Physics Colloquium, Elizabeth von Hauff, Department of Physics & Astronomy, VU Amsterdam

Abstract:

Organic and hybrid semiconductors offer many advantages for energy conversion, saving and storage applications. However, the process of separating photo-generated charge carriers in organic photovoltaics (OPV) is generally less efficient than in conventional inorganic PV technologies due to the large binding energy of the photogenerated excitons and the spatially localized charge carriers in molecular semiconductors. This has motivated intense research into the basic processes that govern charge separation in OPV devices. An increasing number of experimental and theoretical reports show a correlation between molecular vibrational modes, charge delocalization, and the separation of photogenerated excitons. As a result, many researchers have recognised that the electrostatic band diagram of the donor-acceptor system is not sufficient to explain charge separation in OPV.

In this talk, evidence demonstrating dynamic charge separation in emerging photovoltaic devices, such as OPV and perovskite solar cells, is discussed more generally in light of recent results from the theory of open quantum systems. These theoretical results point to the need for a self-oscillating internal degree of freedom, acting as a microscopic piston in order to explain how a solar cell behaves as a heat engine, producing an inexhaustible photovoltage and photocurrent under illumination. The dynamic picture of photovoltaic energy conversion opens up new possibilities for the design and development of efficient new energy transducers.