Flexible AC powder electroluminescent device based on silver nanowire electrode Gemechu Deressa, Kwangwon Park, Hyeongseok Jeong, Seokkyu Lim, Daehan Kim, Jihoon Lee, Jaehyeong Park, Jehong park*, and Jongsu Kim Department of Image Science and Engineering, Pukyong National University, Busan 608-739, Korea * AIDEN, 134, Gongdsn-ro, Heungdeok-gu, Cheongju-si, 361-290, Korea Keywords: electro-luminescence, ZnS phosphor, Ag nano wire ABSTRACT Silver nanowire (Ag NW) electrode-based AC powder electroluminescent device (ACPELD) is demonstrated. Ag NW electrode with the transparency of 90 % and sheet resistance of 50 ohm/sq was bar-coated, and the phosphor/dielectric layers were screen printed. The EL intensity and charge density were as high as that for ITO-based ACPELD. 1. INTRODUCTION Alternating current powder electroluminescent devices (ACPELDs) have a high potential for commercial application, because of their high resolution and brightness, uniform light emission, and low power consumption together with the possibility of a thin architecture (60-100 μm). ACPELDs can be used in liquid crystal display backlight such as cellular phones and personal digital assistants and also in large-scale architectural and decorative lighting [1]. Up to now, transparent conducting oxides such as indium-tin oxide (ITO) electrodes prepared by cost-intensive sputtering techniques constitute the electrode through which the light is extracted. However, low-temperature deposition techniques compatible with flexible polymer substrates lead to higher sheet resistances and surface roughness of the ITO electrode. Moreover, repeated bending of ITO electrodes causes cracking and delamination limiting their flexibility. Referring to these facts and the extremely increasing demand on indium and leading to a strong price advance, transparent silver nanowire (Ag NW) electrodes seem to be a valuable alternative for ITO-based electrodes for applications with moderate requirements on conductivity. Here we report the fabrication of highly efficient blue-green ACPELDs based on the silver nanowire (Ag NW) electrode. 2. Experimental The ACPELDs were prepared by a screen printing method. The devices consist of a PET substrate/transparent Ag NW electrode/phosphor layer/insulating layer/and rear metallic electrode. At first, Ag NWs (20 nm in diameter, 15 μm in length; AIDEN in Korea) together with hydroxypropyl methylcellulose (HPMC) with mixture ratio of 0.015% and 0.875% in weight are dispersed in deionized water, respectively. The homogeneous dispersion was bar-coated on PET substrate heated at 100 °C. The coated AgNW electrode was baked at 120 ° C for 60 s. The resulting coating was approximately 40 nm thick with the transmittance of 90 % in the wavelength range between 450 and 550 nm and a sheet resistance of ∼ 50 ohm/sq. Subsequently the ZnS:Cu, Cl powder phosphor (Osram) were dispersed in dielectric cyanoethylcellulose binder with a weight ratio of 6:4 and deposited on the ITO substrate by screen printing method. The coated phosphor was then dried for 30 min. at 80 ℃. The phosphor layer is about 80 ㎛ thick. The high dielectric BaTiO 3 powder was mixed with the organic binder with weight ratio of 2:1 and printed twice upon the dielectric layer to protect against the electric breakdown. The thickness of dielectric layer is 20 ㎛. The Ag paste as a rear electrode was pasted upon the dielectric layer. The fabricated EL devices are driven by a sinusoidal voltage. 3. Results and Discussion The EL spectra of ACPELD varying from 30 to 500 V for a fixed frequency of 400 Hz are shown in Figure 1. The peaks are slightly red-shifted with increasing applied voltage. This redshift is due to an increase of operation temperature induced by higher applied voltages. As shown in the inset, the ACPELD on Ag NW electrode is flexible. In flexibility test, the EL intensities of Ag NW-based ACPELD show a slighter change than ITO-based ACPELD with increasing numbers of bending-recovery cycles. Luminance (L) versus applied voltage (V) is plotted in Figure 2. In the general powder EL device using ZnS:Cu phosphor, it is well known that the luminance is