Liquid‐Crystalline Small Molecules for Nonfullerene Solar Cells with High Fill Factors and Power Conversion Efficiencies.

Compared with nonfullerene‐based polymer solar cells, all‐small‐molecule solar cells normally show low power conversion efficiencies (PCEs) due to their low fill factors (FFs). Molecular stacking orientation and phase separation are the main factors affecting the performance of all‐small‐molecule solar cells. In this work, two liquid‐crystalline small‐molecule donors are designed and synthesized and a novel nonfullerene acceptor with good crystallinity developed. Owing to the face‐on orientation of the component molecules and appropriate phase separation in the active layer, a high FF of over 70% and a PCE of 10.7% are obtained from the resulting solar cells; these values are among the best obtained thus far for all‐small‐molecule solar cells. The high FF reported here is significant for a further design of high‐performance all‐small‐molecule solar cells. The combination of a liquid‐crystalline small‐molecule donor and a nonfullerene acceptor with good crystallinity provides appropriate phase separation and molecular stacking orientation for all‐small‐molecule solar cells. The fill factors and power conversion efficiencies (PCEs) are obviously improved in the proposed systems, and the maximum PCE reaches 10.7%. The results are significant for the construction and development of all‐small‐molecule solar cells. [ABSTRACT FROM AUTHOR]