Suppressing Bimolecular Charge Recombination and Energetic Disorder with Planar Heterojunction Active Layer Enables 18.1% Efficiency Binary Organic Solar Cells

The performance of organic solar cells has been dramaticallyenhanceddue to the use of bulk heterojunction active layer structure. However,blending donor and acceptor in the bulk volume results in a largeextent of bimolecular charge recombination and increasing energeticdisorder. Herein, we fabricated organic solar cells with polymer donorPM6 and nonfullerene acceptor N3 in bilayer structure to investigatethe impact of planar heterojunction configurations on charge recombinationand energetic landscapes. We find superior crystallinity featuresin the bilayer composed of pure donor and acceptor layers. The bimolecularcharge recombination and energetic disorder are effectively suppressedcompared with the bulk heterojunction counterparts. Thus, a powerconversion efficiency as high as 18.1% (17.8% averaged) is achieved,which stands among the top values of planar heterojunction organicsolar cells. In addition, improved device shelf stability is observedbecause of the fewer donor-acceptor interfaces in the activelayer. Our results suggest that a planar heterojunction structurecould efficiently suppress the bimolecular charge recombination andenergetic disorder, providing an alternative pathway for developingsolution-processed organic solar cells.

Automated summary

The performance of organic solar cells has been greatly improved by using bulk heterojunction active layer structure. However, this structure also leads to higher charge recombination and energetic disorder. In this study, we successfully fabricated organic solar cells with a bilayer structure and achieved a high power conversion efficiency of 18.1%. The superior crystallinity features and suppressed charge recombination and energetic disorder in the bilayer structure contribute to the improved performance.