Efficient white organic light-emitting diodes with double co-host emitting layers
Abstract
A novel device structure that adopts double co-host emitting layers (EMLs) for white organic light-emitting diodes (OLEDs) is described in this paper. In the design, the device structure is fairly simple, consisting only two metal complex emitting dopants and two organic materials in functional layers; the organic molecules function as both the host and transporting materials in the EML and charge-transporting layer, respectively. Such a simple device structure effectively lowers the driving voltage, thereby enhancing the power efficacy (PE) of the devices. Although no spacer or interlayer is inserted between the double EMLs, the EL spectrum of white OLEDs is stable over a large luminance range from 87 to 5100 cd m−2 attributed to the evenly distributed excitons in both co-host EMLs. A maximum PE of 71.9 lm W−1 is achieved with this device, and a high PE of 59.3 lm W−1 is maintained at a high luminance of 1000 cd m−2.