Highly Conductive Polythiophene‐Based Conjugated Polyelectrolyte Toward Efficient Anode Modification in Organic Solar Cells

The scarcity of high‐performance, noncorrosive anode interfacial layers (AILs) remains a key challenge in developing organic solar cells (OSCs). While conjugated polyelectrolytes (CPEs) offer neutral pH and tunable properties, their low doping density typically limits conductivity and device performance. Herein, we report the rational design and synthesis of two novel polythiophene‐based CPEs, pT‐1 and pT‐2 , as efficient, pH‐neutral AILs. Molecular engineering involves a bithiophene monomer functionalized with four sulfonate‐terminated alkoxyl side chains, ensuring solubility while enhancing backbone electron density via p–π conjugation. The incorporation of electron‐rich cyclopentadithiophene units further promotes p‐type self‐doping. Crucially, branched alkyl side chains in pT‐2 induce a more planar backbone conformation than the linear analogs in pT‐1 , yielding a more extended π‐system and higher electron density favorable for doping. Subsequent treatment with polyoxometalates (POMs) drives efficient electron transfer, significantly boosting doping density and conductivity. The optimized pT‐2:POM film achieves a high work function of 4.96 eV and an excellent conductivity of 8.72 × 10 −3 S/m. OSCs employing pT‐2:POM as the AIL deliver a champion power conversion efficiency of 18.42%, surpassing to the PEDOT:PSS reference. Moreover, the high conductivity grants exceptional thickness tolerance, with PCE remaining above 15% even at a 40 nm thickness.