A Universal Poly(3,4‐Ethylenedioxythiophene)‐Based Hole Transport Layer Material for Efficient and Stable Organic Solar Cells

Poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS, AI 4083), is by far the most widely employed hole transport layer (HTL) material, but still suffers from drawbacks of high acidity and strong hydrophilicity, which hamper the device stability in organic solar cells (OSCs). To address these limitations, we designed and synthesized a novel CF 3 ‐containing sulfonated copolymer (PSF) counterion and incorporated it with PEDOT to form the PEDOT:PSF complex, which has excellent solution and film stability. In this work, PSF combines a significant reduction of the acidity with a much decreased hygroscopic nature. When employed in OSCs with different active layers, namely PM6:Y6, PM6:BTP‐eC9, PM6:L8‐BO, and D18:L8‐BO, the PEDOT:PSF‐doped HTL delivered maximum power conversion efficiencies (PCEs) of 16.71%, 17.20%, 18.36%, and 18.55%, respectively, which are consistently slightly better than those achieved by comparable OSCs using PEDOT:PSS as HTL. Notably, this novel HTL displayed significantly enhanced stability and durability of devices; the doped and pristine PEDOT:PSF‐based OSCs retained 83% and 71% of their initial PCE after 730 h of continuous illumination, whereas PEDOT:PSS devices retained merely 58%.