Simulating the growth of amorphous organic thin films

Physical vapor deposition is used widely to produce organic electronics devices, in particular for OLEDs in smartphones, TVs and other display applications. Despite its long history, recent years have seen a number of surprising observations, such as deposition-induced emitter orientation and built-in electrostatic potentials in thin organic films. Modeling the details of these effects is complicated by the long time scales involved in the underlying processes. In this paper, we compare two different modeling approaches, which both aim to simulate the physical vapor deposition (PVD) process for small organic molecules. We compare a molecular dynamics approach, based on a classical bead-spring force field and time integration, with a Metropolis Monte Carlo approach, where the intramolecular degrees are limited to the torsional rotations. To analyze the resulting structures, we calculate the density and radial distribution functions (RDF) of all films. We observe a good agreement for the RDFs, but an approximately 10% higher density for the films generated by the molecular dynamics approach. Additionally, we investigate the anisotropic nature of such morphologies by calculating the ordinary and extra-ordinary refractive index for each material. Finally, we calculate electron and hole mobilities with an Kinetic Monte Carlo protocol.