The charge mobility in polymer LEDs - the low frequency impedance method

The negative contribution to the capacitance found in low frequency dielectric spectroscopy provides an elegant way to measure the hole and electron mobilities in polymer devices. We present a closer look into this method. By analyzing the results of hole only and double carrier PPV devices, we argue that the reference capacitance to choose is not the zero-field capacitance but rather the one which corresponds to the fully depleted state. © 2003 Elsevier Science B.V. All rights reserved

The charge mobility in polymer LEDs - the low frequency impedance method

The negative contribution to the capacitance found in low frequency dielectric spectroscopy provides an elegant way to measure the hole and electron mobilities in polymer devices. We present a closer look into this method. By analyzing the results of hole only and double carrier PPV devices, we argue that the reference capacitance to choose is not the zero-field capacitance but rather the one which corresponds to the fully depleted state. © 2003 Elsevier Science B.V. All rights reserved

Effect of dye doping on the charge carrier balance in PPV light emitting diodes as measured by admittance spectroscopy

Dye doping is a promising way to increase the spectral purity of polymer light-emitting diodes (LEDs). Here we analyze the frequency and field dependence of the complex admittance of Al–Ba–PPV–poly(3,4-ethylenedioxythiophene:polystyrene sulphonic acid)–indium tin oxide LEDs with and without dye. We compare the charge carrier mobilities of pristine and dye-doped double-carrier and hole-only (Au replacing Al–Ba) devices. Dye doping is shown to significantly influence the electron mobilities while the hole mobilities are left unchanged and thereby changing the carrier balance in a double carrier device towards that of a hole only device. The minimum in the LED capacitance as a function of voltage appears to be an excellent probe for the electron trapping phenomenon underlying the reduction of the mobility