Organic semiconductors (OSCs) have been 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 weaker intermolecular bonding and consequently weaker electron delocalization between molecules, which limits 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, methods including employing the use of tunable interfaces and matching over and underlayer unit cells can help in this effort. Therefore, understanding and controlling the structure-property relationships of OSCs through layered fabrication 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), Raman, UV-Vis, and photoluminescence spectroscopy, it was determined that the d-spacing between the π-π stacking plane of the C7-PDI molecules decreases due to the 2D perovskite interface. Moreover, the influence of the underlayer, perovskite, terminating ligand on the structure of the C7-PDI overlayer is examined. Discrete bandgap transition energies and relative differences in steady-state photoluminescence and peak shifting were observed, indicative of variation in intermolecular interactions. Further studies are required to determine the extent of influence the perovskite interface, terminating ligand, has on the resulting structural and optical properties including singlet fission for C7-PDI molecules.
