Research Paper: Optimizing OLED performance on polyimide substrates: Evaluation of ITO and organic layer thicknesses with different encapsulation materials
Scientific Summary
This study aimed to optimise the electro-optical performance of organic light-emitting diodes (OLEDs) on polyimide (PI) substrates by systematically investigating the impact of indium tin oxide (ITO) transparent electrode and electron transporting layer (ETL) thicknesses, alongside thin-film encapsulation (TFE) materials. The goal was to enhance luminance and current efficiency, specifically addressing optical challenges inherent to flexible PI substrates compared to conventional glass.
Key Findings and Conclusions
The research found that OLEDs on PI substrates were more sensitive to ETL thickness variations than ITO thickness, largely due to the similar refractive indices between PI, TFE, ITO, and organic layers. While glass substrates exhibited lower ITO sheet resistance and achieved higher maximum luminance, optimal ITO and ETL thicknesses were identified for both substrates. Crucially, the TFE material choice significantly impacted performance: an initial SiNx/Al2O3 TFE shifted the optimal ITO thickness and slightly reduced luminance. However, replacing SiNx with SiO2, which has a refractive index similar to PI, dramatically increased luminance by 10.1% and helped establish optimal ITO (75-100 nm) and ETL (65 nm) thicknesses. Furthermore, the TFE effectively blocked moisture and oxygen, ensuring long-term stability on PI substrates comparable to glass for up to 150 hours.
Why it matters
These findings are vital for the advancement of flexible OLED technology, providing a comprehensive guide for designing high-performance and durable flexible displays. The study underscores the critical need for tailored optimisation strategies that account for the distinct optical properties of flexible substrates and their encapsulation layers. By demonstrating how specific material choices in TFE can significantly boost luminance and stability, this research accelerates the development of efficient and robust flexible OLEDs for various applications, including foldable smartphones and wearable devices.
Publication Details
Cho, H., Kim, G.H., Lee, W.J. and Kim, Y.H. (2025), Optimizing OLED performance on polyimide substrates: Evaluation of ITO and organic layer thicknesses with different encapsulation materials. ETRI Journal, 1–10. DOI: 10.4218/etrij.2024-0319.
Fluxim Tools Used
SETFOS was the key software employed for optical simulations of the OLED devices. Researchers used SETFOS to model the optical properties, incorporating refractive indices of all layers (substrates, TFE materials, organic layers). This enabled the systematic variation of ITO electrode and electron transporting layer (ETL) thicknesses to predict their effects on the overall optical performance, particularly luminance. The ability of SETFOS to accurately simulate light propagation and interference phenomena within complex multi-layered OLED structures was crucial for identifying optimal layer configurations and subsequently validating these predictions through device fabrication.