Figure 49. a) Chemical structures of INIC Series. GIWAXS intensity profiles along the b) IP and c) OOP directions. Reproduced with permission. [151]

Herein, an emerging acceptor L8-BO as the third component was combined with the B1:BO-4Cl system for constructing efficient ternary all-small-molecule organic solar cells (ASM-OSCs). Theoretical, morphological, and crystallographic studies reveal that L8-BO and BO-4Cl possess good compatibility, resulting in alloy-like state formation of two acceptors in ternary blends. The synergistic effect of two acceptors is conducive to forming favorable phase separation and molecular stacking for promoting charge splitting and extraction, which contributes to simultaneously boosting short-circuit current density and fill factor. Furthermore, the alloy-like state of two acceptors and the higher lowest unoccupied molecular orbital energy level of L8-BO assist ternary ASM-OSCs in achieving lower voltage loss with respect to the binary devices. The optimal ternary ASM-OSCs with 20 wt % L8-BO deliver a top-level efficiency of 17.10%. This work demonstrates that not only the morphology but also the voltage loss of the small molecular matrix can be well-manipulated by employing the ternary strategy.

Integrating desirable light absorption, energy levels, and morphology in one matrix is always the aspiration to construct high‐performance organic solar cells (OSCs). Herein, an asymmetric acceptor Y6‐1O is incorporated into the binary blends of acceptor Y7‐BO and donor PM6 to prepare ternary OSCs. Two isogenous asymmetric–symmetric acceptors with similar chemical skeletons tend to form alloy‐like state in blends due to their good compatibility, which contributes to optimizing the morphology for efficient charge generation and extraction. The complementary absorption of two acceptors helps to improve the photon harvesting of ternary blends, and the higher lowest unoccupied molecular orbital (LUMO) energy level of Y6‐1O offers the chance to uplift the mixed LUMO energy levels of acceptors. Combining the aforesaid benefits, the ternary OSCs with 10 wt% Y6‐1O produce a top‐ranked power conversion efficiency (PCE) of 18.11% with simultaneously elevated short‐circuit current density, open‐circuit voltage, and fill factor in comparison to Y7‐BO‐based binary devices. Furthermore, the optimized ternary OSCs with ≈300 nm active layers obtain a champion PCE of 16.61%, which is the highest value for thick‐film devices reported so far. This work puts forward an avenue for further boosting the performance of OSCs with two isogenous acceptors but different asymmetric structures.

Herein, by using two fluorinated and chlorinated monomers with similar structures in different molar ratios and dithieno­[3′,2′:3,4;2″,3″:5,6]­benzo­[1,2-c]­[1,2,5]­thiadiazole (DTBT) as the third unit, a family of polymer donors D18, D18–20%Cl, D18–40%Cl, and D18–Cl are synthesized for OSCs. With appropriate chlorinated monomer proportion, the terpolymer D18–20%Cl exhibits proper HOMO energy level and higher packing density compared with that of other control polymers. Moreover, the D18–20%Cl:Y6 blend films have favorable morphology with better face-on crystallization and better charge transport. Consequently, the D18–20%Cl:Y6-based OSCs obtain a top-ranked PCE of 18.28% with overall improved device parameters compared to the controlled D18:Y6 or D18-Cl:Y6-based OSCs (17.50% or 17.02%), which represents the highest PCE for the reported terpolymer-based binary OSCs. Notably, the D18–20%Cl:Y6-based OSCs exhibit over 17% efficiency in a wide molecular weight range. These results demonstrate that the ternary copolymerization of DTBT and two similar moieties is an efficient approach for achieving efficient terpolymer donors with well batch-to-batch reproducibility.