Hybrid solar cells based on thin-film silicon and P3HT

International audienceHybrid concepts based on a nanoscale combination of organic and inorganic semiconductors are a promising way to enhance the cost efficiency of solar cells through a better use of the solar spectrum, a higher aspect ratio of the interface, and the good processability of polymers. A new type of solar cells has been investigated. It is based on a heterojunction between regio-regular poly(3-hexylthiophene) as an organic electron donor and silicon as an inorganic electron acceptor. In a first step towards nanostructured devices, cells made of flat thin films of these materials have been studied as a model case of the heterojunction. The materials were characterized through ellipsometry and absorption spectroscopy. The devices were studied by means of their spectral response and their I-V characteristics. By combining these results, the contribution of each layer and the mechanisms of photocurrent generation are explained. The best cells to-date show a power conversion efficiency of 1.6% under AM 1.5 illumination, with a Voc of 0.704 V and a Jsc of 4.22 mA/cm2

Reactive intermediates in the initiation step of the photo-oxidation of MDMO-PPV

International audienceBecause oxygen cannot be fully eliminated from organic solar cells, the occurrence of oxidative photo-degradation of the device in operating conditions has to be considered. Polyphenylene-vinylene-based photovoltaic devices have a short lifetime that currently limits their applications. In this article, we focus on various transient species that are potentially involved in the initiation step of the photo-oxidation of poly[2-methoxy-5-(30,70- dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV). The role of the transient species was investigated by a combination of quenching and sensitization experiments. Complementary information was obtained by transient absorption spectroscopy. Results evidenced the fact that 1O2 was not the principal reactive intermediate involved in the photo-oxidation of MDMO-PPV. This result was in contradiction with previous reports. It was shown that the MDMO-PPV=p radical cation was generated after excitation. The presence of oxygen and the photo-aging favored the formation of the radical cation, suggesting that oxygen and photoproducts act as electron acceptors. The charged radicals formed are likely to evolve and give radicals that initiate the oxidation of the polymer by abstraction of the labile hydrogen in a position of the ether function and by addition on the double bonds

Photo- and thermo-oxidation of poly(p-phenylene-vinylene) and phenylene-vinylene oligomer

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Conjugated alternating copolymer of dialkylquaterthiophene and fluorenone: synthesis, characterisation and photovoltaic properties

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Prevalence and Factors Associated with Maternal Group B Streptococcus Colonization in Madagascar and Senegal

International audienceMaternal group B Streptococcus (GBS) colonization is a major risk factor for neonatal GBS infection. However, data on GBS are scarce in low- and middle-income countries. Using sociodemographic data and vaginal swabs collected from an international cohort of mothers and newborns, this study aimed to estimate the prevalence of GBS colonization among pregnant women in Madagascar ( n = 1,603) and Senegal ( n = 616). The prevalence was 5.0% (95% CI, 3.9–6.1) and 16.1% (95% CI, 13.1–19.0) in Madagascar and Senegal, respectively. No factors among sociodemographic characteristics, living conditions, and obstetric history were found to be associated independently with GBS colonization in both countries. This community-based study provides one of the first estimates of maternal GBS colonization among pregnant women from Madagascar and Senegal