145 research outputs found
Etude des propriétés électrochromes des films anodiques de trioxyde de tungstène.
No full textStudy of the absorption that appears in this material during its colouring and the possibilities of use for the realization of display systems. It is shown that the layers formed by anodic oxidation present a progressive crystallization according to the anodic tension. For low voltages, these layers are amorphous. Calculation of refractive and absorption indices from spectroreflectrometric data. During electrostaining with H**(+), Li**(+), Na**(+), a decrease in Raman peaks of W-O bonds vibrations and an appearance of W=O bonds vibration peaks are observed. .Étude de l'absorption qui apparait dans ce matériau au cours de sa coloration et des possibilités d'utilisation pour la réalisation des systèmes d'affichage. On montre que les couches formées par oxydation anodique présentent une cristallisation progressive en fonction de la tension anodique. Pour de faibles tensions, ces couches sont amorphes. Calcul des indices de réfraction et d'absorption à partir des données spectroreflectrométriques. Au cours de l'électrocoloration avec des ions H**(+), Li**(+), Na**(+), une diminution des pics Raman des vibrations des liaisons W-O et une apparition des pics des vibrations des liaisons W=O sont observées.
Minimizing Energy Losses in Dye‐Sensitized Solar Cells Using Coordination Compounds as Alternative Redox Mediators Coupled with Appropriate Organic Dyes
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Improved seed handling techniques for Juniperus polycarpos : implications for active restoration of degraded Juniper forests in Iran [Elektronisk resurs]
No full textJuniperus polycarpos (K. Koch) is one of six native juniper forest tree species in Iran whose population size is declining continuously. The ultimate aim of the research presented in this thesis was to increase the regeneration potential of J. polycarpos by identifying factors influencing seed quality and develop methods that increase germination capacity and vigor. The research focused on impact of infection by dwarf mistletoe on reproductive output, methods for sorting unproductive seeds from seed lots, improving germination capacity and vigor through sorting techniques and by breaking seed dormancy. The results show that moderate level of infection significantly (p < 0.05) reduced mean number of cones per unit area of the host crown, increasing the number of damaged seeds, reducing seed size and germination capacity. For sorting viable seeds from non-viable seeds, three methods were applied: Incubation, Drying and Separation (IDS), modified specific gravity (SG) separation and near infrared spectroscopy (NIRS). For the IDS experiments, seven days incubation followed by nine hours of drying and sedimentation in pure water or 200 g sucrose /l water solution resulted in 75% and 82% sunken-viable seeds, respectively. For seeds soaked for 48 hours, SG separation in 600 g/l sucrose solution also resulted in 77% sunken-viable seeds. For both sorting techniques, only 4% of viable seeds were lost into the discarded floating fraction. NIR spectroscopy of individual seeds discriminated between viable and non-viable seeds of J. polycarpos with 98% and 100% accuracy, respectively based on spectral differences attributed to seed coat chemical composition and storage reserves. For finding optimal dormancy breaking treatment and subsequent stimulation of germination capacity and vigor of J. polycarpos seeds, different pretreatments were tested. The results showed warm stratification for sixteen weeks followed by twelve weeks of cold stratification resulted in 72% germination after 12 days compared with 16-week cold-stratification alone (42%) and the control (8%). Exogenous application of phytohormones alone or in combination with cold stratification resulted in less than 50% germination, though significantly (p < 0.01) higher than the control (8%). As a whole, the results have strong implication for active restoration by increasing seedling production potential in nurseries. Keywords: dormancy, IDS, NIRS, seed sorting, stratification, seed quality, seed vigor Author’s address: Abolfazl Daneshvar, SLU, Southern Swedish Forest Research Centre, P.O. Box 49, SE-230 53 Alnarp, Sweden. E-mail: [email protected], [email protected]
Solution-processed hydrogen molybdenum bronzes as highly conductive anode interlayers in efficient organic photovoltaics
No full textHighly efficient and stable organic photovoltaic (OPV) cells are demonstrated by incorporating solution-processed hydrogen molybdenum bronzes as anode interlayers. The bronzes are synthesized using a sol-gel method with the critical step being the partial oxide reduction/hydrogenation using an alcohol-based solvent. Their composition, stoichiometry, and electronic properties strongly correlate with the annealing process to which the films are subjected after spin coating. Hydrogen molybdenum bronzes with moderate degree of reduction are found to be highly advantageous when used as anode interlayers in OPVs, as they maintain a high work function similar to the fully stoichiometric metal oxide, whereas they exhibit a high density of occupied gap states, which are beneficial for charge transport. Enhanced short-circuit current, open-circuit voltage and, fill factor, relative to reference devices incorporating either PEDOT-PSS or a solution processed stoichiometric molybdenum oxide, are obtained for a variety of bulk heterojunction mixtures based on different polymeric donors and fullerene acceptors. In particular, high power conversion efficiencies are obtained in devices that employed the s-HxMoO2.75 as the hole extraction layer. The incorporation of solution-processed hydrogen molybdenum bronzes as anode interlayers in organic photovoltaic cells is presented. High power conversion efficiencies are observed in devices based on polymeric donors and fullerene acceptors that include a bronze with a moderate degree of reduction, namely the s-HxMoO2.75, as the anode interlayer.</p
A Review on Emerging Efficient and Stable Perovskite Solar Cells Based on g-C3N4 Nanostructures
No full textPerovskite solar cells (PSCs) have attracted great research interest in the scientific community due to their extraordinary optoelectronic properties and the fact that their power conversion efficiency (PCE) has increased rapidly in recent years, surpassing other 3rd generation photovoltaic (PV) technologies. Graphitic carbon nitride (g-C3N4) presents exceptional optical and electronic properties and its use was recently expanded in the field of PSCs. The addition of g-C3N4 in the perovskite absorber and/or the electron transport layer (ETL) resulted in PCEs exceeding 22%, mainly due to defects passivation, improved conductivity and crystallinity as well as low charge carriers’ recombination rate within the device. Significant performance increase, including stability enhancement, was also achieved when g-C3N4 was applied at the PSC interfaces and the observed improvement was attributed to its wetting (hydrophobic/hydrophilic) nature and the fine tuning of the corresponding interface energetics. The current review summarizes the main innovations for the incorporation of graphitic carbon nitride in PSCs and highlights the significance and perspectives of the g-C3N4 approach for emerging highly efficient and robust PV devices
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