Charge transport in amorphous organic semiconductors

Organic semiconductors with the unique combination of electronic and mechanical properties may offer cost-effective ways of realizing many electronic applications, e.g. large-area flexible displays, printed integrated circuits and plastic solar cells. In order to facilitate the rational compound design of organic semiconductors, it is essential to understand relevant physical properties e.g. charge transport. This, however, is not straightforward, since physical models operating on different time and length scales need to be combined. First, the material morphology has to be known at an atomistic scale. For this atomistic molecular dynamics simulations can be employed, provided that an atomistic force field is available. Otherwise it has to be developed based on the existing force fields and first principle calculations. However, atomistic simulations are typically limited to the nanometer length- and nanosecond time-scales. To overcome these limitations, systematic coarse-graining techniques can be used. In the first part of this thesis, it is demonstrated how a force field can be parameterized for a typical organic molecule. Then different coarse-graining approaches are introduced together with the analysis of their advantages and problems. When atomistic morphology is available, charge transport can be studied by combining the high-temperature Marcus theory with kinetic Monte Carlo simulations. The approach is applied to the hole transport in amorphous films of tris(8-hydroxyquinoline)aluminium (Alq3). First the influence of the force field parameters and the corresponding morphological changes on charge transport is studied. It is shown that the energetic disorder plays an important role for amorphous Alq3, defining charge carrier dynamics. Its spatial correlations govern the Poole-Frenkel behavior of the charge carrier mobility. It is found that hole transport is dispersive for system sizes accessible to simulations, meaning that calculated mobilities depend strongly on the system size. A method for extrapolating calculated mobilities to the infinite system size is proposed, allowing direct comparison of simulation results and time-of-flight experiments. The extracted value of the nondispersive hole mobility and its electric field dependence for amorphous Alq3 agree well with the experimental results.

Zwischen Isolation, Anpassung und räumlicher Mobilität : eine Untersuchung zur Integration von Binnenwanderern in Deutschland

Magdeburg, Univ., Fak. für Geistes-, Sozial- und Erziehungswiss., Diss., 2011

Kinder und Mobilität

[s.c.]

Der Anpassungsprozess von Ost an West - schnell aber nicht homogen. Teil 2 der Serie : Entwicklung der Mobilität im vereinten Deutschland

The article investigates the question, whether and in how far the travel behaviour of the former GDR inhabitants and the former FRG inhabitants has equalled since the years after the German reunification. A person-group specific analysis shows that the major differences still consist only in the elderly of age 60 and above. This is mainly due to the much slower process of motorization within this age group in the former GDR. In the younger age groups the adaption of the travel behaviour has almost been achieved; mainly as a consequence of the fast motorization process since 1990 in these age groups. Where differences are still valid, this stems firstly from worse supply conditions, especially with public transport, but also with road infrastructure, as can be seen by an overall lower system speed in the former GDR. A panel analysis shows, that the dynamics in terms of transport specific life style changes is far more relevant in the former GDR than former FRC. This is linked with higher mobility in the persons with such changes. These changes will probably come to an end once the economic development will have stabilised and the cohort with the biggest behavioural differences will gradually decrease.

Aktive Mobilität und Gesundheit : Hintergrundbericht für den nationalen Gesundheitsbericht 2015

Zu Fuss gehen und Velofahren tragen viel zu einer gesundheitsfördernden Bewegung bei. Die vielfältigen positiven Gesundheitseffekte regelmässiger Bewegung sind heute umfassend belegt. Ob in der Freizeit oder im Alltag, zu Fuss gehen und Velofahren - so genannte aktive Mobilität - können viel zu einer gesundheitsfördernden Bewegung beitragen. Zahlreiche Faktoren beeinflussen indessen die Neigung, zu Fuss zu gehen oder mit dem Velo zu fahren, darunter Wegeigenschaften, Alter, Fitness, aber auch Verkehrssicherheit und ganz allgemein die Merkmale von Quartieren und Städten. Die veränderbaren strukturellen Faktoren, insbesondere die Verkehrsinfrastruktur und -Sicherheit stehen im Zentrum zeitgemässer Förderung der aktiven Mobilität. Aus Sicht der Gesundheitspolitik ist eine intersektorielle Zusammenarbeit zwischen Gesundheitssektor und Verkehrs- und Städteplanung erstrebenswert. Bei den Überlegungen werden dadurch auch Gesundheitsfolgen fokussiert.