투명전극에 따른 교류무기전계발광소자 특성 연구 : ITO, ZnO:Ga, Ag nanowire, PEDOT:PSS

Abstract

The dissertation presents optical and electrical properties of top and bottom-emission structured AC powder electroluminescent (EL) devices for four different transparent electrodes: In2O3-SnO2 (ITO), Ga-doped ZnO (GZO), Ag nanowires (NWs), PEDOT:PSS.. The top-emission EL device was structured as the bottom metal electrode/dielectric layer/phosphor layer/top transparent electrode and the bottom-emission EL device was layered as the bottom transparent electrode/phosphor layer/dielectric layer/top metal electrode. The ITO and GZO electrodes was deposited by the sputter method, and the Ag NW and PEDOT:PSS was deposited through the spin coating method. The yellow-emitting ZnS: Mn, Cu phosphor and the BaTiO3 dielectric layers was coated through the screen printing method. Their sheet resistivities are 121 Ω/□ for ITO, 238 Ω/□ for Ag NW, 275 Ω/□ for GZO, 482 Ω/□ for PEDOT:PSS, Their transmittances at the yellow EL peak are 84 % for ITO, 97 % for Ag NW, 98 % for GZO. 96 % for PEDOT:PSS. Regardless of EL structures and transparent electrodes, EL spectra of all EL devices were exponentially increased with increasing voltages and they were linearly increased with increasing frequencies. It implies that the EL mechanism was attributed to the impact ionization by charges injected from the interface between the transparent electrode and phosphor layer. For the same transparent electrodes, the top-emission EL devices showed higher EL brightness than the bottom-emission. For the top and bottom-emission EL devices with four different transparent electrodes, the EL brightness was ranked in order of ITO, Ag NW, GZO, PEDOT. The transferred charge densities for the sinusoidal applied voltages were recorded through Sawer-Tower measurement, and their ranks were was consistent with the ranking order of the EL brightness. It indicates that the EL brightness was attributed to the charge density injected fron the interface between the transparent electrode and phosphor layer.