Organic photovoltaic (OPV) devices are attracting significant attention due to their potential to be lightweight, flexible, non-toxic, and compatible with large-scale manufacturing. In particular, the development of the new small molecule-based non-fullerene acceptors (NFAs) has enabled OPVs to show remarkable improvements in device efficiency. Although promising, there is still a lack of clear understanding of the impact of molecular structure and orientation of NFAs on photophysical processes critical for device performance. 

In this talk, I will discuss the two key NFA molecular perspectives for high performance OPVs.  First, I will show the molecular-structure dependent photostability, with a particular focus on NFA molecular planarity, rigidity, and end groups [1-3]. Second, I will show the molecular orientation-dependent energetic shifts in NFAs, demonstrating the impact of NFA quadruple moments and molecular orientation on material energetics and thereby on the OPV efficiency [4]. Compared to sublimed small molecules where the molecular orientation control is relatively easy [5], there has been no report, to the best of our knowledge, demonstrating the orientation control of solution-processed NFA molecules leading to an energetic shift large enough to impact exciton separation for free charge generation. As such, it is now critical to understand the molecular origins of OPV performance in much deeper detail than before to direct synthesis of organic semiconductors in more promising directions.

References

[1] “Strong Intermolecular Interactions Induced by High Quadrupole Moments Enable Excellent Photostability of Non‐Fullerene Acceptors for Organic Photovoltaics”, Luke J. et al., ADVANCED ENERGY MATERIALS, (2022), 2201267. doi:10.1002/aenm.202201267

[2] “A Commercial Benchmark: Light-Soaking Free, Fully Scalable, Large-Area Organic Solar Cells for Low-Light Applications”, Luke J. et al., ADVANCED ENERGY MATERIALS, (2021), 11(9), doi:10.1002/aenm.202003405

[3] “Twist and Degrade-Impact of Molecular Structure on the Photostability of Nonfullerene Acceptors and Their Photovoltaic Blends”, Luke J. et al., ADVANCED ENERGY MATERIALS, (2019), 9(15), doi:10.1002/aenm.201803755

[4] “Molecular orientation-dependent energetic shifts in solution processed non-fullerene acceptors and their impact on organic solar cell performance”, Fu Y. et al., NATURE COMMUNICATIONS (in press)

[5] “Orientation dependent molecular electrostatics drives efficient charge generation in homojunction organic solar cells”, Dong Y. et al., NATURE COMMUNICATIONS, (2020),11(1), doi:10.1038/s41467-020-18439-z