Channels of oxygen diffusion in single crystal rubrene revealed

TL;DR

This study maps the 3D distribution of oxygen in single crystal rubrene, revealing channels that influence the material's optical and electrical properties, which is crucial for improving organic electronic device stability.

Contribution

It provides the first high-resolution 3D mapping of oxygen diffusion channels in rubrene, advancing understanding of oxygen's role in organic semiconductor properties.

Findings

Oxygen forms pillars extending over 1.8 μm into rubrene.

Oxygen inclusions affect optical and transport properties.

Channels facilitate oxygen diffusion along the crystal plane.

Abstract

Electronic devices made from organic materials have the potential to support a more ecologically friendly and affordable future. However, the ability to fabricate devices with well-defined and reproducible electrical and optical properties is hindered by the sensitivity to the presence of chemical impurities. Oxygen in particular is an impurity that can trap electrons and modify conductive properties of some organic materials. Until now the 3-dimensional profiling of oxygen species in organic semiconductors has been elusive and the effect of oxygen remains disputed. In this study we map out high-spatial resolution 3-dimensional distributions of oxygen inclusions near the surface of single crystal rubrene, using Time of Flight Secondary Ion Mass Spectroscopy (TOF-SIMS). Channels of diffused oxygen, 'oxygen pillars', are found extending from uniform oxygen inclusion layers at the surface. These pillars extend to depths in excess of 1.8 {\mu}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 binding to rubrene. Our investigation of surfaces at different stages of evolution reveals the extent of oxygen inclusion, which affects rubrene's optical and transport properties, and is consequently of importance for the reliability and longevity of devices.