Impact of energetic disorder and localization on the conductivity and mobility of organic semiconductors

The impact of the energetic disorder and the charge localization on the conductivity, mobility and carrier concentration is investigated both theoretically and experimentally. This study gives three fundamental results: (i) the magnitude of the conductivity is strongly dependent on the spatial charge localization but (ii) the conductivity as a function of temperature and Fermi level is independent on the shape of the Density of States (DOS). On the other hand (iii) the mobility is strongly influenced by the DOS, hence the DOS affect the mobility only indirectly through the charge concentration. We show that many experimental observation and theoretical investigations can be merged in a simple physical framework based on hopping and percolation. The spatial localization and energetic disorder are the key elements to reach an unified picture of the mobility of organic semiconductors.