A unified global investigation on the spectral effects of soiling losses of PV glass substrates: preliminary results

This is the author accepted manuscript. The final version is available from IEEE via the DOI in this recordThe present work reports on the initial results of an international collaboration aiming to investigate the spectral effects of soiling losses. Identical glass coupons have been exposed outdoors for eight weeks in different locations worldwide, and weekly direct and hemispherical transmittance (T%) measurements are compared. Maximum losses as high as 7% and 50% in hemispherical and direct transmittance, respectively, have been found during the 8-week outdoor exposure. At the end of the data collection, a preliminary analysis of the spectral impact of soiling has been performed. The results show that the blue end of the spectrum is more affected and that lower hemispherical T% correlate to larger area covered by particles.Engineering and Physical Sciences Research Council (EPSRC)US Department of Energ

Preparation of nanocrystalline TiO2 electrodes for flexible dye-sensitized solar cells: influence of mechanical compression

Nanocrystalline TiO2 electrodes were prepared using binder-free TiO2 paste on conductive ITO-PEN substrates by the doctor-blade method at significantly low temperature (140 °C), and the electrodes were further processed under different compressions (10−60 MPa) in order to improve interparticle connections and adhesion between the nanoparticles and the ITOPEN substrate. TiO2 electrodes compressed at 30 and 40 MPa had relatively less cracks with low crack width. Electrode compressed at 30 MPa showed the highest internal surface area. Electrode prepared at this compression showed the best dyesensitized solar cell (DSC) performance with Voc of 805 mV, Jsc of 9.24 mA cm−2 , and an overall efficiency of 4.39%. Electrochemical impedance spectroscopy (EIS) studies of the sandwiched cells employing bare nanocrystalline TiO2 electrode and Pt counter electrode in I−/I3 − electrolyte showed that electrode compression significantly influences the stability of the cells. EIS data suggested that degradation/corrosion processes may take place on ITO-PEN for sandwiched cells made by TiO2 electrodes compressed at all pressures. Thirty and 40 MPa compressions showed a minor degradation of ITO. The recombination dynamics at the TiO2/electrolyte interface were influenced by the changes in the nanostructured electrode internal surface area, changes in electron transport properties (due to improved sintering), and possible degradation/corrosion of ITO-PEN. Open-circuit voltage decay (OCVD) measurements showed that the DSC made by the 30 MPa compressed TiO2 electrode had the highest decay time, indicating low recombination properties, which is in a good agreement with other data

Thickness dependence on structural, dielectric and AC conduction studies of vacuum evaporated Sr doped BaTiO3 thin films

Barium titanate (BaTiO3) doped with Strontium (BST) nanoparticles prepared by using wet chemical method were thermally evaporated on to well cleaned glass substrates under the vacuum of 2 × 10−5 Torr, using 12A4 Hind Hivac coating unit. The thickness of the film was measured by quartz crystal monitor. From X-ray analysis, it has been found that BaTiO3 nanoparticles possess tetragonal structure and deposited films has a polycrystalline in nature, whereas the crystallinity of film increases with increase of temperature. Surface morphology of fabricated thin film observed that very homogeneous and uniform size. The transport mechanism in these films under a.c. fields was studied in the frequency range 12 Hz to 100 kHz, at different temperatures (303–483 K). The dependence of dielectric constant and loss factor for different thickness was investigated and results are discussed. The process of a.c. conduction has been explained on the basis of hopping conduction mechanism. The dielectric constant (ɛ′), temperature co-efficient of capacitance (TCC) and temperature co-efficient of permitivity (TCP) were estimated. The dependences of activation energy on thicknesses also studied and reported

Enhanced Performance of Flexible Dye-Sensitized Solar Cells: Electrodeposition of Mg(OH)₂ on a Nanocrystalline TiO₂ Electrode

Nanocrystalline TiO₂ photoanodes were prepared on a conductive indium–tin oxide coated polyethylene naphthalate (ITO-PEN) plastic substrate by the doctor-blade method to fabricate flexible dye-sensitized solar cells (DSCs). The surface of the photoanode was coated with Mg(OH)₂ by electrodeposition and the deposition time was systematically varied (2, 4, 6, 8, and 10 min). Electrodeposited Mg(OH)₂ was confirmed by IR and energy dispersive X-ray (EDX) analysis. The surface morphology was studied by scanning electron microscopy. The internal surface area of TiO₂ was studied against the deposition time by taking into account the projected surface area of the photoelectrode and it shows that the internal surface area of the photoelectrode was reduced as the Mg(OH)₂ deposition time increased. The performance of flexible DSCs on various deposition times of Mg(OH)₂ was evaluated on the basis of their photocurrent density–voltage characteristics. Among the deposition times, 2 min showed the best performance in <i>V</i>_oc on a treated flexible DSC, with resulting 847 mV and a photocurrent density of 7.13 mA/cm², providing an overall light-to-electricity conversion efficiency of 4.01%. This photovoltage is among the highest attained for a flexible DSC to date. This notable increment in <i>V</i>_oc at a thin layer of Mg(OH)₂ was attributed to the suppression of recombination of photogenerated electrons via the exposed surface of ITO as well as TiO₂ without influencing the internal surface area of the photoanode significantly

Design and synthesis of imidazole-triphenylamine based organic materials for dye sensitized solar cells

Two imidazole – triphenylamine based organic dyes (SD1 and SD2) configured with donor -donor-π-acceptor (D2-π-A) structures with reported dye material namely TPA B5 were synthesized using different acceptor units and characterized by various spectroscopic techniques. The optical and electrochemical behavior of the dyes was systematically analyzed. The obtained results were compared with TPA B5 and found that, these dyes are considered to have proper electronic energy levels as promising sensitizers in dye sensitized solar cells (DSC’s). This work could facilitate the development of new way to improve the performance of anchoring units

Characterization of zinc phthalocyanine (ZnPc) for photovoltaic applications

Zinc phthalocyanine (ZnPc) is a promising candidate for solar-cell applications, because it is easily synthesized and is non-toxic to the environment. Recently, phthalocyanine (Pc) was considered by many researchers as the active part in all-organic solar cells, i.e. plastic solar cells. It is a self-assembling liquid crystal developed from a common deep-blue-green pigment. It exhibits a characteristic structural self-organization, which is reflected in an efficient energy migration in the form of extinction transport. In this paper we have report structural, surface morphological, optical and thermal properties of flash-evaporated zinc phthalocyanine thin films. The samples were prepared by using a vacuum coating unit on well-cleaned glass substrates under a pressure of 7×10-6 Torr. A constant rate of evaporation (1 Å/s) was maintained throughout the evaporation of the ZnPc thin films. A rotary drive was employed to obtain uniform thickness during the evaporation. Thicknesses of the films were monitored by a quartz-crystal thickness monitor and were cross verified by the multiple-beam interferometry technique. The X-ray-diffraction pattern reveals the crystalline nature of the films deposited at higher substrate temperatures. Scanning electron microscope and scanning probe microscope nanoscope studies were carried out to determine the surface uniformity and homogeneity of the films for interfacing and application purposes. All the films were found to possess small crystallites less than 100 nm in size. The optical transmittance measurements were carried out using a spectrophotometer in the visible region (400–800 nm) and the films were found to be absorbing in nature. The band gap of the ZnPc thin films is 1.97 eV and the optical transition was found to be direct and allowed. The absorption coefficient, extinction coefficient and refractive index of the ZnPc films were evaluated and the results are discussed. Differential scanning calorimetry studies of ZnPc films were carried out and a phase transition from α to β was observed at 538 K

Genetic diversity of ectomycorrhizal Basidiomycetes from African and Indian tropical rain forests

International audienceEctomycorrhizal (ECM) fungi have a worldwide distribution. However, the ecology of tropical ECM fungi is poorly documented, limiting our understanding of the symbiotic associations between tropical plants and fungi. ECM Basidiomycete diversity was investigated for the first time in two tropical rain forests in Africa (Western Upper Guinea) and in Asia (Western Ghats, India), using a fragment of the mitochondrial large subunit rRNA gene to type 140 sporocarps and 54 ectomycorrhizas. To evaluate taxonomic diversity, phylogenetic analyses were performed, and 40 sequences included from identified European specimens were used as taxonomic benchmarks. Five clades were recovered corresponding to six taxonomic groups: boletoids, sclerodermatoids, russuloids, thelephoroids, and a clade grouping the Amanitaceae and Tricholomataceae families. Our results revealed that the Russulaceae species display a great diversity with several putative new species, especially in Guinea. Other taxonomic issues at family/section levels are also briefly discussed. This study provides preliminary insights into taxonomic diversity, ECM status, and biogeographic patterns of ECM fungi in tropical two rain forest ecosystems, which appear to be as diverse as in temperate and boreal forests

Synthesis and characterization of aligned SiO2 nanosphere arrays: Spray method

The power of nanomaterials has been hampered by the difficulty in controlling their size and morphology. Monodispersed silica particles with different nanometer sizes synthesized by a novel spray method remove the obstacles for the commercialization of nanomaterials at a global level. The size and shape of the silica particles were effectively controlled by simple hydrolysis and condensation reaction. Morphological images (SEM and TEM) reveal the smooth and spherical shaped silica particles with homogeneous distribution. Structural and luminescence properties of the silica particles were examined by FT-IR absorption spectroscopy and photoluminescence. A very low weight percentile loss of the silica particle ensures its high thermal stability. The high surface areas of about 55 and 25 m2/g were achieved for 90 and 220 nm particle sized silica particles, respectively. The resultant silica particles can be easily suspended in water and would be useful for variety of applications