Evaluations of nonlocal electron-phonon couplings in tetracene, rubrene, and C10−DNBDT−NW based on density functional theory

Abstract

In organic molecular semiconductors (OSCs), fluctuation of transfer integrals originating from thermally induced molecular vibrations is suggested to cause large scatterings of carriers, and to be a most important factor for the suppression of their carrier mobility. The intrinsic carrier mobility under such a fluctuation of transfer integrals is calculated using the transient localization theory, in which the estimation of transfer-integral fluctuation depending on each OSC is indispensable. In the present study, we provide a methodology to evaluate nonlocal electron-phonon couplings in OSCs using the density functional theory, which enables us to evaluate precisely the fluctuation magnitude of transfer integrals. Our method is based upon the combination of the frequency correction to reduce numerical inaccuracies in normal-mode frequencies, the extraction of tight binding parameters using maximally localized Wannier functions, and the explicit consideration of anharmonicity of phonons. We apply this method to classical OSCs, tetracene and rubrene, and a recently developed high-mobility OSC, $3,11\text{\ensuremath{-}}\text{didecyl-dinaphtho}[2,3\text{\ensuremath{-}}d:2\ensuremath{'},3\ensuremath{'}\text{\ensuremath{-}}d\ensuremath{'}]\mathrm{benzo}[1,2\text{\ensuremath{-}}b:4,5\text{\ensuremath{-}}b\ensuremath{'}]\mathrm{dithiophene}$ $({\mathrm{C}}_{10}\text{\ensuremath{-}}\mathrm{DNBDT}\text{\ensuremath{-}}\mathrm{NW})$. We succeeded in identifying the low-frequency vibrations dominating the fluctuation of transfer integrals at room temperature, which we consider to be the main factors to limit the intrinsic mobility.