High-Performance Organic Solar Cells Containing Pyrido[2,3-b]quinoxaline-Core-Based Small-Molecule Acceptors with Optimized Orbit Overlap Lengths and Molecular Packing

The central core in A-DA1D-A-type smallmolecule 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 cascadechlorination 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 pi center dot center dot center dot pi 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 pi center dot center dot center dot pi stacking distances and extended orbit overlap lengths in dimers into the development of high-performance SMAs, providing insight into the design of efficient A-DA1DA-type SMAs for OSCs.

Automated summary

This study investigates the design principles of small molecule acceptors (SMAs) for organic solar cells (OSCs) and reveals that the introduction of chlorine atoms can reduce intramolecular charge transfer effects while increasing LUMO values. Among the studied SMAs, Py5 with two chlorine atoms and Py2 with ortho chlorine substitution exhibit the best performance due to their larger dipole moments and smaller pi center dot center dot center dot pi stacking distances, which enable more efficient packing and aggregation behavior.