Why is the electron mobility of organic semiconductors lower than the hole mobility?: First observation of the conduction band structure of organic semiconductors and establishment of the partially-dressed polaron model

Abstract

In organic semiconductors, electron mobilities are generally lower than hole mobilities. It has not been apparent whether this is due to extrinsic factors, such as the electron trap formed by the atmosphere, or whether the electron mobility is inherently low. We developed angle-resolved low-energy inverse photoelectron spectroscopy and succeeded in measuring the energy band structure (the energy–momentum relation) of the conduction band of organic semiconductor for the first time. Through a detailed analysis of the bandwidth, we clarified that the polaron is formed and proposed a new model called a partially dressed polaron model. We incorporate this model into the wave-packet diffusion method to calculate the electron/hole mobilities and proved that the electron mobility is inherently lower than the hole mobility owing to the electron–phonon interaction.