Diblock conjugated polyelectrolyte electron transport layer modulating the morphology of the active layer for efficient nonfullerene organic solar cells

To acquire high-performance nonfullerene organic solar cells (OSCs), the effective approach is to explore new interfacial layer that not only can modulate the interfacial contact, but can also tune the morphology of the active layer. A diblock CPE PF_EO-b-PTNBr with polyfluorene and polythiophene backbone, quaternary ammonium salt and ethylene oxy polar side chains, has been used to modify ZnO as ETL for PBDB-T:ITIC OSCs. The influences of the diblock CPE PF_EO-b-PTNBr electron transport layer (ETL) on the morphology and crystalline properties of the PBDB-T:ITIC, exciton diffusion and transfer, and the device performances have been thoroughly investigated. Remarkably, the self-assembled diblock polymer PF_EO-b-PTNBr can really induce the corresponding PBDB-T:ITIC active layer to obtain an ordered nano-fiber morphology. Consequently, in sharp comparison to the OSC utilizing ZnO as ETL, the performances of the device with the ZnO/PF_EO-b-PTNBr ETL have been simultaneously enhanced, exhibiting a remarkably superior power conversion efficiency of 10.8%. These findings manifest that the diblock CPE PF_EO-b-PTNBr is a promising ETL in nonfullerene OSCs.