Reduced turn-on voltage and improved efficiency with free interfacial energy barrier in organic light-emitting diodes

• The method of interfacial doping is introduced to fabricate organic light-emitting diodes (OLEDs).
• It removed the charge-injection barriers and promoted efficient recombination of excitons in EML.
• HTL doped EML which is employed in OLEDs achieved low turn-on voltages, very high efficiencies.

Interfacial doping is introduced in order to fabricate both fluorescent and phosphorescent organic light-emitting diodes (FOLEDs and PhOLEDs) with low turn-on voltage, high efficiency and low efficiency roll-off, which employed the doping profile of transporting layer with the host of the light emitting layer (EML). Both hole and electron transport layer doped EML are investigated. Through this method, the injection and transport of carriers can be fine-tuned, and the interfacial energy barriers from the transporting layer to EML are effectively eliminated. Furthermore, a better balance of holes and electrons in the combination zone can be obtained by manipulating the molar ratio of the interfacial doping layer. By combing all these factors, the FOLEDs achieved a very low turn-on voltage of 2.3 V, a high current efficiency of 9.90 cd/A and an external quantum efficiency of 3.12% with low roll-off. In addition, a low turn-on voltage of 2.8 V and a high current efficiency of 54.06 cd/A, which increased by 45% compared to reference device in PhOLEDs have also been achieved.