Effect of silver nanoparticles deposited on indium tin oxide by plasma-assisted hot-filament evaporation on phosphorescent organic light-emitting diode performance

Abstract

This study investigates a high-density of silver (Ag) nanoparticles deposition in a two-dimensional array via a plasma-assisted hot-filament evaporation system on indium tin oxide (ITO) anodes for phosphorescent organic light-emitting diodes (PhOLEDs). The nanoparticles deposition process was conducted at substrate temperatures of 25, 80 and 140 °C. It is observed through atomic force microscopy that the deposited Ag nanoparticles size increases with higher substrate temperature. The surface plasmon resonances (SPRs) of the deposited Ag nanoparticles are influenced by particle size and interparticle spacing. The visible light transmittance of PhOLED was improved in the wavelength range from 500 to 600 nm at 25 and 80 °C conditions. The luminance efficiency of PhOLEDs with deposited Ag nanoparticles increased by 11.07, 5.03, and 70.30% with rising temperature compared to the standard PhOLED (no Ag nanoparticle) with colour stability. The enhancement in efficiency resulted from a coupling between the SPR of Ag nanoparticles and excitons in the emitting layer. The maximum efficiency was also due to a mirror-reflected emission effect via the larger Ag nanoparticles size. Moreover, the positive charges from the inner layer of the anode were enhanced by the high-density inserted Ag nanoparticles at 25 and 80 °C, increasing the hole carrier injection. The performance and mechanism of a PhOLED modified with Ag nanoparticles are discussed.