Density of states in locally ordered amorphous organic semiconductors: Emergence of the exponential tails

We present a simple model of the local order in amorphous organic semiconductors, which naturally produces a spatially correlated exponential density of states (DOS). The dominant contribution to the random energy landscape is provided by electrostatic contributions from dipoles or quadrupoles. An assumption of the preferable parallel orientation of neighbor quadrupoles or antiparallel orientation of dipoles directly leads to the formation of the exponential tails of the DOS even for a moderate size of the ordered domains. The insensitivity of the exponential tail formation to the details of the microstructure of the material suggests that this mechanism is rather common in amorphous organic semiconductors.

Automated summary

A simple model of local order in amorphous organic semiconductors is presented, which naturally results in a spatially correlated exponential density of states. The primary contribution to the random energy landscape comes from electrostatic contributions of dipoles or quadrupoles, with an assumption that the preferred parallel orientation of neighboring quadrupoles or antiparallel orientation of dipoles leads directly to the formation of exponential tails in the DOS, even for moderate size ordered domains. The insensitivity of the exponential tail formation to material microstructure details suggests that this mechanism is common in amorphous organic semiconductors.