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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 36: Organic Electronics and Photovoltaics III

CPP 36.1: Talk

Thursday, March 21, 2024, 09:30–09:45, H 0110

How 'Hot' are the Charges in OPV? — •Priya Viji, Constantin Tormann, Clemens Göhler, Dorothea Scheunemann, and Martijn Kemerink — IMSEAM, Universität Heidelberg, Germany

The question of whether charge transport in operational organic solar cells (OSC) occurs far-from-equilibrium or not is of practical and fundamental importance. While the equilibrium picture of the OSC assumes that the photogenerated charge carriers quickly lose their energy and attain lattice temperature, kinetic Monte Carlo (kMC) simulations of OSC have consistently shown that photogenerated charges are extracted before reaching thermal equilibrium energy: the population relaxes, albeit to an effective temperature that exceeds that of the lattice. In this work, we use Johnson thermometry to measure the temperature of the photogenerated carriers by noise spectroscopy. Two systems, P3HT:PCBM and PM6:Y6, are tested against their inorganic counterpart, silicon. The experiments prove, in contrast to silicon PV, charges in operational OSC are not thermalized and are almost twice as hot as the lattice. The experimental findings are confirmed by kMC simulations, which show that the energetic disorder in organic semiconductors is the reason for slow thermalization as well as high effective temperature. Our results imply that OSCs are far from equilibrium systems, which opens realistic prospects to mitigate the thermalization losses and eventually beat the near-equilibrium thermodynamic limit. In fact, the results show that a regular OSC is Hot-Carrier Solar Cell in the sense that excess energy contributes to output power.

Keywords: organic solar cells; thermalization; non-equilibrium; noise spectroscopy; hot-carrier solar cells