On the Conformation of Dimeric Acceptors and Their Polymer Solar Cells with Efficiency over 18.

The determination of molecular conformation of oligomeric acceptors (OAs) and their impact on molecular packing are crucial for understanding the photovoltaic performance of resulting polymer solar cells (PSCs) but have not been well studied yet. Herein, we synthesized two dimeric acceptor materials, DIBP3F-Se and DIBP3F-S, which bridged two segments of Y6-derivatives by selenophene and thiophene, respectively. Theoretical simulation and experimental 1D and 2D NMR spectroscopic studies prove that both dimers exhibit O-shape conformation other than S- or U-shape counter-ones. Notably, this O-shaped conformation is likely governed by a distinctive "conformational lock" mechanism, arising from the intensified intramolecular π-π interaction between the two terminal groups of the dimers. PSCs based on DIBP3F-Se deliver a maximum efficiency of 18.09%, outperforming DIBP3F-S-based cells (16.11%) and ranking among the highest efficiencies for OA-based PSCs. This work demonstrates a facile method to obtain OA conformations and highlights the potential of dimeric acceptors for high-performance PSCs.