Channels of oxygen diffusion in single crystal rubrene revealed

Abstract

Electronic devices made from organic materials have the p otential to support a more ecologically friendly and affordable future. However, the ability to fabr icate devices with well-defined and reproducible electrical and optical properties is hindered by the sen sitivity to the presence of chemical impurities. Oxygen in particular is an impurity that can trap elect rons and modify conductive properties of some organic materials. Until now the 3-dimensional profili ng of oxygen species in organic semiconductors has been elusive and the effect of oxygen remains disput ed. In this study we map out high-spatial resolution 3-dimensional distributions of oxygen inclusi ons near the surface of single crystal rubrene, using Time of Flight Secondary Ion Mass Spectroscopy (TOF -SIMS). Channels of diffused oxygen are found extending from uniform oxygen inclusion layers a t the surface. These channels extend to depths in excess of 1.8 μ m and act as an entry point for oxygen to diffuse along the ab -plane of the crystal with at least some of the diffused oxygen molecularly bindin g to rubrene. Our investigation of surfaces at different stages of evolution reveals the extent of o xygen inclusion, which affects rubrene's optical and transport properties, and is consequently of importance for the reliability and longevity of devices.