Achieving High Doping Density in pH‐neutral Conjugated Polyelectrolyte Toward Effective Hole‐Transporting Materials for Organic Solar Cells

Abstract The lack of effective and non‐corrosive hole‐transporting layer (HTL) materials has remained a long‐standing issue that severely restricts the performance of organic solar cells (OSCs). Most pH‐neutral conjugated polyelectrolytes (CPEs) exhibit inferior performance to the acid‐doped HTL materials due to their low doping density. In this study, a series of pH‐neutral CPEs is designed and synthesized with high doping density as HTL materials. Through an elaborate synthetic route, two sulfonate‐terminating alkoxyl side chains can be introduced into thiophene, by which the electron‐rich, highly soluble, and chemically stable thiophene monomer is synthesized to enable the subsequent polymerization. The CPE PTT‐F exhibit a remarkable self‐doping property with an enhanced doping density from 2.01 × 10 17 to 7.02 × 10 18 cm −3 . The high work function and the increased doping density of PTT‐F‐based HTL decrease the depletion region width from 38.4 to 8.1 nm at the anode interface, which minimized the energy loss in hole transport. Consequently, a binary OSC modified by PTT‐F‐based HTL achieve a high PCE of 18.8%. To the best of the knowledge, this is the highest PCE for OSC employing CPE‐based HTL. The results from this work demonstrate an encouraging achievement of realizing exceptional hole collection ability in pH‐neutral CPEs.