Light Absorption Research Articles

Improved performance in 0D/2D mixed dimensional homojunction MoS2photodetectors by enhancing light absorption.

Molybdenum disulfide (MoS2) possesses excellent potential for applications in the field of optoelectronic detection. However, the atomic-level thickness of the monolayer MoS2leads to weak light absorption and a restricted absorption spectrum. The performance of monolayer MoS2devices has reached a bottleneck. Fortunately, the above issues can be effectively solved by coupling with various types of photosensitivity nanostructures. In this work, we integrated MoS2quantum dots (QDs) with high efficient light absorption with monolayer MoS2to fabricate 0D/2D MoS2QDs/MoS2hybrid dimensional homojunction photodetectors. In this structure, MoS2is used as an efficient carrier transport channel, while MoS2QDs act as effective light absorbers to enhance the local electric field around MoS2. The synergistic effect of MoS2QDs and MoS2is utilized to accelerate the migration rate of photogenerated carriers in the structure, and in particular, the highest responsivity of the MoS2QDs/MoS2hybrid device is 27.6 A W-1with the detectivity as high as 2.13 × 1011Jones under 532 nm laser, which is an order of magnitude higher than that of the pristine MoS2devices. The synergistic effect of MoS2QDs with monolayer MoS2is verified by finite-difference time-domain simulation. The results will pave the way for the future development of high-performance MoS2-based photodetectors.

Thin film photo(electro)catalysts for the generation of energetic vectors: success cases and challenges, a brief review

Abstract Thin-film semiconductors are excellent candidates for converting solar energy into chemical energy via water splitting because of their outstanding physical and chemical properties. This review aims to provide the most recent findings on the production of energetic vectors from photo-(electro-)catalytic water splitting using thin-film semiconductors as catalysts. Recent successful cases are discussed to provide the scientific community with a guide for the design of new and advanced thin-film semiconductors with maximum efficiency for scaling the process. In addition, the use of coatings to provide a higher amount of catalyst for photo(electro)catalytic H2 production is discussed. Some of the most critical challenges in this reaction, such as charge recombination, light absorption, catalyst recovery, and stability, have been effectively addressed by applying thin films. In addition, the design of adequate thin-film photo(electro)chemical reactors is a critical step in improving efficiency and avoiding mass transfer limit steps. However, further research is required to provide continuous and low-cost manufacturing deposition techniques that favor optimal conditions to produce clean and renewable H2.

Near-Infrared Light Driven Reversible Photoelectrochemical Bioassay by S-Scheme All-Polymer Blends for Acetylcholinesterase Activity Monitoring.

Photoelectrochemical (PEC) biosensing, recognized for its heightened sensitivity, faces limitations in its application for in vivo diagnosis due to the inefficiency of UV-visible light-driven photoactive materials in nontransparent biological samples. In this study, we investigate the potential of an S-scheme all-polymer heterojunction comprising a prototype nonfullerene polymeric acceptor (PYIT) and carbon nitride to develop a near-infrared (NIR) light-driven PEC biosensor for monitoring acetylcholinesterase activity in nontransparent human whole blood. The distinct molecular structure of PYIT enables efficient light absorption in the NIR region, enhancing sensitivity in nontransparent biological samples. The biosensor functions via a proton-dependent conversion mechanism between PYIT-OH and PYIT, leveraging the selective and reversible chemical reactivity of the moieties in backbone, eliminating the need for traditional and intricate integration of a biorecognition unit. Our findings demonstrate a direct correlation between variations in photoelectric performance and acetylcholinesterase concentration, showcasing exceptional sensitivity, selectivity, and reversibility.

Molecular-scale kinetic Monte Carlo simulation of pattern formation in photoresist materials for EUV nanolithography

A kinetic Monte Carlo (KMC) simulation tool for modeling the pattern formation process in photoresist materials for extreme ultraviolet (photon energy 92 eV) nanolithography is presented. The availability of such a tool should support the progress toward novel materials and experimental procedures that lead to an improved pattern resolution. The molecular-scale simulations describe the process in a stochastic and mechanistic manner and include the excitation of high-energy electrons upon light absorption, the creation of a charged-particle cloud, electron-induced chemical degradation of the photoresist molecules, the resulting bond formation between neighboring degraded molecules, and a chemical development step after which a pattern of the remaining non-dissolved molecules is obtained. The method is applied to the application-relevant class of Sn-oxocore photoresist materials and uses their known electronic structure and optical electron energy loss function. The validity of the approach is tested by comparing measured and simulated total electron yield spectra and photoelectron spectra. A demonstration of the method is given by calculating the dose and pitch dependent average shape and stochastic variability (line edge roughness) of line patterns that are obtained for rectangular and sine-wave illumination, assuming various scenarios that determine how molecular-scale degradation will lead to bond creation. We show how from these simulations the ultimate pattern resolution can be deduced. The findings are analyzed systematically using results of KMC simulations that reveal the size of the cloud of degraded molecules around a point of absorption (blur length) and that further reveal the sensitivity to uniform illumination (contrast curves), and using percolation theory. We find that KMC modeling captures the consequences of the strong gradients in the density of degraded molecules and of the stochasticity of the patterning process that simplified models do not include, leading to a significantly improved view of the final pattern quality.

Design and analysis of diisobutoxybenzodithiophene based donor for application in organic solar cell: DFT and TD-DFT Study

The newly designed chromophores (BT1-BT7) of the highly unsaturated donor-acceptor (D-A) were theoretically analyzed and recommended for applications in organic solar cells (OSCs). Conjugated A-groups have been replaced in the reference (BTR) during its design. The structural and optoelectronic properties of designed molecules were calculated using density functional theory (DFT) and Time-dependent DFT (TD-DFT) techniques. The frontier molecular orbitals (FMO) study revealed that BT7 has the lowest energy gap of 2.01 eV, which has significantly less than BTR (2.34 eV), and a significant amount of charge transfer (CT) between HOMO and LUMO has been observed. Out of all the newly designed chromophores in chloroform, the highest absorption spectra were found in the visible region with a bathochromic shift up to 768 nm. The dipole moment values of all the new chromophores (BT1-BT7) were significantly higher than the BTR (5.46 D), which resulted in good solvation. ESP analysis revealed electron distribution on various parts of the molecules by colored maps that are found to be effective for better ICT. The electron transition density resulting from light absorption at different chemical sites was shown using TDM plots. The electron and hole reorganization energy (RE) values were proved as highly efficient in promoting charge mobility and hindered charge recombination for new compounds. By scaling our designed donor to the recognized acceptor Y6, which has demonstrated the creation of OSCs, the open circuit voltage of each molecule was ascertained. The designed molecules exhibited higher open circuit voltages than the reference, indicating improved and fine-tuned optoelectronic properties that would aid in the development of solar cell devices in the future.

Exploring the Role of Flexoelectric Effect in Band Modulation in 1D MoS2/Boron Phosphide Nanotube Heterostructures.

Designing and discovering superior type-II band alignment are crucial for advancing optoelectronic device technologies. Here, we employ first-principles calculations to investigate the evolution of band edges in monolayer MoS2, boron phosphide (BP), and MoS2/BP heterostructures before and after their rolling into nanotubes. Our research results indicate that the intrinsic MoS2/BP vertical heterostructures exhibit a type-II direct bandgap, but this feature is not robust under strain. For MoS2/BP coaxial heterotubes, the type of bandgap is influenced by both chirality and diameter. Specifically, when the diameter exceeds 19 Å under zigzag chirality, the system undergoes a transition from a type-I direct bandgap to a type-II direct bandgap, which remains stable within a strain range of -6 to 6%. Furthermore, we delve into the alterations in band edge positions in single-walled nanotubes induced by curvature-driven flexoelectric effects and circumferential tensile strain. In coaxial heterotubes, the transfer of electrons between the inner and outer tubes forms a cylindrical capacitor-like structure. Incorporating the inherent flexoelectric voltage in single-walled nanotubes, we have derived a functional relationship between the counteracting voltage (Vhyb) and their diameter. Finally, the system was explored for its strong light absorption capabilities with absorption levels up to 105, and it was found that strain can effectively modulate the range of light absorption. The findings of this research contribute to new insights and theoretical foundations for the development of novel one-dimensional (1D) van der Waals (vdW) optoelectronic devices.

Controllable Self-Assembly of V═O Metalloradical Complex with Intramolecular Charge Transfer for Enhanced NIR-II Fluorescence Imaging-Guided Photothermal Therapy.

Near-infrared second region (NIR-II) fluorescence imaging provides enhanced tissue penetration, achieving efficient NIR-II fluorescence and photoacoustic imaging (PA)-guided photothermal therapy (PTT) all in one material remains a challenging yet promising approach in cancer treatment. Herein, open-shell V═O metalloradical complex (VONc) is self-assembled into VONc nanospheres (VONc NPs). VONc NPs exhibit light absorption from 300 to 1400 nm, fluorescence spectra ranging from 900 to 1400 nm, and a distinct fluorescence signal even at 1550 nm. Moreover, VONc NPs exhibit outstanding photostability and a higher photothermal conversion efficiency of 46.6% than that of closed-shell zinc naphthalocyanine nanorods (ZnNc NRs). V═O centered metalloradical serves as transient electron-withdrawing groups to facilitate charge transfer (CT), introducing additional nonradiative energy dissipation pathways and enhancing efficient heat generation. In vitro experiments of VONc NPs indicate that a highly effective photothermal action causes harm to both mitochondria and lysosomes, resulting in the death of tumor cells, closed-shell ZnNc NPs exhibit almost no cell killing as contrast. In vivo anti-tumor therapy results of VONc NPs demonstrate excellent NIR-II fluorescence imaging-guided PTT against tumors with a favorable biosafety profile. "Centered metalloradical boosting CT" toward open-shell metal complexes provides significant insight for developing single-material integrated nanosystems for diagnostic and therapeutic applications.

All-dielectric metasurfaces enabled by quasi-BIC for high-Q near-perfect light absorption

All-dielectric metasurface (ADM) absorbers driven by quasi-bound states in the continuum (BIC) are critical for high-performance optoelectronic devices due to their ability to offer high Q-factor absorption. However, these all-dielectric metasurfaces usually require the aid of degenerate critical coupling schemes or back-metal reflective layers to achieve high absorption, which often suffers from limitations such as sensitive geometrical parameters, ohmic losses, and low Q-factors. This work presents an ADM for high-Q near-perfect light absorption, which consists of double Si nanorods and SiO2/Ta2O5 multilayers. By breaking the symmetry of the length of the Si nanorods, this ADM can excite a single quasi-BIC resonance corresponding to the electric dipole. Without introducing a metal layer, we realize the highly asymmetric coupling of quasi-BIC by only 6 layers of SiO2/Ta2O5 films. It is theoretically and numerically demonstrated that the quasi-BIC has more than 98% absorption at 943.68 nm and a Q-factor as high as 2842. In addition, the ADM exhibits excellent tolerance to geometrical parameters while ensuring high absorption performance. Our results provide new ideas for the design of all-dielectric perfect absorbers with large tolerances and high Q-factors and also open up new possibilities for optical filtering, optical sensing, and photon detection devices.

Preparation of Red TiO2 with Excellent Visible Light Absorption from Industrial TiOSO4 Solution for Photocatalytic Degradation of Dyes

Preparation of Red TiO₂ with Excellent Visible Light Absorption from Industrial TiOSO₄ Solution for Photocatalytic Degradation of Dyes

Finite-Difference Time-Domain Simulation of Double-Ridge Superimposed Structures for Optimizing Light-Trapping Characteristics in Ternary Organic Solar Cells

The double-ridge superimposed structures (DRSSs), formed by the superposition of a nano-ridged textured ZnO layer and a ternary organic active layer (PTB7:PC70BM:PC60BM) with self-assembled nano-ridged (SANR) structures, have been preliminarily examined experimentally for its positive effects in light-trapping for organic solar cells (OSCs). To obtain DRSSs with higher-performance light-trapping effects and enhance the light absorption of OSCs, the present work carried out prior theoretical simulations of the light-trapping characteristics of the DRSS using the finite-difference time-domain (FDTD) algorithm. The results show that the DRSS exhibits a significant light-trapping effect, with an active layer absorption peak around 530 nm due to the light-trapping effect. This helps the active layer capture more high-energy photons, significantly enhancing the photon utilization of the DRSS. Interestingly, the intensity of the light-trapping absorption peak is solely dependent on the height or width of the active layer ridges in the DRSS, while the position of the peak is jointly determined by both the ZnO and active layer ridges. By controlling the aspect ratio (W/H) of the dual ridges, the light-trapping absorption peak position can be fine-tuned, enabling precise light-trapping management for specific wavelength bands. It is certain that the outcomes of this work will provide theoretical foundations and practical guidance for the fabrication of light-trapping OSCs.

Improving Room Temperature Formaldehyde Sensitivity with Samarium-Doped Titanium Dioxide

Abstract Samarium (Sm)-doped titanium dioxide (TiO₂) thin films were synthesized using the spray pyrolysis technique at 400°C, with Sm doping concentrations of 0, 2, 4, and 6 Wt.% to enhance structural, optical, morphological, and gas-sensing properties. The films, deposited on ultrasonically cleaned glass substrates, were characterized using X-ray diffraction , scanning electron microscopy, atomic force microscopy (AFM), and UV-Vis spectroscopy. Structural analysis revealed improved crystallinity and uniform surface morphology with Sm doping, while AFM indicated increased surface roughness, promoting gas adsorption. UV-Vis analysis showed a reduced energy bandgap, enhancing visible light absorption and gas-sensing performance. Gas sensing evaluations demonstrated high sensitivity to formaldehyde, with notable selectivity over ethanol, toluene, and xylene at room conditions. The 6 Wt.% Sm-doped TiO₂ film exhibited the highest response (17.4), with a detection limit of 5 ppm, and fast response (23 s) and recovery (27 s) times. These properties underline the potential of Sm-doped TiO₂ films for efficient room-temperature gas sensors. Their enhanced sensitivity, selectivity, and stability suggest promising applications in environmental monitoring and air quality management, particularly for formaldehyde detection and volatile organic compound discrimination.

Prediction of quaternary SnGeS2As4 monolayer as a promising photocatalyst in water splitting: A DFT study

Abstract The SnGeS2As4 monolayer was studied by first-principles calculations to estimate its potential for used as photocatalyst in water splitting process. The stability of this structure is confirmed based on the analysis of its phonon dispersion and AIDM simulation. The electronic features including density of state (DOS), band structure, and Bader charge were calculated. These data show the role of each constitute element in the formation of covalent π− and σ−bonds, which play important role in stabilizing the buckled honeycomb structure. Besides, the DOS and band structure also provide information regarding to the high light absorption rate α(ω) of 105–105 cm−1. The positions of valence band maximum (VBM) and conduction band minimum (CBM) are suitable for generation of hydrogen and oxygen gases. The SnGeS2As4 monolayer also has optimal work function 5.16 eV for water splitting process and a rather high solar-to-hydrogen efficiency ηSTH = 13.11%. It is worth to note that SnGeS2As4 monolayers with strains ranging from −2% to 6% are still capable to trigger redox reactions in the water splitting process. Moreover, the tensile trains slightly increase the light absorption rates. Such characteristics not only make SnGeS2As4 monolayer a suitable photocatalyst for water splitting but also ensure its performance in wider range of applications

Effect of Strain on the Photocatalytic Reaction of Graphitic Carbon Nitride: Insight from Single-Molecule Localization Microscopy.

Strain engineering in two-dimensional nanomaterials holds significant potential for modulating the lattice and band structure, particularly through localized strain, which enables modulation at specific regions. Despite the remarkable effects of local strain, the relationships among local strain, spatial correlation of photogenerated charge carriers, and photocatalytic performance remain elusive. The current study coupled single-molecule localization microscopy with coordinate-based colocalization (CBC) analysis to explain these relationships. The methodology involved mapping the spatial distributions of photoinduced oxidation and reduction reaction sites across graphitic carbon nitride (g-C3N4) nanosheets, quantifying and spatially resolving their spatial correlation, and also evaluating their photocatalytic activity. The study examined 65 individual g-C3N4 nanosheets, revealing interparticle and intraparticle heterogeneity, which was classified based on their CBC score distributions. Among the 65 g-C3N4 nanosheets, type A nanosheets predominated (45 out of 65) and demonstrated both correlated and noncorrelated subregions along some wrinkles. In contrast, type B nanosheets (20 out of 65) were primarily characterized by noncorrelated subregions with minimal correlated localizations. The coexistence of both noncorrelated and correlated subregions inferred the structure of the wrinkles as folding wrinkles, which have larger tensile-strained areas than rippling wrinkles. Folding wrinkles promote colocalization through the formation of type I band alignment at tensile-strained subregions. This band alignment also enhances photocatalytic activity through a funneling effect and improved light absorption, leading to higher specific activity in correlated subregions compared to noncorrelated ones. The role of strain-induced band alignment in modulating the spatial correlation of the photoredox reaction and the photocatalytic performance at the subregion level is highlighted.

DFT investigation on thermoelectric, electronic, optoelectronic, elastic, and structural properties of sodium‐based halide double perovskites Rb2NaSbZ6 (Z = Cl, Br, and I)

AbstractSodium‐based halide double perovskites (HDPs) present a promising alternative to Pb‐based perovskites for safe solar and thermal energy conversion devices due to their high durability and non‐toxic elements. This study examines the electronic, thermoelectric, elastic, optoelectronic, and structural properties of Rb2NaSbZ6 (Z = I, Br, Cl) double perovskite compounds using density functional theory (DFT). These compounds, characterized by a cubic structure, show increasing structural parameters as halogens are substituted from chlorine to iodine. Structural stability is confirmed by evaluating the enthalpy of formation, Gibbs free energy, Born and Huang criteria, and tolerance factor. Pugh's ratio indicates the ductile nature of the compounds. All investigated halide compounds exhibit an indirect band gap ranging from 3.9 to 2.34 eV, with valence and conduction band extrema located at different symmetry points, and a higher effective mass of holes is noted. This study also analyzes the refractive index, optical loss, light absorption, and polarization across the energy range of 0–10 eV. The spectral characteristics indicate that these HDPs are suitable for optoelectronic and photovoltaic devices due to their absorption in the visible and near‐ultraviolet spectra. High figures of merit (0.45–0.6) derived from power factor and thermal conductivity calculations suggest the potential of these compositions as thermoelectric devices. These findings provide a comprehensive understanding of these materials, facilitating their further deployment.

Bismuth-Metal and Carbon Quantum Dot Co-Doped NiAl-LDH Heterojunctions for Promoting the Photothermal Catalytic Reduction of CO2.

The quest for sustainable photocatalytic CO2 reduction reactions (CRR) emphasizes the development of high-efficiency, economically viable, and durable photocatalysts. A novel approach involving the synthesis of Bi-CDs/LDH heterojunctions, incorporating plasma metals and carbon quantum dots via hydrothermal and co-precipitation methods, yields remarkable results. The optimized BCL-4 photocatalyst demonstrates exceptional performance, with C2H4 and C2H6 yields of 1.35 and 2.17µmolg-1h-1, respectively, representing substantial enhancements of 11.25 and 14.47 times compared to the LDH monomer. Moreover, the catalyst exhibits a notable selectivity of 36.6% for C2 products. Plasmonic Bi with high conductivity and carbon quantum dots synergistically enhances visible light absorption and generated additional hot electrons. The electron-trapping ability of carbon quantum dots is pivotal in creating elevated electron and CO2 concentrations at the catalyst interface, fostering conditions conducive to promoting C─C coupling reactions for the generation of C2 products.

Thermodynamic Optoelectronic and Photovoltaic Properties of Al-doped Boron Arsenide alloy

Abstract This study investigates the electronic, optical, thermoelectric, and thermodynamic properties of BAs using Density Functional (DFT) and Semi-Classical Boltzmann theories. The band gap, initially determined by the GGA approximation, is refined using the TB-mBJ method, HSE, SOC and GGA+U inelectronic property. Our calculations show a significant reduction in the band gap closed by the various approaches when aluminum (Al) is introduced into the BAs lattice, extending the material`s light absorption spectrum into the visible range. The thermoelectric properties of both pure and Al-doped BAs are evaluated near the Fermi level at various temperatures. The positive Seebeck coefficient indicates p-type behavior, and Al incorporation enhances electrical conductivity. The mechanical properties indicate that the compounds are stable. These findings denote potential applications for Al-doped BAs in thermoelectric and optoelectronic devices.

Effect of Calcination-Induced Oxidation on the Photocatalytic H2 Production Performance of Cubic Cu2O/CuO Composite Photocatalysts

This study explores the H2 production performance of CuO/Cu2O with different morphology (nanocubes) synthesized by different methods using different sacrificial reagent (lactic acid), compared with the other three reported CuO/Cu2O photocatalysts used for H2 production. A cubic Cu2O photocatalyst was prepared using a hydrothermal method. It was then calcined at a certain temperature to form a cubic Cu2O/CuO composite photocatalyst. XRD, TEM, and XPS spectra confirmed the successful synthesis of cubic Cu2O/CuO composite photocatalysts by calcination-induced oxidation at a certain temperature. As the calcination temperature increases, the crystal phase of the photocatalyst changes from Cu2O to Cu2O/CuO and then to CuO. The effects of calcination-induced oxidation on morphology, light absorption, the separation of photoexcited carriers, and the H2 production activity of photocatalysts were studied. EPR spectra were monitored to analyze the oxygen vacancies in different samples. Mott–Schottky and Tauc plots were utilized to establish the band structure of the composite photocatalyst. Cu2O/CuO is a type II photocatalyst with a heterogeneous structure that helps to improve electron–hole separation efficiency. The H2 production efficiency of Cu2O/CuO composite photocatalyst reaches 11,888 μmol h−1g−1, 1.6 times that of Cu2O. The formation of the Cu2O/CuO heterojunction leads to enhanced light absorption, charge separation, and hydrogen production activity.

Hierarchically Promoted Light Harvesting and Management in Photothermal Solar Steam Generation.

Solar steam generation (SSG) presents a promising approach to addressing the global water crisis. Central to SSG is solar photothermal conversion that requires efficient light harvesting and management. Hierarchical structures with multi-scale light management are therefore crucial for SSG. At the molecular and sub-nanoscale levels, materials are fine-tuned for broadband light absorption. Advancing to the nano- and microscale, structures are tailored to enhance light harvesting through internal reflections, scattering, and diverse confinement effects. At the macroscopic level, light capture is optimized through rationally designed device geometries, configurations, and arrangements of solar absorber materials. While the performance of SSG relies on various factors including heat transport, physicochemical interactions at the water/air and material/water interfaces, salt dynamics, etc., efficient light capture and utilization holds a predominant role because sunlight is the sole energy source. This review focuses on the critical, yet often underestimated, role of hierarchical light harvesting/management at different dimensional scales in SSG. By correlating light management with the structure-property relationships, the recent advances in SSG are discussed, shedding light on the current challenges and possible future trends and opportunities in this domain.

Fabrication of Black Silicon Antireflection Coatings to Enhance Light Harvesting in Photovoltaics

Black silicon has attracted significant interest for various engineering applications, including solar cells, due to its ability to create highly absorbent surfaces or interfaces for light. It enhances light absorption in crystalline solar cells, improving the efficiency of converting incident light into electricity for photovoltaic applications. This research focused on fabricating nanostructures that played a critical role in enhancing light absorption in the upper layers of solar cells. These nanostructures were created using the black silicon method, forming a layer known as “black silicon”. The coating not only improved the efficiency of crystalline solar cells but also enhanced their stability. The antireflection coating, composed of nanostructures with various shapes, including conical, pillar-like, and spike-like forms, achieved a reflectivity as low as 10% in the spectral range of 400–700 nm. This corresponded to a sample with α = 0.85 and a chuck bias of 4 W. An Inductively Coupled Plasma Reactive Ion Etching (ICP RIE) machine was employed to develop and control the specific shape, size, and density of the fabricated black silicon, which was then subjected to testing. The efficiency of the black silicon photovoltaic cell was 23.3%.

YOLOV7-BASED MOVING OBJECT DETECTION IN DENSE FOG CONDITIONS

Detecting moving objects in dense foggy conditions is a challenging problem in computer vision, with critical applications in smart transportation systems, surveillance, and autonomous driving. Fog particles scatter and absorb light, significantly reducing visibility and making it difficult for traditional computer vision algorithms to accurately detect moving objects. To address this challenge, researchers have proposed learning-based approaches that leverage deep neural networks to recognize moving objects and adapt to the unique characteristics of foggy environments. In this study, we present a learning-based method utilizing the YOLOv7 framework to effectively detect moving objects in dense fog conditions. The proposed approach involves four key stages: feature extraction, feature fusion, object detection, and non-maximum suppression. The results achieved are highly promising when compared to state-of-the-art techniques.