Highly Efficient Inverted Organic Light-Emitting Diodes Adopting a Self-Assembled Modification Layer.

Area of Science:

• Materials Science
• Organic Electronics
• Device Physics

Background:

• Inverted organic light-emitting diodes (IOLEDs) are crucial for active-matrix OLEDs (AMOLEDs) but face challenges with electron injection.
• Conventional indium tin oxide (ITO) cathodes exhibit a significant electron injection barrier, limiting device performance.

Purpose of the Study:

• To develop efficient electron injection layers (EILs) for IOLEDs by modifying ZnO with arginine (Arg).
• To investigate the impact of ZnO/Arg EILs on electron injection efficiency, device performance, and operational stability.

Main Methods:

• Fabrication of IOLEDs utilizing ZnO modified with arginine (Arg) as the EIL.
• Characterization of the work function (WF) of ZnO/Arg EILs and comparison with ZnO/poly(ethylenimine) (PEI).
• Evaluation of device performance metrics including turn-on voltage (V_on), current efficiency (CE_max), external quantum efficiency (EQE_max), and operational half-life.

Main Results:

• ZnO/Arg EILs achieved an ultralow work function of 2.35 eV, significantly lower than ZnO/PEI (2.77 eV), attributed to molecular and interface dipoles.
• Green fluorescent IOLEDs with ZnO/Arg exhibited a low V_on of 3.5 V and CE_max of 4.5 cd/A.
• The ZnO/Arg device demonstrated a remarkable half-life of 3600 h, 36 times longer than ZnO/PEI devices.
• Green phosphorescent IOLEDs showed V_on of 3.5 V, CE_max of 59.1 cd/A, and EQE_max of 16.8% with minimal efficiency roll-off (6.3% at 10,000 cd/m²).

Conclusions:

• Arginine-modified ZnO serves as a highly effective EIL for enhancing electron injection in IOLEDs.
• The developed IOLEDs exhibit superior performance characteristics, including low operating voltage, high efficiency, and exceptional operational stability.
• This advancement holds significant potential for improving the performance and longevity of active-matrix OLED displays.