Concentrated sunlight for accelerated stability testing of organic photovoltaic materials: towards decoupling light intensity and temperature

Solar Energy Materials & Solar Cells

Author(s): I. Visoly-Fisher, A. Mescheloff, M. Gabay, C. Bounioux, L. Zeiri, M.Sansotera, A.E. Goryachev, A. Braun, Y. Galagan, E.A. Katz

Source: Solar Energy Materials & Solar Cells
Volume: 134 Pages: 99-107
Published: Mar (2015)
DOI: 10.1016/j.solmat.2014.11.033


We have demonstrated accelerated degradation studies of organic photovoltaic materials using concentrated sunlight, where the atmosphere, temperature and illumination intensity were independently controlled. Testing various schemes for controlling the sample temperature under concentrated sunlight showed that heating of P3HT:PCBM was caused by photons at the absorbed wavelength range and dissipation of excess photon energy, and not necessarily by IR photon absorption. Sunlight chopping was found to be an effective method for independent temperature control under illumination by concentrated sunlight.
The first accelerated degradation tests using sunlight concentration applied to P3HT:PCBM blends were reported. P3HT:PCBM blends exposed to concentrated sunlight in the presence of traces of oxygen/ humidity showed degradation induced by photo-oxidation of the P3HT backbone within the P3HT:PCBM blend, which is significantly thermally accelerated, in agreement with previous observations. However, this could be demonstrated in a time scale of minutes and hours, that is, significantly accelerated. Exposure of well encapsulated P3HT:PCBM films to concentrated sunlight demonstrated stability up to 3,600 sun?hours, corresponding to about 1.6 years of operating time. This result was obtained at 300 suns exposure after merely 12 h, demonstrating the advantage of using concentrated sunlight for accelerated stability tests. These tests can therefore combine extremely high acceleration factors with profound understanding of the effect of various, independently controlled factors on the degradation mechanisms.

Surface fluorination on TiO2 catalyst induced by photodegradation of perfluorooctanoic acid

Catalysis Today

Author(s): Sara Gatto, Maurizio Sansotera, Federico Persico, Massimo Gola, Carlo Pirola, Walter Panzeri, Walter Navarrini, Claudia L. Bianchi

Source: Catalysis Today
Volume: 241 Pages: 8-14
Published: Mar (2015)
DOI: 10.1016/j.cattod.2014.04.031


The photoabatement of perfluorooctanoic acid in aqueous solution has been performed with a commercial nano-sized TiO2-based photocatalyst content of 0.66 g/L under an UV irradiation of 95 W/m2. PFOA degradation intermediates were investigated by HPLC-MS and 19F-NMR analysis. Evidences of adegradation mechanism based on two competitive pathways are discussed: photo-redox and beta-scission pathways. Shorter perfluorinated carboxylic acids, CnF2n+1COOH (n = 1-6), as expected degradation intermediates, were identified and their concentration trends over time were determined. The apparent pseudo-first order kinetic constant expressed as rate of PFOA disappearance was also measured: kapp 0.1296 h-1. The influence of fluoride ions on TiO2 surface was analyzed by XPS technique, revealing asurface modification that affects the performances of the catalyst.

Photocatalytic activity of TiO2-embedded fluorinated transparentcoating for oxidation of hydrosoluble pollutants in turbid suspensions

Applied Catalysis B: Environmental

Author(s): Federico Persico, Maurizio Sansotera, Claudia L. Bianchi, Carlo Cavallotti, Walter Navarrini

Source: Applied Catalysis B: Environmental
Volume: 170 Pages: 83-89
Published: Jan (2015)
DOI: 10.1016/j.apcatb.2015.01.033


The photodegradative activity of titanium dioxide immobilized into a multilayered transparent fluoropolymeric matrix was studied. The photoactive coating was developed by applying a TiO2-containing fluorinated ionomeric dispersion and a perfluorinated amorphous polymer in an appropriate sequence directly on the UV source. The multilayered coating photocatalytic activity toward hydrosoluble organic pollutants was evaluated in clear as well as in highly turbid conditions obtained by dispersing barium sulfate microparticles in the polluted solution. Rhodamine B-base was chosen as reference organic pollutant. The photoabatement rates with TiO2-embedded fluorinated coating in clear solution and turbid conditions were 0.0923 min-1 and 0.0546 min-1, respectively. In both clear and turbid conditions, TiO2-embedded transparent coating revealed higher photocatalytic activity than merely dispersed TiO2. This behavior was particularly evident at low pollutant concentrations. In addition, catalyst immobilization prevented TiO2 separation and catalyst losses, allowing the development of a simple and efficientcontinuous apparatus.