Freezing-in orientational disorder induces crossover from thermally-activated to temperature-independent transport in organic semiconductors.

K P Goetz, A Fonari, D Vermeulen, P Hu, H Jiang, P J Diemer, J W Ward, M E Payne, C S Day, C Kloc, V Coropceanu, L E McNeil, O D Jurchescu

Index: Nat. Commun. 5 , 5642, (2014)

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Abstract

The crystalline structure of organic materials dictates their physical properties, but while significant research effort is geared towards understanding structure-property relationships in such materials, the details remain unclear. Many organic crystals exhibit transitions in their electrical properties as a function of temperature. One example is the 1:1 charge-transfer complex trans--stilbene-2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane. Here we show that the mobility and resistivity of this material undergo a transition from being thermally activated at temperatures above 235 K to being temperature independent at low temperatures. On the basis of our experimental and theoretical results, we attribute this behaviour to the presence of a glass-like transition and the accompanied freezing-in of orientational disorder of the stilbene molecule.