ELECTRIC-FIELD REDISTRIBUTION AND ELECTROLUMINESCENCE RESPONSE-TIME IN POLYMERIC LIGHT-EMITTING-DIODES

The electric field redistribution due to injected and trapped charge c arriers in Langmuir-Blodgett (LB) films of poly(3-hexylthiophene) (P3H T) sandwiched between indium tin oxide and aluminum (Al) electrodes as function of applied voltage has been studied using charge collection measurements by the time-of-flight technique. For mu tau E<d (the drif t distance shorter than the interelectrode distance) the amount of the collected photocharge is a function of electric field near the Al ele ctrode and has been used to probe the time evolution of it. The respon se time for the field to redistribute inside the P3HT LB film was foun d to be of the order of 5-200 mu s, in good agreement with the delay t ime observed in time-resolved electroluminescence measurements in ligh t-emitting diodes (LED) of similar LB films. We suggest a model for th e response times in organic LEDs based on these results. (C) 1998 Amer ican Institute of Physics.