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Modeling Polaron Diffusion in Oligoacene-like Crystals

Pereira, Marcelo Lopes, de Sousa, Rafael Timóteo, e Silva, Geraldo Magela, Ribeiro, Luiz Antonio
Journal of physical chemistry 2019 v.123 no.8 pp. 4715-4720
activation energy, ambient temperature, crystals, diffusivity, models, physical chemistry, semiconductors
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.