Optical Degradation Research Articles

Simulation study on the degradation process of photovoltaic modules

Degradation decreases photovoltaic power delivery capacity over time. Studies on photovoltaic degradation are usually based on accelerated tests or filed tests which are time-consuming and require much effort. This paper investigates the degradation process of photovoltaic modules by simulation studies. A circuit-based model is employed to describe photovoltaic characteristics to environmental conditions and to the aging factors of photovoltaic modules. Analysis of each aging factor shows that the decrease of short-circuit current, the main reason of power loss, is mainly caused by optical degradation. The decay of fill factor mainly due to degradation of parasitic resistances worsens the power output. The statistical analysis of photovoltaic characteristic parameters based on a great number of photovoltaic modules with the same technology indicates that the degradation process can be very complicated depending on the degradation patterns of aging factors. Generally, the power loss tends to increase and the mismatch among photovoltaic modules becomes more remarkable through the time.

Dynamics and Control for Nonideal Solar Sails Around Artificial Lagrangian Points

Due to their lack of fuel consumption, solar sails have potential applications for deep space exploration. However, due to the optical degradation and deformation of such a sail, a nonideal model is preferable for investigating their dynamics and control when moving around an artificial Lagrangian point. An improved imperfectly reflecting sail model is constructed to compare with the ideal one. With a Hamiltonian structure-preserving controller adopted, the trajectory around an artificial Lagrangian point is generated for ideal solar sails. The original trajectory changes and migrates when the imperfectly reflecting sail model is used. Two improvement strategies are proposed to adjust the changed trajectory. One strategy is to adjust the input parameters of the actuator to compensate for the change in acceleration. The other strategy is to design a new controller to enhance the change and migration of the trajectories. The effectiveness of the two strategies for coping with imperfectly reflecting solar sails is verified via numerical simulations.

In-situ evaluation of radiation induced optical degradation of candidate scintillator materials for ITER’s gamma and neutron detectors

Neutron and gamma detectors will play an essential role during operation of ITER and future fusion reactors. They are required in systems to monitor the total neutron production from the plasma for control and safety. Neutron and gamma detectors being considered employ scintillators that will be exposed to high neutron and gamma radiation levels. In this work a systematic study of the effect of gamma radiation on different types of scintillators (plastics, liquids and single crystal), candidates for detectors in future machines, has been done. The experiments were performed at the CIEMAT Nayade 60Co gamma irradiation facility, measuring in-situ radiation induced optical absorption (RIA) and radioluminescence (RIL) from 370 to 730 nm. The RIA and RIL at 0.2 Gy/s up to 40 kGy and at 1.2 Gy/s to 240 kGy show reduced efficiency with dose, i.e. increased absorption and reduced luminescence. Rapid degradation for the single crystal Stilbene, with a drastic light emission drop by 20 kGy due to self-absorption, has been observed. Of the solid plastic scintillators, BC-418 exhibits the best behaviour. Liquid scintillators for a high radiation environment show negligible radiation induced absorption and emission loss. Details of the RIA and RIL degradation with dose for the different scintillators are presented.

An Online Tilt Estimation and Compensation Algorithm for a Small Satellite Camera

In the case of a satellite camera designed to execute an Earth observation mission, even after a pre-launch precision alignment process has been carried out, misalignment will occur due to external factors during the launch and in the operating environment. In particular, for high-resolution satellite cameras, which require submicron accuracy for alignment between optical components, misalignment is a major cause of image quality degradation. To compensate for this, most high-resolution satellite cameras undergo a precise realignment process called refocusing before and during the operation process. However, conventional Earth observation satellites only execute refocusing upon de-space. Thus, in this paper, an online tilt estimation and compensation algorithm that can be utilized after de-space correction is executed. Although the sensitivity of the optical performance degradation due to the misalignment is highest in de-space, the MTF can be additionally increased by correcting tilt after refocusing. The algorithm proposed in this research can be used to estimate the amount of tilt that occurs by taking star images, and it can also be used to carry out automatic tilt corrections by employing a compensation mechanism that gives angular motion to the secondary mirror. Crucially, this algorithm is developed using an online processing system so that it can operate without communication with the ground.

The role of zinc metal salts on size, morphology and photocatalytic activity of ZnO

AbstractHerein, we report on the syntheses of ZnO nanoparticles using different precursors Zn(NO3)2•6H2O, Zn(CH3COO)2•2H2O, ZnCl2, and ZnSO4.H2O by a microwave assisted method. The different precursors resulted in different structural, optical and photocatalytic degradation of Rhodamine B dye. The nanoparticles resulted in rod-like and pseudo-spherical morphologies when the ZnO2•6H2O, (Zn(CH3COO)2•2H2O and ZnCl2 precursors were used, with the proportion of the spherical morphology in each photocatalyst varying in the order Zn(NO3)2•6H2O > Zn(CH3COO)2•2H2O > ZnCl2. The ZnSO4.H2O precursor yielded trapezium shaped particles that were agglomerated through oriented attachment. For photocatalytic degradation studies, the fastest degradation was achieved using the SNO3- photocatalyst, which degraded the dye in a period of 120 min, followed by SCH3COO- at 150 min, SCl- at 180 min and SSO42- managing to degrade only 15 % of the dye after 240 min. The difference in the activity was attributed to surface area differences, which followed the order SNO3- > SCH3COO- >SCl- > SSO42-, with the photocatalyst that had the highest surface area showing high degradation rates. The high degradation rate observed for the SNO3- photocatalyst was also attributed to the presence of a large number of spherical particles thereby having a larger proportion of the high energy [0001] and [000-1] faces known to be highly active.

Electrical and optical degradation study of methylammonium-based perovskite materials under ambient conditions

Hybrid perovskites have emerged over the past five years as absorber layers for novel high-efficiency low-cost solar cells which combine the advantages of organic and inorganic semiconductors. One of the main obstacles to their commercialization is their poor stability under light, humidity, oxygen, and high temperatures. In this work, we compare the optical and the electrical light-induced degradation of CH3NH3PbI3 (“MAPI”)-based solar cells using real-time ellipsometry measurements, electrical measurements and X-Ray Diffraction (XRD) techniques. We evidence that while the electrical degradation takes place on a short time scale (2–3 days of exposure to ambient light conditions in a nitrogen atmosphere), no optical degradation is observed before 10 days when the dissociation reaction of methylammonium lead iodide starts acting. We find a very good agreement between XRD and ellipsometry measurements; both show the appearance of PbI2 after 1 week of exposure. We also confirm that the main mechanism at play is a light-induced degradation affecting the edges of the stack and the interfaces between the perovskite and the neighbouring layers. Last, a very good match is obtained on the optical constants of MAPI between our ellipsometry measurements and density functional theory calculations we performed, and we confirm the behavior of MAPI as an inorganic semiconductor.

Improvement of the Photostability of Low-Density Polyethylene and Ethylene Vinyl Acetate Blends with Nanoclay: Toward Durable Nanocomposites for Potential Application in Greenhouse Cover Films

ABSTRACTThe effect of three different organomodified nanoclays (Cloisite 20A, Cloisite 30B, and Nanomer I28E) as well as the effect of a compatibilizer (PEgMA) was studied, with the purpose of developing greenhouse cover films based on polyethylene/ethylene vinyl acetate blends. Three organomodified clays were analyzed. The influence of organomodifier clay on film optical, morphology, mechanical, and photo-oxidative degradation properties as well as the effect of incorporation of maleic anhydride-grafted polyethylene as a compatibilizer was studied. The combined effect of these nanoclays with two different UV-oxidative protection systems for polyethylene/ethylene vinyl acetate-nanostructured films was evaluated. Two types of UV stabilizer combination systems were studied; one with a combination of heat and light stabilizers of mixture of antioxidants (phenolic and metal deactivator, Irgatec NC66) with hindered amines, Tinuvin 494AR (designated as system-A) and other with a combination of metal deactivator antioxidant, Irganox MD1024 with hindered amines Tinuvin NOR 371 and benzophenones, Chimasorb 81 (designated as system-B). A strong influence is observed in the use of compatibilizing agent, type, and content of nanoclay in the degree of dispersion as well as in the photo-oxidation behavior. The structure obtained is very dependent on the modified clay used; mostly, intercalated–exfoliated clay structure is produced. The induction period for the photodegradation reaction to start is shorter in the samples with the nanoclay than in the pure polymer. There was a difference in the effectiveness of two stabilizing systems used. It was found a better performance for the stabilizer system-A, regardless of the type of clay used. These greenhouse cover films should allow the pass-through of visible light into the greenhouse during day but restrict the pass-through of the infrared radiation out of the greenhouse during night.

Positive effects of phosphotungstic acid on the in-situ solid-state polymerization and visible light photocatalytic activity of polyimide-based photocatalyst

A series of H3PW12O40 (HPW)-containing polyimide (PI) hybrid composites (TPI) are prepared through in-situ solid-state polymerization using HPW, melem and pyromellitic dianhydride as precursors. The effect of HPW on the morphology, porosity, chemical structure, and optical and visible-light photocatalytic degradation efficiency of TPI composites are systematically investigated by various characteristic methods. By comparing the structure, property and photocatalytic activity of the TPI composites and the HPW-PI composites (prepared by the impregnation method), it indicates that HPW can promote the formation of CN bond in the five-membered imide rings between amines and anhydrides during the in-situ solid-state condensation process. Subsequently, the visible-light (λ > 400 nm) photocatalytic degradation efficiency of imidacloprid on TPI composites is also enhanced compared with the pristine PI because of the enhancement of the in-situ solid-state condensation reaction, photogenerated electron-hole separation efficiency and visible-light utilization efficiency after the introduction of HPW. The visible-light photocatalytic degradation rate constant k of 15% TPI composites prepared at 300 °C and 5% TPI composites prepared at 325 °C are about 10.33 and 2.42 times of the corresponding pristine PI, respectively. Compared with commercial P25, the photocatalytic degradation efficiency of 15% TPI-300 and 5% TPI-325 are about 4.58 and 5.13 times of P25 under visible light irradiation.

Anatomy of cornea and ocular surface.

Important functions of cornea in the eye include protecting the structures inside the eye, contributing to the refractive power of the eye, and focusing light rays on the retina with minimum scatter and optical degradation. Considerable advances have taken place in understanding the organization of collagen in the corneal stroma and its clinical significance. In this review, the structure and function of various components of cornea and ocular surface are presented.

Hybrid Collagen-NaCMC Matrices Loaded with Mefenamic Acid for Wound Healing

Fire and burns represent the fourth cause of death in the world. Numerous options for dressings exist, but their selection should be based on several factors such as burn severity, wound location and water retention. Collagen (COLL) is the most common protein in the human body and, due to its biocompatibility, is the main component in biomaterials development. Mefenamic acid (MA) is a non-steroidal anti-inflammatory drug with analgesic properties, and carboxymethylcellulose (NaCMC) is a biocompatible and biodegradable polymer that is commonly used in biomedical field. Collagen - carboxymethylcellulose - mefenamic acid hydrogels, developed in order to be used in burn treatments were lyophilized and the corresponding spongious matrices were investigated by optical microscopy, FT-IR spectroscopy, water absorption, enzymatic degradation and drug release kinetics studies. All tests revealed proper morphological structure, favourable release patterns, convenient swelling capacity and degradation profiles, indicating the possibility of their use for medical applications.

Highly efficient red single transverse mode superluminescent diodes

Optimisation of the epitaxial growth of AlGaInP/GaInPAs nanoheterostructures and improvement of the technologies of active channel formation and p-contact deposition made it possible to considerably increase the external differential quantum efficiency (up to 0.5 mW mA−1), the catastrophic optical degradation threshold (up to 40 mW), and the spectral width (to FWHM exceeding 15 nm) of single transverse mode superluminescent diodes with the centre wavelength of about 675 nm. Lifetime tests demonstrated high reliability of these diodes at a cw output optical power up to 30 mW.

Mitigation of Optical Nonlinear Degradation by Optical Spread Spectrum in Coherent Optical Fiber Transmission Systems

We have theoretically investigated the nonlinear noise suppression by means of optical spread spectrum technology in DP-QPSK and DP-16QAM optical coherent transmission systems, and clarified the dependence of SNR improvement on the number of multiplexed channels.

Brilliant Pitaya‐Type Silica Colloids with Central–Radial and High‐Density Quantum Dots Incorporation for Ultrasensitive Fluorescence Immunoassays

AbstractCreating secondary nanostructures from fundamental building blocks with simultaneous high loading capacity and well‐controlled size/uniformity, is highly desired for nanoscale synergism and integration of functional units. Here a novel strategy is reported for hydrophobic quantum dots (QDs) assembley with porous templates, to form pitaya‐type fluorescent silica colloids with densely packed and intact QDs throughout the silica matrix. The mercapto‐terminated dendritic silica spheres with highly accessible central–radial pores and metal‐affinity interior surface, are adopted as a powerful absorbent host for direct immobilization of QDs from organic phase with high loading capacity. The alkylsilane mediated silica encapsulation prevents QDs' optical degradation induced by ligand exchange and favors the homogeneous silica shell formation. These multiple QD embedded silica spheres exhibit good compatibility for different colored QDs with well‐preserved fluorescence, high colloidal/optical stability, and versatile surface functionality. It is demonstrated that after integration with a lateral flow strip platform, these silica colloids provide an ultrasensitive, specific, and robust immunoassay for C‐reaction protein in clinical samples as promising fluorescent reporters.

Raman mapping of the S3− chromophore in degraded ultramarine blue paints

AbstractA specific case of degradation was observed in synthetic ultramarine paint within 3 paintings from the early 20th century, manifesting as an intricate pattern of white lines criss‐crossing the blue paint surface. Raman spectroscopy can be performed directly on untreated sample surfaces and is sensitive to the colour components in ultramarine (S3− and S2− chromophores). This method was chosen to map the chromophore intensity distribution and to relate it to the surface degradation pattern. Raman signal intensity, however, decreases when the laser is out of focus, providing a challenge when mapping signal intensity across rough or undulating surfaces. To account for this, a series of experiments was conducted to determine the laser and objective combination least sensitive to changes in surface topography. The optimal settings were found to be the 785‐nm excitation wavelength with the 50× long working distance objective (numerical aperture 0.50). This combination gave the smallest focus‐dependent signal decrease on test samples: When shifted 5 μm out of focus above or below the sample surface, the signal from the same spot showed a decrease of 7% only. Maps of the blue (S3−) chromophore signal at 548 cm−1 taken from 3 samples showed a clear decrease in intensity on the degraded white lines. Patterns of signal intensity distribution matched well with the optical degradation pattern. From this observation, in conjunction with previous surface characterisation reported elsewhere, it was concluded that the surface phenomenon was indeed a discolouration of the ultramarine pigment, caused by a reduction in the concentration of the chromophore.

Ionizing radiation impact on communications performance of optical multi-hop inter-satellite relay link

Ionizing radiation impact on communications performance of optical multi-hop inter-satellite relay links is studied in this paper. Essential optoelectronic devices involved in optical communication system were irradiated by Co60 gamma ray and BER models of OOK, DPSK and homodyne BPSK of multi-hop inter-satellite links were proposed. On this basis, performance degradations under ionizing radiation were simulated, and on-orbit performance degradations were further discussed. Research results show that EDFA of ionizing radiation is the dominant cause of optical relay link communication performance degradation and the choosing of relay satellite has significant influence on on-orbit performance of links. The anti-ionizing radiation capability of homodyne BPSK model obviously outperforms OOK and DPSK models.

Effect of open ultraviolet germicidal irradiation lamps on functionality of excimer lasers used in cornea surgery.

We report on the impact of direct ultraviolet germicidal irradiation (UVGI) on reflective optics, used in the excimer laser system Allegretto Eye-Q. The aim of our work was to confirm our hypothesis based on long-rate observations of obtained anomalies in post-operative results that are attributed to degradation of reflective optics upon ultraviolet radiation. The presence of direct UVGI coupled with humidity in the operating environment caused merging anomalies and unwanted post-operative correction values. Ultraviolet-A radiation caused a similar effect on the reflective cover of the mirrors.

MODIS Aqua Optical Throughput Degradation Impact on Relative Spectral Response and Calibration of Ocean Color Products

Since Moderate Resolution Imaging Spectroradiometer Aqua’s launch in 2002, the radiometric system gains of the reflective solar bands have been degrading, indicating changes in the system’s optical throughput. To estimate the optical throughput degradation, the electronic gain changes were estimated and removed from the measured system gain. The derived optical throughput degradation shows a rate that is much faster in the shorter wavelengths than the longer wavelengths. The wavelength-dependent optical throughput degradation modulated the relative spectral response (RSR) of the bands. In addition, the optical degradation is also scan angle-dependent due to large changes in response versus the scan angle over time. We estimated the modulated RSR as a function of time and scan angles and its impacts on sensor radiometric calibration for the ocean science. Our results show that the calibration bias could be up to 1.8% for band 8 (412 nm) due to its larger out-of-band response. For the other ocean bands, the calibration biases are much smaller with magnitudes at least one order smaller.

Oxygen pressure effect on optical properties and dye degradation of ZnO nanostructured films prepared by sputtering

The effect of oxygen pressure on structural, morphological and photocatalytic properties of ZnO nanostructured films deposited on glass substrates via RF magnetron sputtering was investigated. The structural, morphology and oxidation states of the films were investigated by x-ray diffraction, scanning electron microscopy, atomic force microscopy, and x-ray photoelectron spectroscopy. UV–vis spectroscopy and photoluminescence spectroscopy were used to analyze the degradation and optical properties of ZnO thin films. The grown films showed wurtzite hexagonal crystalline nanostructures with a favored orientation along the direction of (0 0 2) lattice plane. The morphology images showed a hierarchical ZnO nanostructured films with various shapes from circulars to foils and even much more multifaceted circular shapes and triangular sheets-like shapes by varying the oxygen pressure. The foil type ZnO nanostructured films showed significant photocatalytic activity concerning the degradation of methyl orange, mainly due to their surface-to-volume ratio.

Degradation Mechanism of Crystalline Quality and Luminescence in In0.42Ga0.58N/GaN Double Heterostructures with Porous InGaN Layer

In0.42Ga0.58N/GaN double heterostructures on c-plane sapphire substrate were grown by metal–organic chemical vapor deposition. High-angle annular dark field scanning transmission electron microscopy revealed that the In0.42Ga0.58N layer features a porous structure consisting of multifaceted voids with a density of 109 cm–2 and an average diameter of 74.6 nm, which was attributed to thermodynamically preferential vacancies aggregation. Both photoluminescence and cathodoluminescence showed luminescence quenching in the In0.42Ga0.58N layer. A void model involving void surface trapping and hindered radiative recombination quantitatively described the luminescence quenching mechanism. Moreover, it is found that the indium (In) precipitates within the In0.42Ga0.58N layer were void-In complexes in nature, consisting of the same quenching centers as voids and adversely affecting the luminescence. These results will provide critical insight into the optical degradation of InGaN-based light-emitting devices with hi...

Degradation Mechanisms of Heterogeneous III-V/Silicon 1.55- $\mu \text{m}$ DBR Laser Diodes

This paper reports an extensive analysis of the degradation processes of heterogeneous III-V/Silicon infrared laser diodes designed for integrated telecommunications and interconnects. By submitting the devices to a series of constant current stress tests, a gradual degradation of the main device parameters was observed. In particular, in every stress scenario the devices under test showed: 1) an increase in the threshold current; 2) a decrease of the turn-ON voltage; and 3) an increase in the apparent carrier concentration within the space charge region. The variation of the electrical parameters (turn-ON voltage and apparent charge concentration) was found to be significantly correlated to the optical degradation for long stress times; the results support the hypothesis that degradation originates from an increase in the non-radiative recombination rate, possibly due to the diffusion of defects toward the active region of the devices. In order to investigate the physical origin of those defects, a capacitance deep level transient spectroscopy analysis was performed. The results indicate the presence of five different deep levels, with a main trap located around 0.43 eV above the valence band energy. This trap is compatible with an interface defect located between the In 0.53 Al x Ga 0.47-x As separate confinement heterostructure region and the InP layer.