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In the development of high‐performance organic solar cells (OSCs), the self‐organization of organic semiconductors plays a crucial role. This study focuses on the precisely manipulation of molecular assemble via tuning alkyl side‐chain topology in a series of low‐cost nonfused‐ring electron acceptors (NFREAs). Among the three NFREAs investigated, DPA‐4, which possesses an asymmetric alkyl side‐chain length, exhibits a tight packing in the crystal and high crystallinity in the film, contributing to improved electron mobility and favorable film morphology for DPA‐4. As a result, the OSC device based on DPA‐4 achieves an excellent power conversion efficiency of 16.67 %, ranking among the highest efficiencies for NFREA‐based OSCs. [ABSTRACT FROM AUTHOR]

The central core in A‐DA1D‐A‐type small‐molecule acceptor (SMAs) plays an important role in determining the efficiency of organic solar cells (OSCs), while the principles governing the efficient design of SMAs remain elusive. Herein, we developed a series of SMAs with pyrido[2,3‐b]quinoxaline (PyQx) as new electron‐deficient unit by combining with the cascade‐chlorination strategy, namely Py1, Py2, Py3, Py4 and Py5. The introduction of chlorine atoms reduces the intramolecular charge transfer effects but elevates the LUMO values. Density functional theory (DFT) reveals that Py2 with ortho chlorine substituted PyQx and Py5 with two chlorine atoms yield larger dipole moments and smaller π⋅⋅⋅π stacking distances, as compared with the other three acceptors. Moreover, Py2 shows the strongest light absorption capability induced by extended orbit overlap lengths and more efficient packing structures in the dimers. These features endow the best device performance of Py2 due to the better molecular packing and aggregation behaviors, more suitable domain sizes with better exciton dissociation and charge recombination. This study highlights the significance of incorporating large dipole moments, small π⋅⋅⋅π stacking distances and extended orbit overlap lengths in dimers into the development of high‐performance SMAs, providing insight into the design of efficient A‐DA1D‐A‐type SMAs for OSCs. [ABSTRACT FROM AUTHOR]

Moving one subunit of the central core to the other side in a small‐molecule acceptor (SMA) is an effective approach to achieve the goal of isomerization, which has proven viable to enhance photovoltaic performance. Herein, two isomeric SMAs of ThPy5 and ThPy6 are developed by changing the position of the thiophene unit of the dithieno[3,2‐b:2′,3′‐d]pyrrol in IDTP‐4F. The effect of altering the thiophene position on morphological characteristics, macroscopic factors, and device performance is thoroughly investigated among these three isomeric SMAs. Compared to ThPy5, IDTP‐4F and ThPy6 show planar molecular structures and better molecular orientation. Moreover, tighter π–π stacking as well as enhanced electron mobility is observed in ThPy6 relative to IDTP‐4F. PM6:ThPy6‐based organic solar cells (OSCs) achieve the maximum efficiency of 16.11%, along with an excellent fill factor (FF) of 0.789, which are among the best results for A‐D‐A‐type SMA‐based OSCs. The high FF ascribes to the improved molecular packing and charge collection/extraction efficacy and the reduced charge recombination. The structure–morphology–performance relationship drawn from this work can offer better guidance for designing the molecular structure, especially the central cores of SMAs. [ABSTRACT FROM AUTHOR]