Constant Light Illumination Research Articles

Frequency-selective perovskite photodetector for anti-interference optical communications

Free-space coupling, essential for various communication applications, often faces significant signal loss and interference from ambient light. Traditional methods rely on integrating complex optical and electronic systems, leading to bulkier and costlier communication equipment. Here, we show an asymmetric 2D–3D–2D perovskite structure device to achieve a frequency-selective photoresponse in a single device. By combining two electromotive forces of equal magnitude in the opposite directions, the device output is attenuated to zero under constant light illumination. Because these reverse photodiodes have different response speeds, the device only responds near a certain frequency, which can be tuned by manipulating the 2D perovskite components. The target device achieves an ultrafast response of 19.7/18.3 ns in the frequency-selective photoresponse range 0.8–9.7 MHz. This anti-interference photodetector can accurately transmit character and video data under strong light interference with a source intensity of up to 454 mW cm−2.

Self-regulated reversal deformation and locomotion of structurally homogenous hydrogels subjected to constant light illumination

Environmentally adaptive hydrogels that are capable of reconfiguration in response to external stimuli have shown great potential toward bioinspired actuation and soft robotics. Previous efforts have focused mainly on either the sophisticated design of heterogeneously structured hydrogels or the complex manipulation of external stimuli, and achieving self-regulated reversal shape deformation in homogenous hydrogels under a constant stimulus has been challenging. Here, we report the molecular design of structurally homogenous hydrogels containing simultaneously two spiropyrans that exhibit self-regulated transient deformation reversal when subjected to constant illumination. The deformation reversal mechanism originates from the molecular sequential descending-ascending charge variation of two coexisting spiropyrans upon irradiation, resulting in a macroscale volumetric contraction-expansion of the hydrogels. Hydrogel film actuators were developed to display complex temporary bidirectional shape transformations and self-regulated reversal rolling under constant illumination. Our work represents an innovative strategy for programming complex shape transformations of homogeneous hydrogels using a single constant stimulus.

Light‐Fueled Nonequilibrium and Adaptable Hydrogels for Highly Tunable Autonomous Self‐Oscillating Functions

AbstractNonequilibrium oscillation fueled by dissipating chemical energy is ubiquitous in living systems for realizing a broad range of complex functions. The design of synthetic materials that can mimic their biological counterparts in the production of dissipative structures and autonomous oscillations is of great interest but remains challenging. Here, a series of environmentally adaptable hydrogels functionalized with photoswitchable spiropyran derivatives that display a tunable equilibrium‐shifting capability, thus endowing those hydrogels with a high degree of freedom and flexibility is reported. Such nonequilibrium hydrogels are able to responsively adapt their shapes under constant light illumination due to asymmetric deswelling, which in turn generates self‐shadowing and consequently creates autonomous self‐oscillating behaviors through a negative feedback process. Diverse oscillation modes including bending, twisting, and snap‐through buckling with tunable frequency and amplitude are widely observed in three different molecular systems. Density functional theory calculations and finite element simulations further demonstrated the robustness of such a photoadaptable self‐oscillation mechanism. This study provides a useful molecular design strategy for construction of highly adaptable hydrogels with potential applications in self‐sustained soft robots and autonomous devices.

Design of SnO2 Electron Transport Layer in Perovskite Solar Cells to Achieve 2000 h Stability Under 1 Sun Illumination and 85 °C

AbstractIn order to realize both efficient and stable perovskite solar cells, designing electron transport layer (ETL) is of crucial importance to withstand constant light illumination and thermal stress while maintaining high charge extractability. Herein, commonly used SnO2 nanoparticle‐based ETL for perovskite solar cells is modified by ionic‐salt ammonium chloride (NH4Cl) and tin chloride dihydrate (SnCl2∙2H2O) as additives, which is easily fabricated by simple one‐step spin coating of single precursor solution. With the presence of these dual additives at the ETL, the crystallinity of the upper perovskite layer is clearly enhanced. Defect analyses on the devices suggest that these modifications can effectively passivate trap sites that reside within the ETL and at the perovskite interfaces with the carrier‐transport layers. As a result, the modified SnO2 ETL results in an improvement of device stability under thermal or light stress condition, maintaining over 80% of its initial efficiency after ≈2000 h storage under elevated temperature (85 °C) and after ≈2400 h of operation under 1 sun illumination.

High efficiency inverted organic solar cells with photo annealing titanium oxide films as electron extract layer

Photo-annealing treatment has successfully been demonstrated in organic solar cells (OSCs) with solution-processable titanium (diisopropoxide) bis(2,4-pentanedionate) (TIPD) as an electron extraction layer; this process was shown without thermal annealing treatment. The power conversion efficiency (PCE) is quite low in the initial stage, though it dramatically increases following constant light illumination and reaches a saturated state after 9 min of light illumination. X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) and ultraviolet photoemission spectroscopy (UPS) were used, and they showed that the TIPD molecules decomposed and formed stable TiO bonds. According to photocurrent density-effective voltage curve (Jph-Veff), short-circuit current density (JSC) and open-circuit voltage (VOC) value under different light intensity, the photo-annealed TIPD-based OSCs showed efficient charge transport and suppressed charge recombination. Thus, after a fresh TIPD solution was spin-coated onto the indium tin oxide (ITO) surface and photo-annealed for 9 min, the OSCs showed the highest photovoltaic performance compared to ZnO-based OSCs.

Light-activated interlayer contraction in two-dimensional perovskites for high-efficiency solar cells.

Understanding and tailoring the physical behaviour of halide perovskites under practical environments is critical for designing efficient and durable optoelectronic devices. Here, we report that continuous light illumination leads to >1% contraction in the out-of-plane direction in two-dimensional hybrid perovskites, which is reversible and strongly dependent on the specific superlattice packing. X-ray photoelectron spectroscopy measurements show that constant light illumination results in the accumulation of positive charges in the terminal iodine atoms, thereby enhancing the bonding character of inter-slab I-I interactions across the organic barrier and activating out-of-plane contraction. Correlated charge transport, structural and photovoltaic measurements confirm that the onset of the light-induced contraction is synchronized to a threefold increase in carrier mobility and conductivity, which is consistent with an increase in the electronic band dispersion predicted by first-principles calculations. Flux-dependent space-charge-limited current measurement reveals that light-induced interlayer contraction activates interlayer charge transport. The enhanced charge transport boosts the photovoltaic efficiency of two-dimensional perovskite solar cells up to 18.3% by increasing the device's fill factor and open-circuit voltage.

Enhanced photovoltaic performance of polymer solar cells with photo-annealed titanium chelate

Photo-annealing treatment titanium chelate (TIPD) layer, which was the indium tin oxide (ITO) interface-modified layer, was used as a replacement for the thermal annealing treatment of TIPD. The power conversion efficiency (PCE) of photo-annealed TIPD-based polymer solar cells (PSCs) is quite low in the initial stage, but it dramatically increases following constant light illumination, and the cell achieves a saturated state after 9 min of light illumination. By employing the mixed films poly[1-(5-(4,8-bis(5-(2-ethylhexyl)-4-fluorothiophen-2-yl)-6-methylbenzo[1,2-b:4,5-b′]dithiophen-2-yl)thiophen-2-yl)-5,7-bis(2-ethylhexyl)-3-(5-methylthiophen-2-yl)-4H,8H-benzo[1,2-c:4,5-c′]dithiophene-4,8-dione] (PBDB-TF) and 2,2′-((2Z,2′Z)-(((4,4,9,9-tetrakis-(4-hexylphenyl)-4,9-dihydro-sindaceno[1,2-b:5,6-b’]-dithiophene-2,7-diyl)bis(4-((2-ethylhexyl)oxy)thiophene-5,2-diyl))bis(methanylylidene))bis(5,6-difluoro-3-oxo-2,3-dihydro-1H-indene-2,1-diylidene)) dimalononitrile (IEICO-4F) as photoactive layers, we improved the photovoltaic performance. The enhanced photovoltaic performance of TIPD films treated with photo-annealing was explained by the increased short-circuit current density (JSC). Efficient medium- and long-wavelength light transmittance and suppression of charge recombination are beneficial for enhancing the JSC value.

Piezoresistive Microcantilever with SAM-Modified ZnO-Nanorods@Silicon-Nanopillars for Room-Temperature Parts-per-Billion NO2 Detection

Organic–inorganic hybrids are ideal for gas detection, considering their selectivity and sensitivity to single gas species under moderate working conditions. However, the poor surface-to-volume ratio and low electron density of organic materials hinder their application in high-performance resistive gas sensors. Instead herein, a gravimetric sensor is realized on the basis of an in-plane self-actuating and self-reading piezoresistive microcantilever-chip (PMC), which is patterned with an (inorganic) 3D framework of ZnO nanorods on a Si-nanopillar array (3D ZnO-NRs@Si-NPLs) and functionalized by a thin (organic) self-assembled monolayer (SAM, (3-aminopropyl)­trimethoxysilane (APTES)) for interacting with NO2. For stable adsorption/desorption rates of NO2, this SAM-on-3D ZnO-NRs@Si-NPL PMC (S3-PMC) was exposed to constant light illumination by an LED (wavelength: 530 nm, intensity: 10 mW/cm2), realizing a limit of detection (LOD) of about 2 parts per billion by volume (ppbv) for NO2 at room temperature, together with fast response and complete recovery within times of 42.1 ± 6.6 s and 112 ± 17.4 s, respectively, to NO2 concentrations ranging up to 1000 ppbv. Moreover, the sensor shows reliable stability under both short- and long-time (31 days) exposure to NO2, where resonance frequency-shift deviations of merely at most ±5% and ±9%, respectively, are observed. These unprecedented results indicate an enormous potential of the S3-PMC for portable gas sensor arrays in high-resolution real-time-monitoring applications.

An Autonomous Soft Actuator with Light‐Driven Self‐Sustained Wavelike Oscillation for Phototactic Self‐Locomotion and Power Generation

AbstractMimicking the intelligence of biological organisms in artificial systems to design smart actuators that act autonomously in response to constant environmental stimuli is crucial to the construction of intelligent biomimetic robots and devices, but remains a great challenge. Here, a light‐driven autonomous carbon‐nanotube‐based bimorph actuator is developed through an elaborate structural design. This curled droplet‐shaped actuator can be simply driven by constant white light irradiation, self‐propelled by a light‐mechanical negative feedback loop created by light‐driven actuation, time delay in the photothermal response along the actuator, and good elasticity from the curled structure, performing a continuously self‐oscillating motion in a wavelike fashion, which mimics the human sit‐up motion. Moreover, this autonomous self‐oscillating motion can be further tuned by controlling the intensity and direction of the incident light. The autonomous actuator with continuous wavelike oscillating motion shows immense potential in light‐driven biomimetic soft robots and optical‐energy‐harvesting devices. Furthermore, a self‐locomotive artificial snake with phototaxis is constructed, which autonomously and continuously crawls toward the light source in a wave‐propagating manner under constant light irradiation. This snake can be placed on a substrate made of triboelectric materials to realize continuous electric output when exposed to constant light illumination.

Retinal tissue oxygen tension and consumption during light flicker stimulation in rat

Light flicker stimulation has been shown to increase inner retinal oxygen metabolism and supply. The purpose of the study was to test the hypothesis that sustained light flicker stimulation of various durations alters the depth profile metrics of oxygen partial pressure in the retinal tissue (tPO2) but not the outer retinal oxygen consumption rate (QO2). In 17 rats, tPO2 depth profiles were derived by phosphorescence lifetime imaging after intravitreal injection of an oxyphor. tPO2 profile metrics, including mean inner retinal tPO2, maximum outer retinal tPO2 and minimum outer retinal tPO2 were determined. QO2 was calculated using a one-dimensional oxygen diffusion model. Data were acquired at baseline (constant light illumination) and during light flicker stimulation at 10 Hz under the same mean illumination levels, and differences between values obtained during flicker and baseline were calculated. None of the tPO2 profile metrics or QO2 differences depended on the duration of light flicker stimulation (R2 ≤ 0.03). No significant change in any of the tPO2 profile metrics was detected with light flicker compared with constant light (P ≥ 0.08). Light flicker decreased QO2 from 0.53 ± 0.29 to 0.38 ± 0.30 mL O2/(min*100 gm), a reduction of 28% (P = 0.02). The retinal compensatory responses to the physiologic challenge of light flicker stimulation were effective in maintaining the levels of oxygen at or near baseline in the inner retina. Oxygen availability to the inner retina during light flicker may also have been enhanced by the decrease in QO2.

Growth Kinetics for Microalgae Grown in Palm Oil Mill Effluent (POME) medium at various CO2 Levels

This paper sought to find the growth kinetic data of maximum specific growth rate (μmax) and substrate saturation constant (KS) for a microalgal reaction system over various dissolved CO2 levels (0.04, 0.1, 0.3, 0.5, 0.8, 1.0, 5.0, 10.0% v/v) at a constant sparging rate of 1.2 vvm, by using logistic model and Monod kinetics. The reaction system consisted of microalgae growing in palm oil mill effluent (POME) medium in 1 L flask with constant light illumination and sparged with the specified CO2 gas mixture. It is found from the experimental works that the values of μmax and KS to be at 0.04958 h-1 and 0.03523% (v/v) respectively. The results also showed that utilizing CO2 levels (v/v) in the sparging gas mixture more than 1% (v/v) would not improve microalgae growth significantly as expressed in the values of specific growth rate µ. These data and information are critically important for bioreactor scaling up purposes, especially bioreactor system dedicated for microalgae products and CO2 sequestration.

Making waves in a photoactive polymer film.

Oscillating materials1–4 that adapt their shape in response to an external stimulus are of interest for emerging applications in medicine and robotics. Liquid crystal networks have a prominent role in this area because they can be programmed to undergo stimulus-induced deformations in a variety of geometries, including in response to light5,6. In order to make these polymer networks photoresponsive, azobenzene molecules are often incorporated7–11. Most examples in the literature report on bending responses of these azobenzene modified films, where relaxation after photo-isomerization is rather slow. Modification of the core or addition of substituents to the azobenzene moiety can lead to drastic changes in photophysical and photochemical properties12–15 giving opportunity to circumvent the use of a complex set-up. Here we report on the incorporation of azo-derivatives with fast thermal relaxation into liquid crystal network films (LCN), to generate films that can exhibit continuous, directional macroscopic mechanical waves under constant light illumination, with a feedback loop driven by self-shadowing. A theoretical model and numerical simulation demonstrate this mechanism and show good qualitative agreement with experiments. We explore potential applications in light-driven locomotion and self-cleaning surfaces.

Core–shell photoanode developed by atomic layer deposition of Bi2O3 on Si nanowires for enhanced photoelectrochemical water splitting

Core–shell nanowire (NW) arrays, which feature a vertically aligned n-type Si NW core and a p-type α-Bi2O3 shell, are developed as a highly efficient photoanode that is suitable for water splitting. The morphology and structure of the heterostructure were characterized by scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDS), high-resolution transmission electron microscopy (HRTEM), x-ray photoelectron spectroscopy (XPS), and x-ray diffraction (XRD). The deposition of Bi2O3 nanolayers on the surface of the smooth Si NWs causes the surface of the NWs to become rough. The as-prepared core–shell NW photoelectrode has a relatively low reflectance in the visible light region, suggesting good light absorption. The core–shell NW arrays show greatly improved photoelectrochemical water-splitting performance. Photoelectrochemical stability for over 16 h under constant light illumination and fixed bias potential was achieved, illustrating the good stability of this core–shell NW photoanode. These Si/Bi2O3 core–shell NW arrays effectively combine the light absorption ability of the Si NWs and the wide energy gap and chemical stability of Bi2O3 for water splitting. This study furthers the attempts to design photoanodes from low-cost, abundant materials for applications in water splitting and photovoltaics.

Tailoring n-ZnO/p-Si Branched Nanowire Heterostructures for Selective Photoelectrochemical Water Oxidation or Reduction

We report the fabrication of three-dimensional (3D) branched nanowire (NW) heterostructures, consisting of periodically ordered vertical Si NW trunks and ZnO NW branches, and their application for solar water splitting. The branched NW photoelectrodes show orders of magnitudes higher photocurrent compared to the bare Si NW electrodes. More interestingly, selective photoelectrochemical cathodic or anodic behavior resulting in either solar water oxidation or reduction was achieved by tuning the doping concentration of the p-type Si NW core. Specifically, n-ZnO/p-Si branched NW array electrodes with lightly doped core show broadband absorption from UV to near IR region and photocathodic water reduction, while n-ZnO/p(+)-Si branched NW arrays show photoanodic water oxidation with photoresponse only to UV light. The photoelectrochemical stability for over 24 h under constant light illumination and fixed biasing potential was achieved by coating the branched NW array with thin layers of TiO2 and Pt. These studies not only reveal the promise of 3D branched NW photoelectrodes for high efficiency solar energy harvesting and conversion to clean chemical fuels, but also developing understanding enabling rational design of high efficiency robust photocathodes and photoanodes from low-cost and earth-abundant materials allowing practical applications in clean renewable energy.

The fire-through processed screen-printed Ag thick film metal contacts formed on an electrochemically etched porous silicon antireflection coating of silicon solar cells

The fabrication of reproducible low resistance ohmic contacts on electrochemically etched porous silicon is an existing challenge due to the irregular and nanoscale sized Si crystallites and the voids in the structure of the porous silicon. In this study, the effect of the peak firing treatment by a fire-through process at different temperatures (700–825 °C) and electroless Ag deposition steps on the electrical properties of the Ag electrodes have been investigated. The cross-sectional view of the Ag metal/doped Si region by SEM shows that Ag metal firmly coalesces with the doped Si surface. The sintering of the metal contact at a higher peak firing temperature enables the firing-through of the Ag metal paste onto the high resistivity porous silicon that leads to the interaction with the doped Si region. As a result, a good ohmic contact between the Ag metal and doped Si emitter is formed. The specific contact resistance, ρc (Ω.cm2) measurement of the Ag electrode by the three-point probe method shows that the ohmic properties of the just sintered Ag electrodes are very good, with ρc ≅ 1.025 × 10−4 Ω.cm2. An electroless Ag deposition step using AgNO3 solution under constant light illumination was applied to improve the electrical properties of the sintered Ag contacts. It is found that the ρc of the Ag electrodes was improved to about 3.25 × 10−5 Ω.cm2 after applying the electroless Ag deposition on the sintered Ag contacts. The deposition of the pure silver metal on the Ag contacts fills up the micropores and voids and improves the electrical properties of the contact structure.

Investigation of Carrier Transient Response of Nanopatterned n-ZnO/a-Si(i)/p$^{+}$-Si Photodiodes

We investigated the carrier transient response of the nanopatterned silicon heterojunction photodiodes using ZnO as the n-type semiconductor. The results show that under the constant light illumination intensity, the planar structure has faster carrier response than the nanopatterned amorphous silicon (intrinsic) (a-Si(i)) diodes. It is attributed to a higher number of generated carriers in the nanostructure (due to the lower surface reflectivity) that increases the probability of collisions. On the other hand, the shortest response time of the device with nanopatterned p+-Si suggests that carriers can be effectively transported vertically and horizontally through the p-i(intrinsic)-n structure. Furthermore, the wavelength-dependent rise time is correlated to the different transport distance between electrons and holes at different excited wavelengths.

Evaluation of Dye-Sensitized Solar Cells using Forward Bias Applied Impedance Spectroscopy Under Dark

Dye-sensitized solar cells (DSSCs) are promising as low cost, highly efficient solar cells. Internal resistance analysis using impedance spectra (IS) is an effective method for improving the performance of DSSCs. However, it is questionable if resistances obtained from different DSSCs by using IS are comparable under constant light illumination, because the internal resistances of DSSC might depend on current. In this study, we investigated the origin of four resistances (R1~R4) measured using IS under dark conditions, and the similarity and the difference between different three IS methods were discussed. The results revealed that forward bias applied impedance spectroscopy at constant current under dark conditions is a simple, practical method to evaluate internal resistance of DSSCs. In conclusion, development of high efficiency DSSCs will require low resistances of the ohmic (R1), redox reactions on the counter electrode (R2, 100~10k Hz) and I-/I3- diffusion (R4, 2~100 Hz) and high resistance of back charge transfer from TiO2 to electrolyte (R3, 100m~2 Hz).

A novel photoelectrochromic device with dual application based on poly(3,4-alkylenedioxythiophene) thin film and an organic dye

A novel photoelectrochromic device (PECD) with dual application was studied using an electrochromic polymer thin film, poly(3,3-diethyl-3,4-dihydro-2 H-thieno-[3,4- b][1,4]dioxepine) (PProDot-Et 2), and an organic photosensitive dye, FL dye1, which was adsorbed on a TiO 2 electrode. In the presence of the redox couple, the electron transfer reaction at the electrolyte/PProDot-Et 2 conducting polymer interface was found to determine the electrochromism of the PECD. The rate constants of the electron transfer ( k 0) for different redox couples at the PProDot-Et 2 film were obtained by using electrochemical impedance spectroscopy (EIS) and were correlated with the coloration depth of the thin film. Since I −/I 3 − and Br −/Br 3 − couples possess the highest and the lowest k 0 value, respectively, the PECD was investigated using these two redox couples under constant light illumination of 50 mW cm −2. The I −/I 3 − couple provided a higher short circuit current density ( J SC) when acting as a dye-sensitized solar cell (DSSC), thus the switching response upon coloration ( ca. 3 s) was much faster than that of the PECD using the Br −/Br 3 − couple ( ca. 2 min). On the contrary, the PECD using Br −/Br 3 − exhibited a larger transmittance attenuation of ca. 33.7%, in comparison to that using I −/I 3 − ( ca. 14.1%).

P3-419: Melatonin revised constant light illumination induced tau hyperphosphorylation and memory deficit in rat by inhibiting ER stress

P3-419: Melatonin revised constant light illumination induced tau hyperphosphorylation and memory deficit in rat by inhibiting ER stress

Optical filtering removes non-homogenous illumination artifacts in optical imaging

Under constant light illumination, cortical neuronal activity slightly modulates intensity of the light reflected from cortical surface. Optical imaging of the reflected light from the cortex has now become a popular method to obtain cortical functional maps. Since the modulation signal is small, this method is very sensitive to other sources of the light intensity changes. A well-known artifact in this signal is the bias in the reflected light intensity due to the curvature of the cortex. The curvature of the cortex creates inhomogeneity in reflected light intensity with characteristic concentric-ring pattern in the functional maps (known as ring-shape artifact). It is particularly visible in single-condition maps if the number of trials is small. We demonstrate a method that can remove this and similar artifacts using an optical filter to equalize the reflected light intensity. Functional images recorded with the application of our filter – inserted into the optics between the cortex and the camera – became more uniform and distortion-free. Our approach consisting of the equalization optical filter is appropriate for experiments where inhomogeneous light reflection, single-condition maps, and a small number of trials exist, e.g. imaging studies of higher cortices in behaving monkeys.