Regensburg 2016 – wissenschaftliches Programm
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 38: Organic Photovoltaics and Electronics (joint session CPP/HL, organized by HL)
CPP 38.4: Vortrag
Mittwoch, 9. März 2016, 15:45–16:00, H2
Energy-Gap Law of Non-Radiative Voltage Losses in Organic Solar Cells — •Johannes Benduhn1, Kristofer Tvingstedt2, Fortunato Piersimoni3, Olaf Zeika1, Donato Spoltore1, Dieter Neher3, and Koen Vandewal1 — 1IAPP, TU Dresden, Germany — 2EP VI, Julius-Maximillian University of Würzburg, Germany — 3IPA, University of Potsdam, Germany
The open-circuit voltage of organic solar cells is low as compared to their optical gap, indicating large energy losses per absorbed photon. These losses arise from the necessity of an electron transfer from an electron donor to an electron acceptor to dissociate the excitons, and furthermore from the recombination of the resulting free charge carriers. It has been shown that the energy loss in the electron transfer event can be below 0.1 eV, while radiative recombination losses are in principle unavoidable.
In this work, we investigate the remaining voltage losses due to non-radiative decay of charge carriers. We find that the non-radiative voltage losses increase when the energy difference between charge transfer (CT) state and ground state decreases. This behaviour is consistent with the "energy gap law for non-radiative transitions", which implies that internal conversion from CT state to ground state is facilitated by molecular vibrations. With this work, we identify a possibly intrinsic loss mechanism, which until now has not been thoroughly considered for organic photovoltaics, and which is different in its very nature as compared to the commonly considered inorganic photovoltaic loss mechanisms of defect, surface, and Auger recombination.