Temperature and electric-field dependences of hole mobility in light-emitting diodes based on poly [2-methoxy-5-(2-ethylhexoxy)-1,4-phenylene vinylene]

The current-voltage characteristics of poly [2-methoxy-5-(2-ethylhexoxy)-1,4-phenylene vinylene] (MEH-PPV)-based hole-only light-emitting diodes are measured as a function of temperature. The hole current is found to be space-charge limited, providing a direct measure of the mobility as a function of temperature and electric field. A thermal activation energy of 0.2 eV is obtained for the zero-field mobility, with a room-temperature low-field mobility value for holes of 3.3×10^-7 cm²/V s. The hole mobility exhibits field dependence in accordance with the Poole-Frenkel effect. The combination of space-charge effects and field-dependent mobility thus provides a consistent description of hole transport as a function of temperature and bias voltage in MEH-PPV films.