B─N Covalent Bond-Based Nonfullerene Electron Acceptors for Efficient Organic Solar Cells.

The optoelectronic properties and photovoltaic performance of nonfullerene electron acceptors (NFEAs) in organic solar cells (OSCs) are greatly influenced by the rational structure regulation of the central core unit. This study introduces a novel type of six-membered fused electron-donating core containing B─N covalent bonds to construct acceptor-donor-acceptor (A-D-A)-type NFEAs. By modulating the branching alkyl chains on the nitrogen atom, two NFEAs, BN910 and BN1014, are synthesized and characterized. Both molecules exhibit strong near-infrared absorption, narrow bandgaps (≈1.45 eV), appropriate energy levels, and tunable molecular packing behaviors, positioning them as promising candidates for efficient NFEAs in OSCs. The investigation reveals that BN1014, with longer and C2-branched alkyl chains, demonstrates superior intermolecular packing and morphology within active layers, leading to enhanced exciton dissociation, improved charge transfer, and reduced charge recombination in OSCs. As a result, a power conversion efficiency (PCE) of 10.02% is achieved for D18:BN1014-based binary OSCs. Notably, BN1014 can be utilized as the third component in the D18:DT-Y6 binary system to fabricate the ternary OSCs, and a PCE of 17.65% is achieved, outperforming 17.05% of D18:DT-Y6-based binary OSCs. These findings highlight the potential of heteroarenes featuring B─N covalent bonds for constructing high-efficiency NFEAs in OSCs.