From Event: SPIE Organic Photonics + Electronics, 2017
OLEDs are key devices for realizing next-generation displays such as flexible displays. Although the emission mechanism along with new luminescence materials have been intensively studied with the goal of harvesting all excitons as emission, it has not been uncommon to hear of devices with internal quantum efficiencies of approximately 100% that use phosphorescent or thermally activated delayed fluorescent (TADF) emitters in recent years. Thus, the device performances directly related to practical applications, such as operational lifetime and color purity, have begun to attract much attention. Here, we report on recent advances in phosphorescent OLEDs (PHOLEDs) related to these two device performances. First, the molecular design of the host material to obtain an operationally stable PHOLED is clarified. By analysing the device characteristics of several PHOLEDs utilising similar TADF materials as hosts, a TADF material with a small molecular size is found to be suitable for the phosphorescent host. Second, we demonstrated efficient green OLEDs with high color purity utilising a platinum complex with a rigid molecular structure. A current efficiency of 84 cd/A was obtained from a bottom-emitting OLED with CIE x-y coordinates of (0.27, 0.67), which is much greater than that of a bottom-emitting green OLED using conventional iridium complexes with CIE x-y coordinates of (0.33, 0.62). Furthermore, the CIE x-y coordinates reached (0.18, 0.74) upon employing a top-emitting structure.
Hirohiko Fukagawa, Takahisa Shimizu, Yukiko Iwasaki, Taku Oono, and Toshihiro Yamamoto, "Recent advances in phosphorescent OLEDs: Molecular design for long lifetime and high color purity (Conference Presentation)," Proc. SPIE 10362, Organic Light Emitting Materials and Devices XXI, 103620O (Presented at SPIE Organic Photonics + Electronics: August 07, 2017; Published: 19 September 2017); https://doi.org/10.1117/12.2275795.5581137548001.
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