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 11.4: Talk
Monday, March 27, 2023, 16:00–16:15, GÖR 226
On the impact of the energy level offset on carrier recombination in organic non-fullerene acceptor-based solar cells — •Nurlan Tokmoldin1, Bowen Sun1, Floriana Moruzzi2, Obaid Alqahtani3, Brian Collins3, Iain McCulloch2, Dieter Neher1, and Safa Shoaee1 — 1University of Potsdam, Potsdam-Golm, Germany — 2University of Oxford, Oxford, UK — 3Washington State University, Pullman, USA
The energetic offset between the highest occupied molecular orbital (HOMO) levels of the donor and acceptor components of the organic photovoltaic (OPV) blends is well-known to affect the efficiency of the singlet exciton (S1) dissociation into separated charges (CS) via the charge-transfer (CT) state, however the impact of this offset on bimolecular recombination of free charge carriers has not been explored. In this study, using three different non-fullerene acceptors Y6, ITIC and o-IDBTR, blended with the same donor polymer PM6, we demonstrate that, apart from reducing the driving force for charge generation, diminishing HOMO-HOMO energy offset also activates exciton reformation as a channel for bimolecular recombination of free charges. This is accompanied by the rise in the respective bimolecular recombination coefficient, which in turn influences the device fill-factor. Using the comparison between PM6:ITIC and PM6:o-IDBTR, we show that neither morphology, nor carrier mobilities can on their own explain the observed difference in performance, signaling the importance of the energy landscape in controlling the OPV device efficiency, both through generation and recombination of charge carriers.