Koen Vandewal

Learn More
The increasing amount of research on solution-processable, organic donor-acceptor bulk heterojunction photovoltaic systems, based on blends of conjugated polymers and fullerenes has resulted in devices with an overall power-conversion efficiency of 6%. For the best devices, absorbed photon-to-electron quantum efficiencies approaching 100% have been shown.(More)
Interfaces between organic electron-donating (D) and electron-accepting (A) materials have the ability to generate charge carriers on illumination. Efficient organic solar cells require a high yield for this process, combined with a minimum of energy losses. Here, we investigate the role of the lowest energy emissive interfacial charge-transfer state (CT1)(More)
Conjugated polymer chains have many degrees of conformational freedom and interact weakly with each other, resulting in complex microstructures in the solid state. Understanding charge transport in such systems, which have amorphous and ordered phases exhibiting varying degrees of order, has proved difficult owing to the contribution of electronic processes(More)
We examine the significance of hot exciton dissociation in two archetypical polymer-fullerene blend solar cells. Rather than evolving through a bound charge transfer state, hot processes are proposed to convert excitons directly into free charges. But we find that the internal quantum yields of carrier photogeneration are similar for both excitons and(More)
In this article we report the weak but omnipresent electroluminescence (EL) from several types of organic polymer:fullerene bulk heterojunction solar cells biased in the forward direction. The light emitted from blends of some commonly used polymers and the fullerene molecule is significantly different from that of any of the pure materials comprising the(More)
Dr. Y. Zhou, Dr. T. Kurosawa, Dr. L. Fang, Dr. Y. Diao, Dr. J. Reinspach, Dr. J. Mei, Dr. A. L. Appleton, Dr. G. I. Koleilat, Prof. Z. Bao Department of Chemical Engineering Stanford University Stanford , California 94305 , USA E-mail: zbao@stanford.edu Y. Guo, Dr. Q. Yan, Prof. D. Zhao College of Chemistry Peking University Beijing 100871 , China E-mail:(More)
Organic photovoltaics (OPV) are a promising technology with the potential for large scale production at very low cost. An industrial application of this technology could signicantly contribute to the global energy production, but was impeded by low efficiencies and lifetimes of organic photovoltaics. With power conversion efficiencies recently surpassing(More)
An N-Type organic thin-film transistor (OTFT) based on doped 6,13-Bis(triisopropylsilylethynyl)pentacene is presented. A transition from p-type to n-type occurrs with increasing doping concentrations, and the highest performing n-channel OTFTs are obtained with 50 mol% dopant. X-ray diffraction, scanning Auger microscopy, and secondary ionization mass(More)
Dr. K. Vandewal, Prof. M. D. McGehee, Prof. A. Salleo Department of materials science and engineering Stanford University Stanford , CA94305 , USA E-mail: koen.vandewal@iapp.de; asalleo@stanford.edu Dr. K. Vandewal, Dr. J. Widmer, Prof. K. Leo, Dr. M. Riede Institut für Angewandte Photophysik Technische Universität Dresden George-Bähr-Straße 1, 01069 ,(More)