Modeling Polaron Diffusion in Oligoacene-like Crystals

• Published in: Journal of physical chemistry. C 2019-02, Vol.123 (8), p.4715-4720
• Main Authors: Pereira, Marcelo Lopes, de Sousa, Rafael Timóteo, e Silva, Geraldo Magela, Ribeiro, Luiz Antonio
• Format: Article
• Language: English
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/acs.jpcc.8b11459

Due to the polaronic self-localization of carriers at one or few molecules in organic crystalline semiconductors, the net mobility of a polaron is suppressed and it becomes thermally activated. As a consequence, incoherent hopping of small or large polarons governs the charge transport mechanism, which incorporates crucial contributions of the carriers’ diffusion. Here, we develop a model Hamiltonian to theoretically investigate the polaron diffusion as well as its underlying properties in highly ordered two-dimensional arrays of molecules. Our findings show that the polaron diffuses in a typical random-walk motion. Within this transport picture, a critical limit is established for the room temperature diffusivity and activation energy, being the later considerably small. This critical limit for the polaron diffusivity is based on a systematic study of the role of temperature and dimensionality on charge transport with a specific choice of parameters. Moreover, such a low barrier for the activation energy is a straightforward consequence of adopting pristine lattices. We also discuss the polaron stability and mobility as a function of different regimes of the thermal bath. Importantly, these results may provide options to derive the Seebeck coefficient in organic crystalline semiconductors.