Polaron stability in molecular semiconductors: theoretical insight into the impact of the temperature, electric field and the system dimensionality.
A semi-empirical Holstein-Peierls model is used to study the temperature effects on the polaron stability in organic semiconductors at a molecular scale. The approach takes into account both intra- and inter-molecular electron-lattice interactions and is aimed at describing charge transport in the system. Particularly, we present a systematic numerical investigation to characterize the influence of both temperature and electric field on the stability as well as mobility of the polaron. It is found that the parameter space for which the polaron is dynamically stable is quite limited and the variations in some of these parameters strongly depend on the temperature. The electric field can play a role in further localizing the charge causing a compression of the lattice distortions associated with the polaron, increasing thereby its stability, up to a field strength of approximately 2.0 mV Å(-1). Considering field strengths higher than this critical value, the polaron is annihilated spreading charge through the lattice. Furthermore, we have studied the polaron mobility as a function of the anisotropy of the system, going from a one-dimensional system via a highly anisotropic two-dimensional system to a uniform two-dimensional system. There is a clearly observed mobility edge for the polaron; it exhibits a high mobility in the one-dimensional system but as the coupling in the second dimension is turned on the polaron slows down and becomes immobile in the uniform system. The results provided by this transport mechanism are in good agreement with experimental observations and may provide guidance to improve the charge transport in organic optoelectronic devices.
Department of Physics, Chemistry and Biology (IFM), Linköping University, SE-581 83 Linköping, Sweden. luiju@ifm.liu.se svens@ifm.liu.se.
Luiz Antonio
LA
Ribeiro Junior
Sven
S
Stafström