Exponential-type density of states with clearly cutting tail for organic semiconductors

Abstract

It was recently demonstrated that the density of states (DOS) is the key factor to determine charge transport, photoelectric and contact properties in disordered organic semiconductors. However, the density of states in organic semiconductors is unclear at present. Although the Gaussian DOS is the most popular, some works support the exponential DOS or combination of both forms. In this paper, we propose three exponential-type DOS, one has complete exponential tail, and other two cuts tails at some places. The variations of mobility with carrier density are obtained through numerically solving variable range hopping (VRH) equations. It is shown that the relationships of mobility with density and Fermi level are very different among results obtained from Gaussian, un-cutting and cutting exponential-type DOS. The results show that the experimental mobility-density data can be well fitted by using single cutting exponential-type DOS in the wide ranges of density, but cannot be fitted by using single Gaussian and un-cutting exponential-type DOS. Instead of the Gaussian and pure exponential DOS, the DOS with exponential core and clearly cutting tail is recommended.