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By combining measurements of photocatalysis under solar irradiation with measurements of total organic carbon, we have compared the performance of two TiO2-based photocatalysts in the photodegradation of the dye Reactive Blue 49 (RB49). TiO2-P25 and TiO2-UV100 commercial photocatalysts were tested within a concentration ranging from 0.5 to 4 g/L. The dye solution concentration was varied from 10 to 50 mg/L and its pH was increased from 3 to 9. Extensive characterization of the photocatalysts was performed using Fourier-transform infrared spectroscopy, scanning electron microscopy and X-ray diffraction. TiO2-UV100 proved to be more active in adsorbing RB49 dye than TiO2-P25. At low dye concentrations, the adsorption equilibrium is reached in 15 min. This time increases to 1 h at higher concentrations. The photocatalytic degradation of aqueous RB49 under sunlight was monitored by UV-Vis spectrophotometry. The apparent rate constant of dye photodegradation with TiO2-UV100 is twice that of TiO2-P25. The total organic carbon (TOC) analysis showed a removal of around 98% with TiO2-UV100 and only 85% with TiO2-P25 after 3 h of solar irradiation. Over five photocatalytic cycles of 3 h, TiO2-UV100 maintained a more stable and higher efficient photocatalytic performance. All our results converge toward a better photocatalytic performance of TiO2-UV100 for the photodegradation of RB49 dye and indicate that the most decisive factor is its greater capacity to adsorb the pollutant. [ABSTRACT FROM AUTHOR]

When atomic hydrogen interacts with hydrogenated amorphous silicon (a-Si:H), the induced modifications are of crucial importance during a-Si:H based devices manufacturing or processing. In the case of hydrogen plasma, the depth of the modified zone depends not only on the plasma processing parameters but also on the material. In this work, we exposed a-Si:H thin films to H² plasma just after their deposition. In situ UV-visible spectroscopic ellipsometry measurements were performed to track the H-induced changes in the material. The competition between hydrogen insertion and silicon etching leads to first order kinetics in the time-evolution of the thickness of the H-modified zone. We analyzed the correlation between the steady state structural parameters of the H-modified layer and the main levers that control the plasma-surface interaction. In comparison with a simple doped layer, exposure of a-Si:H based junctions to the same plasma treatment leads to a thinner H-rich subsurface layer, suggesting a possible charged state of hydrogen diffusing. [ABSTRACT FROM AUTHOR]

ZnO thin films have been prepared by sol gel and deposited by spin coating. The dielectric function has been determined by spectroscopic ellipsometry. Ellipsometric spectra are inverted by a direct numerical method without using the standard fitting procedures. The obtained dielectric function presents a broad excitonic effect. The dielectric function is studied using Elliot excitonic theory including exciton plus band-to-band Coulomb interactions with standard Lorentzian broadening. A modification of this model dielectric function with independent bound and unbound exciton contributions is empirically proposed to improve modelling of the band gap excitonic peak. [ABSTRACT FROM AUTHOR]

Nano-granular ZnO layers have been grown using a sol–gel synthesis and spin-coating deposition process. Thin films with thicknesses ranging from 15 to 150 nm have been obtained by varying the number of deposition cycles and prepared with different synthesis conditions. Morphologies and optical properties have been carefully investigated by joint spectroscopic ellipsometry and atomic force microscopy. A correlation between the evolution of optical properties and grains morphology has been observed. It is shown that both synthesis temperature and concentration similarly allow us to change the correlated growth and properties evolution rate. Thickness variation associated to choice of synthesis parameters could be a useful way to tune morphology and optical properties of the nanostructured ZnO layers. [ABSTRACT FROM AUTHOR]

Blending perovskite with different cations has been successful in improving performance of perovskite solar cells, but the complex pathway of perovskite crystal formation remains a mystery, hindering its further development. In this paper, the detailed crystallization process of formamidinium lead iodide (FAPbI3) perovskite films doped by methylammonium lead bromide (MAPbBr3) additive was investigated by in situ grazing incident wide-angle X-ray scattering measurements during both spin coating and annealing. During spin-coating, it was found that the FAPbI3 perovskite precursor easily formed a mixture of black perovskite phase (α phase) and non-perovskite yellow phase (δ phase) after the addition of MAPbBr3, whereas only δ phase formed without MAPbBr3. The δ phase gradually converted to α phase during annealing and there was only α phase left in both films with and without MAPbBr3. However, the doped films presented high film quality without PbI2 residue in contrast to the undoped films. These findings imply that the MAPbBr3 additive can effectively suppress the formation of the unfavorable δ phase and trigger the formation of the optically active α phase even during spin-coating, which enhances the film quality possibly by removing the energy barriers from δ phase to α phase at room temperature. Finally, PSCs based on MAPbBr3-doped FAPbI3 were fabricated with a champion efficiency as high as 19.4% from 14.2% for the PSCs based on undoped FAPbI3. [ABSTRACT FROM AUTHOR]