Enhancing the performances of all-small-molecule ternary organic solar cells via achieving optimized morphology and 3D charge pathways

With the emergence of non-fullerene acceptors (NFAs), the power conversion efficiencies (PCEs) of all-small-molecule organic solar cells (ASM-OSCs) have been significantly improved. However, due to the strong crystallinities of small molecules, it is much more challenging to obtain the ideal phase separation morphology and efficient charge transport pathways for ASM-OSCs. Here, a high-efficiency ternary ASM-OSC has been successfully constructed based on H11/IDIC-4F system by introduction of IDIC with a similar backbone as IDIC-4F but weak crystallinity. Notably, the addition of IDIC has effectively suppressed large-scale phase aggregation and optimized the morphology of the blend film. More importantly, the molecular orientation has also been significantly adjusted, and a mixed face-on and edge-on orientation has formed, thus establishing a more favorable three-dimensional (3D) charge pathways in the active layer. With these improvements, the enhanced short-circuit current density (J_SC) and fill factor (FF) of the ternary system have been achieved. In addition, because of the high lowest unoccupied molecular orbital (LUMO) energy level of IDIC as well as the alloyed structure of the IDIC and IDIC-4F, the promoted open circuit voltage (V_OC) of the ternary system has also been realized.