Bulk electrical properties of rubrene single crystals: Measurements and analysis
Abstract
Rubrene single crystals with well-developed 100 faces extending along the 010 direction were equipped with two planar gold electrodes deposited under low thermal load on the same crystal surface. The currentvoltage curves measured on crystals with various thicknesses were analyzed by means of the space-chargelimited current model. In all cases, the curves present a clear trap-filled transition that allows extracting the trap-free mobility along the b axis. Working in a gap-type geometry and by comparing the mobility calculated from the Geurst two-dimensional and Mott-Gurney three-dimensional models, a clear 2D to 3D transition is established for a thickness that roughly corresponds to half the distance between the two electrodes. Further quantitative analysis of the data with a differential method leads to the conclusion that charge-transport properties at room temperature are affected by a discrete trap level pointing at 0.48 0.02 eV above the valence band.