Balancing charge generation and voltage loss toward efficient nonfullerene organic solar cells

The inherently large exciton binding energy for photo-generated electron-hole pairs has hindered the charge generation and photons utilization in organic solar cells (OSCs) for decades, thereby constraining their performance to an inferior regime with relatively low current density and high voltage loss. Recently emerging OSCs based on nonfullerene electron acceptors have proven their potential to relieve this constraint, delivering high charge carriers yield and cell voltage at the same time. In this short review, we briefly summarize the current understandings of charge generation and voltage loss of nonfullerene OSCs. Recent advances in minimizing voltage loss and manipulating energy offset for charge separation are highlighted. To obtain a better compromise between efficient charge separation and low voltage loss that allow for further improvements in nonfullerene OSCs, we propose some basic design strategies for nonfullerene acceptors. (c) 2019 The Author(s). Published by Elsevier Ltd.