Investigating Exciton Dynamics of Y6 Non-fullerene Acceptor Using Time-Resolved Spectroscopies
Nisreen Alshehri a
a KAUST Solar Center, Physical Sciences and Engineering Division (PSE), Applied Physics Program (AP) and Materials Science and Engineering Program (MSE), King Abdullah University of Science and Technology (KAUST), Thuwal, Kingdom of Saudi Arabia
International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV23)
London, United Kingdom, 2023 June 12th - 14th
Organizers: Tracey Clarke, James Durrant and Trystan Watson
Poster, Nisreen Alshehri, 288
Publication date: 30th March 2023

Organic photovoltaic development has progressed rapidly in recent years due to the emergence of non-fullerene acceptors (NFAs). These materials outperform their fullerene counterparts in strong and broad light absorption, narrow bandgap, good (photo) stability, high electron mobility, and efficient charge generation via the acceptor's exciton. Recently, there has been evidence that Y6 generates free charge carriers immediately after photoexcitation without needing a donor/acceptor interface. However, the mechanism of this intrinsic charge generation has yet to be fully understood. This work presents a comprehensive photo-physics study of Y6 excitons in a thin film, diluted solid state, and solution via transient absorption (TA) and time-resolved photoluminescence (TRPL) spectroscopies. The assignment of excited states’ spectral features observed in TA experiments was done with the help of reference spectra from chemical- and photo-induced absorption with photosensitizer at cryogenic and room temperatures. The excited states’ kinetics at these characteristic energies at different fluences were also explored. Under excitation with high-energy photons, we observed an electroabsorption signature due to the fast generation of long-lived radical holes at ~1.56eV in a few 100ps. In contrast, a broad charge peak at 1.9eV was also observed upon excitation at lower photon energy. In addition, the exciton diffusion length of 46nm was also determined through exciton-exciton annihilation via fluence-dependent TA measurements.

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