Temperature-Dependent Structural Phase Transition in Rubrene Single Crystals: The Missing Piece from the Charge Mobility Puzzle?
Arie van der Lee, Maurizio Polentarutti, Gilles H. Roche, Olivier J. Dautel, Guillaume Wantz, Frédéric Castet, Luca Muccioli
Abstract
Accurate structural models for rubrene, the benchmark organic semiconductor, derived from synchrotron X-ray data in the temperature range of 100–300 K, show that its cofacially stacked tetracene backbone units remain blocked with respect to each other upon cooling to 200 K and start to slip below that temperature. The release of the blocked slippage occurs at approximately the same temperature as the hole mobility crossover. The blocking between 200 and 300 K is caused by a negative correlation between the relatively small thermal expansion along the crystallographic b-axis and the relatively large widening of the angle between herringbone-stacked tetracene units. DFT calculations reveal that this blocked slippage is accompanied by a discontinuity in the variation with temperature of the electronic couplings associated with hole transport between cofacially stacked tetracene backbones.