Theoretical study of charge transport properties of curved PAH organic semiconductors

Abstract

Curved polycyclic aromatic hydrocarbons (PAHs) exhibit distinctive geometric and electronic structures, rendering them highly promising for addressing solubility and air stability challenges encountered by large linear π-conjugated organic semiconductors. In this study, a series of surface-curved PAHs and heteroatom-doped derivatives are selected and designed, and the relationship between their electronic structures and charge transport properties is investigated using density functional theory. The effects of sulfur/oxygen (S/O), nitrogen (N) and boron (B) doping on charge transport performance are further explored. The results indicate that curved PAHs exhibit enhanced solubility and stability, with molecular curvature significantly influencing charge transport properties. PAHs of series A with deeper bowl depths (d > 1.0 Å) and their N/B dopants tend to form quasi-one-dimensional, slightly sliding, compact π-stack structures with concave-to-convex configurations, exhibiting superior hole transport properties compared to those with shallower bowl-like structures (0.5 Å < d < 1.0 Å) and loose stacking motifs (B2, B4, B6). S/O doping between benzene rings to form seven-membered rings can significantly reduce the bowl shaped depth (d < 1.0 Å) but increases reorganization energy, promoting 2D π–π stacking. However, the N/B atom at the edges or core of the PAHs can fine-tune the bowl shaped depth, and suppress the increase in hole reorganization energy caused by S/O doping, maintaining the hole reorganization energy of heteroatom-doped PAHs (ca. 200 meV), which is essential for high mobility materials. Introducing S/O/N atoms can increase the bandgap and enhance the optical stability of PAHs. In summary, simultaneous incorporation of sulfur (inhibiting intermolecular rotational motion) and boron (enhancing intermolecular overlap and transfer integrals) in derivative B5 leads to a substantial hole mobility enhancement (3.49 cm² V⁻¹ s⁻¹). These findings demonstrate that strategic heteroatom doping and curvature control synergistically optimize the charge transport functionality of curved PAH semiconductors.