CPOS Seminar: "Strategies to determine the charge carrier density and related quantities in organic solar cells "
Speaker: Dr. Joachim Vollbrecht, Institute for Solar Energy Research in Hamelin (ISFH), Germany
Abstract: The increase in the performance of organic solar cells observed over the past few years has reinvigorated the search for a deeper understanding of the loss and extraction processes in this class of device. A detailed knowledge of the density of free charge carriers under different operating conditions and illumination intensities is a prerequisite to quantify the recombination and extraction dynamics. Differential charging techniques are a promising approach to experimentally obtain the charge carrier density under the aforementioned conditions. In particular, impedance and capacitance spectroscopy have been successfully used in past studies to determine the charge carrier density of organic solar cells. However, the combination of transient photovoltage and photocurrent measurements can also be used to reliably quantify the charge carrier density with less specialized equipment, offering an alternative route for a detailed analysis of the recombination and extraction dynamics. In this talk, these two different experimental techniques will be discussed in detail, highlighting fundamental principles, practical considerations, necessary corrections, advantages, drawbacks, and ultimately their limitations. In addition, more advanced concepts related to the determination of drift and diffusion lengths as well as the effective mobility will be presented as well.
Bio: Dr. Joachim Vollbrecht investigated experimental methods to reliably characterize the recombination and extraction dynamics of organic solar cells at the Institute of Physics and Astronomy at the University of Potsdam. Previously, he was as a Feodor Lynen postdoctoral fellow at CPOS - Department of Chemistry and Biochemistry, University of California, Santa Barbara. He obtained his doctoral degree doing research in physical chemistry researching organic light emitting diodes, organic field effect transistors, and organic semiconductor materials. Currently, he works on perovskite solar cells as a staff researcher at the Institute for Solar Energy Research in Hamelin (ISFH).
