Effects of pressure and temperature on the carrier transports in organic crystal: A first-principles study

Abstract

By employing density-functional theory coupled with Holstein-Peierls model, we investigate the pressure and temperature dependence of the hole and electron mobilities in naphthalene single crystal from atmospheric pressure up to 2.1 GPa (at room temperature) and from 5 to 296 K (at ambient pressure). It is found that the pressure reduces the electron-phonon coupling strength and enhances the mobilities. Importantly, we point out that only when temperature-dependent structure modifications are taken into account can one better describe the temperature-dependent transport behavior. Especially, the band to hopping crossover transition temperature for the electron transport in the c'-axis is calculated to be around 153 K, which is close to the experimental result of between 100 and 150 K. If this temperature-dependent structure modifications were neglected, the transition temperature would be only about 23 K, as previously obtained [L. J. Wang et al., J. Chem. Phys. 127, 044506 (2007)].

Polaron Mechanism

“…From hole transport, we can find that better agreement with experimental temperature dependence is achieved even within high temperature range. For electron transport, the band-hopping crossover temperature is calculated as 153 K [20], which is close to the experimental result of between 100 and 150 K [10]. Therefore we point out that the thermal expansion of lattice for organic molecular systems, which is generally neglected in theoretical studies for charge transport studies, can be very important to get the correct temperature dependence of mobility.…”

“…3.14, both the interlayer and intralayer transfer integrals are largely increased under pressure. Generally, the transfer integral is doubled when the pressure is increased from 1 atm to 2.1 GPa [20]. For some of the interlayer pathways, the increase of transfer integral can be even larger due to the weaker interaction between layers and thus high sensitivity of pressure.…”

“…With the increase of temperature, there is significant amount of lattice expansion, therefore the electronic properties and the charge mobility should change accordingly [20]. Here we numerically investigate how much the temperature dependence of mobility can be influenced by natural thermal expansion of lattice.…”

“…To get a smooth temperature dependence of lattice constant, we make appropriate interpolation among the experimental lattice constants for the whole temperature range by using analytic functions (see Fig. 3.10) [20]. It should be noted that due to limited experimental data, such interpolation does not reveal the physical law.…”

Evaluation of Charge Mobility in Organic Materials: From Localized to Delocalized Descriptions at a First‐Principles Level

“…We performed the fi rst numerical study considering all the electron-phonon couplings at the DFT level for naphthalene crystals, [26][27][28] which have been extensively studied by Karl in purifying the samples and carrying out transport measurements over four decades. [ 43 ] The computational workhorse is the Vienna ab initio Simulation Package (VASP), [ 44 ] The Perdew-Burke-Ernzerhof (PBE) exchange-correlation (XC) functional [ 45 ] was chosen because it works better for molecular crystals than other functionals.…”