Safakath Karutehdath - Role of Ionization Energy Offset in Binary and Ternary Organic Solar Cells

Relevant papers:
https://doi.org/10.1038/s41563-020-00...
https://arxiv.org/abs/2112.06245

For more information about the NGSE PhD-Postdoc series and register for future talks go to:
https://www.ngse.info/phd-postdoc-ser...

Follow us on Twitter at:
  / imeet_pv  
  / ngse_conf  
Talk by Dr. Safakath Karutehdath currently a postdoc in KAUST (KSA) on May 25th, 2022
Abstract:
Non-fullerene acceptor-based ternary organic solar cells have demonstrated better photo charge generation than their binary counterparts.[1] But, underlying photophysics and the trade-off between complementary absorption and the energy offset between donor and acceptor(s) on the charge generation is not fully understood. This understanding is critical for material synthesis and device design.[2] In this presentation, I will talk about the impact of IE offset in charge generation by using different spectroscopic methods in PM6-based OSCs as an example. The selective photoexcitation of PM6 leads to ultrafast singlet exciton energy transfer to the NFAs, outcompeting electron transfer. Subsequently, singlet excitons in the NFA undergo hole transfer to the donor, resulting in free charge generation. This requires sufficient ionization energy offset between donor and acceptors to ensure efficient free charge generation. We observe that in ternary OSCs charge generation is controlled by the difference between the IE of the donor and the weighted-average IE of both NFAs rather than the individual IE differences. While broad absorption spectrum is important for photon collection, but having sufficient ionization energy offset is crucial for charge generation and hence the quantum efficiency in ternary organic solar cells.

1. Cui, Y. et al., Single-Junction Organic Photovoltaic Cell with 19% Efficiency. Advanced Materials, 2102420.
2. Karuthedath, S. et al, Intrinsic efficiency limits in low-bandgap non-fullerene acceptor organic solar cells. Nature Materials 2021, 20 (3), 378-384.