State‐of‐art Y‐series polymer acceptors are typically based on a mono‐thiophene linker, which can cause some twisted molecular conformations and thus limit the performance of all‐polymer solar cells (all‐PSCs). Here, a high‐performance polymer acceptor based on vinylene linkers is reported, which leads to surprising changes in the polymers’ molecular conformations, optoelectronic properties, and enhanced photovoltaic performance. It is found that the polymer acceptors based on thiophene or bithiophene linkers (PY‐T‐γ and PY‐2T‐γ) display significant molecular twisting between end‐groups and linker units, while the vinylene‐based polymer (PY‐V‐γ) exhibits a more coplanar and rigid molecular conformation. As a result, PY‐V‐γ demonstrates a better conjugation and tighter interchain stacking, which results in higher mobility and a reduced energetic disorder. Furthermore, detailed morphology investigations reveal that the PY‐V‐γ‐based blend exhibits high domain purity and thus a better fill factor in its all‐PSCs. With these, a higher efficiency of 17.1% is achieved in PY‐V‐γ‐based all‐PSCs, which is the highest efficiency reported for binary all‐PSCs to date. This work demonstrates that the vinylene‐linker is a superior unit to build polymer acceptors with more coplanar and rigid chain conformation, which is beneficial for polymer aggregation and efficient all‐PSCs.

All‐polymer solar cells (all‐PSCs) have achieved impressive progress in photovoltaic performance and stabilities recently. However, their power conversion efficiencies (PCEs) still trail that of small‐molecular acceptor‐based organic solar cells (>19%) mainly because of the inferior fill factor (FF). Herein, a combined homo hydrocarbon solvent and sequential deposition (SD) strategy is presented to boost the FF of rigid all‐PSCs to 77.7% and achieve a superior PCE of 17.7% with excellent stability, which is among the highest efficiencies reported for all‐PSCs thus far. Meanwhile, a remarkable PCE of 14.5% is realized for flexible all‐PSCs with outstanding mechanical stability. The blend film morphologies measurements suggest that the SD method enables the formation of an ideal pseudo‐bilayer film with bicontinuous interdigitated structure and ordered polymer packing. The numerical simulation result indicates that the FF enhancement mainly results from the efficient exciton diffusion dynamics, increased carrier mobilities, and more balanced electron/hole mobility ratio induced by the developed SD method. This is also confirmed by the FF loss analysis, which manifests that the reduced series resistance and increased shunt resistance are the main reasons for the reduction of FF loss. This work provides a promising strategy to fabricate highly efficient and stable all‐PSCs to promote their future development and practical manufacturing.

Benefiting from the simple building blocks and facile synthetic processes, IDIC derivatives based on indacenodithiophene (IDT) core and 2-(2,3-dihydro-3-oxo-1H-inden-1-ylidene) propanedinitrile (IC) terminal groups have been widely studied since the early emerging of non-fullerene acceptors (NFAs) in organic solar cells (OSCs). Although the pristine IDIC molecule possesses a low material cost, its photovoltaic performance is unsatisfactory. Thus, this work conducts the modification of IDIC by alternating the terminal groups and the molecular symmetry. Differing from the typical NFAs in which the fluorinated terminal groups can promote photon harvest and charge mobility to optimize the photovoltaic properties, the material ID4F-C8 with the fluorine substitution exhibits inferior performance compared with the IDIC-C8 with the normal IC groups. Such unexpected results are rationalized by the varied molecular packing in the solid state, i.e., IDIC-C8 has a typical three-dimensional (3D) reticular motif and ID4F-C8 possesses a two-dimensional (2D) packing without an obvious π–π stacking. When two different groups with and without fluorine substitution are utilized as the terminals, the asymmetric ID2F-C8 retains both of the merits of the IDIC-C8 and ID4F-C8, exhibiting strong absorption, suitable energy levels, and highly ordered packing. Thus, the OSC device based on ID2F-C8 acquires the highest PCE of 11.67%. This encouraging result suggests the potential of the asymmetric strategy to develop high-performance and low-cost photovoltaic materials.