Understanding Molecular Nature of Organic Semiconductors – Fundamentals and Applications

Prof Ji-Seon Kim^1,2

¹Department of Physics & Centre for Processable Electronics, Imperial College London, UK

²Department of Chemistry, University of Oxford, UK

(Email: ji-seon.kim@imperial.ac.uk, ji-seon.kim@chem.ox.ac.uk)

Organic semiconductors combine the semiconductor properties traditionally associated with inorganic materials with the more desirable properties of soft plastics. Moreover, the organic syntheses of these materials allow for great flexibility in the tuning of their electronic and optical properties. In particular, the development of small molecule-based non-fullerene acceptors has enabled organic photoconversion devices such as photovoltaics and photodetectors to show remarkable improvements in device efficiency. Although promising, there is still a lack of fundamental understanding of the impact of molecular structure and orientation on photophysical processes critical for device performance.  

In this talk, I will discuss the molecular perspectives of organic semiconductors for high performance photoconversion devices. First, I will show the molecular-structure dependent photostability, with a particular focus on molecular planarity, rigidity, and end groups [1, 2]. Second, I will show the molecular orientation-dependent energy level shifts, demonstrating the impact of molecular quadruple moments on thin film energetics and thereby on free charge generation [3-5]. Finally, I will discuss how the minor modification of sidechains affects the structural relaxation dynamics via strong electron-phonon coupling and hence the excited states formation upon photoexcitation [6]. These results provide key fundamental understanding of molecular semiconductors critical for future electronic applications.

References

[1] Luke et al., (2023) “Key molecular perspectives for high stability in organic photovoltaics”, NATURE REVIEWS MATERIALS, doi:10.1038/s41578-023-00606-5

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

[3] Fu et al., (2023) “Molecular orientation-dependent energetic shifts in solution processed non-fullerene acceptors and their impact on organic solar cell performance”, NATURE COMMUNICATIONS, 14, 1870, doi:10.1038/s41467-023-37234-0

[4] Park et al., (2023) “The State-of-the-Art Solution-Processed Single Component Organic Photodetectors Achieved by Strong Quenching of Intermolecular Emissive State and High Quadrupole Moment in Non-Fullerene Acceptors”, ADVANCED MATERIALS, doi:10.1002/adma.202306655

[5] Rana et al, (2024) “Octupole Moment Driven Free Charge Generation in Partially Chlorinated Subphthalocyanine for Planar Heterojunction Organic Photodetectors”, NATURE COMMUNICATIONS, 15(1), 5058. doi:10.1038/s41467-024-49169-1

[6] Pagano et al., (2024) “Slow vibrational relaxation drives ultrafast formation of photoexcited polaron pair states in glycolated conjugated polymers”. NATURE COMMUNICATIONS, 15(1), 6153. doi:10.1038/s41467-024-50530-7