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 11.2: Talk

Monday, March 27, 2023, 15:30–15:45, GÖR 226

Increasing the ionization offset to increase the quantum efficiency in non-fullerene acceptor based organic solar cells: How far can we go? — •Julien Gorenflot, Wejdan Alsufyani, Maryam Alqurashi, Sri Harish Kumar Paleti, Anirudh Sharma, Derya Baran, and Frédéric Laquai — KAUST Solar Center, King Abdullah University of Science and Technology, Thuwal, Kingdom of Saudi Arabia

Molecular engineering offers a virtually unlimited number of unique semiconductors for organic photovoltaics applications, that can be tailored to adapt specific needs, but only a handful of combinations enables to reach state-of-the art efficiencies. Rules are thus strongly needed to guide the design of promising systems. A recently unraveled rule is that the electron acceptor molecule requires an ionization energy 0.5 eV deeper than that of the electron donor to overcome the bending of the energy levels at the donor acceptor heterojunction interface, maximizing the charge transfer, hence the cell’s quantum efficiency. Here we study the energy losses associated to this Δ IE increase. Based on 30+ blends, we show that those losses remain minimal up to an offset of 0.7 eV. We then use electroluminescence spectroscopy to evaluate the charge transfer state energy (E_CT) and find that this low energy losses range is associated to E_CT remaining at most similar to the NFA’s optical bandgap (E_g,NFA), while further Δ IE increase pulls E_CT below E_g,NFA, accordingly decreasing V_OC. We finally study the evolution of the fill factor (FF) within this maximum quantum efficiency – minimal energy losses Δ IE range.