Highly efficient blue organic light-emitting diodes using DPASN quantum well structure
- PDF / 6,045,864 Bytes
- 7 Pages / 612 x 792 pts (letter) Page_size
- 1 Downloads / 186 Views
Highly efficient blue organic light-emitting diodes using DPASN quantum well structure Ju-An Yoon1, You-Hyun Kim1, Nam Ho Kim1, Seung Il Yoo1, Sang Youn Lee1, and Woo Young Kim1,2 * 1
Department of Green Energy & Semiconductor Engineering, Hoseo University, Asan, Korea 2 Department of Engineering Physics, McMaster University, Hamilton, Canada
ABSTRACT In this study, we fabricated blue OLEDs with quantum well structure (QWS) using four different blue emissive materials such as DPVBi, ADN and DPASN, and BAlq as QWS material. Conventional QWS blue OLEDs used to be composed of emissive layer and charge blocking layer with lower HOMO-LUMO energy level, but we designed triple emitting layer for more significant hole-electron recombination in EML and a wider region of exciton generation as forming QWS spontaneously. The structure of triple emitting layered blue OLED is ITO / NPB(700 Å) / X(100 Å) / BAlq(100 Å) /X (100 Å) / Bphen(300 Å) / Liq(20 Å) / Al(1200 Å) (X= DPVBi, ADN, DPASN). HOMO-LUMO energy levels of DPVBi, ADN, DPASN and BAlq were 2.8-5.9, 2.6-5.6, 2.3-5.2 and 2.9-5.9 eV, respectively. The maximum luminous efficiency was 5.32 cd/A at 3.5 V in a blue OLED with DPASN / BAlq / DPASN QWS. INTRODUCTION Since the report by Tang & VanSlyke on organic light-emitting diodes(OLEDs),[1-2] OLEDs have attracted much research interests due to its several technical advantages such as reduced power consumption, compatibility with flexible substrates, high color rendering index, high contrast and wide viewing angle. OLEDs have emerged as strong candidates for next generation flat panel displays and solid-state lighting sources,[3-5] Recently, many studies have focused on improving OLEDs efficiency but performance of blue OLEDs still needs improvement.[6-8] Various methods have been developed to optimize blue OLED's performance. One method was to replace emitters from fluorescent to phosphorescent materials [9] and the other was to balance the carrier ratio in the EML.[10] Another method was to design a better surface texture for improving external quantum efficiency.[11] Among various method for enhanced efficiency, the QWS has been proved to be an effective approach for high device performance, [12 13] by confining charge carriers and exciton within the multi emitting layer. Thus the charge carrier recombination efficiency and exciton formation probability can be beneficially enhanced.[14] The organic molecules were weakly restricted by Van der Waals force among molecules in the organic quantum-well. The main features of QWS were high EL efficiency,[15] tunable EL zone,[16] and great carriers balance.[17-21] In this work, blue OLEDs using four fluorescent materials of DPVBi, ADN, DPASN and BAlq. These materials have difference HOMO-LUMO energy level. Emissive layers were fabricated under different order to form QWS and obtain optimized electrical and optical performances. Luminous efficiency and I-V-L characteristics were observed considering the effects of QWS and the variation of recombination region in EML.
EXPERIMENT IT
Data Loading...
