SKM 2023 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 11: Focus: Organic Solar Cells Based on Non-fullerene Acceptors: Loss Mechanism and Options for Above 20 % Efficiencies II

CPP 11.3: Talk

Monday, March 27, 2023, 15:45–16:00, GÖR 226

The excess energy optimum to minimize recombination losses in organic solar cells — •Clemens Göhler, Alexander Flamm, and Martijn Kemerink — Institute for Molecular Systems Engineering and Advanced Materials, Universität Heidelberg, Im Neunheimer Feld 225, 69120 Heidelberg

Semiconductor blends that incorporate non-fullerene acceptors (NFA) have pushed organic solar cells to efficiency records based on an established principle: enhancing the generation yield of free charge carriers from tightly bound molecular excitations via interfacial charge transfer between donor and acceptor phases. Their success can in huge parts be attributed to an increase of the photocurrent; however, in comparison to less-effective systems, NFA blends possess a similar overall absorbance and lack the distinct low-energy absorption typically associated with charge transfer (CT) excitons.

The increased charge carrier densities are thus based on reduced recombination yields. As further improvements of the photocurrent are necessary to reach higher efficiencies, a thorough understanding of the mechanisms behind the cut in recombination losses compared to fullerene solar cells is invaluable. To contribute, we have investigated recombination signatures of both systems with respect to the available excess energy by combining field and excitation dependent electro-optical absorption spectroscopy in the steady state and close to solar cell working conditions with kinetic Monte-Carlo simulations. Our findings indicate towards an optimal excess energy which minimizes non-geminate recombination in CT processes.