Mechanism for oxygen-enhanced photoconductivity in rubrene: electron transfer doping

This paper was selected because it provides important information on rubrene properties which enhance photoconduction. An integrate analysis of the rubrene crystals was performed using experimental techniques and theoretical methods. The oxygen-enhanced photoconductivity observed in crystalline rubrene is investigated using electron paramagnetic resonance (EPR) spectroscopy and steady-state and time dependent photoconductivity (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 transient 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