Central unit hetero-di-halogenation of acceptors enables organic solar cells with 19% efficiency.

ABSTRACT

Although peripheral hetero-di-halogenation of non-fullerene acceptors (NFAs) would allow more precise optimization of molecular properties by providing the complementary advantages of two different halogens, thus enabling further improvements of organic solar cells (OSCs), hetero-di-halogenated NFAs are seldom prepared due to the challenging construction of building blocks with two adjacent hetero-halogens. Herein, three CH-series acceptors with hetero-di-halogenated central units, named CH-FC, CH-FB and CH-CB, are constructed successfully. PM6D18CH-FB-based OSCs afforded an attractive PCE of 19.0% due to tighter intermolecular packing at both the single-crystal and blended-film levels, more efficient charge transfer/dissociation, and superior film morphology compared to those of PM6D18CH-FC (PCE 18.41%) and PM6D18CH-CB (PCE 18.21%). Our work highlights the effectiveness of such a CH-series molecular platform in conducting hetero-di-halogenation and achieving high-performance OSCs, and will stimulate further exploration of hetero-substitution-based acceptors.