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

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

Structural relaxation of E' gamma centers in amorphous silica

We report experimental evidence of the existence of two variants of the E' gamma centers induced in silica by gamma rays at room temperature. The two variants are distinguishable by the fine features of their line shapes in paramagnetic resonance spectra. These features suggest that the two E' gamma differ for their topology. We find a thermally induced interconversion between the centers with an activation energy of about 34 meV. Hints are also found for the existence of a structural configuration of minimum energy and of a metastable state.Comment: 4 pages, 2 figures, submitted to Phys. Rev. Let

Supply chain coordination in a HMMS-type supply chain with purchasing

Absztrakt. Egy ellátási láncot vizsgálunk egy beszállítóval és egy termelővel. A termelő kereslete időben ismert. A termelő és a beszállító költségfüggvénye kvadratikus termelési és készlettartási költségből áll. Ezen kívül értelmezünk egy lineáris beszerzési költséget termelő és a beszállító között. A modell ebben az értelmezésben egy differenciáljátékként értelmezhető. A beszállító döntési változója az értékesítési (beszerzési) ár és a termelési rátája, míg a termelőnek a beszerzési mennyiség és a termelési ráta. A problémát, mint egy Nash-játékot és mint kooperatív játékot értelmezzük, amit a Pareto-megoldásként értelmezünk. A feladatot így visszavezethetjük egy Holt-Modigliani-Muth-Simon (HMMS) problémára. ----- Abstract. We investigate a supply chain with a supplier and a manufacturer. The manufacturer knows the demand for her product. The product is produced from a product supplied by the supplier. The purchased product is stored in a cross-docking way, i.e. there is no inventory of the purchased product and the planned production is ordered from the supplier. The costs of the manufacturer consist of quadratic inventory holding costs, quadratic production cost, and linear purchasing cost. It is assumed that the market price of the end product is known as well, so the sales of the producer are calculated. The linear purchasing cost is paid to the supplier. The goal of the manufacturer is maximize her cumulated profits. The sales of the supplier are the ordering cost of the manufacturer. The costs of the supplier are the quadratic manufacturing and inventory holding costs. The goal of the supplier is to maximize the sales reduced with the relevant costs. The supplier and the manufacturer want to negotiate about the sales price of the supplier and the quantity ordered by the manufacturer. In this paper we will not examine the bargaining process which determines the adequate price and quantity. The situation is modeled as a differential game. The decision variables of the supplier are the sales price and the production quantity of the supplier. The manufacturer will choose the cost minimal production plan to minimize her costs, so maximize the cumulated profits. The problem is a differential game with two players. The basic problem is a Holt-Modigliani-Muth-Simon (HMMS) problem extended with linear purchasing costs. We will examine two cases: the decentralized Nash-solution and a centralized Pareto-solution to optimize the behaviors of the players of the game