Impact of regio-isomeric monochlorinated end groups on packing mode, miscibility, and photovoltaic performance of asymmetric selenophene-fused M-series acceptors

Optimal bulk-heterojunction (BHJ) morphology is crucial for efficient charge transport and good photovoltaic performance in organic solar cells (OSCs). Yet, the correlation between chemical structures of nonfullerene acceptors (NFAs) and molecular interaction in the BHJ blends remains opaque. Herein, we study three isomeric NFAs referred to as MQ1-x (x = P, y, or 8) that shared an asymmetric selenophene-fused heteroheptacene backbone end-capped by two monochlorinated end groups. Remarkably, miscibility between the polymer donor of PM6 and MQ1-x successively elevates as the chlorine atoms move from P- , to y - , to 8-position of terminals. Combined with the varied molecular crystallinity of these NFAs, diverse BHJ morphologies are observed in their blend films. As a result, the MQ1- 8-based devices present the highest PCE of 12.08% owing to the efficient charge dissociation and transport induced by the compact molecular packing and optimal BHJ morphology. Our investigation provides a new insight in the material design that has a good balance in molecular packing and film morphology for high-performance OSCs. & COPY; 2023 Published by Elsevier B.V. on behalf of Chinese Chemical Society and Institute of Materia Medica, Chinese Academy of Medical Sciences.

Automated summary

This study investigates the interaction between three different nonfullerene acceptors (NFAs) with varied chemical structures in bulk-heterojunction (BHJ) blends. It is found that the compatibility between the NFAs and the polymer donor increases as the position of the monochlorinated end groups changes, resulting in different BHJ morphologies. Among these morphologies, the MQ1-8 blend exhibits the highest photoconversion efficiency.