Extremely Low Turn‐On Voltage and Negligible Efficiency Roll‐Off in OLEDs by Controlling the Penetration of Cathode Magnesium Atoms Into Electron Transport Layer

Abstract Efficient carrier injection from electrodes into organic layers is of significance for designing high‐performance organic light‐emitting diodes (OLEDs), but the high work function of the metal cathode is often unfavorable for electron injection. Herein, a novel electron injection method is demonstrated for OLEDs using magnesium/silver (Mg/Ag) electrode. By controlling the penetration of Mg atoms into the electron transport layer (ETL), electrons can be efficiently injected through conducting defect levels within ETL generated during the Mg deposition process. The undoped device using the typical Tris(8‐hydroxyquinolinato)aluminum (Alq 3 ) emitter, Bathophenanthroline (Bphen) ETL, and Mg/Ag electrode exhibits record‐low turn‐on voltage of 2.4 V and negligible efficiency roll‐off. The doping device using Mg/Ag electrode also shows a low turn‐on voltage of 2.7 V, a 2.7‐fold enhancement in brightness from 43138 to 116611 cd m − 2 , and an amazing suppression in efficiency roll‐off from 51.8% to 12.7% compared to those of the device with commonly‐used LiF/Al electrode. More importantly, the efficient electron injection still keeps even under low driving voltage (3 V) and low ambient temperature (225 K). This advantage overcomes the critical drawback of OLEDs whose electron injection heavily depends on the applied electric field and operational temperature, thus promising for developing top‐class widely‐used devices.