Impact of the molecular size of the perylenediimide-derived electron transport materials on the efficiency and stability of p-i-n perovskite solar cells

Herein, we report the synthesis and application of a series of perylenediimide (PDI) derivatives with octyldodecyl substituents, including a PDI monomer, formal dimer, and polymer obtained via thiophene block-mediated dimerization and polymerization. Infrared-scattering scanning near-field optical microscopy (IR s-SNOM) characterization demonstrated that, compared to monomeric and dimeric PDIs, the PDI polymer forms significantly more uniform films with reduced defect density, indicating that increasing molecular weight improves the surface coverage of the perovskite layer. Consequently, PSCs incorporating polymeric PDI as the ETL exhibited the best photovoltaic performance, while monomeric PDI-based devices showed the lowest efficiency due to poor film quality. These findings highlight the promising potential of macromolecular PDI-based ETLs for achieving further advancements in perovskite photovoltaics.