Charge Carrier Mobility of Siliconized Liquid Triarylamine Organic Semiconductors by Time-of-Flight Spectroscopy

Triarylamines are a well-established family of organic semiconductors. Recently, we have attached short silicone chains to these molecules to alter their mechanical properties. The resulting compounds are liquids at room temperature. We have undertaken to confirm the suitability of these molecules for use in thin film flexible devices. One fundamental property of semiconductors is the charge carrier mobility, which provides a quantitative estimate for how rapidly charge percolates through a material. The charge carrier mobility for a series of six recently developed liquid siliconized triarylamines was measured using time-of-flight spectroscopy (TOF). In order to evaluate the effect of glass transition temperature on mobility, TOF was performed for different electric fields at temperatures above and below the glass transition temperature. Mobilities were found to compare favorably to the charge carrier mobilities of conventional nonliquid triarylamines. It was further observed that the mobilities conform to the predictions of the disorder formalism for a disordered solid both above and below the glass transition temperature. This suggests that charge transport is dominated by thermally activated intermolecular hopping rather than by any convective or diffusive mass transport within the liquid phase.