Soichi Watanabe

High‐Efficiency Blue and White Organic Light‐Emitting Devices Incorporating a Blue Iridium Carbene Complex

High-effi ciency white organic light-emitting devices (OLEDs) have great potential for energy saving solid-state lighting and eco-friendly fl at-display panels. [ 1 ] In addition, white OLEDs are expected to open new designs in lighting technology, such as transparent lighting panels or luminescent wallpapers because of being able to form paper-like thin fi lms. Phosphorescent OLED technology is an imperative methodology to realize higheffi ciency white OLEDs because phosphors, such as fac -tris(2phenylpyridine)iridium( III ) [Ir(ppy) 3 ] and iridium( III )bis(4,6(difl uorophenyl)pyridinatoN , C 2 ′ )picolinate (FIrpic) enable an internal effi ciency as high as 100% converting both singlet and triplet excitons into photons. [ 2 ] There are two effective approaches to obtain white OLEDs by using phosphors. One is to combine a blue fl uorophore and phosphors for the other colors, a so-called hybrid white OLED. [ 3 ] A key requirement is the use of a blue fl uorophore with higher triplet energy ( E T1 ) than that of the other phosphors. The blue fl uorophore also needs to have a high photoluminescent quantum yield ( η PL ). Schwartz and coworkers reported hybrid white OLEDs with a power effi ciency at 1000 cd m − 2 ( η p,1000 ) of 22 lm W − 1 (external quantum effi ciency (EQE) of 10.4%) by using N , N ′ -di-1-naphthalenylN , N ′ -diphenyl-[1,1 ′ :4 ′ ,1 ′ ′ :4 ′ ′ ,1 ′ ′ ′ -quaterphenyl]-4,4 ′ ′ ′ -diamine (4P-NPD) as a blue fl uorophore, and Ir(ppy) 3 and iridium( III ) bis(2-methyldibenzo-[ f , h ]quinoxaline)(acetylacetonate) [Ir(MDQ) 2 ( acac)] as green and red phosphors, respectively. [ 4 ]

High-Efficiency Green Phosphorescent Organic Light-Emitting Devices with Chemically Doped Layers

We have developed green phosphorescent organic light-emitting devices (OLEDs) with high quantum and luminous efficiencies. A green phosphorescent metal complex, fac-tris(2-phenylpyridine) iridium [Ir(ppy)3], was used as an emitter material. Wide-energy-gap materials with high triplet excited energy levels were used as host materials for Ir(ppy)3 and as carrier transport materials. Hole injection and electron injection from the electrodes were balanced by placing chemically doped layers at the interface between the electrodes and the organic layers. In addition, a highly reflective Ag cathode was employed as an anode, instead of a conventional Al cathode to enhance the reflectivity of the cathode metal. An optimized device exhibited an external quantum efficiency (EQE) of 27% (95 cd/A) and a high power efficiency of 97 lm/W at 100 cd/m2 at 3.1 V.