Multi‐Selenophene‐Containing Narrow Bandgap Polymer Acceptors for All‐Polymer Solar Cells with over 15 % Efficiency and High Reproducibility

Abstract All‐polymer solar cells (all‐PSCs) progressed tremendously due to recent advances in polymerized small molecule acceptors (PSMAs), and their power conversion efficiencies (PCEs) have exceeded 15 %. However, the practical applications of all‐PSCs are still restricted by a lack of PSMAs with a broad absorption, high electron mobility, low energy loss, and good batch‐to‐batch reproducibility. A multi‐selenophene‐containing PSMA, PFY‐3Se, was developed based on a selenophene‐fused SMA framework and a selenophene π‐spacer. Compared to its thiophene analogue PFY‐0Se, PFY‐3Se shows a ≈30 nm red‐shifted absorption, increased electron mobility, and improved intermolecular interaction. In all‐PSCs, PFY‐3Se achieved an impressive PCE of 15.1 % with both high short‐circuit current density of 23.6 mA cm −2 and high fill factor of 0.737, and a low energy loss, which are among the best values in all‐PSCs reported to date and much better than PFY‐0Se (PCE=13.0 %). Notably, PFY‐3Se maintains similarly good batch‐to‐batch properties for realizing reproducible device performance, which is the first reported and also very rare for the PSMAs. Moreover, the PFY‐3Se‐based all‐PSCs show low dependence of PCE on device area (0.045–1.0 cm 2 ) and active layer thickness (110–250 nm), indicating the great potential toward practical applications.