Photovoltaic performance and scanning tunneling microscopy analysis of PM6:Y7 based organic solar cells

Abstract

Organic solar cells (OSCs) based on PM6 donor polymer and the low bandgap chlorinated acceptor molecule Y7 were fabricated and analyzed. Photovoltaic devices were manufactured and tested under regular atmospheric conditions, by using the top electrode field's metal (FM) easily deposited by drop casting at 90 °C. OSCs reached a power conversion efficiency (PCE) of 11.37 ± 0.17% (best PCE = 11.54%). AFM measurements of PM6:Y7 blend topography were examined through statistical parameters such as root-mean-square (RMS), skewness and kurtosis. Moreover, the nano-morphology of PM6, Y7 and PM6:Y7 monolayers (film thickness <1 nm) was analyzed by scanning tunneling microscopy (STM), under the liquid/solid interface approach. STM images of the very thin PM6 sheets show that they tend to form strand-like pattern domains (amorphous type) with an average chain-to-chain distance of ∼4.8 Å and monolayers of Y7 show intermolecular/intramolecular distance in the range 1.7–2.8 Å. Finally, the PM6:Y7 monolayer shows a kind of superficial interpenetrated network of the donor–acceptor.