Highly enhanced light recycling for quantum dot displays via high-aspect-ratio Ag reflector

Abstract

Quantum dots (QDs) based display is one of the most promising next-generation devices because of their superior emitting properties in terms of color expression. However, the present QD based display composed of wall structure, several capping layers, and QD, has been suffering from low luminance caused by light propagating to the side directions that is not the light extraction gain. Particularly, this problem remains even if all other factors are improved. In order to solve this problem, the formation of the reflective metal layer on the side surface of the pixel defining layer (PDL) is the most efficient and practical method to recycle the light traveling to side directions. However, existing QD displays having color converting structure have been only employed the black matrix (BM) or organic wall structures, because the formation of the reflective layer on the PDL requires complicated multi-step photolithography processes and cause damage the metal layer during the wet etching process. In this work, a significant step was taken towards overcoming limitations of light extraction from pixel structure through high-aspect-ratio Ag reflector at the surface of PDL via one-step Ar ion bombardment technique referred as secondary sputtering lithography (SSL). Because of light recycling effect on metal reflector (thickness ~60 nm, high-aspect-ratio ~>20), light extraction efficiency (LEE) was significantly enhanced, depending on pixel resolutions (1.15 $\pm$ 0.02, 1.34 $\pm$ 0.04, 1.60 $\pm$ 0.06 and 1.92 $\pm$ 0.10 folds @ 80, 190, 270, 400PPI). In particular, this approach is not only structurally low-risk but also cost-effective methodology, thus can be considered to be the most practical and commercial alternative to improve the LEE in all color converting structures that utilize the materials having omnidirectional emitting feature.