Thomas Brenner

Ag-nanowire films coated with ZnO nanoparticles as a transparent electrode for solar cells

We demonstrate that solution-processible silver-nanowire films coated with zinc-oxide-nanoparticles (ZnO-NPs) can be used as transparent electrodes in organic photovoltaic devices. The ZnO-NP coating acts as electron extraction layer and as encapsulating agent, protecting the wires from oxidation and improving their mechanical stability. Scanning photocurrent microscopy showed photocurrent generation to be more efficient at the active material surrounding the wires. Ultra-violet illumination as present in the solar spectrum was found to enhance photocurrent by improving the ZnO in-layer conductivity through the photoconductive effect. Inverted polythiophene:fullerene devices using ZnO-NP coated silver-nanowires or indium-tin-oxide as transparent electrode reached power conversion efficiencies of 2.4%.

Highly Efficient Single-Layer Polymer Ambipolar Light-Emitting Field-Effect Transistors

Single-layer polymer light-emitting field-effect transistors (LEFETs) that yield EQEs of >8% and luminance efficiencies >28 cd A(-1) are demonstrated. These values are the highest reported for LEFETs and amongst the highest values for fluorescent OLEDs. Due to the electrostatics of the ambipolar LEFET channel, LEFETs provide an inherent advantage over OLEDs in terms of minimizing exciton-polaron quenching.

Innovation and cooperation during the emergence of local industrial clusters: An empirical study in Germany

This paper studies the dynamics that cause the emergence of local industrial clusters at a general level. Predictions about these dynamics are deduced from theoretical modelling. The predictions are tested with the help of empirical data from Germany. Three-digit manufacturing industries are classified according to their dynamics. It is examined whether certain industrial characteristics are able to predict the type of dynamics occurring. It is shown that a high number of process innovations and a high share of regional cooperation with suppliers and public research institutes characterize those industries in which local clusters emerge.

Computational Techniques for Modelling Learning in Economics

Preface. List of Contributors. Part One: Simulating in Economics. Evolutionary Economics and Simulation W. Kwasnicki. Simulation as a Tool to Model Stochastic Processes in Complex Systems K.G. Troitzsch. Part Two: Evolutionary Approaches. Learning by Genetic Algorithms in Economics? F. Beckenbach. Can Learning-Agent Simulations Be Used for Computer Assisted Design in Economics? T.C. Price. On the Emergence of Attitudes towards Risk S. Huck, et al. Interdependencies, Nearly-decomposability and Adaptation K. Frenken, et al. Part Three: Neural Networks and Local Interaction. Neural Networks in Economics R. Herbrich, et al. Genetic Algorithms and Neural Networks: A Comparison Based on the Repeated Prisoners Dilemma R.E. Marks, H. Schnabl. Local Interaction as a Model of Social Interaction? D.K. Herreiner. Part Four: Boundedly Rational and Rational Models. Memory, Learning and the Selection of Equilibria in a Model with Non-Uniqueness E. Barucci. A Behavioral Approach to a Strategic Market Game M. Shubik, N.J. Vriend. Bayesian Learning in Optimal Growth Models under Uncertainty S.M.N. Islam. Part Five: Cognitive Learning Models. Modelling Bounded Rationality in Agent-based Simulations Using the Evolution of Mental Models B. Edmonds. Cognitive Learning in Prisoners Dilemma Situations T. Brenner. A Cognitively Rich Methodology for Modelling Emergent Socioeconomic Phenomena S. Moss. Index.

Network-induced oscillatory behavior in material flow networks and irregular business cycles

Network theory is rapidly changing our understanding of complex systems, but the relevance of topological features for the dynamic behavior of metabolic networks, food webs, production systems, information networks, or cascade failures of power grids remains to be explored. Based on a simple model of supply networks, we offer an interpretation of instabilities and oscillations observed in biological, ecological, economic, and engineering systems. We find that most supply networks display damped oscillations, even when their units--and linear chains of these units--behave in a nonoscillatory way. Moreover, networks of damped oscillators tend to produce growing oscillations. This surprising behavior offers, for example, a different interpretation of business cycles and of oscillating or pulsating processes. The network structure of material flows itself turns out to be a source of instability, and cyclical variations are an inherent feature of decentralized adjustments.

Chapter 18 Agent Learning Representation: Advice on Modelling Economic Learning

This paper presents an overview on the existing learning models in the economic literature. Furthermore, it discusses which of these models should be used under what circumstances and how adequate learning models can be chosen in simulation approaches. It gives advice for getting along with the many models existing and picking the right one for the own application.

Local Knowledge Resources and Knowledge Flows

In recent years, knowledge has become a major research topic in economics. In the literature it is even claimed that we have a knowledge-based economy (Foray and Lundvall, 1996; Godin, 2006) and some researchers talk about the New Economy (Godin, 2004) in this context. This might be an exaggerated view. Knowledge always played an important role in the economy. However, the stock of knowledge on which economic activity is based today is definitely much larger than in previous eras. Foray and Lundvall (1996) argue that knowledge has become quantitatively and qualitatively more important than before. Furthermore, in recent years technologies have been developed that have tremendously improved the ways of storing, transporting and transferring knowledge. This has caused a division of knowledge. It is long ago that one person was able to command the available knowledge to such an extent that he could work on the scientific frontiers in all disciplines. It seems as if it is today even impossible to command the knowledge that is necessary to develop one technology further. Often many different knowledge resources have to be employed in an innovation process. Hence, one major capability of a researcher or innovator is to be able to command knowledge flows and collect knowledge to such an extent that knowledge is at hand if needed. Information technology makes it much easier nowadays to track down relevant available knowledge. This holds to a large degree for the scientific world where almost all knowledge is written down and published. It holds much less for research in private companies where technological knowledge often is a major factor of competitiveness (some proof for this difference is given by Sorenson and Singh in this issue). Researchers in private companies have usually no incentive to write down their knowledge. It holds also much less for knowledge that is related to research practices. While the methods applied have to be published in the scientific world many other aspects of conducting research are less well described in the literature. Private firms do not at all make public the way they

The Dependence of Innovativeness on the Local Firm Population—An Empirical Study of German Patents

Local clusters and the co‐location of firms are repeatedly related to a high level of innovativeness in the literature. The underlying argument is that firms that are co‐located with other firms of the same industry undertake more innovation than “lonely” firms because of spillovers, local labour markets and cooperations. These arguments are tested here for four industries in Germany. To this end, four different hypotheses about the impact of co‐location on the innovativeness of firms are formulated and empirically compared. The results show that the innovativeness of firms indeed depends on the existence of other firms in the same region. However, the relationship between co‐location and innovation output depends on the industry studied.

The long-term Implications of Local Industrial Clusters

ABSTRACT Local industrial clusters have attracted much attention in recent economic and geographic literature. The focus has been on identifying the conditions for the emergence of such clusters. Here the long-term implications of local industrial clusters are studied. To this end, we examine German regions where those that contain long-existing industrial clusters are compared to all other regions. We statistically examine what characterizes regions that have contained local industrial clusters for quite some time. The analysis is conducted separately for three industries.

White-light bias external quantum efficiency measurements of standard and inverted P3HT : PCBM photovoltaic cells

We have investigated the behaviour of inverted poly(3-hexylthiophene) : [6,6]-phenyl- C61-butyric acid methyl ester (P3HT : PCBM) solar cells with different active layer thickness upon changing light intensity. Using white-light bias external quantum efficiency (EQE) measurements and photocurrent transient measurements we explain the different thickness dependence of device performance of inverted (ITO/ZnO/P3HT : PCBM/WO3/Ag) and standard (ITO/PEDOT : PSS/P3HT : PCBM/Ca/Al) cells. Whereas for inverted devices where high EQEs of up to 68% are measured under low light intensities (~3.5 mW cm−2), a dramatic reduction in EQE is observed with increasing white-light bias (up to ~141.5 mW cm−2) accompanied by a severe distortion of the EQE spectrum. For the inverted device this spectral distortion is characterized by a dip in the EQE spectrum for wavelengths corresponding to maximum light absorption and becomes more prominent with increasing active layer thickness. For regular P3HT : PCBM devices, in contrast, a less dramatic reduction in EQE with increasing light intensity and only a mild change in EQE spectral shape are observed. The change in EQE spectral shape is also different for standard devices with a relative reduction in EQE for spectral regions where light is absorbed less strongly. This asymmetry in device behaviour is attributed to unbalanced charge transport with the lower mobility carrier having to travel further on average in the inverted device structure. Thus at high light intensities charge recombination is more pronounced at the front half of the device (close to the transparent electrode) for inverted cells where most of the light is absorbed, and more pronounced at the back half of the device for standard cells. Our results therefore indicate that bulk charge transport mobilities rather than vertical composition gradients are the dominant factor in determining the performance of standard and inverted P3HT : PCBM cells.