Modification of the electronic properties of rubrene crystals by water and oxygen-related species

The presence of impurities in organic semiconductors is an important limitation for the performance of related devices. Here, we investigate with density-functional theory calculations the effect of water and oxygen related species on the properties of the prototype system of rubrene, the current record-holder organic semiconductor in terms of carrier mobilities. We identify the most stable impurity structures, with species in either substitutional or interstitial configurations, and we analyze their complex role in changing the shape and profile of rubrene energy bands. In certain cases the impurities either give rise or help annihilate carrier traps, and we discuss the relevance of our findings for the optimizition of rubrene-based electronic systems. (C) 2008 Elsevier B.V. All rights reserved.