Characterization of Hybrid Dual Emitting Layers in Blue Organic Light-Emitting Diodes by Controlling the Fluorescent Dop
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Characterization of Hybrid Dual Emitting Layers in Blue Organic Light-Emitting Diodes by Controlling the Fluorescent Doping Concentration Bo Mi Lee1, Nam Ho Kim2, Ju-An Yoon2, Woo Young Kim1,2, Peter Mascher1 1
Department of Engineering Physics and Centre for Emerging Device Technologies, McMaster University, Hamilton ON, Canada 2 Department of Green Energy & Semiconductor Engineering, Hoseo University, Asan, Korea ABSTRACT In this study, we demonstrate blue organic light-emitting diodes (OLEDs) with a dual emitting layer (EML) configuration consisting of fluorescent and phosphorescent emitting materials. We investigated the influence of dopants on the electrical and optical characteristics of devices when controlling the fluorescent dopant concentration. The current density and luminance of device B doped with 12wt% BCzVBi was 141.6 mA/cm2 and 6582 cd/m2 at 10V, respectively. In addition, a maximum luminous efficiency of 8.11 cd/A, was achieved from device B. The corresponding Commission Internationale de l’E´ clairage (CIExy) coordinates of device D doped with 5wt% BCzVBi were (0.143, 0.255) at 6V. INTODUCTION Ever since Tang and Van Slyke [1] reported the first multilayered OLEDs in 1987, OLEDs have been considered as an excellent candidate for solid-state light sources, and full color display applications [2-3] because OLEDs have several advantages such as low driving voltage, low power consumption, high contrast ratio, rapid respond time, wide viewing angle, and ultra-thin thickness [1, 4-9]. The three primary colors, red, green and blue, are critical to create light sources or full color display applications. There have been a variety of efficient and stable red and green emitting materials and devices reported; however, in the case of blue organic emitting materials and devices, there is still much research required to improve luminous efficiency and color stability. To overcome some technological issues to achieve high quality blue emission, the key factors are to find the best emitting material with a wide energy gap and perfectly matched host and dopant materials with a large triplet energy state to prevent non-radiative quenching [10-11] and enhance quantum efficiency [12]. Small molecular emitters are divided into fluorescent and phosphorescent emitters. Phosphorescent materials have high efficiency; however, for blue emission, there have been many non-saturated blue or sky blue devices with blue phosphorescent materials reported [13-14]. On the other hand, blue fluorescent materials generate better deep blue emission although they are still less efficient than phosphorescent materials due to only being able to collect singlet-singlet excitons. Therefore, with respect to these issues, further research is needed to optimize a trade-off between fluorescent and phosphorescent material characteristics In this paper, we report on the design of blue OLEDs based on dual EMLs with fluorescent and phosphorescent emitting materials by tuning the fluorescent doping concentration and also
investigated how the flu
