Charge transport in organic molecular semiconductors from first principles: The bandlike hole mobility in a naphthalene crystal

Abstract

Predicting charge transport in organic molecular crystals is notoriously challenging. Carrier mobility calculations in organic semiconductors are dominated by quantum chemistry methods based on charge hopping, which are laborious and only moderately accurate. We compute from first principles the electron-phonon scattering and the phonon-limited hole mobility of naphthalene crystal in the framework of ab initio band theory. Our calculations combine GW electronic bandstructures, ab initio electron-phonon scattering, and the Boltzmann transport equation. The calculated hole mobility is in very good agreement with experiment between 100-300 K, and we can predict its temperature dependence with high accuracy. We show that scattering between intermolecular phonons and holes regulates the mobility, though intramolecular phonons possess the strongest coupling with holes. We revisit the common belief that only rigid molecular motions affect carrier dynamics in organic molecular crystals. Our paper provides a quantitative and rigorous framework to compute charge transport in organic crystals and is a first step toward reconciling band theory and carrier hopping computational methods.

Charge transport in high-mobility conjugated polymers and molecular semiconductors

“…, with λ a dimensionless electron-phonon coupling strength and μ ¼ ea 2 =ℏ I carrying the mobility units. The exponent p was calculated within a model system approach 38 and was found to be material-dependent, ranging in the interval 0.5 < p < 1.2 when only intermolecular fluctuations are considered, whereas a higher exponent p ≈ 2.6 was reported from a fully ab initio calculation in naphthalene 44 . Unlike the TL result, the band mobility within the thermal regime relevant to OSCs, k B T≳ħω 0 /2, is independent of ω 0 .…”

Molecular Semiconductors for Logic Operations: Dead‐End or Bright Future?

“…As pointed out in the Introduction, the charge transport mechanism taking place in organic solids has been a topic of debate for many years, as a result of its complexity . Indeed, a clear description of the charge transport in solids exists in the two extreme limits of very low ( µ ≪ cm 2 V −1 s −1 ) and very high charge carrier mobility values (µ ≫ cm 2 V −1 s −1 ), where transport can be described in terms of incoherent hopping of localized charges between sites and Boltzmann band transport of delocalized Bloch electrons, respectively. As a result of joint academic and industrial research, the last decade has witnessed a drastic improvement of the charge carrier mobility µ , reaching values ranging between 1 and 10 cm 2 V −1 s −1 for state‐of‐the‐art molecular semiconductors, an intermediate range where hopping transport is no longer applicable.…”

Efficientab initiocalculations of electron-defect scattering and defect-limited carrier mobility

“…At room temperature, where e-ph interactions typically dominate, charge transport can be accurately predicted from first principles in several families of materials [26][27][28][29][30]. However, many devices and experiments operate at low temperature, where charge transport is governed by e-d interactions.…”