Insights into OLED functioning through coordinated experimental measurements and numerical model simulations

Abstract

AbstractApplying this method to the standard OLED device structure that has received broad attention in the literature, we have found a number of surprising results. From our experiments, we have demonstrated that the average electric field inside the hole transport layer is larger than or equal to the average field in the emission layer over the entire current range. The device simulations fully clarify the situation, giving insight into the space charge effects as well as the hole and the electron current distributions in the device. In particular, we found that there is a leakage of unrecombined holes towards the cathode at low voltages. We also found a strong variation of the electric field in the Alq3 layer due to space charge effects. By using the laser dye derivatives DCM‐TPA with electron trapping capabilities and DCM‐II with both electron and hole trapping capabilities as dopants in a standard OLED architecture, we could study the effect on transport and emission characteristics. In the case of the exclusively electron trapping dopant, a blue‐shift of the emission color with increasing bias is observed which we find is due to a splitting of the recombination zone.Applying this method to the standard OLED device structure that has received broad attention in the literature, we have found a number of surprising results. From our experiments, we have demonstrated that the average electric field inside the hole transport layer is larger than or equal to the average field in the emission layer over the entire current range. The device simulations fully clarify the situation, giving insight into the space charge effects as well as the hole and the electron current distributions in the device. In particular, we found that there is a leakage of unrecombined holes towards the cathode at low voltages. We also found a strong variation of the electric field in the Alq3 layer due to space charge effects. By using the laser dye derivatives DCM‐TPA with electron trapping capabilities and DCM‐II with both electron and hole trapping capabilities as dopants in a standard OLED architecture, we could study the effect on transport and emission characteristics. In the case of the exclusively electron trapping dopant, a blue‐shift of the emission color with increasing bias is observed which we find is due to a splitting of the recombination zone.