Constant Illumination Research Articles

The Effect оf Laser Radiation оn Functional Properties of MOS Structures

The electrophysical properties of instrument MOSFET structures (capacitor, field-effect transistor with an isolated gate and an induced channel, CMOS integrated circuit) when exposed to unmodulated laser radiation are studied. Static and dynamic characteristics were measured. The theoretical study was carried out using the developed SPICE models and numerical experiments. An expression is obtained for the volt-ampere characteristic of a field-effect transistor operating in a mode with constant optical illumination. It is shown that the characteristics of the structures are determined by the generation and recombination of nonequilibrium charge carriers, the field effect, the photovoltaic effect in p—n junctions, the photo-Dember effect and tunneling of charge carriers through a gate dielectric. The results of the work are of interest from the point of view of creating high-speed transistors and integrated circuits of a new type.

Self-Oscillations of Submerged Liquid Crystal Elastomer Beams Driven by Light and Self-Shadowing

Liquid Crystal Elastomers (LCEs) are responsive materials that undergo significant, reversible deformations when exposed to external stimuli such as light, heat, and humidity. Light actuation, in particular, offers versatile control over LCE properties, enabling complex deformations. A notable phenomenon in LCEs is self-oscillation under constant illumination. Understanding the physics underlying this dynamic response, and especially the role of interactions with a surrounding fluid medium, is still crucial for optimizing the performance of LCEs. In this study, we have developed a multi-physics fluid-structure interaction model to explore the self-oscillation phenomenon of immersed LCE beams exposed to light. We consider a beam clamped at one end, originally vertical, and exposed to horizontal light rays of constant intensity focused near the fixed edge. Illumination causes the beam to bend towards the light due to a temperature gradient. As the free end of the beam surpasses the horizontal line through the clamp, self-shadowing induces cooling, initiating the self-oscillation phenomenon. The negative feedback resulting from self-shadowing injects energy into the system, with sustained self-oscillations in spite of the energy dissipation in the surrounding fluid. Our investigation involves parametric studies exploring the impact of beam length and light intensity on the amplitude, frequency, and mode of oscillation. Our findings indicate that the self-oscillation initiates above a certain critical light intensity, which is length-dependent. Also, shorter lengths induce oscillations in the beam with the first mode of vibration, while increasing the length changes the elasticity property of the beam and triggers the second mode. Additionally, applying higher light intensity may trigger composite complex modes, while the frequency of oscillation increases with the intensity of the light if the mode of oscillation remains constant.

Testing the use of daylight-linked control systems to address integrative lighting and energy savings in office buildings

Daylight-linked control systems (DLCSs) are used to maintain constant work plane illuminance and save energy. If properly calibrated, they could be used to guarantee circadian requirements fulfilment as well. In this study, the functioning of a closed-loop proportional dimming system is simulated based on on-field measurements. Simulations are performed calibrating the system to achieve different targets: three work plane task illuminances (300 lx, 500 lx, 750 lx) and one melanopic equivalent daylight illuminance (melEDI) value (250 lx) alternatively. Four electric light CCT profiles (stable at 3000 K, 4000 K, and 6500 K, and variable during the day) are considered. Results demonstrate that when the system is calibrated according to work plane illuminance, melEDI values are always fulfilled under clear sky and with overcast sky when task illuminance and CCT are high. When the system is calibrated to meet circadian requirements, the CCT choice is crucial to guarantee work plane illuminance.

Long-term carrier lifetime instabilities in n-type FZ- and Cz-silicon under illumination at elevated temperature

Even though n-type Si wafers show a lower extent of light-induced degradation, similar degradation and regeneration behavior as in p-type Si materials has been observed for various n-type Si monocrystalline materials. In this work, the long-term behavior of minority charge carrier lifetime in non-diffused n-type FZ-Si and Cz-Si wafers during illumination at elevated temperatures is investigated. Thereby, various influencing factors such as peak firing temperature and treatment temperature are considered. Degradation and a very strong regeneration effect, which exceeds the initial effective lifetime value, can be observed in the samples. Since surface-related saturation current density remains almost constant during degradation and regeneration, the effect seems to be bulk related. The extent of degradation and regeneration could be shown to be firing temperature-dependent. It could also be shown for n-type FZ-Si wafers that higher firing temperatures result in an increased H2 content within the silicon bulk. Investigations of the injection-dependent defect density revealed that the defect formed during degradation is not a deep level Shockley-Read-Hall defect. Observations at different treatment temperatures and constant illumination of 0.9(1) sun photon flux equivalent have shown that a higher treatment temperature leads to faster degradation and regeneration kinetics. Similarly, higher injection rates also speed up regeneration kinetics. Since degradation also occurs in darkness, the bulk related degradation effect in n-type FZ-Si is charge carrier-induced and not necessarily light-induced.

Improving Perovskite Solar Cell Performance and Stability via Thermal Imprinting-Assisted Ion Exchange Passivation.

The latest development in perovskite solar cell (PSC) technology has been significantly influenced by advanced techniques aimed at passivating surface defects. This work presents a new approach called thermal imprinting-assisted ion exchange passivation (TIAIEP), which delivers a different approach to conventional solution-based methods. TIAIEP focuses on addressing surface imperfections in solid-state films by using a passivator that promotes ion exchange specifically at the defect sites within the perovskite layer. By adjusting the time and temperature of the TIAIEP process, we achieve substantial enhancement in the creation of a compositional gradient within the films. This optimization slows the cooling rate of hot carriers, leading to minimizing charge recombination and improving the device performance. Remarkably, devices treated with TIAIEP achieve a 22.29% power conversion efficiency and show outstanding stability, with unencapsulated PSCs maintaining 91% of their original efficiency after over 2000 h of storage and 90% efficiency after 1200 h of constant illumination. These results highlight TIAIEP's effectiveness in mitigating surface defects, improving both the photoelectric and stability performance of PSCs, and indicating significant potential for large-scale application in perovskite film passivation, promoting the widespread adoption of this technology.

Enhanced Responsivity and Photostability of Cs3Bi2I9-Based Self-Powered Photodetector via Chemical Vapor Deposition Engineering.

Lead-based halide perovskites have gained significant prominence in recent years in optoelectronics and photovoltaics, owing to their exceptional optoelectronic properties. Nonetheless, the toxicity of lead (Pb) and the stability concern pose obstacles to their potential for future large-scale market development. Herein, stable lead-free Cs3Bi2I9 (CBI) films are presented with smooth and compact morphologies synthesized via chemical vapor deposition (CVD), demonstrating their application as an UV photodetector in a self-powered way. The self-powered photodetectors (SPDs) exhibit remarkable characteristics, including a responsivity of 1.57 AW-1 and an impressive specific detectivity of 3.38 × 1013 Jones under the illumination of 365nm at zero bias. Furthermore, the SPDs exhibit a nominal decline (≈2.2%) in the photocurrent under constant illumination over 500h, highlighting its impressive long-term operational stability. Finally, the real-time UV-detection capability of the device is demonstrated by measuring the photocurrent under various conditions, including room light and sunlight at different times. These findings offer a new platform for synthesizing stable and high-quality perovskite films, and SPDs for advancing the development of wearable and portable electronics.

Self-rotation of a liquid crystal elastomer rod under constant illumination

Self-sustaining systems can generate and maintain periodic or chaotic motion under constant external stimulation, and has potential applications in fields such as soft robotics, energy harvesting, and active machinery. However, self-sustaining systems often come with excessive oscillations and increased friction, which limit their applications. Unlike oscillatory self-sustaining systems, we have developed a novel steadily self-sustaining system, which is composed of a liquid crystal elastomer rod and a support sleeve. Experiments demonstrate that the liquid crystal elastomer rod on a support sleeve can self-rotate steadily and continuously under constant small area illumination. During the self-rotation, the shape of the liquid crystal elastomer rod remains unchanged, which avoids excessive oscillations and decreases friction. Based on a photothermal-responsive liquid crystal elastomer model, we derived the lateral curvature and the actuating rotation moment. Numerical simulations reveal that the liquid crystal elastomer system balances damping dissipation during motion by absorbing heat converted from constant illumination. The angular velocity of the self-rotation is influenced by parameters such as heat flux, heat transfer coefficient, length of the rod, and damping rotation moment. The theoretical predictions match the experimental results. The novel steadily self-rotating system not only has the advantages of maintaining shape and reducing friction, but also offers benefits such as structural simplicity, small illumination area, and higher energy efficiency compared to other steadily self-sustaining systems driven by large illumination areas or hot surfaces. This research is anticipated to offer valuable insights for applications in soft robotics, energy harvesting, and active machinery.

Artificial Amacrine Retinal Circuits.

Event-based imaging represents a new paradigm in visual information processing that addresses the speed and energy efficiency shortcomings inherently present in the current complementary metal oxide semiconductor-based machine vision. Realizing such imaging systems has previously been sought using very large-scale integration technologies that have complex circuitries consisting of many photodiodes, differential amplifiers, capacitors, and resistors. Here, we demonstrate that event-driven sensing can be achieved using a simple one-resistor, one-capacitor (1R1C) circuit, where the capacitor is modified with colloidal quantum dots (CQDs) to have a photoresponse. This sensory circuit emulates the motion-tracking function of the biological retina, in which the amacrine cells in the bipolar-to-ganglion synaptic pathway produce a transient spiking signal only in response to changes in light intensity but remain inactive under constant illumination. When extended to a 2D imaging array, the individual sensors work independently and output signals only when a change in the light intensity is detected; hence, the concept of the frame in image processing is thereby removed. In this work, we present the fabrication and characterization of a CQD photocapacitor-based 1R1C circuit that has a spectral response at 1550 nm in the short-wave infrared (SWIR). We report on the key performance parameters including peak responsivity, noise, and optical noise equivalent power and discuss the operating mechanism that is responsible for spiking responses in these artificial retinal circuits. The present work sets the foundation for expanding the bioinspired vision sensor capability toward midwave infrared (MWIR) and long-wave infrared (LWIR) spectral regions that are invisible to human eyes and mainstream semiconductor technologies.

An Accurate Non-contact Photoplethysmography via Active Cancellation of Reflective Interference.

Imaging Photoplethysmography (IPPG) is an emerging and efficient optical method for non-contact measurement of pulse waves using an image sensor. While the contactless way brings convenience, the inevitable distance between the sensor and the subject results in massive specular reflection interference on the skin surface, which leads to a low Signal to Interference plus Noise Ratio (SINR) of IPPG. To ease this challenge, this work proposes a novel modulation illumination approach to measure the accurate arterial pulse wave via surface reflection interference isolation from IPPG. Based on the proposed skin reflection model, a specific modulation illumination is designed to separate the surface reflections and obtain the subcutaneous diffuse reflections containing the pulse wave information. Compared with the results under ambient illumination and constant supplemental illumination, the SINR of the proposed method is improved by 4.56 and 3.74 dB, respectively.

Effects of the incorporation of copper on the micro structure, charge transport and photoelectrical properties of sputtered ZnTe:Cu films

Advances in solar cell technology require improving the relevant physical properties of the constituent materials. One important functionality in photovoltaic devices is the efficient charge transport through the cell. Copper-doped zinc telluride (ZnTe:Cu) has been used as contact to cadmium telluride, the light-absorbing layer in photovoltaic devices. Out of the various deposition techniques, radio frequency sputtering is one of the most versatile and widely employed in research laboratories and industry. In this work, is presented a thorough characterization of ZnTe and ZnTe:Cu films grown by sputtering as a function of substrate temperature (Ts = 300 and 350 °C) and copper concentration (1, 3 and 5 at%). Besides the structural (X-ray diffraction), optical (UV-Vis spectroscopy) and electrical (Hall effect) characterizations, the present study included other studies relevant for optoelectronic applications such as photoluminescence, photoconductivity (under constant or transient illumination) and, in order to determine the effect of copper on the work function, Kelvin probe force microscopy was applied to the samples. Our results show important improvements in crystallite size, conductivity and photoconducting properties derived from the incorporation of copper in the ZnTe lattice.

Development of lignin-based 3D-printable light responsive shape memory materials: Design of optically controlled devices

This study employs simple approaches involving melt blending and Fused Deposition Modeling (FDM) 3D printing to fabricate a light-responsive shape memory composite. And, this composite material is used for the design of optically controlled devices that mimics the blooming of flowers in the natural environment. The composite material utilizes poly(ε-caprolactone) (PCL) and thermoplastic polyurethane (TPU) as the matrix, with lignin (L) serving as a functional filler. The analysis indicates that, due to the excellent photothermal conversion efficiency of lignin, under constant illumination the shape memory materials heat up to 50 °C within 40 s, the shape recovery rate exceeds 95.06 %. Lignin ameliorated the rheological deficiencies of TPU, with the composite material viscosity decreasing from 103 to 101 at an angular frequency of 100 rad/s, enhancing its compatibility with FDM processes. This research offers greater economic efficiency compared to conventional light-responsive materials and a simpler production method.

Solar Heating Modulated by Evaporative Cooling Provides Intermittent Temperature Gradients for Ionic Thermoelectric Supercapacitors

AbstractSolar heating is important for many applications but less attractive for concepts requiring intermittent heating, such as ionic thermoelectric supercapacitors (ITESCs). However, the heating process even at constant solar illumination can be converted to temperature oscillations through water infiltration and evaporation. Here, this process is demonstrated for a carbon nanotube‐cellulose membrane and used to induce temporally varying temperature gradients across an ITESC, which enables continuous operation through repeated charge and discharge cycles. A temperature variation of 10 K can be generated on the top electrode, which leads to a variation in the temperature difference across the ITESC of 7.5 K. Precise control over charge and discharge durations can be achieved by adjusting the volume and interval of the added water. The concept of temporarily adjusting temperatures by evaporative cooling may be extended to create intermittent heating also for other heat sources that are typically constant.

The Effects of Eye Illuminance Distribution in the Horizontal Field of View on Human Performance in a Home Paper-Based Learning Situation

Previous studies have focused on task/ambient illumination for visual effects and eye illumination for non-visual effects. In this context, eye illumination within the non-visual realm was defined as vertical non-visual eye illuminance. Considering the functional specificity of central vision and peripheral vision, this study aims to explore whether the distribution of eye illuminance in the horizontal field of view (FOV) affects human performance in home paper-based learning settings. In this study, a within-subject design was used to investigate the effects of eye illuminance distribution on mental perception, task performance, and physiological health while maintaining constant task illuminance and correlated color temperature (CCT). The findings revealed that eye illuminance and its distribution in the horizontal FOV had complex effects on visual fatigue, Landolt ring performance, heart rate variability, and luminous environment appraisal. A relatively optimal lighting configuration was suggested—Scene 4, which was characterized by an eye illuminance level in central FOV of 186 lx and an “m” shaped eye illuminance distribution pattern. This indicates the importance of considering eye illuminance distribution in the horizontal FOV, rather than solely focusing on vertical eye illuminance.

Study on Illuminance Control based on Arduino Method

The paper presents a method for achieving constant illumination control by integrating various technologies, including Arduino technology, LED driver technology, and control technology. The HV9910B constant current drive chip is used to design a high-power LED driver in the form of an Arduino expansion board. The performance of the driver is tested, including efficiency testing and waveform testing. The PID control library of Arduino is utilized to write the control program rapidly. Illumination control experiments are conducted with expected results.

Determining Quasi-Equilibrium Electron and Hole Distributions of Plasmonic Photocatalysts Using Photomodulated X-ray Absorption Spectroscopy.

Most photocatalytic and photovoltaic devices operate under broadband, constant illumination. Electron and hole dynamics in these devices, however, are usually measured by using ultrafast pulsed lasers in a narrow wavelength range. In this work, we use excited-state X-ray theory originally developed for transient X-ray experiments to study steady-state photomodulated X-ray spectra. We use this method to attempt to extract electron and hole distributions from spectra collected at a nontime-resolved synchrotron beamline. A set of plasmonic metal core-shell nanoparticles is designed as the control experiment because they can systematically isolate photothermal, hot electron, and thermalized electron-hole pairs in a TiO2 shell. Steady-state changes in the Ti L2,3 edge are measured with and without continuous-wave illumination of the nanoparticle's localized surface plasmon resonance. The results suggest that within error the quasi-equilibrium carrier distribution can be determined even from relatively noisy data with mixed excited-state phenomena. Just as importantly, the theoretical analysis of noisy data is used to provide guidelines for the beamline development of photomodulated steady-state spectroscopy.

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.

Slot‐Die Deposition of CuSCN Using Asymmetric Alkyl Sulfides as Cosolvent for Low‐Cost and Fully Scalable Perovskite Solar Cell Fabrication

The development of industrially relevant deposition processes for efficient, stable, and inexpensive charge extracting layers is crucial for the commercialization of perovskite solar cells (PSCs). This work demonstrates, for the first time, the deposition of copper thiocyanate (CuSCN) as a low‐cost and reliable hole‐transport layer using slot‐die coating. Methyl ethyl sulfide is thereby used as an asymmetric cosolvent to significantly increase the solubility of CuSCN in the utilized slot‐die ink compared to traditional pure diethyl sulfide‐based solutions. Optimized CuSCN inks allow for the deposition of CuSCN layers on 5 × 10 cm2 substrates with a wide range of thicknesses. Multidimensional imaging photoluminescence techniques are used to investigate the uniformity of the CuSCN thin films deposition as well as the influence of the solvent on charge losses. Finally, the CuSCN slot‐die deposition is integrated into a fully upscalable PSC fabrication process showing 19.1% power conversion efficiency for small laboratory cells and 14.7% for 9 cm2 minimodules. Furthermore, semitransparent minimodules retain 80% of their initial efficiency after 500 h of constant illumination.

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.

Phenyltrimethylammonium chloride additive for highly efficient and stable FAPbI3 perovskite solar cells

Formamidinium lead triiodide (FAPbI3)-rich perovskite absorbers have emerged as the frontrunners for the development of perovskite solar cells (PSCs), but pristine FAPbI3 absorber exhibits phase instability because of external stressors during device manufacture and operation. In this work, we systematically study the function of a trace amount of phenyltrimethylammonium chloride (PTAC) additive in FAPbI3-based perovskites. The introduced PTAC have a strong electrostatic interaction with perovskite because of the coordination of electron-rich benzene ring unit and under-coordinated Pb2+, which leads to the decrease of the trap density and the release of the lattice strain. Simultaneously, the increased work function of modulated film optimizes the band alignment, promoting carrier transport and reducing nonradiative recombination, thereby improving the open-circuit voltages and fill factors. Consequently, the modulated PSCs achieve a champion power conversion efficiency of 24.51%, and exhibit much better stability by retaining 90% of their initial efficiency after 1000 hours constant illumination under maximum power point tracking measurement.

Analyzing the effects of illuminance variations on occupants’ visual perceptions to determine permissible dimming controls of lighting in a small office

This study investigated the influence of illuminance variations on visual responses to suggest permissible dimming ranges of lighting control systems in office. A series of experiments were conducted with 33 participants for workplane illuminances of 500 lx, 650 lx, and 800 lx in real office environments under five levels of illuminance variations. Paper-based and computer-based reading tasks were conducted for each condition. The results indicated that none of the constant workplane illuminance caused visual discomfort or dissatisfaction. Illuminance variation was perceived most strongly under the workplane illuminance of 500 lx, and the effect of illuminance variation on the perception of glare was the weakest under the workplane illuminance of 800 lx. As the variation ranges in illuminance increased, the degree of perceived visual satisfaction diminished stably compared with the degree of perceived glare and illuminance change. Strong linear relationships existed between illuminance variation and visual comfort. The maximum permissible ranges of illuminance variations that maintained visual comfort were 150.0 lx, 135.2 lx, and 121.9 lx for paper-based tasks and 126.9 lx, 115.8 lx, and 80.8 lx for computer-based tasks when the workplane illuminance were 500 lx, 650 lx, and 800 lx, respectively. The perception of eye fatigue was a common factor that affected the perception of visual comfort when illuminance variations occurred under the three workplane illuminance conditions. The influences of glare, visual stimuli, and eye fatigue were the factors that degraded the perception of visual comfort.