A Pyrrole-Fused Asymmetrical Electron Acceptor for Polymer Solar Cells with Approaching 16% Efficiency

Selecting suitable aromatic rings to develop asymmetric small-molecule acceptors (SMAs) is of great significance. Herein, two asymmetric SMAs, namely, BTN-4F and BTSe-4F, are successfully synthesized by incorporating pyrrole and selenophene unit into the cores, respectively. Compared with the selenophenefused counterpart BTSe-4F, BTN-4F displays slightly upshifted energy levels and red-shifted absorption spectrum (about 40 nm in film) due to the strong electron-donating ability of N atoms in pyrrole. When matching with PM6, the BTN-4F-based device gives a higher power conversion efficiency (PCE) (15.82%) due to the simultaneously enhanced open circuit voltage (V-OC), short-circuit current density (J(SC)), and fill factor (FF), compared with those of the BTSe-4F-based device. The higher V-OC coincides with the shallower lowest unoccupied molecular orbital (LUMO) energy level of BTN-4F; the enhanced J(SC) mainly results from the broadened and enhanced absorption; the increased FF can be ascribed to the weaker bimolecular recombination, more balance charge transport, and more favorable morphology. It should be mentioned that the BTN-4F-based device yields a lower energy loss than that of the BTSe-4F-based device. Overall, the work demonstrates that pyrrole-fused SMAs shows great potential in realizing low E-loss while yielding high J(SC) and PCE, which paves a new way to develop high-performance SMAs.

Automated summary

The study synthesized two asymmetric SMAs, BTN-4F and BTSe-4F, with BTN-4F demonstrating higher power conversion efficiency and lower energy loss due to weaker bimolecular recombination, more balanced charge transport, and more favorable morphology.