(543g) Elucidating Influence of Thermal Annealing and Tunable Interfaces on the Structure-Property Relationships of Small-Molecule Organic Semiconductors

Organic semiconductors (OSCs) have been extensively studied in a variety of fields such as device engineering, and solid-state physics for their optical and electronic properties. Their potential for flexible device fabrication as well as their lightweight, low-temperature, and solution-processable characteristics make them ideal for the next generation of photovoltaics and electronic devices. However, small molecule OSCs are van der Waals bonded implying a weaker intermolecular bonding and consequently a weaker delocalization of electrons between molecules, limiting OSC charge carrier transport capabilities relative to their inorganic counterparts. Moreover, OSCs can pack in a variety of polymorphic structures and molecular packing motifs which has direct implications on the macroscopic properties these materials exhibit. Control over the morphology and molecular packing of OSCs is difficult, therefore, understanding and controlling the structure-property relationships of OSCs is vital for their commercialization.

In this study, physical vapor deposition and dynamic spin coating was used to fabricate C7-perylene diimide (C7-PDI) and 2D perovskite bilayer thin films. Using grazing incidence x-ray diffraction (GIXRD), UV-Vis, and photoluminescence spectroscopy it was determined that the d-spacing between the π-π stacking plane of the C7-PDI molecules had incremental changes, spanning a small range of 0.10 Angstroms due to the 2D perovskite interface. Discrete bandgap transition energies and relative differences in steady-state photoluminescence and peak shifting were observed, indicative of variation in intermolecular interactions. Furthermore, the addition of post-deposition thermal annealing results in increased photoluminescence intensity and promotes further changes in the π-π stacking distance implicating changes in the singlet fission rate for C7-PDI. Further studies are required to determine the extent of influence the perovskite interface and thermal annealing has on the resulting structural and optical properties including singlet fission for C7-PDI molecules.