A molecular dynamics study on the interface morphology of vapor-deposited amorphous organic thin films

• Published in: Physical chemistry chemical physics : PCCP Vol. 21; no. 3; pp. 1484 - 1490
• Main Authors: Yoo, Dongsun, Song, Hochul, Youn, Yong, Jeon, Sang Ho, Cho, Youngmi, Han, Seungwu
• Format: Journal Article
• Language: English
• Published: England Royal Society of Chemistry 2019
• Subjects: Computer simulation; Dynamic structural analysis; Interdiffusion; Mathematical morphology; Molecular dynamics; Molecular structure; Morphology; Organic light emitting diodes; Thickness; Thin films; Vapor deposition; Vapors
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/c8cp05294h

The interfaces between amorphous organic layers play an important role in the efficiency and lifetime of organic light emitting diodes (OLEDs). However, an atomistic understanding of the interface morphology is still poor. In this study, we theoretically investigate the interfacial structure of amorphous organic films using molecular dynamics simulations that mimic vapor-deposition processes. We find that molecularly sharp interfaces are formed by the vapor-deposition process as the interface thickness spans only a mono- or double-layer in terms of lie-down geometry. Interestingly, the interface is more diffusive into the upper layer due to asymmetric interdiffusion during the vapor-deposition process, which is well described by a simple random-walk model. Additionally, we investigate the change in the molecular orientation of interdiffused molecules, which is crucial for device performance.