Effects of Thermal Treatment on DC Voltage-Driven Color Conversion in Organic Light-Emitting Diode

Area of Science:

• Organic electronics
• Solid-state lighting
• Materials science

Background:

• Organic light-emitting diodes (OLEDs) are crucial for advanced lighting.
• Achieving stable and tunable color emission in OLEDs remains a challenge.
• Metal-free phthalocyanine (H2Pc) offers potential for novel optoelectronic properties.

Purpose of the Study:

• To propose and investigate a DC voltage-dependent color-tunable OLED (CTOLED) for lighting applications.
• To understand the impact of thermal treatment on the CTOLED's performance and color emission.
• To elucidate the underlying mechanisms of color tuning using device simulation.

Main Methods:

• Fabrication of a CTOLED device with six organic layers, including H2Pc as an emissive layer.
• Characterization of current density-voltage-luminance properties before and after thermal treatment.
• Analysis of electroluminescent spectra using multipeak fitting and Technology Computer-Aided Design (TCAD) simulation.

Main Results:

• The CTOLED without thermal treatment predominantly emitted green light with minor blue and infrared emissions.
• After thermal treatment, the CTOLED exhibited a dominant color conversion from blue to green with increasing voltage.
• TCAD simulations revealed that reduced traps at the H2Pc-HBL interface after treatment led to blue emission, while resonant tunneling facilitated green emission at higher voltages.

Conclusions:

• Thermal treatment significantly enhances the color-tunable properties of the H2Pc-based CTOLED.
• The observed color tuning is attributed to voltage-dependent changes in exciton generation sites, influenced by trap states and electron transport dynamics.
• The developed CTOLED demonstrates promising potential for efficient and tunable solid-state lighting solutions.