Effects of internal luminescence and internal optics on V-oc and J(sc) of III-V solar cells

For solar cells dominated by radiative recombination, the performance can be significantly enhanced by improving the internal optics. Internally radiated photons can be directly emitted from the cell, but if confined by good internal reflectors at the front and back of the cell they can also be re-absorbed with a significant probability. This so-called photon recycling leads to an increase in the equilibrium minority carrier concentration and therefore the open-circuit voltage, Voc. In multijunction cells, the internal luminescence from a particular junction can also be coupled into a lower bandgap junction where it generates photocurrent in addition to the externally generated photocurrent, and affects the overall performance of the tandem. We demonstrate and discuss the implications of a detailed model that we have developed for real, non-idealized solar cells that calculates the external luminescent efficiency, accounting for wavelength-dependent optical properties in each layer, parasitic optical and electrical losses, multiple reflections within the cell and isotropic internal emission. The calculation leads to Voc, and we show data on high quality GaAs cells that agree with the trends in the model as the optics are systematically varied. For multijunction cells the calculation also leads to the luminescent coupling efficiency, and we show data on GaInP/GaAs tandems where the trends also agree as the coupling is systematically varied. In both cases, the effects of the optics are most prominent in cells with good material quality. The model is applicable to any solar cell for which the optical properties of each layer are well-characterized, and can be used to explore a wide phase space of design for single junction and multijunction solar cells

Mechanically stacked four-junction concentrator solar cells

Multijunction solar cells can be fabricated by bonding together component cells that are grown separately. Because the component cells are each grown lattice-matched to suitable substrates, this technique allows alloys of different lattice constants to be combined without the structural defects introduced when using metamorphic buffers. Here we present results on the fabrication and performance of four-junction mechanical stacks composed of GaInP/GaAs and GaInAsP/GaInAs tandems, grown on GaAs and InP substrates, respectively. The two tandems were bonded together with a lowindex, transparent epoxy that acts as an omni-directional reflector to the GaAs bandedge luminescence, while simultaneously transmitting nearly all of the sub-bandgap light. As determined by electroluminescence measurements and optical modeling, the GaAs subcell demonstrates a higher internal radiative limit and thus higher subcell voltage, compared with GaAs subcells without enhanced internal optics; all four subcells exhibit excellent material quality. The device was fabricated with four contact terminals so that each tandem can be operated at its maximum power point, which raises the cumulative efficiency and decreases spectral sensitivity. Efficiencies exceeding 38% at one-sun have been demonstrated. Eliminating the series resistance is the key challenge for the concentrator cells. We will discuss the performance of one-sun and concentrator versions of the device, and compare the results to recently fabricated monolithic four-junction cells

Die Theorie der komparativen Kosten als Unsichtbare-Hand Erklaerung

Available from Bibliothek des Instituts fuer Weltwirtschaft, ZBW, Duesternbrook Weg 120, D-24105 Kiel C 145993 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Europa: eine Bundesrepublik mit begrenzten Kompetenzen? Die Europapolitik der SPD im internationalen Vergleich

'Rechtzeitig zum Parteikongress der Europaeischen Sozialdemokraten (SPE) veroeffentlichte die SPD am 30. April 2001 ihren Entwurf fuer einen Leitantrag zur Europapolitik. Das Dokument mit dem Titel 'Verantwortung fuer Europa' ist lediglich ein Entwurf, der zunaechst vom Praesidium der Partei und letztlich vom Parteitag der SPD in Nuernberg am 19.-23.11.2001 zu verabschieden ist. Erst dann waere es eine verbindliche Darstellung der SPD-Position, aber auch dann noch keine offizielle Position der Bundesregierung, als die es international gern gehandelt wird. Das vorliegende Papier versucht, zentrale Aussagen dieses Entwurfs mit den Positionen wichtiger deutscher und europaeischer Partner zu vergleichen, insbesondere Delors, Prodi, Blair, Fischer, franzoesische und europaeische Sozialisten. Der groesste Teil des SPD-Papiers (die ersten acht von zehn Abschnitten) beschaeftigt sich mit inhaltlichen Zielen, also damit, was Europa mit der Integration erreichen will (Wohlstand, soziale Gerechtigkeit, Sicherheit etc.). Dieser 'Output' steht auch bei den meisten anderen Autoren (vor allem Blair und den franzoesischen Sozialisten) im Vordergrund und die Differenzen halten sich in Grenzen. Die Unterschiede bestehen mehr bei den Verfahren, den institutionellen Fragen und der Reform wichtiger Politiken. Darauf konzentriert sich der vorliegende Beitrag.' (Autorenreferat)Available from <a href=http://library.fes.de/fulltext/id/01036.htm target=NewWindow>http://library.fes.de/fulltext/id/01036.htm</a> / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Unterschiedliche Startbedingungen haben langfristige Folgen Der Einmuendungsverlauf der Geburtskohorten 1964 und 1971 in Ausbildung und Beschaeftigung; Befunde aus einem IAB-Projekt

Im Mittelpunkt des Beitrags steht die Frage nach dem Uebergang Jugendlicher von der allgemeinbildenden Schule in die erste unbefristete sozialversicherungspflichtige Beschaeftigung. Hierzu wurde 1998/1999 eine retrospektiv angelegte empirische Erhebung der Geburtskohorten 1964 und 1971 durchgefuehrt, die 2911 auswertbare Interviews erbrachte. Obwohl die beiden Kohorten nur sieben Jahre auseinander liegen, haben sie den Uebergang unter sehr unterschiedlichen demografischen, konjunkturellen und institutionellen Rahmenbedingungen vollzogen. Die Untersuchung zeigt, das diese unterschiedlichen Startbedingungen langfristige Folgen haben, die sich vor allem in einem qualifikatorischen Aufwaertstrend aeussern. (IAB)Available from IAB / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Dos decenios de actividad universitaria en economía social, cooperativismo y emprendimiento desde el Instituto Universitario IUDESCOOP

Durante las últimas dos décadas, el Instituto Universitario de Investigación en Economía Social, Emprendimiento y Cooperativismo IUDESCOOP ha desarrollado una intensa actividad de promoción y avance de los modelos económicos que fomentan la igualdad social, la democracia, la solidaridad y la sostenibilidad. Fundado con unos valores y una visión clara, este centro ha cultivado un ambiente propicio para la investigación y la enseñanza en el ámbito de las cooperativas y la economía social. El IUDESCOOP, gracias a la implicación de las más de treinta personas que lo han impulsado, ha logrado consolidarse como un referente en la investigación sobre estas áreas cruciales, generando conocimientos relevantes que han influido en políticas públicas, legislaciones y estrategias empresariales orientadas hacia un enfoque más humano y participativo. Además, su compromiso con la docencia ha sido continuo, formando a profesionales y líderes comprometidos con la promoción de modelos económicos más justos y centrados en las personas. También ha fomentado colaboraciones interdisciplinarias y establecido alianzas estratégicas con otras universidades e instituciones académicas, organizaciones gubernamentales y entidades del ámbito de la economía social, consolidando así un legado de impacto positivo en la sociedad. Tras una necesaria introducción que relata la trayectoria de esta institución universitaria, la presente obra contiene más de treinta contribuciones versadas sobre temas muy diversos pero de plena actualidad, realizadas por miembros del IUDESCOOP, por otros profesores tanto de la Universitat de València como de otras universidades, así como personas, expertas y activistas de la economía social, tanto del sector cooperativo y de la economía social como de las administraciones públicas, que han tejido fuertes vínculos con el proyecto del IUDESCOOP. Todos ellos presentan en común la vocación por generar conocimiento para un futuro con mayor prosperidad inclusiva y sostenible.S5428000 Generalitat ValencianaDuring the last two decades, the University Institute of Research in Social Economy, Entrepreneurship, and Cooperativism (IUDESCOOP) has engaged in an intense promotion and advancement of economic models that foster social equality, democracy, solidarity, and sustainability. Founded with clear values and vision, this center has nurtured an environment conducive to research and education in the field of cooperatives and social economy. Thanks to the dedication of over thirty individuals who have driven its mission, IUDESCOOP has established itself as a reference in research on these crucial areas, generating relevant knowledge that has influenced public policies, legislations, and business strategies oriented towards a more humane and participatory approach. Additionally, its commitment to education has been continuous, shaping professionals and leaders dedicated to promoting fairer economic models focused on people. It has also encouraged interdisciplinary collaborations and formed strategic alliances with other universities, academic institutions, government organizations, and entities in the social economy domain, thus solidifying a legacy of positive impact on society. Following a necessary introduction narrating the trajectory of this university institution, this work comprises over thirty contributions covering diverse and highly relevant topics. These contributions are authored by members of IUDESCOOP, other professors from both the University of Valencia and other universities, as well as experts and activists in the social economy sector, including cooperatives, social economy, and public administrations. They all share a common commitment to generating knowledge for a future characterized by greater inclusive and sustainable prosperit