Optimized Transmittance and Anti-Reflective Multi-Layer Design for Improved Green OLED Performance

Abstract

The internal quantum efficiency of organic light-emitting diodes (OLEDs) has approached nearly 100 %, making further enhancements in their external quantum efficiency crucial for improving their performance. Traditionally, achieving high outcoupling efficiency has relied on external optical elements, which increase manufacturing costs. This paper presents a novel approach of sandwiching a silver film between silver oxide and Di(1-naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine (NPB) films on a glass substrate to form a glass/silver oxide/silver/NPB system designed to enhance anti-reflective (AR) properties to improve the performance of green OLEDs. Experimental investigations revealed that incorporating 2 nm thick silver oxide (Ag₂O) layer between the glass substrate and silver film results in a notable increase in the light transmittance of the electrode from 18 to 40 %. This enhancement is attributed to the formation of a silver film with conical surface structures, which reduce reflection and improve light coupling. The application of an AR NPB layer on the silver surface further increases the transmittance to ~70 %, demonstrating the effectiveness of the double anti-reflective coating. The devices with the Ag₂O/Ag electrode exhibited significant performance improvements, achieving a maximum luminance of 9573Cd/m², which is approximately 75.3-fold higher than the plain Ag electrode and current efficiency of the Ag₂O/Ag device reached 4.26 Cd/A.