Water-soluble anionic polymer electrolytes based on polyfluorene as the universal interlayer for organic solar cells

Conjugated polymers derived from polyfluorene and featuring sulfonate groups in their side chains were synthesized for interlayer in both fullerene and non-fullerene organic solar cells (OSCs). These polymers, specifically denoted as PFS-T-x (x = H, Li), establish an advantageous interfacial dipole through the ionic functionality located at the side chains. Remarkably, the key parameters of organic solar cells, such as Jsc\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${J}_{sc}$$\end{document} and FF,\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$FF,$$\end{document} exhibit improvements as the size of the cation increases. The highest power conversion efficiency (PCE) was achieved using PFS-T-Li as interlayer, reaching up to 9.11% and 16.3% for the device based on fullerene and non-fullerene, respectively. This study can provide a deeper understanding and potential enhancements in the performance of OSCs utilizing polymers as universal interlayers.Graphic abstract This study explored the impact of different countercations in conjugated polymers used as an interlayer in organic solar cells. It was discovered that the conjugated polyelectrolyte containing lithium countercations produced the highest power conversion efficiency, ascribed to the creation of an advantageous interfacial dipole.