O, S, and N Bridged Atoms Screening on 2D Conjugated Central Units of High-Performance Acceptors

Almost all of central cores in high-performance acceptors are limited to the electron-withdrawing diimide structure currently, which constrains further acceptor structural innovation greatly. Herein, oxygen (O), sulfur (S), and nitrogen (N) atoms are adopted to bridge the 2D conjugated central cores, yielding three acceptor platforms of CH─O, CH─S, and CH─N that differ in structure by only two atoms. Because of the characteristic atomic outer electron configuration and hybrid orbital orientation, O-, S-, and N-bridged central cores display quite different conformations and electronic properties, namely, dibenzodioxin (planar, non-aromatic), thianthrene (puckered, non-aromatic) and phenazine (planar, aromatic), respectively. A systematic investigation discloses how the central core, especially its p-π orbital overlap between lone pair on O/S/N and coterminous benzene planes, affect the intrinsic photoelectronic properties of acceptors for the first time. Finally, CH─N-based binary device affords the highest fill factor of 83.13% in organic photovoltaics along with a first-class efficiency of 20.23%. By evaluating the strictly controlled O-, S-, and N-bridged molecular platforms comprehensively, the work reveals the potential uniqueness of diimide in determining the excellent photovoltaic outcomes of acceptors.