Dual Polymerized Y‐Acceptors of Distinct‐Dimensionality Create Neuron‐Like Interpenetrating Hierarchical Network towards Efficient and Stable All‐Polymer Solar Cells

Abstract

AbstractAll‐polymer solar cells have garnered particular attention thanks to their superior thermal, photo, and mechanical stabilities for large‐scale manufacturing, yet the performance enhancement remains largely restrained by inherent morphological challenges of the bulk‐heterojunction active layer. Herein, a 3D Y‐branched polymerized small‐molecule acceptor named PYBF, characteristic of high molecular weight and glass transition temperature, is designed and synthesized by precisely linking C3h‐symmetric benzotrifuran with Y6 acceptors. In comparison to the benchmark thiophene‐bridged linear PYIT acceptor, an optical blue‐shift absorption is observed for PYBF yet a slightly higher power conversion efficiency (PCE) of 15.7% (vs 15.14%) is obtained when paired with polymer donor PM6, which benefit from the more crystalline and face‐on‐oriented PYBF domains. However, the star‐like bulky structure of PYBF results in the nucleation‐growth dominant phase‐separation in polymeric blends, which generates stumpy droplet‐like acceptor fibrils and impairs the continuity of acceptor phases. This issue is however surprisingly resolved by incorporating a small amount of PYIT, which leads to the formation of the more interconnective neuron‐like dual‐acceptor domains by long‐chain entanglements of linear acceptors and alleviates bimolecular recombination. Thus, the champion device realizes a respectable PCE of up to ≈17% and importantly exhibits thermal and storage stabilities superior to the linear counterpart.