Space-charge-limited current in organic light emitting diodes

A physically based mathematical model for the dc current of single-carrier organic light emitting diodes is presented. The model accounts for the most important physical quantities that influence the carrier mobility and thus the device current itself: temperature, charge carrier concentration, and electric field. It is rigorously developed basing on the variable range hopping transport theory and extends the pioneering work of Mark and Helfrich [J. Appl. Phys. 33, 205 (1962)] to large electric fields typical of light emitting diodes. It was validated on experimental data collected from devices of different materials in a wide range of operating conditions. Thanks to the effective electric field approach, the mathematical expression is simple, accurate and suitable for CAD applications.