Demystifying the Impact of Strong Light-Matter Coupling on the Charge-Transfer Dynamics of Donor:Acceptor Photovoltaic Blend Thin Films

Embedding molecules in optical microcavities is an emerging method of controlling excited-state processes of optoelectronic materials without synthetic modification. This has potential benefit in organic photovoltaics, where the strong light-matter coupling achieved in optical cavities could be used to assist energy transfer and charge formation, and mitigate loss pathways. Transient absorption (TA) spectroscopy is often used to gain insight into the photophysics of organic photovoltaic systems and would be an ideal technique for determining the effect of strong coupling on exciton dynamics. However, conducting TA spectroscopy on optical microcavities results in several challenges, such as excitonic signals being masked and large artifacts arising from transient changes in the cavity structure. Here, we study blend films of PTB7-Th:PC71BM cavities, which have previously been found to exhibit altered performance between noncavity and cavity photovoltaic devices. We use transfer matrix simulations to reproduce the cavity TA spectra, and show that, when artifacts are accounted for, there is no significant difference between cavity and noncavity photophysics for this photovoltaic blend.