Highly Efficient Nonfullerene Organic Solar Cells: Morphology Control and Characterizations

Nonfullerene acceptors (NFAs) are currently a major research focus in the development of organic solar cells (OSCs) because of their readily tunable optical and electronic properties, enabling bulk heterojunction (BHJ) NFA‐based OSCs to achieve photovoltaic efficiencies exceeding 19%. Significant efforts have been made to yield the optimal nanoscale morphology, enabling the achievement of highly efficient NFA‐based OSCs. This review discusses the structural characteristics of NFAs and their relationship with morphology. Subsequently, the correlation between the morphology and photovoltaic parameters is introduced, which provides a fundamental basis for morphology modulation. This review then points out the major challenges of morphological characterization of NFA‐based blend films while using some conventional real‐space techniques due to low phase contrast and summarizes recently emerging characterization techniques capable of characterizing high‐contrast phase morphologies at multiple length scales. Finally, strategies for targeted morphological optimization through materials design, processing solvents, posttreatment, and ternary strategies are presented, although it is challenging to obtain an ideal morphology (e.g., appropriate phase separation and ideal donor/acceptor molecular interactions) due to the anisotropic structural characteristics of NFAs in the as‐cast films. This review is expected to provide guidance to continuously advancing the success of NFA‐based OSCs from the morphology perspective in the future.