Efficient tandem organic light-emitting diodes with non-doped structures

Area of Science:

• Organic electronics
• Materials science
• Device physics

Background:

• Tandem organic light-emitting diodes (TOLEDs) offer enhanced efficiency but require optimized charge generation units (CGUs).
• Non-doped CGUs are desirable for simplified fabrication and potentially higher performance.

Purpose of the Study:

• To develop and investigate a highly efficient non-doped CGU for TOLEDs.
• To elucidate the charge generation and injection mechanisms within the CGU.
• To optimize TOLED performance using the developed CGU.

Main Methods:

• Fabrication of TOLEDs utilizing a LiF/Al/C60/m-MTDATA based non-doped CGU.
• Characterization of current-voltage (I-V) and capacitance-voltage (C-V) properties of CGU and electron-only devices.
• Analysis of charge transfer dynamics at the C60/m-MTDATA interface.

Main Results:

• A non-doped CGU comprising LiF/Al/C60/m-MTDATA was successfully implemented.
• Charge generation was confirmed to occur via electron transfer from m-MTDATA to C60 at their interface.
• A thinner C60 layer was found to improve electron injection efficiency.
• Optimized blue TOLEDs achieved a maximum current efficiency (CEmax) of 43.3 cd/A.
• Optimized white TOLEDs reached a maximum CEmax of 84.6 cd/A and a maximum external quantum efficiency (EQEmax) of 26.7%.

Conclusions:

• The developed non-doped CGU enables highly efficient TOLEDs.
• Understanding the charge transfer mechanism is crucial for optimizing electron injection.
• The achieved efficiencies demonstrate the potential of this approach for advanced display and lighting applications.