Rational Design of Two Well‐Compatible Dimeric Acceptors Through Regulating Chalcogen‐Substituted Conjugated Backbone Enable Ternary Organic Solar Cells with 19.4% Efficiency

To enhance the performance of dimeric acceptors (DMAs) based organic solar cells (OSCs), two new DMAs, designated as DC9‐HD and DYSe‐3, are rationally developed and employed to fabricate ternary OSCs. The substitution of the sulfur atom on the outer ring of the fused‐ring core of DC9‐HD with a selenium atom resultes in the red‐shifted DYSe‐3. Despite these minor differences, DC9‐HD and DYSe‐3 possess nearly identical conjugated skeletons, which contribute to their similar packing motifs and crystallinities, ultimately enabling a high degree of miscibility between two DMAs. Upon incorporating DYSe‐3 into the host PM6:DC9‐HD binary blend, fibril‐like morphologies featured with diameters of ≈16.9 nm and reduced charge recombination are observed in the PM6:DC9‐HD:DYSe‐3 ternary blend. More importantly, owing to their long exciton diffusion lengths and low voltage losses, a remarkable power conversion efficiency of 19.4% is achieved for the ternary OSCs, alongside a delicate balance between open‐circuit voltage and short‐circuit current density. This super result is comparable to the best performance of oligomer acceptor based OSCs reported to date. Furthermore, the proposed ternary strategy, which combines one polymer donor and two well‐compatible DMAs, not only retains the advantages of DMAs but also offers a streamlined approach for fabricating high‐performance ternary OSCs.