Mechanism for Oxygen-Enhanced Photoconductivity in Rubrene: Electron Transfer Doping▽This publication involves research sponsored by the U.S. Department of Energy under grant no. DE FG02-04ER 46118 and Columbia University.

Abstract

The oxygen-enhanced photoconductivity observed in crystalline rubrene is investigated using
\nelectron paramagnetic resonance (EPR) spectroscopy and steady-state and time dependent photoconductivity
\n(PC) measurements. The EPR data indicate the presence of rubrene radical cation and oxygen radical anion pairs formed within the crystalline structure when rubrene is irradiated in the presence of oxygen. Radical lifetimes determined using EPR spectroscopy correlate well with
\ntransient PC data and provide strong evidence that the rubrene radical cation is the charge carrier responsible for enhanced conduction. This process is reversible, although photodegradation is also observed. The oxygen-enhanced PC of rubrene is thus explained by an electron transfer mechanism that generates radical cation “hole” carriers within the crystal via the oxygen acceptor