Proceedings of nanoGe Fall Meeting 2021 (NFM21)
DOI: https://doi.org/10.29363/nanoge.nfm.2021.098
Publication date: 23rd September 2021
Understanding the role that exciton diffusion plays in organic solar cells is a crucial to understanding the recent rise in power conversion efficiencies brought about by non-fullerene
acceptors (NFAs) [1]. In this presentation I will discuss the role that exciton diffusion plays in efficient charge generation.
Firstly, I will outline how one can measure the exciton diffusion lengths through quenching experiments using time resolved photoluminescence, and through exciton-exciton annihilation (EEA) using high resolution TRPL [2]. I will then introduce a novel technique, coined pulsed-PLQY, to measure the diffusion length through EEA without the need for any temporal measurements, greatly increasing the speed and ease of the measurement while reducing the operational costs.
Traditional and pulsed-PLQY EEA techniques are simulated using a Kinetic Monte-Carlo approach and the limits of both techniques are discussed. It is found that pulsed-PLQY is less sensitive to the choice of excitation density and has increasing confidence with increasing densities measured. The simulations are validated by performing both experimental techniques on organic thin films, reproducing the predicted trends. Pulsed-PLQY is then used to measure the diffusion length in a range of organic semiconductors, including technologically relevant NFAs. We find that the NFAs show an increase in diffusion length, driven by an increase in diffusivity, compared to a benchmark fullerene acceptor [3].
This work was supported by the Welsh Government's Ser Cymru II Program through the European Regional Development Fund, Welsh European Funding Office, and Swansea University strategic initiative in Sustainable Advanced Materials. A.A. is a Ser Cymru II Rising Star Fellow and P.M. is a Ser Cymru II National Research Chair. This work was also funded by UKRI through the EPSRC Program Grant EP/T028511/1 Application Targeted Integrated Photovoltaics. D.B.R. acknowledges the support of the Natural Sciences and Engineering Research Council of Canada (NSERC), [PGSD3-545694-2020]. The authors acknowledge the support of the Supercomputing Wales project, which is part-funded by the European Regional Development Fund (ERDF) via the Welsh Government. The authors thank Dr. Nasim Zarrabi for her insight and fruitful discussions.
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