Emission Wavelength Control Based on Coupling of Surface Plasmon and Microcavity Mode in Organic Light-Emitting Diodes with Metal/Dielectric/Metal Anodes

Abstract

Ag/ZnS/Ag (AZA) multilayer films with various ZnS interlayer thicknesses were deposited on glass substrates via thermal vacuum evaporation. The sheet resistances, work functions, transmittances, and reflectances of the AZA structures were characterized to evaluate whether their electrical and optical properties are suitable for application as organic light-emitting diode (OLED) electrodes. The transmittance peak and reflectance dip could be red-shifted by changing the interlayer thickness of the AZA structure, which resulted in a surface plasmon (SP) color filter effect. OLED devices with AZA multilayers of different interlayer thicknesses were then fabricated. Instead of the expected red shift in the emission spectrum due to the surface plasmon color filter effect of the AZA structure, two electroluminescence (EL) peaks were obtained in the AZA OLEDs with 45 and 60 nm thick ZnS interlayers. From the results of the finite-difference time-domain calculations, we conclude that the two split EL peaks are attributed to mode coupling between the optically active surface plasmons of the AZA structure and the microcavity of the OLED structure. The proposed OLED design with a metal/dielectric/metal electrode allows the control of the EL spectral shape and emission color without changing the thickness of the OLED organic layers.