Light-induced Aging Research Articles

Experience of Replicating Historical Inks of the 15th–18th Centuries: Studying the Properties of Model Samples

The method of natural sciences of replication (reproduction of historical technologies) is promising in the study of cultural-heritage objects. By applying this method, models of the method of information recording are obtained, made using authentic raw materials and in accordance with historical chemical techniques (cold and hot extraction, fermentation, reactions with the formation of colloidal solutions in open reaction vessels at atmospheric pressure). The purpose of the study is to trace the dynamics of changes in the properties of model ink using the methods of natural sciences, in particular chemistry and physics. This is necessary to understand the causes of damage to cultural-heritage objects, such as written artifacts of the 15th–18th centuries. The use of replication is the only way to apply in research not only nondestructive, but also destructive natural-science methods. The results of replication of ten ink formulations of two groups are presented. In the first, iron vitriol served as a source of iron ions, in the second, rusty iron. The yellowing and color characteristics in the process of light-induced aging, chemical properties and microstructure of the ink are determined. The characteristic features of each of the groups are described.

Degradation of electrical characteristics in low-bandgap polymer solar cells associated with light-induced aging

Abstract As the efficiency of organic solar cells has been consistently improved, interest is being raised to understand degradation mechanisms inside the solar cells. Among many factors that affect solar cell deterioration, light is the most crucial factor in the degradation mechanism. Here we report degradation under the continuous light-induced conditions for PTB7:PC70BM organic solar cells during the first 24 h with maintaining the temperature at 25 °C. It revealed 30% of initial performance drop after 24 h of light-induced aging, mostly through a decrease in JSC and FF. The morphological and electrical characteristics of the active layer and devices were investigated by atomic force microscopy, impedance spectroscopy, and temperature-dependent current density–voltage characteristics to figure out the origin of the photo-induced degradation. As a result, the light-induced traps were found to be a primary cause of loss. Furthermore, this trap formation was observed with an energy of 78 meV leading to trapped charge limited conduction properties and electrical degradation of solar cells.

Evaluation of Polymer Solar Cell Efficiency To Understand the Burn-in Loss

In this study, the degradation process of a conventional P3HT:PC61BM bulk heterojunction solar cell device due to light-induced aging is evaluated. This structure is chosen so as to reduce the numb...

Aging effects in interface-engineered perovskite solar cells with 2D nanomaterials: A depth profile analysis

The stability of perovskite solar cells (PSCs) is a major factor limiting the market breakthrough of this technology. To understand the aging effects in PSCs is mandatory to rationally design implemented architectures and materials combining a viable deposition process, efficiency and stability. Despite of this evidence, only few experimental works succeeded in the direct quantitative characterization of aging effects in PSCs. In this work, we apply state-of-the-art X-ray photoelectron spectroscopy (XPS) depth profile analysis and time-of-flight secondary ion mass spectrometry (ToF-SIMS) 3D imaging to investigate the light-induced degradation of layers and interfaces in reference (Au/Spiro-OMeTAD/CH3NH3PbI3/m-TiO2/cTiO2/FTO) and interface-engineered mesoscopic PSCs in which graphene flakes are added into the mesoscopic TiO2 layer and a solution-processed 2H-MoS2 flakes buffer layer is added at the Spiro-OMeTAD/CH3NH3PbI3 interface. Results show that the graphene addition into the mesoscopic TiO2 layer improves the stability of the PSC by reducing the locally-inhomogeneous light-induced back-conversion of the CH3NH3PbI3 layer into PbIx and PbOx species and the consequent release of iodine species, which diffuse across the interfaces and causes the modifications at the gold electrode (Au-I bonding) and the mesoscopic TiO2 (Ti-I bonding) interfaces. Moreover, where the CH3NH3PbI3 layer is preserved the gold diffusion across the entire device structure is strongly reduced even after the aging. The 2H-MoS2 flakes buffer layer allows limiting the localized diffusion of gold and the iodine diffusion in as-prepared PSCs while it is rather ineffective in preventing light-induced aging effects. Overall, thanks to the lower average degradation of the layers and interfaces, interface engineered PSCs could retain ∼60% of their initial PCE after the aging respect to less than ∼25% in the reference cells.

UV–Vis Light-induced Aging of Titan’s Haze and Ice

Abstract The study of the photochemical aging of aerosols is an important tool for understanding Titan’s stratosphere/troposphere composition and evolution, particularly the haze. Laboratory simulations of the photoreactivity of the haze aerosol analogs provide insight into the photochemical evolution of Titan’s atmosphere at and below the haze layers. Here we use experimental simulations to investigate the evolution of the laboratory analogs of these organic aerosols under ultraviolet (UV)–visible (Vis) photons, which make it through the haze layers during their sedimentation process. We present experimental results for the aging of Titan’s aerosol analogs obtained from two dominant nitrogen-containing organics, HC3N and HCN, under simulated Titan atmospheric conditions (photons and temperature). We report that volatile nitriles condensed on haze particles could be incorporated through photochemistry and provide one such sink mechanism for nitrile compounds. We provide laboratory evidence that the organic aerosols could photochemically evolve during their sedimentation through Titan’s atmosphere.

Light-induced alterations of pineapple (Ananas comosus [L.] Merr.) juice volatiles during accelerated ageing and mass spectrometric studies into their precursors

Alterations of volatiles during accelerated light-induced ageing of pineapple juice were assessed by HS-SPME-GC–MS in a non-targeted profiling analysis over a 16-week period. Multivariate statistics permitted to reveal substantial chemical markers generally describing the effect of light storage. Volatiles generated comprised phenylpropenes, carbonyls, 2-methylthiophene, toluene, and furfural, while concentrations of methyl and ethyl esters, terpenes, and furanones decreased. In addition, the qualitative composition of phenolic compounds and glycoside-bound volatiles in selected samples was characterized by HPLC-DAD-ESI-MSn as well as HR-ESI-MS. The fresh juice contained unique pineapple metabolites such as S-p-coumaryl, S-coniferyl, S-sinapylglutathione, and structurally related derivatives. Among others, the presence of p-coumaroyl, feruloyl, and caffeoylisocitrate as well as three 4-hydroxy-2,5-dimethyl-3(2H)-furanone glycosides in pineapples could be substantiated by the HR-ESI-MS experiment. Mass spectrometric assignments of selected metabolites are presented, and putative linkages between volatiles and their precursors are established.

Light damage to selected organic materials in display cases: A study of different light sources

The protection of works of art and cultural assets against light-induced aging is vital when planning exhibitions. Newly developed lighting systems render the selection of suitable light sources more difficult, not least in the context of energy–economical systems. This study accordingly examines different lighting systems (fluorescent tubes, halogen lamps, low-voltage metal halide lamps, and LED lamps) in terms of the damage potential they hold for the materials concerned. The changes in color were evaluated using the CIEDE2000 color-difference formula. This study focuses on selected organic materials and shows that changes in color already occur after only a brief exposure time. The color changes induced by the fluorescent tubes were consistently more intense than those induced by the other light sources. The results obtained with the remaining lamps show that the color changes depend more on the material under investigation than on the source used. The changes determined after a relatively short exposure period (five months) vividly demonstrate that exposing sensitive materials to light for longer terms (as is the case during a permanent exhibition) is most definitely a non-viable option.

Markers for Identification of Faded Safflower (Carthamus tinctorius L.) Colorants by HPLC-PDA-MS - Ancient Fibres, Pigments, Paints and Cosmetics Derived from Antique Recipes

Safflower red was prepared by extracting safflower petals (carthamus tinctorius L.) at alkaline pH, after the preliminary removal of water-soluble safflower yellow. Alkaline extracts were used to prepare dyed silk, wool, cotton and paper, to precipitate the pigment, to prepare paint and to produce the antique Chinese cosmetic rouge. All reference samples were analyzed with high-performance liquid chromatography–photodiode array–mass spectrometric detection (HPLC-PDA-MS) after colorant was removed from its substrate by both a harsh and mild acid hydrolysis method. In addition to the red colorant carthamin, four colorless components are markers for safflower. These components were characterized by their retention times, ultraviolet–visible (UV-Vis) spectra and mass spectra and were given the codes Ct1, Ct2, Ct3 and Ct4. Experiments on references clearly indicated that these Ct components, unlike carthamin, withstood harsh acid hydrolysis as well as light-induced accelerated ageing, and that they could be found even in a completely faded wool sample. This made them excellent markers to identify safflower red, even in discolored historical samples or in samples that must be treated in a way that destroys carthamin. These findings may contribute to a better understanding of the manufacturing technology and to better conservation of objects that have already undergone considerable light-induced ageing.

Light-induced yellowing of mecanical and chemimecanical pulp sheets – influence of wood raw material, process and aging method

The light-induced brightness reversion of different types of unbleached and bleached high-yield pulps was studied under both accelerated and long-term ambient light-induced ageing conditions. It wa ...

ACCELERATED LIGHT-INDUCED AGING OF α-, β-, AND γ-13C-ENRICHED CELL WALL-DEHYDROGENATION POLYMERS STUDIED WITH SOLID STATE 13C NMR SPECTROSCOPY

ABSTRACT Light-induced aging of lignocellulosic materials has been studied with a new technique involving selectively α-, β-, and γ-13C-enriched cell wall-dehydrogenation polymers (CW-DHPs) and solid state 13C NMR spectroscopy. The results from cross-polarization magic angle spinning (CP/MAS) 13C NMR experiments of unirradiated and irradiated CW-DHP have revealed mainly a decrease in the amount of end-groups of both coniferaldehyde and coniferyl alcohol type. The results suggest that these end-groups become saturated and that the terminal functionalites, i.e., γ-aldehyde and γ-hydroxymethyl groups, at least to some extent, are retained. The results indicate further that no detectable cleavage of the β-O-4 bonds occurs in the examined lignocellulosic model. In terms of proposed mechanisms of yellowing, there is marginal evidence that up to 2% of the α-labeled sites are converted by irradiation to α-carbonyls (aldehyde or ketones); moreover, we cannot dismiss the possibility that the precursor structures giving rise to these few α-carbonyls are β-O-4 structures. The 13C-enriched CW-DHP was formed directly on spruce (Picea abies) wood tissue (differentiating xylem) by administering selectively 13C-labeled coniferin at pH 6.0 in the presence of glucose oxidase and β-glucosidase, i.e., no phenol-oxidizing enzyme was added and the wood cells’ own enzymes polymerized the precursor.

PHOTOYELLOWING OF UNTREATED AND ACETYLATED ASPEN CHEMITHERMOMECHANICAL PULP UNDER ARGON, AMBIENT, AND OXYGEN ATMOSPHERES

Untreated and acetylated hydrogen peroxide-bleached aspen chemithermomechanical pulp (CTMP) was subjected to accelerated light-induced aging in various atmospheres (argon, ambient, or oxygen). The photochemical changes that took place during irradiation were followed by solid-state UV/VIS diffuse reflectance spectroscopy. The degree of photoyellowing of the untreated CTMP decreased when the air in the surrounding atmosphere was replaced with oxygen-free argon. The decrease was only moderate, indicating that atmospheric oxygen is not of sole importance for the light-induced discoloration or that only a trace amount of oxygen (strongly adsorbed to the fiber material) is necessary to cause discoloration. Acetylation clearly diminished the kinetics of photoyellowing in all atmospheres resulting in substantially less absorption in the entire visible range (λ > 400 nm). However, the development of chromophores was attenuated in an oxygen-enriched atmosphere, suggesting that oxygen is important for the color-retarding or photobleaching reactions of acetylated lignocellulosic materials. Independently of the degree of acetylation and the surrounding atmosphere, irradiation with UV/VIS fluorescent lamps generated an apparent absorption maximum around 360 nm with a shoulder at approximately 420 nm.

A Graphite-Assisted Laser Desorption/Ionization Study of Light-Induced Aging in Triterpene Dammar and Mastic Varnishes

The light-induced aging of natural triterpenes used in varnishes was studied using graphite-assisted laser desorption/ionization mass spectrometry. This method was found to be superior to conventio...

Sunlight-induced cancer: some new aspects and implications of the xeroderma pigmentosum model

Symptoms of xeroderma pigmentosum, a hereditary disease characterized by accelerated light-induced ageing of the skin, are due to deficiencies in the repair of damaged DNA. Following UV irradiation a high incidence of thioguanine-resistant mutations have been observed, which may be a model for the abnormally high incidence of freckling and benign and malignant transformation observed in these patients. Cells from patients with Cockayne's syndrome and trichothiodystrophy have also been shown to be hypermutable by UV radiation with a similar DNA repair defect, but unlike xeroderma pigmentosum patients they do not experience a higher incidence of skin cancer or freckling. An immunological defect may be a further crucial factor determining the dermatological symptoms of xeroderma pigmentosum patients. Much can be learned about the way normal individuals function from a study of aberrant functioning of individuals with defined genetic deficiencies. In the field of senescence of the skin, the disease xeroderma pigmentosum (XP) has been of particular value, as the exposed skin of these sun-sensitive individuals shows at an early age many of the features of aged sun-exposed skin of normal individuals. These features of XP skin include hyperkeratosis, freckling, benign lesions and malignant tumours, including melanomas. A full discussion of this syndrome has been given by Kraemer et al.

Open-circuit, photoinduced aging of polycrystalline CdSe photoelectrodes in liquid-junction solar cells

We utilized photoluminescence (PL) spectroscopy under in situ conditions to study slow chemical changes on CdSe/polysulfide liquid-junction solar cells, as a function of aging procedures. The aging conditions were (1) focused light under open-circuit conditions; (2) focused light under short-circuit conditions; and (3) total darkness. For the first time we report that cells do age under open-circuit conditions, and that the decrease in stability and the changes in the PL, with aging time, are similar to those observed for cells which are aged under short-circuit conditions. At the initial stages of the light-induced aging processes, changes in the defect concentration in the photoanode were observed. In addition to the CdSe PL there is a broad PL in the spectral range of 1.7 eV (CdSe) up to 2.4 eV (CdS). This PL is identified to be due to the mixed phase compound of CdSe1−xSx. At the final stages of the aging processes characteristic CdS Raman spectra was detected. Such PL and Raman changes were not detected for the cells which were aged under total darkness. Under ex situ conditions the envelope of two PL spectra due to CdSe and CdSe1−xSx compound changes with the excitation light. Variation of efficiency and PL peak intensity with aging time shows a good correlation between PL peak intensity and the efficiency of the cell.

Characterization of polycrystalline electrodeposited CdSe photoelectrodes using photoluminescence spectroscopy

We have utilized both photoluminescence (PL) and Raman spectroscopy to nondestructively study the surface of polycrystalline electrodeposited CdSe photoelectrodes as a function of surface preparation and aging procedures. The excitation energy dependence of the PL efficiency at 77 K, which depends on surface band bending, is consistent with increased concentration of shallow levels in electrodeposited CdSe compared with single crystal material. No PL was observed for unannealed CdSe films; for annealed, unaged films the spectra at 77 K were qualitatively similar to those of single crystals in that spectral features could be identified with the A exciton at 1.815 eV and with a donor-acceptor-pair band at 1.70 eV exhibiting phonon replicas. The PL and Raman spectra of light-aged electrodes exhibit features which we identify with the formation of a surface layer of CdS and the presence of mixed compounds CdSxSe1−x, which are formed by chemical exchange with the polysulfide electrolyte during light-induced aging. The PL spectra at 4.2 K for the unaged and dark-aged electrodes exhibit sharp lines in the vicinity of 1.81 eV which we identify as due to bound-exciton recombination, but which differ in energy from those exhibited by the light-aged film.

Effect of 6-Benzyl Aminopurine on the Stabilization of Absorption Spectrum and Hill Activity of Isolated Chloroplasts

Summary Beet spinach chloroplasts isolated in the presence or absence of BAP (6-benzyl aminopurine) were suspended in sugar or salt medium and were allowed to age in light (1,000 JM -2 s -1 ). Loss in the Hill activity (H 2 0 to ferricyanide (Fe (CN 6 ) 3- ) due to light-induced ageing could be partly protected by the inclusion of the hormone (BAP). The extent and pattern of protection of chloroplast function by the hormone is similar for both salt and sugar media. During light-induced ageing, chloroplasts also lose the capacity to use the artificial electron donor DPC (diphenyl carbazide) for photoreduction of DCPIP. This loss is fast er for chloroplasts suspended in salt medium than for chloroplasts incubated in sugar medium. BAP could not provide any protection for this loss in DPC supported DCPIP photoreduction ability of chloroplasts. Loss in chlorophyll contents during light induced ageing was found to be negligible. However, absorption spectrum for chloroplasts showed changes in t he blue to red peak ratio upon ageing in light. This was found to be more pronounced in chloroplasts incubated in salt medium wih or without BAP treatment than in chloroplasts incubated in sugar medium. Accompanied this change in peak ratio, there is a small blue shift (1-2 nm) in the position of red absorption peak. BAP seems to arrest this shift.

Light-induced aging effects in Schottky diodes on sputtered hydrogenated amorphous silicon (a-SiH) : interpretation of the photovoltaic stability

We study the evolution of the electrical characteristics (current-voltage I(V) versus temperature, capacitance-voltage versus frequency, I(V) under illumination) of Pt and Au Schottky diodes prepared on sputtered a-SiH after exposure to light (AM1). A reversible light-induced bulk effect is put forward : the density of states in the bandgap of a-SiH increases after illumination leading to a shift from the conduction band edge of the Fermi level in the bulk of the material. The surprising stability of the photovoltaic working of the device is due to the trapping of photogenerated holes which acts as an optical doping of the material.