Wolfgang Tress is currently a senior lecturer at Zurich University of Applied Sciences (ZHAW) in Switzerland leading the ERC-funded novel semiconductor devices group at the Institute of Computational Physics. He studied electrical engineering at the University of Ulm and obtained his PhD degree in physics in 2012 at the TU Dresden (Germany). Supervised by Prof. Leo and Prof. Riede, he was working on the device physics and modelling of organic solar cells. After a postdoc stay in the Inganäs group in Linköping (Sweden), he joined the Graetzel and Hagfeldt labs at EPFL (Switzerland), where he started working on perovskite solar cells. For his research on the electroluminescence and hysteresis in perovskite solar cells he received various awards such as the Energy & Environmental Science Readers’ Choice Lectureship by the Royal Society of Chemistry or the Award in Applied Physics awarded by the Swiss Physical Society.

He continued his research with an Ambizione fellowship at EPFL and a Marie Curie Fellowship at the LMU in Munich, where he analyzed loss mechanisms in lead-free perovskites. Currently, he is working on the device physics and the mixed ionic-electronic conductivity of perovskite optoelectronic devices including light emitting diodes and memristors. Wolfgang Tress published more than 100 articles including influential reviews, perspectives, and book chapters. After graduation he wrote a monograph on organic solar cells. Since 2019 he is listed as Web of Science Highly Cited Researcher.

Device Physics of Perovskite Solar Cells

In the last decade, metal-halide perovskite semiconductors have received tremendous attention in research due to their excellent optoelectronic properties, making them highly interesting materials for solar cells and light emitting diodes (LEDs). It is fascinating that these perovskites are highly tolerant against electronic defects, which allowed for solar-cell efficiencies >25%, and at the same time show ionic conductivity meditated through mobile lattice defects. In this talk the device physics of perovskite solar cells is discussed. Focus is on the peculiar properties of the material, which enable low recombination losses and thus high photovoltages. Furthermore, the various effects of ion migration on device performance are described. They range from hysteresis in the current-voltage curve of solar cells to phase segregation and reversible degradation during long-term operation. Key in understanding these phenomena is the interplay between ionic and electronic conductivity, where the ionic response belatedly modifies the electronic response, which is the one commonly observed in devices. This interplay has consequences on how to interpret the results of common characterization techniques. In addition, the real-world long-term operation of perovskite optoelectronic devices under varied ambient conditions is affected. These points lead towards the open challenges, which conclude the talk.