Charge Generation in Non-Fullerene Acceptors
Natalie Banerji a
a Department of Chemistry, Biochemistry and Pharmaceutical Sciences (DCBP), University of Bern, 3012 Bern, Switzerland
Materials for Sustainable Development Conference (MATSUS)
Proceedings of MATSUS Spring 2025 Conference (MATSUSSpring25)
Understanding success of OSCs: stability and efficiency - #SuccessOPV
Sevilla, Spain, 2025 March 3rd - 7th
Organizers: Tracey Clarke and Vida Engmann
Invited Speaker, Natalie Banerji, presentation 414
DOI: https://doi.org/10.29363/nanoge.matsusspring.2025.414
Publication date: 16th December 2024

Non-fullerene acceptors (NFAs) are exciting molecules allowing high efficiency in organic photovoltaic (OPV) blends with conjugated polymers. Interestingly, charges can also be generated by neat NFA films without additional donor. To understand the origins of exciton dissociation in neat NFAs, we have looked at the impact of aggregation, external electric field and non-linear effects. We used solvatochromism in order to gain insight on charge redistribution after excitation in isolated NFAs. We found that unaggregated NFAs feature a more dipolar excited state, revealing intramolecular charge transfer (ICT) character. This ICT character, however, is not enough to generate separated charges. Aggregation is the key to exciton dissociation in neat NFAs, which we observe with TA of solutions and films of several different NFAs. To explore the impact of an electric field on exciton dissociation in neat NFA devices, we used bias-dependent external quantum efficiency (EQE) and transient absorption (TA) spectroscopy. Electromodulated differential absorption (EDA) measurements then allowed us to observe charge transport under bias. Excitation correlation spectroscopy and fluence-dependent TA finally revealed how non-linear effects can increase the charge yield. Lastly, we comment on whether the neat domain charge generation significantly affects the photophysics of blends or not.

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