Based on Ultrathin Indium Oxide

One of the key requirements to emulate synaptic features in optoelectronic devices is the presence of persistent photoconductivity (PPC). While there are several visible-active materials, transparent semiconducting oxides (TSOs) have commercially established production processes and applications. Despite the inherently exceptional optoelectronic properties in many atomically thin TSOs along with PPC, their wide band gap renders them feasible only for ultraviolet (UV)-active synaptic applications. Hence, approaches need to be developed that allow one to tailor such semiconductors for visible-active optoelectronic synapses that are a strong emerging area of research. Over the past few years, liquid metal (LM) printing techniques have enabled the realization of many nonstratified oxides in an atomically thin form, resulting in oxide systems with enhanced optoelectronic performances, which can be further engineered using postsynthesis processing techniques. Here, we utilize a nonlayered ultrathin oxide, indium oxide (In2O3), engineered to demonstrate a photoelectrical response in the visible spectrum with a peak responsivity of 6.67 × 103 A/W at 455 nm. The 2.2 nm thin sheets operating under a driving voltage of 200 mV are successfully able to detect short pulses under 500 ms while showcasing PPC characteristics without additional bias. Key synaptic and multisynaptic functionalities are replicated using blue and green light sources, demonstrating a viable pathway to integrate atomically thin oxide semiconductors for visible light-active optoelectronic synaptic applications