Low Incident Light Intensity Research Articles

High Rejection‐Ratio IGZO Ultraviolet Phototransistor via Additional Solution Processed ZnO Absorption Layer

AbstractThe depletion of the ozone layer over the last four decades has increased Earth's exposure to ultraviolet (UV) radiation, posing significant health risks. Indium‐Gallium‐Zinc‐Oxide (IGZO) phototransistors have emerged as promising UV detection candidates, boasting a wide bandgap (>3 eV), low off‐current, high on‐current, and stability. However, previous efforts to enhance the photoresponse of IGZO phototransistors focused on visible light absorption layers, neglecting UV detection. Here, zinc oxide (ZnO) nanoparticles (NPs) as an absorption layer in IGZO TFTs for UV phototransistors are introduced. IGZO/ZnO TFTs exhibit robust photoresponsivity for UV light below 360 nm, showcasing rejection ratios (Ruv / Rvis) of 20 258, 62 261, 193 649, and 401 582 for wavelengths of 360, 340, 320, and 300 nm, respectively. The combination of IGZO's wide bandgap with ZnO NPs proves effective for detecting UV light below 360 nm, even at low incident light intensities (15 µW cm−2). Enhanced photoresponse characteristics are confirmed via ultraviolet photoelectron spectroscopy. This research highlights the potential of IGZO materials for UV phototransistors and introduces a novel perspective on the utilization of an additional absorption layer traditionally employed for the conventional extension into the visible light range.

High‐Performance Air‐Stable 2D‐WSe2/P3HT Based Inorganic–Organic Hybrid Photodetector with Broadband Visible to Near‐IR Light Detection

AbstractPhotodetectors that can achieve high‐speed photoresponse and high responsivity with broadband detection are essential for bio‐health monitoring, imaging, chemical sensing, and many other applications. Herein a high‐performance inorganic–organic hybrid photodetector based on a heterojunction of exfoliated 2D tungsten diselenide (WSe2) layers and solution‐processable poly(3‐hexylthiophene‐2,5‐diyl), P3HT is reported. The heterojunction shows enhanced exciton harvesting through long‐range energy transfer from P3HT to WSe2, which is confirmed using photoluminescence quenching and fluorescence decay measurements. The detector shows broadband light detection from visible to near‐infrared (NIR) (400−1100 nm), and air‐stable device performance. The device exhibits the highest responsivity of 17.6 AW−1 for low incident light intensity (<10−5 W cm−2) at 640 nm wavelength of light. Furthermore, a fast photoresponse speed with a rise/fall time of 9.5/5.1 µs, which retained its performance for more than four months under ambient conditions is demonstrated. The superior device performance presented here using an inorganic–organic hybrid heterojunction is the key to producing novel high‐performance and air‐stable photodetectors with broad spectral bandwidth.

SnO2-NiO heterojunction based self-powered UV photodetectors

Thin film p-n heterojunction diodes using NiO and SnO2 are fabricated, and the performances are studied. NiO was deposited using rf magnetron sputtering and SnO2 using the electron beam evaporation technique. The diodes are fabricated in the configuration, FTO/SnO2/NiO/Au, with two different device areas; smaller with 0.35 mm circular diameter and larger with 2 × 2 mm square. The smaller device has a reverse leakage current of 20 µA at − 2 V, turn-on voltage of 1.2 V, and diode rectification ratio of 160, which are much higher than the reported SnO2/NiObased diodes. On the other hand, the larger area device exhibits a smaller rectification ratio of 4. UV photoelectron spectroscopy (UPS) analysis was carried out, and the work function of NiO was calculated as 5.31 eV. The deduced staggered band alignment of SnO2/NiO favors the effective separation of photogenerated charge carriers when illuminated with UV light. Subsequently, the diodes were tested for UV photodetection. Remarkably, the FTO/SnO2/NiO/Au diodes display self-powered UV photodiode characteristics using 365 nm light. Photoresponsivity of 3.3 mA/W, ON/OFF ratio of 4.16 × 104, and detectivity of 7.4 × 1010 Jones are obtained for the larger area device. At low incident light intensity, the larger area device exhibited a response time of 89 ms.

Detection model of copper based on polarization degree induced by low-energy density laser.

In order to analyze the mechanism of plasma polarization characteristics and the improvement effect of spectral signal-to-back ratio, the intensity formulas of continuous spectrum and discrete spectrum were derived by exploring the path of the radiation spectrum. At the Brewster angle, the model of polarization degree was established based on the measured spectral data to identify the radiation intensity of plasma. The experimental results showed that the polarization characteristics of the background and discrete spectrum were both observed in the plasma spectrum of a copper element, and there were obvious differences in polarization degree and vibration direction. Moreover, cadmium and chromium were used to verify the detection model. It was found that the characteristic signals of the polarization spectrum were more than the effective peaks in laser-induced breakdown spectroscopy, and the variation trend was relatively gentle. The model retained the effective information in the continuum spectrum and fully explored the basic polarization mechanism of plasma. The measured data were not only convenient to observe the characteristic signal peaks of elements, but also greatly improved the recognition effect. This method could extract effective information of illumination plasma under the condition of low incident light intensity and reduce the damage of medium surface, which is a more effective nondestructive testing technology.

Silver Nanowires Modified Flexible Dye-Sensitive Solar Cells and Application With the Internet of Things Under Low Illumination

Silver nanowires (AgNWs) possess excellent mechanical strength, electrical conductivity, and superior flexibility, thus making them exceptional candidates for dopant nanometal. A photoanode modified with AgNWs-titanium dioxide (TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) composite film was prepared and used in flexible dye-sensitized solar cells (DSSCs). The AgNWs were synthesized by a stable polyol method. We employed the field-emission scanning electron microscope and an X-ray diffractometer to characterize the AgNWs. The measurement of the photovoltaic parameters of flexible DSSCs in the basic environment was conducted (air mass (AM) 1.5, 100 mW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ). Compared with the flexible DSSC based on pure TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , the flexible DSSCs based on AgNWs-TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> had a higher short-circuit current density and photovoltaic conversion efficiency, and the efficiency was increased by 37.40%. The impedance among the photoanode, dye, and electrolyte interface was identified by the electrochemical impedance spectroscopy. We also employed filters to better investigate the photovoltaic conversion efficiency at low incident light intensity. Furthermore, the flexible DSSCs devices were interfaced with an IoT system for the measurement of the stability of flexible DSSCs under long-term use to occur. We measured the flexible DSSCs continuously for 30 days. The photovoltaic conversion efficiency was lost only 10% in 20 days. This suggests that the flexible DSSCs have good mechanical stability, and the adhesion between the AgNWs-TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> photoanodes and the flexible substrate.

Suppressing material loss in the visible and near-infrared range for functional nanophotonics using bandgap engineering

All-dielectric nanostructures have recently opened exciting opportunities for functional nanophotonics, owing to their strong optical resonances along with low material loss in the near-infrared range. Pushing these concepts to the visible range is hindered by their larger absorption coefficient, thus encouraging the search for alternative dielectrics for nanophotonics. Here, we employ bandgap engineering to synthesize hydrogenated amorphous Si nanoparticles (a-Si:H NPs) offering ideal features for functional nanophotonics. We observe significant material loss suppression in a-Si:H NPs in the visible range caused by hydrogenation-induced bandgap renormalization, producing strong higher-order resonant modes in single NPs with Q factors up to ~100 in the visible and near-IR range. We also realize highly tunable all-dielectric meta-atoms by coupling a-Si:H NPs to photochromic spiropyran molecules. ~70% reversible all-optical tuning of light scattering at the higher-order resonant mode under a low incident light intensity is demonstrated. Our results promote the development of high-efficiency visible nanophotonic devices.

Recent Progress in Solar Cell Technology for Low-Light Indoor Applications

Photovoltaic cells have recently attracted considerable attention for indoor energy harvesting for low-power-consumption electronic products due to the rapid growth of the Internet of Things (IoT). The IoT platform is being developed with a vision of connecting a variety of wireless electronic devices, such as sensors, household products, and personal data storage devices, which will be able to sense and communicate with their internal states or the external environment. A self-sustainable power source is required to power such devices under low light indoor environments. Inorganic photovoltaic cells show excellent device performance under 1 Sun illumination and dominate the market for outdoor applications. However, their performance is limited for indoor applications with low incident light intensities as they exhibit low photo-voltage. Among the emerging photovoltaic technologies, organic photovoltaics have unique advantages, including solution processibility, flexibility, and lightweight tailorable design; hence, they are considered the best solution for indoor light harvesting applications due to their high photo-voltage, strong absorption of UV-visible wavelengths, and a spectral response similar to that emitted by modern indoor lighting systems. In this review article, we discuss the factors affecting device performance of different photovoltaic technologies under low incident light intensities or indoor conditions and provide a comprehensive analysis of future opportunities for enhancing indoor performance of the photovoltaic devices. Furthermore, we discuss some of the results of semi-transparent organic solar cell which is operated under complex environmental conditions like low illumination, incident light angle etc. Based on the results, one can suggest that semi-transparent organic solar cell is more suitable for progressive indoor solar cell. After highlighting the factors that limit indoor device performance of photovoltaic cells, we discuss potential applications of IoT devices powered by organic photovoltaic cells in indoor lighting environments.

Interference-enhanced infrared-to-visible upconversion in solid-state thin films sensitized by colloidal nanocrystals

Infrared-to-visible photon upconversion has potential applications in photovoltaics, sensing, and bioimaging. We demonstrate a solid-state thin-film device that utilizes sensitized triplet-triplet exciton annihilation, converting infrared photons absorbed by colloidal lead sulfide nanocrystals (NCs) into visible photons emitted from a luminescent dopant in rubrene at low incident light intensities. A typical bilayer device consisting of a monolayer of NCs and a doped film of rubrene is limited by low infrared absorption in the thin NC film. Here, we augment the bilayer with an optical spacer layer and a silver-film back reflector, resulting in interference effects that enhance the optical field and thus the absorption in the NC film. The interference-enhanced device shows an order-of-magnitude increase in the upconverted emission at the wavelength of λ = 610 nm when excited at λ = 980 nm. At incident light intensities above 1.1 W/cm2, the device attains maximum efficiency, converting (1.6 ± 0.2)% of absorbed infrared photons into higher-energy singlet excitons in rubrene.

Large enhancement of third-order nonlinear effects with a resonant all-dielectric metasurface

A novel low-profile nonlinear metasurface, consisting of a single-layer of all-dielectric material, is proposed and numerically investigated by a nonlinear full-wave finite-difference time-domain (FDTD) method. The proposed metasurface is transparent for low, and opaque for high values of incident light intensity. The metasurface design is broadly applicable to enhancement of intrinsic nonlinearities of any material with a sufficiently high refractive index contrast. We illustrate the ability of this design to enhance intrinsic nonlinear absorption of a transition metal oxide, vanadium pentoxide (V2O5), with resonant metasurface elements. The complex third-order nonlinear susceptibility (χ(3)) for V2O5, representing both nonlinear refraction and absorption is considered in FDTD simulations. Our design achieves high initial transparency (&amp;gt;90%) for low incident light intensity. An order of magnitude decrease in the required input light intensity threshold for nonlinear response of the metasurface is observed in comparison with an unpatterend film. The proposed all-dielectric metasurface in this work is ultrathin and easy to fabricate. We envision a number of applications of this design for thin film coatings that offer protection against high-power laser radiation.

Visible-near infrared ultra-broadband polarization-independent metamaterial perfect absorber involving phase-change materials

We numerically demonstrate a novel ultra-broadband polarization-independent metamaterial perfect absorber in the visible and near-infrared region involving the phase-change material Ge2Sb2Te5 (GST). The novel perfect absorber scheme consists of an array of high-index strong-absorbance GST square resonators separated from a continuous Au substrate by a low-index lossless dielectric layer (silica) and a high-index GST planar cavity. Three absorption peaks with the maximal absorbance up to 99.94% are achieved, owing to the excitation of plasmon-like dipolar or quadrupole resonances from the high-index GST resonators and cavity resonances generated by the GST planar cavity. The intensities and positions of the absorption peaks show strong dependence on structural parameters. A heat transfer model is used to investigate the temporal variation of temperature within the GST region. The results show that the temperature of amorphous GST can reach up to 433 K of the phase transition temperature from room temperature in just 0.37 ns with a relatively low incident light intensity of 1.11×108 W/m2, due to the enhanced ultra-broadband light absorbance through strong plasmon resonances and cavity resonance in the absorber. The study suggests a feasible means to lower the power requirements for photonic devices based on a thermal phase change via engineering ultra-broadband light absorbers.

Strongly tunable circular dichroism in gammadion chiral phase-change metamaterials

A metal/phase-change material/metal tri-layer planar chiral metamaterial in the shape of a gammadion is numerically modelled. The chiral metamaterial is integrated with Ge2Sb2Te5 phase-change material (PCM) to accomplish a wide tuning range of the circular dichroism (CD) in the mid-infrared wavelength regime. A photothermal model is used to study the temporal variation of the temperature of the Ge2Sb2Te5 layer and to show the potential for fast switching the phase of Ge2Sb2Te5 under a low incident light intensity of 0.016mW/μm2.

Silver-nanoparticles immobilized initiators and co-initiators for free radical polymerization

Summary — The specific properties of silver-nanoparticles immobilized initiator and co-initiators for free radical polymerization have been described. The silver-nanoparticles immobilized mercaptobenzophenone (Bp-MPCs) photoinitiates free radical polymerization in both UV and visible regions. The photoinitiation ability of Bp-MPCs in visible region, e.g. in the region in which benzophenone chromophore does not absorb a light, indicates a possible two-photon action even at low incident light intensity. The co-initiation process caused by silver-nanoparticles immobilized mercaptoamino acids (MA-MPCs) is more efficient in comparison to co-initiation observed for corresponding free mercaptoamino acid. This behavior can be attributed the specific interaction of sulfur electrons with surface plasmon electrons that make an electron transfer from mercaptoamino acid to excited electron acceptor more efficient, or to a high concentration of the elec

Squeezing in strong light scattered by a regular structure of atoms

Squeezing in the resonance fluorescence emitted by a regular structure of atoms is discussed. Intense squeezed light fields are a prerequisite, e.g., for efficient measurements with sensitivity below the standard quantum limit. Regular structures are known to offer macroscopic squeezed light due to the fixed phase relation between the light scattered by the respective atoms, but typically restrict squeezing to low incident light intensity. As our main result, we demonstrate that this restriction to low driving field intensity can be circumvented. For this, we assume a suitable modification of the surrounding electromagnetic bath, as it can be achieved, e.g., with a cavity. The modified environment leads to a redistribution of the collective dressed state populations, such that squeezing is recovered at strong driving. In such modified environments, squeezing even occurs for a resonant driving field, in contrast to the regular vacuum case.

Semiconductor-Metal Nanoparticle Molecules: Hybrid Excitons and the Nonlinear Fano Effect

Modern nanotechnology opens the possibility of combining nanocrystals of various materials with very different characteristics in one superstructure. Here we study theoretically the optical properties of hybrid molecules composed of semiconductor and metal nanoparticles. Excitons and plasmons in such a hybrid molecule become strongly coupled and demonstrate novel properties. At low incident light intensity, the exciton peak in the absorption spectrum is broadened and shifted due to incoherent and coherent interactions between metal and semiconductor nanoparticles. At high light intensity, the absorption spectrum demonstrates a surprising, strongly asymmetric shape. This shape originates from the coherent internanoparticle Coulomb interaction and can be viewed as a nonlinear Fano effect which is quite different from the usual linear Fano resonance.

Balance between microbial calcification and metazoan bioerosion in modern stromatolitic oncolites

ABSTRACTStromatolites date back some 3.5 billion years and constitute the most common and conspicuous fossils through the Proterozoic. These organosedimentary structures decreased dramatically in diversity and abundance by the late Neoproterozoic, a phenomenon often ascribed to destructive grazing by newly evolved metazoans. We investigated the concurrent processes of microbial calcification and metazoan bioerosion in one of the few locations (Rio Mesquites, Cuatro Ciénegas, Coahuila, Mexico) where living freshwater stromatolites, formed by cyanobacteria and diatoms, coexist with significant populations of metazoan grazers. We used microsensor chemical profiling and monitoring of bulk water Ca2+concentrations to determine calcification rates and their dependence on microbial metabolism. The bioerosive impact resulting from grazing by endemic hydrobiid gastropods was assessed by gravimetric quantification of carbonaceous faecal pellet production. Calcification was clearly light‐dependent, reaching maximal rates (saturation) at low incident light intensity, and was surprisingly efficient, with O2/Ca2+exchange ratios well above unity, and with absolute rates similar to those found in corals. However, the erosive action of grazing snails removed most of these carbonate inputs from the oncolites. Thus, a precarious balance between constructive and destructive geobiological processes was at play in the system. The fact that accretion barely exceeded bioerosion in an environment highly conducive to calcification supports the potential impact of faunal grazing as causal agent in the demise of stromatolites in the late Proterozoic. Our findings indicate that a search for fossil evidence of bioerosive grazing in the form of carbonaceous faecal pellets associated with fossil stromatolites may provide a means to test that hypothesis directly.

Dependence of the Photocurrent Conversion Efficiency of Dye-Sensitized Solar Cells on the Incident Light Intensity

The incident photon to current conversion efficiency (IPCE) of dye-sensitized solar cells is measured as a function of the incident photon current density. A characteristic dependence of the IPCE on the incident light intensity with a maximum value for absorbed photon current densities in the range of jγ,abs = 1017 cm-2 s-1 is observed for all cells investigated in this study. The IPCE decreases significantly for large absorbed photon current densities (jγ,abs > 1018 cm-2 s-1) and for small absorbed photon current densities (jγ,abs < 1016 cm-2 s-1). The decrease of the IPCE at large incident light intensities is due to the diffusion limitation of the electrolyte within the nanocrystalline TiO2 electrode. The decrease of the IPCE at low incident light intensities can be explained by the loss of photogenerated electrons via surface-state-mediated electron transfer into the electrolyte. The strong dependence of the IPCE on the incident light intensity has consequences for the efficiency of a dye-sensitized solar cell at low illumination levels. It also suggests that spectral measurements of the IPCE of dye-sensitized solar cells and of nanocrystalline electrodes cannot be used to predict the solar or white light IPCE unless they were taken with bias light or with very high intensities of monochromatic light, especially at weakly absorbed wavelengths.

Photoelectrical properties of double-layer organic solar cells using C60 and phthalocyanines

The photoelectrical properties of p-n junction organic solar cells based on C60 and phthalocyanines (mainly oxotitanium (IV) phthalocyanine (OTiPc)) were investigated. With the Al/C60/OTiPc/ITO configuration, the energy conversion efficiencies (η) are high at low incident light intensities (pin), due to the formation of a p-n junction between C60 and OTiPc, but decrease with an increase in pin. On the other hand, ITOC60OTiPcCr·Au cells are stable even under white-light illumination at high pin. It was found that the insertion of an SiO2 insulator layer between OTiPc and Cr· Au significantly enhances the short-circuit current, the open-circuit voltage and η.

Photolithotrophic cultivation of Laminaria saccharina gametophyte cells in a bubble-column bioreactor

The photolithotrophic cultivation of a novel cell suspension culture derived from the microscopic, filamentous gametophyte life phase of the complex brown alga Laminaria saccharina was feasible in an illuminated bubble-column bioreactor at 13°C using CO 2 in air as the sole carbon source for growth. Maximum cell densities exceeding 1,000 mg dry cell weight (dcw) l −1 and specific growth rates of 0.15 day −1 were attained within a 20-day cultivation period. Initial cell density had a significant effect on the final biomass density of the clumped cell suspension, but no significant effect on the specific growth rate. Although the optimum aeration rate for culture growth was 1.0 l air min −1 l −1 culture (vvm), the culture was not CO 2-transport limited at 0.17–2.0 vvm. Initial nitrate concentrations at or above 63.5 mg NaNO 3 l −1 in the GP2 artificial seawater medium had no significant effect on the specific growth rate or final biomass density. Both specific growth rate and final biomass density data were correlated to incident light intensity over the range of 1–91.2 μE m −2 s −1 using an exponential model for light-saturated growth where light-saturated growth was achieved within a low-incident light intensity of 20 μE m −2 s −1.

Photobiotechnology: Application of photosynthesis to the production of renewable fuels and chemicals

Sustained hydrogen photoevolution fromChlamydomonas reinhardtii and C.moewusii was measured under an anoxic, CO2-containing atmosphere. It has been discovered that light intensity-and temperature influence the partitioning of reductant between the hydrogen photoevolution pathway and the Calvin cycle. Under low incident light intensity (1-3 Wm-2) or low temperature (≈ 0‡C), the flow of photosynthetic reductant to the Calvin cycle was reduced, and reductant was partitioned to the hydrogen pathway as evidenced by sustained H2 photoevolution. Under saturating light (25 W m-2) and moderate temperature (20 ± 5‡C), the Calvin cycle became the absolute sink for reductant with the exception of a burst of H2 occurring at light on. A novel photobiophysical phenomenon was observed in isolated spinach chloroplasts that were metalized by precipitating colloidal platinum onto the surface of the thylakoid membranes. A two-point irradiation and detection system was constructed in which a continuous beam helium-neon laser (λ = 632.8nm) was used to irradiate the platinized chloroplasts at varying perpendicular distances from a single linear platinum electrode in pressure contact with the platinized chloroplasts. No external voltage bias was applied to the system. The key objective of the experiments reported in this report was to measure the relative photoconductivity of the chloroplast-metal composite matrix.

Real-Time Edge Enhancement Using KNSBN at 633 nm

Edge enhancement has been performed in Ce-doped (K0.5Na0.5)2y (Sr0.61Ba0.39)1-yNb2O6 (KNSBN) crystal at 633 nm with low incident-light intensities (10-3 W/cm2). We calculated the expected images which show good agreement with the images that we have experimentally observed.