High-Efficiency Binary Organic Solar Cells Enabled by Pseudo-Bilayer Configuration in Dilute Solution

Forming proper film morphology in organic solar cells (OSCs) is important to govern the exciton dissociation and charge transport. Herein, high-performance pseudo-bilayer heterojunction (PBHJ) OSCs with donor:acceptor (D:A) bilayer architecture are reported by sequentially depositing two layers of diluted active solution with different D:A ratios. Such pseudo-bilayer films can not only enable the cascaded components distributed in the vertical direction, but also afford large donor and acceptor (D/A) interfaces for efficient exciton dissociation. Additionally, the D:A active layer on the bottom substrate can act as a seed to promote the crystallization process of the upper film during the sequential casting process. The PBHJ strategy on two representative D:A blends, PM6:Y6 and PTQ10:Y6, is implemented. Benefiting from the synergetic effects of efficient exciton dissociation and balanced charge transport, the devices based on PM6:Y6 and PTQ10:Y6 show high power conversion efficiencies of 17.73% and 17.81%, respectively. Notably, the presented PBHJ devices are fabricated by using dilute chloroform solution (4 mg mL(-1) for donor), demonstrating the excellent potential for poorly soluble donors and acceptors in future OSCs applications.