Highly Efficient Warm White Organic Light‐Emitting Diodes by Triplet Exciton Conversion

Abstract

White organic light‐emitting diodes (WOLEDs) are currently under intensive research and development worldwide as a new generation light source to replace problematic incandescent bulbs and fluorescent tubes. One of the major challenges facing WOLEDs has been to achieve high energy efficiency and high color rendering index simultaneously to make the technology competitive against other alternative technologies such as inorganic LEDs. Here, an all‐phosphor, four‐color WOLEDs is presented, employing a novel device design principle utilizing molecular energy transfer or, specifically, triplet exciton conversion within common organic layers in a cascaded emissive zone configuration to achieve exceptional performance: an 24.5% external quantum efficiency (EQE) at 1000 cd/m2 with a color rendering index (CRI) of 81, and an EQE at 5000 cd/m2 of 20.4% with a CRI of 85, using standard phosphors. The EQEs achieved are the highest reported to date among WOLEDs of single or multiple emitters possessing such high CRI, which represents a significant step towards the realization of WOLEDs in solid‐state lighting.

High-efficiency/CRI/color stability warm white organic light-emitting diodes by incorporating ultrathin phosphorescence layers in a blue fluorescence layer

“…White organic light-emitting diodes (WOLEDs) have been widely studied in the past decades for their potential utilization in flat-panel displays and solid-state lighting, mainly due to their advantages, such as their high efficiency, transparency, flexibility, and exceptional light-weight, ultra-thin characteristics, to name a few [1][2][3][4]. In order to achieve high device efficiency, phosphorescent materials have been widely used to fabricate such devices because they allow manufacturers to harvest 25% singlet excitons and 75% triplet excitons, thus achieving internal quantum efficiency of 100%, compared with the 25% theoretical value for fluorescent materials [3][4][5][6][7][8].…”

“…In order to achieve high device efficiency, phosphorescent materials have been widely used to fabricate such devices because they allow manufacturers to harvest 25% singlet excitons and 75% triplet excitons, thus achieving internal quantum efficiency of 100%, compared with the 25% theoretical value for fluorescent materials [3][4][5][6][7][8]. However, the all-phosphorescent WOLEDs are limited by i) the absence of efficient blue phosphors with long operational lifetimes that are suitable for commercial applications [9,10], and ii) the difficulty of conducting carrier injection from an adjacent carrier transporting layer to the large-bandgap host material with higher triplet state energy [11].…”

Yellow, Orange, and Red Phosphorescent Materials for OLED Lightings

“…OLED 조명은 red, green, blue (RGB) 발광체를 이용한 three color white OLED (WOLED) [7,8,9] 2012년에 Pi-Tai Chou 그룹은 3-(thiazol-2-yl), 3-(benzothiazol-2-yl), 3-(imidazol-2-yl) and 3-(benzimidazol-2-yl) azole chelate를 가지는 새 로운 발광체 16을 개발하였다 [19]. …”

Formulating CdSe quantum dots for white light-emitting diodes with high color rendering index

“…As lighting accounts for ~20% of the energy consumption worldwide, replacement of existing lighting with efficient high-quality solid-state lighting has the potential to reduce total lighting energy usage and current trends have boosted the demand for white light-emitting diodes [5,6]. Two major methods have been employed to generate white LEDs: one is based on a blue LED chip that excites yellow-emitting phosphors to generate white light, and the other is to assemble a near ultraviolet (NUV) LED chip with red, green and blue tri-color phosphors to generate white light [4,7].…”