Christoph Lienau plenary: Ultrafast Coherent Charge Transfer in Solar Cells and Artificial Light Harvesting Systems -- Toward Movies of Electronic Motion

In this plenary talk, Christoph Lienau of University of Oldenburg discusses his group's most recent findings and their implications for the light-to-current conversion in solar cells.

The efficient conversion of (sun-)light into electrical or chemical energy is one of the most fundamental and relevant challenges in current energy research. Our ability to construct artificial molecular or nanostructured devices that can harvest and exploit sunlight inevitably relies on an in-depth understanding of the elementary microscopic principles that govern the underlying light conversion processes. Generally, these processes happen on an exceedingly short femtosecond time scale, making real time studies of the light-driven dynamics particularly important.

To elucidate these dynamics, Lienau's team has recently combined coherent femtosecond spectroscopy and first-principles quantum dynamics simulations and have used this approach to explore the primary photoinduced electronic charge transfer in two prototypical structures: (i) a carotene-porphyrin-fullerene triad, an elementary component for an artificial light harvesting system and (ii) a polymer:fullerene blend as a model for an organic solar cell. Surprisingly, the experimental and theoretical results provide strong evidence that in both systems, at room temperature, the driving mechanism of the primary step within the current generation cycle is a quantum-correlated wavelike motion of electrons and nuclei on a timescale of few tens of femtoseconds. These results suggest that the strong coupling between electronic and vibrational degrees of freedom is of key importance for the dynamics and yield of the charge separation process.

Christoph Lienau is a professor in experimental physics at the University of Oldenburg. After receiving a PhD in physical chemistry in Göttingen, he worked as a postdoc with Ahmed H. Zewail at Caltech, studying femtosecond dynamics in solution. In 1995, he became a scientific staff member of of the newly founded Max Born Institute in the department of Thomas Elsässer. Here, he initiated a research activity in "ultrafast nano-optics", combining low-temperature and ultrafast near-field spectroscopy and their applications to nano-spectroscopy. In 2006, he became a full professor in physics in Oldenburg. He has published more than 150 publications in refereed international journals and has given more than 100 invited and plenary talks at major international conferences. He holds 5 patents. He is a Fellow of the Optical Society of America and vice-chair of the semiconductor physics division of the German Physical Society. His research interests are in ultrafast, nano and quantum optics.