A High-Efficiency Organic Solar Cell Enabled by the Strong Intramolecular Electron Push–Pull Effect of the Nonfullerene Acceptor

Abstract

Besides broadening of the absorption spectrum, modulating molecular energy levels, and other well-studied properties, a stronger intramolecular electron push–pull effect also affords other advantages in nonfullerene acceptors. A strong push–pull effect improves the dipole moment of the wings in IT-4F over IT-M and results in a lower miscibility than IT-M when blended with PBDB-TF. This feature leads to higher domain purity in the PBDB-TF:IT-4F blend and makes a contribution to the better photovoltaic performance. Moreover, the strong push–pull effect also decreases the vibrational relaxation, which makes IT-4F more promising than IT-M in reducing the energetic loss of organic solar cells. Above all, a power conversion efficiency of 13.7% is recorded in PBDB-TF:IT-4F-based devices.

Two critical factors (miscibility and vibrational relaxation) of nonfullerene molecular acceptors with the intramolecular electron push–pull effect are analyzed and related to their photovoltaic properties in organic solar cells (OSCs). A power conversion efficiency of 13.7% is recorded in OSCs by using a nonfullerene acceptor IT-4F, which shows a stronger intramolecular electron push–pull effect than its nonfluorinated counterpart.

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