Investigating polaron dynamics in PM6:Y6 films for use in organic photovoltaics using time-resolved infrared spectroscopy

Abstract

In the last 10 years, there has been a boom in the organic photovoltaic (OPV) community, with new devices achieving power conversion efficiencies (PCEs) of ~18%. This significant increase in device performance is due to a switch from polymer:fullerenes, such as P3HT:PCBM, to polymer:non-fullerenes, like PM6:Y6. These films are often created with the use of solvent additives which, when correctly chosen, increase the device performance. However, because many of these polymer:non-fullerene systems have only recently been developed the exact effect that these solvent additives have on the morphology, performance and electronic properties is not well understood. Here we use a combination of photoluminescence and time-resolved spectroscopy along with grazing-incidence wide-angle x-ray scattering to fully understand what is occurring at both an electronic and morphological level in a series of PM6:Y6 films with varying amounts of acetone used as a solvent additive. From these data we find that acetone changes the degree of mixing and crystal grain size, which leads to changes in polaron yield and recombination, which is reflected in device performance.