The role of acoustic phonon scattering in charge transport in organic semiconductors: a first-principles deformation-potential study

The electron-acoustic phonon scattering for charge transport in organic semiconductors has been studied by first-principles density functional theory and the Boltzmann transport equation with relaxation time approximation. Within the framework of deformation-potential theory, the electron-longitudinal acoustic phonon scattering probability and the corresponding relaxation time have been obtained for oligoacene single crystals (naphthalene, anthracene, tetracene and pentacene). Previously, the electron-optic phonon scattering mechanism has been investigated through Holstein-Peierls model coupled with DFT calculations for naphthalene. Numerical results indicate that the acoustic phonon scattering intensity is about 3 times as large as that for the optic phonon and the obtained mobility is in much better agreement with the result of the experiment done for ultrapure single crystals. It is thus concluded that for closely packed molecular crystal where the electron is partly delocalized, acoustic phonon scattering mechanism prevails in the charge transport. Moreover, it is found that the intrinsic electron mobility is even larger than hole mobility. A frontier orbital overlap analysis can well rationalize such behavior.