Johannes Kepler University of Linz

About: Johannes Kepler University of Linz is a education organization based out in Linz, Oberösterreich, Austria. It is known for research contribution in the topics: Thin film & Quantum dot. The organization has 6605 authors who have published 19243 publications receiving 385667 citations.

Social Representations and beyond: Brute Facts, Symbolic Coping and Domesticated Worlds:

Abstract: Social representation theory is scrutinized for its capacity to ask new questions and to give new answers to social psychological problems. Its social constructionist implications and relationship to brute facts are investigated. It is shown that social representations result from collective symbolic coping with 'brute' facts. Consequently representations create the domesticated world of social objects which implies considering activity as part of a representation. Culture change in modern societies is shown to produce 'cognitive polyphasia' by adding alternative representations to existing ones instead of replacing them.

Phase-Field Relaxation of Topology Optimization with Local Stress Constraints

Abstract: We introduce a new relaxation scheme for structural topology optimization problems with local stress constraints based on a phase-field method In the basic formulation we have a PDE-constrained optimization problem, where the finite element and design analysis are solved simultaneously The starting point of the relaxation is a reformulation of the material problem involving linear and 0-1 constraints only The 0-1 constraints are then relaxed and approximated by a Cahn-Hilliard-type penalty in the objective functional, which yields convergence of minimizers to 0-1 designs as the penalty parameter decreases to zero A major advantage of this kind of relaxation opposed to standard approaches is a uniform constraint qualification that is satisfied for any positive value of the penalization parameter The relaxation scheme yields a large-scale optimization problem with a high number of linear inequality constraints We discretize the problem by finite elements and solve the arising finite-dimensional programming problems by a primal-dual interior point method Numerical experiments for problems with local stress constraints based on different criteria indicate the success and robustness of the new approach

Bipolar Charge Transport in PCPDTBT‐PCBM Bulk‐Heterojunctions for Photovoltaic Applications

Abstract: An experimental study of the transport properties of a low-bandgap conjugated polymer giving high photovoltaic quantum efficiencies in the near infrared spectral region (Eg-opt ∼ 1.35 eV) is presented. Using a organic thin film transistor geometry, we demonstrate a relatively high in-plane hole mobility, up to 1.5 · × 10−2 cm2 V−1 s−1 and quantify the electron mobility at 3 × · 10−5 cm2 V−1 s−1 on a SiO2 dielectric. In addition, singular contact behavior results in bipolar quasi-Ohmic injection both from low and high workfunction metals like LiF/Al and Au. X-ray investigations revealed a degree of interchain π-stacking that is probably embedded in a disordered matrix. Disorder also manifests itself in a strong positive field dependence of the hole mobility from the electric field. In blends made with the electron acceptor methanofullerene [6,6]-phenyl C61 butyric acid methyl ester (PCBM), the transistor characteristics suggest a relatively unfavorable intermixing of the two components for the application to photovoltaic devices. We attribute this to a too fine dispersion of [C60]-PCBM in the polymer matrix, that is also confirmed by the quenching of the photoluminescence signal measured in PCPDTBT [C60]-PCBM films with various composition. We show that a higher degree of phase separation can be induced during the film formation by using 1,8-octanedithiol (ODT), which leads to a more efficient electron percolation in the [C60]-PCBM. In addition, the experimental results, in combination with those of solar cells seem to support the correlation between the blend morphology and charge recombination. We tentatively propose that the drift length, and similarly the electrical fill factor, can be limited by the recombination of holes with electrons trapped on isolated [C60]-PCBM clusters. Ionized and isolated [C60]-PCBM molecules can modify the local electric field in the solar cell by build-up of a space-charge. The results also suggest that further improvements of the fill factor may also be limited by a strong electrical-field dependence of the hole transport.