Selenium‐Based Nonfused Electron Acceptors for Efficient Organic Photovoltaic Cells

Selenium heterocycles are widely used in constructing organic semiconductors due to their advantages in narrowing the bandgap and enhancing the intermolecular packing. Herein, the application of Se substitution in designing nonfused electron acceptors (nfEAs) is studied. From a thiophene analog (A4T‐16), three nfEAs with two (ASe‐1 and ASe‐2) or four (ASe‐3) selenophene units are synthesized. The results suggest that the incorporation of Se atoms will downshift the lowest unoccupied molecular orbit level, upshift the highest occupied molecular orbit level, and exhibit redshifted absorption spectra due to the enhanced quinoidal character. The crystallographic data indicate that Se‐containing molecules exhibit more planar conjugate skeleton and thus lead to the improvement of carrier mobility. When blended with a polymer donor PBDB‐TF, ASe‐1‐, ASe‐2‐, and ASe‐3‐based organic photovoltaic (OPV) cells obtain power conversion efficiencies of 12.7%, 11.0%, and 10.4%, respectively. This work provides a comprehensive study of the application of Se substitution in designing low bandgap nfEAs for efficient OPV cells.