German-Algerian university exchange from the perspective of students and teachers results of an intercultural survey

Academic exchange programs provide students and teachers with the opportunity to study or work temporarily at educational institutions abroad. For exchange programs to be successful in promoting intercultural education, they must be designed with their participants in mind. The present study constitutes an investigation of attitudes and expectations of students and teachers with respect to a German–Algerian university exchange program. Germany and Algeria belong to separate cultural spheres—the Western/European and the Arabic/Islamic—and almost no academic exchange has taken place between them to date. The survey’s four participant groups were German (n = 270) and Algerian students (n = 214), and German (n = 24) and Algerian teachers (n = 43). The study revealed large differences in the hopes and fears that German and Algerian university students and teachers attach to reciprocal academic exchange. The study’s ramifications for the future planning of a German–Algerian university exchange program are discussed

Influence of doping on charge carrier collection in normal and inverted geometry polymer: fullerene solar cells

While organic semiconductors used in polymer:fullerene photovoltaics are generally not intentionally doped, significant levels of unintentional doping have previously been reported in the literature. Here, we explain the differences in photocurrent collection between standard (transparent anode) and inverted (transparent cathode) low band-gap polymer:fullerene solar cells in terms of unintentional p-type doping. Using capacitance/voltage measurements, we find that the devices exhibit doping levels of order 1016 cm−3, resulting in space-charge regions ~100 nm thick at short circuit. As a result, low field regions form in devices thicker than 100 nm. Because more of the light is absorbed in the low field region in standard than in inverted architectures, the losses due to inefficient charge collection are greater in standard architectures. Using optical modelling, we show that the observed trends in photocurrent with device architecture and thickness can be explained if only charge carriers photogenerated in the depletion region contribute to the photocurrent

Long-Term Stabilization of Organic Solar Cells Using Hindered Phenols as Additives

We report on the improvement of long-term stability of organic solar cells (OPV) using hindered phenol based antioxidants as stabilizing additives. A set of seven commercially available hindered phenols are investigated for use in bulk-heterojunction OPV. Polymer:fullerene films based on poly­(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) are characterized with respect to the initial power conversion efficiency and the long-term stability improvement under illumination in ambient conditions. FTIR spectroscopy is used to trace chemical degradation over time. OPV performance is recorded under ISOS-3 conditions, and an improved long-term performance of OPV devices, manifested in increased accumulated power generation (APG), is found for octadecyl 3-(3,5-di-<i>tert</i>-butyl-4-hydroxyphenyl)­propionate. Using this additive, APG is increased by a factor of 3 compared to the reference. Observed differences in the stabilization of tested additives are discussed in terms of energetic trap states formation within the HOMO/LUMO gap of the photoactive material, morphological changes, and chemical structure