Manipulating Side‐Chains to Obtain Compatible Donor‐Acceptor Miscibility for Low Energy Losses and High‐Performance All‐Polymer Solar Cells

Abstract Although all‐polymer solar cells (All‐PSCs) have attached increasing attention for their remarkable stability advantages, their photovoltaic performance significantly lags behind organic solar cells based on small molecule acceptors. This is primarily due to their limited entropy increase in the active layer and poor compatibility between polymer donors and acceptors, leading to excessive phase separation. To address this limitation, two novel copolymer donors, PBDTF‐ttTPD and PBDTSi‐ttTPD, are designed and synthesized, which are explored by polymerizing fluorine‐modified benzodithiophene (BDT) and alkylsilyl‐functionalized BDT units with thieno[3,4‐c]pyrrole‐4,6(5H)‐dione (TPD) unit, respectively. Both the two TPD‐copolymers demonstrate comparable energy levels and optical absorption properties, while the incorporating of alkylsilyl groups in PBDTSi‐ttTPD improves solubility, lowers electrostatic potential (ESP), and facilitates optimal molecular stacking. Consequently, the blend film of PBDTSi‐ttTPD:PY‐IT achieves an optimal interpenetrating network, reducing phase separation and significantly improving miscibility compared to PBDTF‐ttTPD:PY‐IT blends. This morphological evolution significantly boosts device performance, including extended carrier lifetime, improved charge transport, and minimized energy disorder. Ultimately, these advancements resulted in a substantial increase in power conversion efficiency, from 13.93% to 18.03%. Furthermore, the relationship between polymer donors/acceptors miscibility and energy loss are deeply explored, providing insights for future optimizations.