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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 36: Organic Electronics and Photovoltaics III

CPP 36.4: Talk

Thursday, March 21, 2024, 10:15–10:30, H 0110

Role of energetic offset in low-offset organic solar cells and its effect on loss pathways — •Bowen Sun and Safa Shoaee — Institute of Physics and Astronomy, University of Potsdam, Germany

While efficient charge generation despite ultra-low energy offsets (down to 0 eV offsets) between donor and acceptor in non-fullerene acceptor (NFA) based organic solar cells (OSCs) has been often reported, the physical meaning of this observation is discussable and unclear.

In this work, we have performed advanced optoelectronic and morphology characterization, as well as optical simulation for a series of donor:NFA systems. The energetic offsets between CT and excitons, as well as the effect of this energetic offset on the carrier loss pathways in different bias conditions have been studied in detail. From our work, we reached several important conslusions: 1) the short circuit current density and fill-factor of low-offset systems are largely determined by a field-dependent exciton dissociation yield. 2) The energetic offset also affects the recombination dynamics. Our analysis clearly shows that this enhanced recombination is contributed by a highly non-radiative channel, indicating the significance of triplet states in the recombination process. 3) It is strongly indicated that the charge generation and recombination (losses) proceed via different energetic states. The losses during charge generation process occur via highly radiative channels, while that during charge recombination process proceed via highly non-radiative channels. In general, our study clarifies the role and effect of energetic offset in low-offset OSCs, and provides a guideline for the further improvement of OSCs.

Keywords: non-fullerene acceptors; exciton dissociation; low-offset organic solar cell; Exciton-CT interplay; Charge generation