Temperature- and field-dependent electron and hole mobilities in polymer light-emitting diodes

We have studied the transport properties of electron- and hole-dominated MEH-PPV, poly(2-methoxy,5-(2'-ethyl-hexoxy)-p-phenylene vinylene), devices in the trap- free limit and have derived the temperature-dependent electron and hole mobilities (mu = mu(0)e(gamma root E)) from the space-charge-limited behavior at high electric fields. Both the zero-field mobility mu(0) and electric-field coefficient gamma are temperature dependent with an activation energy of the hole and electron mobility of 0.38 +/- 0.02 and 0.34 +/- 0.02 eV, respectively. At 300 K, we find a zero-field mobility mu(0) on the order of 1 +/- 0.5 x 10(-7) cm(2)/V s and an electric-field coefficient gamma of 4.8 +/- 0.3 x 10(-4) (m/V)(1/2) for holes. For electrons, we find a mu(0) an order of magnitude below that for holes but a larger gamma of 7.8 +/- 0.5 x 10(-4) (m/V)(1/2). Due to the stronger field dependence of the electron mobility, the electron and hole mobilities are comparable at working voltages in the trap- free limit, applicable to thin films of MEH-PPV. (C) 1999 American Institute of Physics. [S0003-6951(99)01708-8].