Berlin 2024 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 31: Organic Electronics and Photovoltaics II

CPP 31.6: Talk

Wednesday, March 20, 2024, 16:30–16:45, H 0110

Charge transfer states do not like cold charges — •Tobias Krebs, Clemens Göhler, and Martijn Kemerink — Institute for Molecular Systems Engineering and Advanced Materials, Heidelberg University

The power conversion efficiency of organic solar cells still lags behind their inorganic counterparts. Especially the open circuit voltage (Voc) losses are currently hard to reduce without knowing their exact origins. As different loss mechanisms have distinct temperature and light intensity dependencies, looking at Voc not only at room temperature and 1 sun illumination but also at lower and higher temperatures as well as at lower light intensities to pinpoint the dominant loss channel is imperative. We develop a new analytical rate-equation model based on previous work by Koster et al. [1], which allows us to distinguish different loss channels and incorporates the specific, far-from-equilibrium charge carrier dynamics in organics. For our PM6:Y6 solar cells, the model fits the experimental data over the range of applied temperatures down to 90K and light intensities as low as 1e-6 suns. Our results further suggest that the voltage losses at low light intensities and temperatures are mostly due to charges being stuck in the interfacial charge transfer state. Additionally, we benchmark the model against kinetic Monte Carlo simulations and find good agreement of Voc as well as recombination and escape yields.

[1] *Quantifying Bimolecular Recombination Losses in Organic Bulk Heterojunction Solar Cells*, Koster et al. Advanced Materials 23, 1670*1674 (2011).

Keywords: Organic Solar Cells; Charge Transfer; Rate Equation