A yellow-emitting iridium complex for use in phosphorescent multiple-emissive-layer white organic light-emitting diodes with high color quality and efficiency

A cyclometalated iridium(III) complex containing 2-(9,9-diethylfluoren-2-yl)pyridine [Ir(Flpy)3] was prepared and used in the fabrication of both yellow and white organic light-emitting diodes (OLEDs). A hole-blocking material has been used as a hole barrier layer in-between different emission layers, helping the formation of the hole limitation region. With the proper position of a hole barrier layer and the construction of a four-emission-layer structure involving the use of [Ir(Flpy)3], the resulting WOLED shows sound device performance as well as very stable color even at high luminances. Such WOLEDs have been demonstrated to reveal superior white light color stability/efficiency trade-off optimization. The Commission Internationale de L'Eclairage (CIE) coordinate differences Δx and Δy are confined to ±0.015 when the luminance increases from 13 to 14806 cd/m2. The color rendering index (CRI) of the device is also very good, which varies only from 86 to 87 by changing from the normal direction to 80° off-normal at 12 V. The peak electrophosphorescence efficiency can reach as high as 24.6 cd/A at 168 cd/m2and it can still be kept at 17.2 cd/A at 10834 cd/m2. Such outstanding performance renders this all-phosphor WOLED very attractive as a white light source for illumination applications, which typically demand high efficiency, high CRI, and stable color in high brightness work conditions.