Effect Of Light Illumination Research Articles

Device performance analysis for lead‐free perovskite solar cell optimisation

A comprehensive numerical analysis for a lead-free perovskite solar cell (PSC) has been carried out using device simulation software. Various factors affecting the solar cell's performance have been investigated for device optimisation; more specifically optimisation of device buffer and the absorber layer. Different design strategies for optimising the power conversion efficiency (PCE) through solar cell capacitance simulator numerical simulation have been proposed. Enumerated study of the effects of thickness, band gap, light illumination and defect area on the PCE is carried out. In this study, two types of configurations (La 0.7 Sr 0.3 MnO 3 /zinc oxide and La 0.7 Sr 0.3 MnO 3 /Nb:SrTiO 3 ) are simulated which gives highest conversion efficiency of 11% at 600 nm and 32% at 350 nm wavelength. The impact of defect density has also been addressed to analyse the performance of cell module. The optimisation of device parameters pinpoints enormous potential for the enhancement of conversion efficiency of high-efficient PSC.

Effect of Different UV Light Intensity on Porous Silicon Fabricated by Using Alternating Current Photo-Assisted Electrochemical Etching (ACPEC) Technique

Alternating current (sine-wave a.c (50Hz)) photo-assisted electrochemical etching (ACPEC) process was used to produce the formation of porous silicon with different ultraviolet (UV) light intensity. The study aims to investigate the effect of different UV light illumination on the properties of porous silicon. The surface of n-type silicon (111) was selectively etched in the HF and ethanol solution with a ratio (5:20) for 30 minutes under different UV lamp intensity; 10%, 30% and 60%. The samples were characterized by using atomic force microscopy (AFM) and X-ray diffraction (XRD). The AFM measurements revealed porous silicon with 30% of UV light intensity has the highest surface roughness value with a pyramidal shape. XRD analysis showed FWHM value of etched samples increased as the crystallite size of the etched sample decreased.

Effect of UV light illumination on the corrosion behavior of electrodeposited TiO2-Ni composite foils

Effects of ultraviolet (UV) light illumination on the corrosion behavior, surface state, and activities of electrodeposited micro-TiO2/Ni and nano-TiO2/Ni composite foils in 3.5% NaCl solution were investigated by means of polarization measurement, electrochemical impedance spectra (EIS), electron work function mapping (EWF) and XPS spectra analysis using an electrochemical system, the atom force microscopy (AFM) and X-ray photoelectric spectroscopy (XPS), respectively. The UV light illumination resulted in a considerable decrease in corrosion resistance of the nano-TiO2/Ni composite foil but showed much less effect on the micro-TiO2/Ni composite foil. Surface state analysis demonstrated that the UV illumination stimulated the nano-TiO2 semiconductor with elevated conductivity in favor of passing corrosion current. The UV illumination increased the fraction of Ni2O3 component in formed oxide film on the nano-TiO2/Ni foil, which is porous, loose, brittle and less protective, compared to the naturally formed NiO film on Ni. The changes in surface state were responsible for variations in the corrosion behavior of micro-TiO2/Ni and nano-TiO2/Ni composite foils caused by the UV light illumination.

Ar-Plasma-Modulated Optical Reset in the SiO2/Cu Conductive-Bridge Resistive Memory Stack

Resistive Random Access Memory (RRAM) has been widely studied as a promising next-generation memory with advantageous characteristics such as high-speed and low-power operation[1]. In particular, the SiO2/Cu conductive-bridge random access memory (CBRAM), where electric-field-driven formation/dissolution of Cu metal filaments provides resistance switching, has been drawing much attention because of its compatibility with the backend interconnect process. Recently, we have demonstrated negative photo conductivity (NPC) or light-induced resistance reset (LIR) in the SiO2/Cu stack by disrupting the electrically-formed filamentary breakdown path[2]. It is considered that the NPC is caused by recombination of light-excited oxygen ions and oxygen vacancies created in the breakdown path during electrical forming. Although the exact mechanism is still elusive, the finding suggests a potential to realize an electro-optical control of memory devices. In our pursuit of the mechanism(s) behind the abovementioned NPC phenomenon, we reveal here an impact on NPC by Ar plasma surface treatment, which is reported to increase oxygen vacancies in the oxide electrolyte[3]. The effect of light illumination on the electrical property of the Ar-plasma-treated Cu sample (SiO2 10nm/Cu) and control sample (SiO2 5nm/Si) is investigated via ultra-high vacuum conductive atomic force microscope or CAFM (Fig. 1). During forming, a negative bias voltage is supplied to the probe with a preset current compliance of 1.1 nA. The area of the probe-oxide contact is estimated to be ~26nm2[4]. From the current-voltage (I-V) curves for the Cu or control sample depicted in Fig. 2, it is evident that the switching voltage from the high resistance state (HRS) to the low resistance state (LRS) in the Cu sample is shifted from -6V to -4V by 33% after the Ar plasma treatment, while the breakdown voltage in the control sample is almost unchanged. Therefore, the electrical formation of Cu filaments is considered to be accelerated by Ar plasma treatment. Fig. 3 shows typical response to light in the post-forming Cu sample and percentage of NPC occurrence calculated from 30 tested locations in each of the Cu and control sample. The light intensity used was 1 mW/cm2. Clearly, Ar plasma treatment suppresses the NPC in both samples and especially enlarges the proportion of no-NPC cases in the Cu sample. The FT-IR spectra (Fig. 4) of the pre- and post-plasma-treated SiO2 film show the intensities of HO-H stretching (3300cm-1) and SiO-H stretching (3650cm-1) become higher after the Ar plasma treatment. This rise implies the destruction of the Si-O network near the surface and the increase of various defects like Si dangling bonds and oxygen vacancies where water in the air may be adsorbed. Based on the results, we propose a possible explanation for the mechanism of the lower switching voltage in the Cu sample and the decreased percentage of NPC occurrence with Ar plasma treatment in both samples. For the control sample, Ar plasma treatment may sputter oxygen ions and create more oxygen vacancies near the surface of SiO2 [3], which helps forming a larger conducting filament composed of oxygen vacancies. This can be confirmed by a higher current in the reverse I-V curve after Ar plasma exposure (Fig. 2 (c)(d)). Since oxygen ions are depleted, the NPC response (due to recombination of light-excited oxygen ions and vacancies) is suppressed. In the case of the Cu sample, the oxygen vacancies created in the surface of SiO2 by Ar sputtering may adsorb water molecules. The resultant hydroxyl groups (OH-) reportedly promote Cu ion (Cu+) diffusion into SiO2 [5] and reduce the switching voltage during forming (Fig. 5). When more Cu ions migrate into SiO2, part of the conducting filament made up of oxygen vacancies there is replaced by a Cu filament (Fig. 5 (e)), which is not readily disrupted due to the stronger metal-metal bond (which requires higher energy for cleavage than that of the light used[2]). Therefore, the conducting path composed of more Cu metal filaments remain after light illumination (Fig.5 (f)), leading to the suppression of the NPC response.

(Invited) Illumination Light Wavelength Effects on Double-Gate a-IGZO Thin Film Transistor with Top-Gate-to-Source/Drain Offset Structure

Electrical properties of the double-gate amorphous In-Ga-Zn-O thin film transistor with the top-gate-to-source/drain offset structure were investigated in dark and under visible and UV light illumination conditions. With the increase of the band gap energy of the incident light, the amount of charge carries generated in the semiconductor channel layer was increased, which enhanced the field effect mobility and increased the leakage current. At the same time, defects were created, which deteriorated the threshold voltage and subthreshold slope. For the top-gate thin film transistor, the UV illumination seriously deteriorated all device characteristics except the leakage current because of the reduction of oxygen vacancies. The performance of the double-gate thin film transistor was dominated by the bottom-gate transistor. Light illumination effects in the bottom- and double-gate transistors were similar but much less serious than those of the top-gate transistor. The understanding of the wavelength-dependent light illumination effect is critical to double-gate thin film transistor applications.

Effect of Light Illumination on the Corrosion Behavior of Mg-RE Alloy EV31A in Chloride-Alkaline Solutions

The effect of white light illumination on the corrosion behavior of a Mg - Rare Earth (RE) alloy EV31A specimens in peak aged condition was investigated in 0.1 M NaOH solution containing 0, 80, 100 and 200 ppm chloride ions at room temperature. The passivation current density decreased upon illumination in the 0.1 NaOH solution without chloride addition. On the other hand, increased passive current densities were observed in the chloride containing solutions upon illumination. The white light illumination did not affect the open circuit potential of the EV31A. This result indicated that alloying additions did not significantly alter the bandgap of the passive layer or induce bandgap states in the passive layer in order to harvest the longer wave lengths of the white light. The incubation time for passivity perturbation decreased with illumination. The charge carrier density increased significantly upon illumination. The exchange current density for hydrogen evolution increased under the illuminated conditions. The Mott-Schottky results pointed out that light illumination induced surface defects of n-type character. These defects could have been potential sites for chloride adsorption that decreased the stability of the passive film. The white light illumination did not result in induced photo potential due to wide bandgap of the passive layer. Since the band bending was not altered, the electric field remained the same in both illuminated and non-illuminated condition. Overall, illumination of white light did not offer significant benefit to the localized corrosion resistance of the Mg-RE alloy in alkaline-chloride solutions.

Effect of Light Illumination on the Corrosion Behavior of Mg-RE Alloy EV31A in Chloride-Alkaline Solutions

Mg-RE alloy EV31A is a Mg-Zn-Gd-Nd-Zr alloy used in aerospace and high performance automobile applications where creep and corrosion resistance are required. These alloys can also be used in Mg-air batteries as possible anode materials in alkaline electrolytes in order to minimize the negative difference effect. EV31A is an age hardenable alloy. The precipitation reactions occurring during the aging process follow the sequence of a-Mg →β'' → β' → β (Mg3RE) → Mg41RE5. The alloy showed excellent passivity in the 0.1 M NaOH solution. More than 80 ppm of chloride was required to induce passivity breakdown in any heat treatment condition. Peak aging at 200 °C for 16 h imparted better resistance for localized corrosion than the solution treated or over aged conditions[1]. Light illumination has been reported to increase the resistance to passivity breakdown of various metals and alloys such as iron[2], copper[3], aluminum[4], and stainless steel. During illumination, the band bending of the passive layer is modified by the electron-hole pair generation and the electric field that drives the transport of point defects across the passive layer is considerably decreased. This quenched electric field is considered to improve the localized corrosion resistance of the material. Light illumination also modifies the electronic properties of the passive film. The effect of white light illumination on the corrosion behavior of peak aged EV31A specimens was investigated in 0.1 M NaOH solution containing 0, 80, 100 and 200 ppm chloride ions at room temperature. The passivation current density decreased upon illumination in the 0.1 NaOH solution without chloride addition. On the other hand, increased passive current densities were observed in the chloride containing solutions upon illumination. The white light illumination did not affect the open circuit potential of the EV31A. This result indicated that alloying additions did not significantly alter the band gap of the passive layer or induce band gap states in the passive layer in order to harvest the longer wave lengths of the white light. The incubation time for passivity perturbation decreased with illumination. The charge carrier density increased significantly upon illumination. The exchange current density for hydrogen evolution increased under the illuminated conditions. The Mott-Schottky results pointed out that light illumination induced surface defects of n-type character, possibly oxygen vacancies. These defects could have been potential sites for chloride adsorption that decreased the corrosion resistance. The white light illumination did not result in induced photo potential due to wide band gap of the passive layer. Since the band bending was not altered, the electric field remained the same in both illuminated and non-illuminated condition. Overall, illumination of white light was not beneficial to the localized corrosion resistance of the Mg-RE alloy in alkaline-chloride solutions. [1] J. Ninlachart, K.S. Raja, Acta Metallurgica Sinica (English Letters), 2017, 30(4), 352–366 [2] P. Schmuki, H. Bohni, Electrochimica Acta, Vol. 40, No. 6, pp. 775-783, 1995 [3] C. B. Breslin, D. D. Macdonald, Electrochimica Acta 44 (1998) 643±651 [4] M. A. Amin, Electrochimica Acta 56 (2011) 2518–2531

Plasmonic effects on CO2 reduction over bimetallic Ni-Au catalysts

The anthropogenic rise of carbon emissions has led to increased interest in the innovative utilisation of CO2. CO2 reduction via the Sabatier reaction presents a thermodynamically favourable pathway to reduce CO2; however, to date, there has been a lack of understanding of how plasmonic enhancement may be utilised for this reaction particularly with respect to the role of bimetallic catalysts. In this study, the effect of laser light illumination on Ni-Au/SiO2, at 520 nm and 660 nm, was studied for CO2 reduction over a temperature range of 150 °C to 450 °C, with the catalytic performance being assessed by CO2 conversion along with CH4 and CO selectivity. Under laser light illumination, at 520 nm and 450 °C, CO2 conversion for Ni–Au/SiO2 increased by 79% whilst simultaneously lowering CH4 selectivity, which was attributed to localised surface plasmon resonance effects and promotion of the reverse water-gas shift reaction by the Au. Laser light illumination at 660 nm also introduced a mild conversion increase, however not to the same extent as for 520 nm. XPS analysis of Ni-Au/SiO2 implied that the observed photo-enhancement could be due to plasmonic mediated electron charge transfer from the Au deposits to the Ni deposits. Monometallic Ni and Au samples were examined and compared with the bimetallic system to elucidate the origin of the photo enhancement and to understand the plasmonic and catalytic interactions. The Au/SiO2 and Ni/SiO2 samples demonstrated that the photo-enhancement arose from the presence of the Au, with the increase in CO2 conversion at 520 nm increasing with increasing Au content; Au (∼110%) > Ni-Au (∼80%) > Ni (∼21%). However, the overall better performance of the Ni/SiO2 sample, facilitating high CO2 conversion and CH4 selectivity emphasises that, while plasmonic metal inclusion can induce synergistic effects, the benefits can be muted if it is unable to promote the target reaction.

Enhanced nitrate-nitrogen removal by modified attapulgite-supported nanoscale zero-valent iron treating simulated groundwater

Attapulgite (or palygorskite) is a magnesium aluminium phyllosilicate. Modified attapulgite-supported nanoscale zero-valent iron (NZVI) was created by a liquid-phase reduction method and then applied for nitrate-nitrogen (NO3-N) removal (transformation) in simulated groundwater. Nanoscale zero-valent iron was sufficiently dispersed on the surface of thermally modified attapulgite. The NO3-N removal efficiency reached up to approximately 83.8% with an initial pH values of 7.0. The corresponding thermally modified attapulgite-supported nanoscale zero-valent iron (TATP-NZVI) and NO3-N concentrations were 2.0 g/L and 20 mg/L respectively. Moreover, 72.1% of the water column NO3-N was converted to ammonium-nitrogen (NH4-N) within 6 h. The influence of environmental boundary conditions including dissolved oxygen (DO) concentration, light illumination and water temperature on NO3-N removal was also investigated with batch experiments. The results indicated that the DO concentration greatly impacted on NO3-N removal in the TATP-NZVI-contained solution, and the NO3-N removal efficiencies were 58.5% and 83.3% with the corresponding DO concentrations of 9.0 and 0.3 mg/L after 6 h of treatment, respectively. Compared to DO concentrations, no significant (p > 0.05) effect of light illumination on NO3-N removal and NH4-N generation was detected. The water temperature also has great importance concerning NO3-N reduction, and the removal efficiency of NO3-N at 25 °C was 1.25 times than that at 15 °C. For groundwater, therefore, environmental factors such as water temperature, anaerobic conditions and darkness could influence the NO3-N removal efficiency when TATP-NZVI is present. This study also demonstrated that TATP-NZVI has the potential to be developed as a suitable material for direct remediation of NO3-N-contaminated groundwater.

VUV Pump and Probe of Phase Separation and Oxygen Interstitials in La2NiO4+y Using Spectromicroscopy

While it is known that strongly correlated transition metal oxides described by a multi-band Hubbard model show microscopic multiscale phase separation, little is known about the possibility to manipulate them with vacuum ultraviolet (VUV), 27 eV lighting. We have investigated the photo-induced effects of VUV light illumination of a super-oxygenated La2NiO4+y single crystal by means of scanning photoelectron microscopy. VUV light exposure induces the increase of the density of states (DOS) in the binding energy range around Eb = 1.4 eV below EF. The photo-induced states in this energy region have been predicted due to clustering of oxygen interstitials by band structure calculations for large supercell of La2CuO4.125. We finally show that it is possible to generate and manipulate oxygen rich domains by VUV illumination as it was reported for X-ray illumination of La2CuO4+y. This phenomenology is assigned to oxygen-interstitials ordering and clustering by photo-illumination forming segregated domains in the La2NiO4+y surface.

Combined Effects of Light Illumination and Various Bottom Gate Length on the Instability of Via-Contact-Type Amorphous InGaZnO Thin-Film Transistors

This paper utilizes electrical analyses and a study of physical mechanisms to investigate metal gate structure-dependent performance in amorphous InGaZnO (a-IGZO) thin-film transistors. The effects of different shielding areas between the IGZO layer and metal gate are investigated. In devices with shorter metal gate lengths, an abnormal rise in capacitance at the off-state in capacitance–voltage ( ${C}-{V}$ ) characteristic curves can be observed. This can be attributed to the stronger electric field induced by the edge of the metal gate under bias sweep when the metal gate length is shorter than the IGZO layer length. Light illumination measurements indicate a negative shift in threshold voltage and an increase in subthreshold-leakage current regardless of relative metal gate length. Moreover, negative threshold voltage shift becomes more severe with a more obvious hump in ${C}-{V}$ characteristic curves under back-light illumination of a shorter width device, a phenomenon which has been verified by simulation.

Joint effect of gate bias and light illumination on metallic LaAlO3/SrTiO3 interface

We presented a systemic investigation on the joint effect of gate bias and light illumination on a metallic LaAlO3/SrTiO3 interface in the temperature range from 15 K to 300 K. We showed that the photo excitation significantly enhanced the gating effect for the metallic two-dimensional electron gas. However, its effect is strongly temperature dependent; it is strong at low and high temperatures, and weak in the intermediate temperature range. There are evidences that the amplified gating effect stemmed from enhanced carrier depletion while the Hall mobility remains nearly unaffected. Acceleration of the gating process, together with a training effect marked by a strong dependence on gating history of the getting effect, is induced by repeating the electric cycling, indicating atomic reconfiguration due to oxygen migration and the memory of the migration paths.

Numerical studies of surface potential, mobility and Seebeck coefficient of organic thin film transistor based on 2,3 benzanthracene: Light effect

The white light illumination effect has a large influence on charge carrier transport in organic thin-film transistors (OTFTs). In this work, an analytical model is presented for OTFTs using the variable range hopping (VRH) theory to discuss the Gaussian DOS distribution, the surface potential, the mobility and the Seebeck coefficient of the 2,3 benzanthracene thin-film transistor under dark and white light illuminations. This model explains the influence of illumination on the carrier density, the Gaussian DOS distribution effectively on the surface potential and the Seebeck coefficient. The White light illumination effect can remarkably enhance the surface potential at high gate voltages, as well as reduce the energetic disorder dependence of the Seebeck coefficient. Finally, according to the variable range hopping (VRH) model an analytical model has been also developed to simulate the transfer characteristics of organic phototransistor based on 2,3 benzanthracene and the obtained theoretical results show an excellent agreement with the experimental data.

Various LED Wavelengths Affected Myofiber Development and Satellite Cell Proliferation of Chick Embryos via the IGF-1 Signaling Pathway.

An effect of monochromatic light illumination on muscle mass has been discovered in chickens; however, its effect on the development of embryonic muscle remains unclear. Our previous studies demonstrated that monochromatic green light promoted satellite cell proliferation and muscle growth in posthatching broilers. In this study, we investigated the effects and mechanisms of monochromatic light exposure on muscle development in late embryogenesis. Seven hundred and fifty fertile broiler eggs were randomly assigned to blue (B-group), green (G-group), red (R-group), white (W-group) lights or darkness (D-group) throughout the incubation period. The muscle weight and fiber size were highest in the G-group compared to the other groups during embryonic days (E) 17 to E20. The proliferation of satellite cells isolated from the G-group was highest, and invivo green light remarkably increased the number of proliferating cell nuclear antigen (PCNA)-positive cells in skeletal muscle. Meanwhile, plasma IGF-1 was higher (15.5-16.2%) in the G-group than that in D- and R-groups, and the satellite cells isolated from the G-group had a more sensitive response to IGF-1. These findings demonstrate green monochromatic photobiomodulation promoted the muscle growth and satellite cell proliferation was related to the IGF-1 signaling pathway in late embryogenesis.

Transcranial Light Alters Melanopsin and Monoamine Production in Mouse ( Mus musculus ) Brain

Background: The mammalian circadian system sets a rhythm for the appropriate occurrence of physiological and behavioral phenomena during a 24-h period. Since the duration of the circadian system is usually less or more than 24 h, it must be entrained regularly and light is the governing stimulus of the rhythm. The target for light stimulus is the master circadian clock, which is located in the suprachiasmatic nucleus in the hypothalamus. One of the key molecules transmitting light information and entraining the clock is melanopsin (OPN4), a G protein-coupled molecule that is found most abundantly in the retina and brain. Although light stimulus is usually mediated through the eyes, light has an ability to penetrate the skull. Here, we present the effect of transcranial light illumination on OPN4 and serotonin expression in the mouse brain. Methods: Male mice were randomly assigned to a control group, morning-light group and evening-light group, and animals were illuminated transcranially five times a week for 8 min for a total of 4 weeks. The concentrations of OPN4 and monoamines were analyzed with Western blot and high-performance liquid chromatography (HPLC) techniques, respectively. Results: Our results show that transcranial light illumination increases the amount of OPN4 in the hypothalamus and cerebellum. Additionally, the production of serotonin in the cortex was shown to decrease in the morning-light group. Conclusions: With this study, we provide novel information on the effects of light administration through the skull on transmitters regulating circadian rhythmicity by showing that transcranial light affects molecules involved in circadian rhythmicity. J Neurol Res. 2017;7(3):39-45 doi: https://doi.org/10.14740/jnr427w

Impact of White Light Illumination on the Electronic and Chemical Structures of Mixed Halide and Single Crystal Perovskites

This study investigates the effect of white light illumination on the electronic and chemical properties of mixed halide perovskite (CH3NH3PbI3−xClx) thin films and CH3NH3PbI3 single crystals using photoelectron and absorption spectroscopy. The pristine materials' surfaces are found to be n‐type because of surface band bending due to the presence of donor levels, likely consisting of reduced lead (Pb0) that acts as surface traps. When illuminating the sample with white light (up to 1 sun), the valence features shifted to lower binding energy due to surface photovoltage, i.e., the bulk of the materials is much less n‐type. However, the surface photovoltage is only partially reversible and vanishes for prolonged illumination time. Concomitantly, a high concentration of metallic Pb0 is found, which induces strong Fermi‐level pinning and quenching of the surface photovoltage. This is accompanied also by the formation of PbI2 defects. Similar experiments on single crystals reveal the presence of a high concentration of reduced (metallic) Pb0 at the sample surface after cleaving. The present findings indicate that the chemical and electronic properties of perovskite films are very sensitive to white light illumination. Accounting for these light‐induced material changes is important to fully understand its photophysical properties and for improving the lifetime of perovskite‐based devices.

Layer Dependence and Light Tuning Surface Potential of 2D MoS2 on Various Substrates.

Here surface potential of chemical vapor deposition (CVD) grown 2D MoS2 with various layers is reported, and the effect of adherent substrate and light illumination on surface potential of monolayer MoS2 are investigated. The surface potential of MoS2 on Si/SiO2 substrate decreases from 4.93 to 4.84 eV with the increase in the number of layer from 1 to 4 or more. Especially, the surface potentials of monolayer MoS2 are strongly dependent on its adherent substrate, which are determined to be 4.55, 4.88, 4.93, 5.10, and 5.50 eV on Ag, graphene, Si/SiO2 , Au, and Pt substrates, respectively. Light irradiation is introduced to tuning the surface potential of monolayer MoS2 , with the increase in light intensity, the surface potential of MoS2 on Si/SiO2 substrate decreases from 4.93 to 4.74 eV, while increases from 5.50 to 5.56 eV on Pt substrate. The I-V curves on vertical of monolayer MoS2 /Pt heterojunction show the decrease in current with the increase of light intensity, and Schottky barrier height at MoS2 /Pt junctions increases from 0.302 to 0.342 eV. The changed surface potential can be explained by trapped charges on surface, photoinduced carriers, charge transfer, and local electric field.

Light Illumination Induced Photoluminescence Enhancement and Quenching in Lead Halide Perovskite

It has been found that light illumination (soaking) can significantly change the optical and electronic properties of perovskites and the performance of perovskite solar cells. Here using steady state and time‐resolved photoluminescence (PL) techniques, we investigate systematically the effect of light illumination on a well encapsulated CH3NH3PbI3 perovskites. Under a continuous constant illumination at low intensity, the PL exhibits either enhancement or constant; dependent on the detrapping rate and density of the defect states in the perovskite which in turn is determined by fabrication methods. Defect curing is attributed to the origin of the PL enhancement. Under a continuous higher intensity illumination, PL quenching is observed with different thresholds relevant to the sample fabrication. This is ascribed to mobile ion accumulation resulting in increased electron/ hole non‐radiative recombination. We confirmed the PL enhancement and quenching under continuous illumination (light soaking) partly originate from the intrinsic contribution of the perovskite, closely correlated to the defect density therefore the fabrication. These findings provide novel insight into the carrier dynamics correlated to the defect trapping and mobile ions which helps to understand the instability of perovskite solar cells.

The study of the contribution of the surface and bulk traps to the dynamic Rdson in AlGaN/GaN HEMT by light illumination

The effects of the surface and bulk traps on current collapse in AlGaN/GaN high electron mobility transistor were investigated by the transient behaviors of the devices. The results proved that the traps at the surface had little effect on current collapse when the device was well passivated, but the traps in the buffer layer played an important role. Two bulk trap levels were observed in these devices. In addition, the effects of light illumination on the bulk traps were studied in detail. It was found that light illumination enhanced the resumption of the current collapse after the field stress. The contribution of lights illumination with various wavelengths to the current collapse was also investigated to study the trap energy levels.

Photo-catalytic polymerization of catechin molecules in alkaline aqueous

Polyphenols are associated with a wide range of physiological properties. Catechin is a flavan-3-ol with five phenolic hydroxyl groups. After blue light illumination, the transparent solution of catechin became yellowish. The effects of visible light illumination (400–800nm) were investigated on molecular structures and antioxidant capacities of catechin. Under the neutral or alkaline aqueous with the illumination of blue light, the photolysis and polymerization of catechin were observed in this study. A chromogenic catechin dimer was separated and identified as a proanthocyanidin by the chromatographic technique and mass spectrometry. For quantitative evaluation, the signal intensities of the catechin and the photochemical product show a negative correlation in the liquid chromatograms. The oligomer of flavan-3-ols (catechin dimer) is suggested as a dimeric B type proanthocyanidin, which has the molecular formula C30H26O12 and 578.14g/mol in exact mass. The mass spectrum of catechin dimer had characteristic ion signals in m/z 577, 560, 439Da. However, the total phenolic contents and scavenging O2− activity of catechin treated by blue light illumination are not changed significantly at the neutral or alkaline aqueous. Our results of photocatalytic oligomers of catechin provide a novel way to explain the sensory changes of green tea and a biochemical mechanism under the irradiation environments.