Effects of surface plasmon resonance of the Ag nanoparticles on the efficiency and color stability of the blue light phosphorescent organic light emitting diodes

The electroluminescence (EL) performance of the blue light phosphorescent organic light emitting diode (OLED) incorporating Ag nanoparticles (Ag NPs) beneath or within the PEDOT:PSS hole injection layer (HIL) has been investigated, and the surface plasmon-enhanced EL efficiency has been demonstrated. The OLED with the structures of Ag NPs beneath and within the HIL exhibit the respective optimal power efficiency of 43 lm/w (EQE of 31%) and 35 lm/w (EQE of 25%) at the brightness of 1000 cd/m(2) compared to that of 15 lm/w (EQE of 13%) for the control device without Ag NPs incorporated. The mixing volume ratio of Ag NPs to PEDOT:PSS reveals remarkable influence on the OLEDs EL efficiency, and ratio of 1:3 is proved to be optimal due to the sufficient coupling between the surface plasmon of Ag NPs and excitons in the emission layer without significant exciton quenching from the Ag NPs. The blue OLEDs with Ag NPs beneath HIL also reveal considerable color shifting with the increasing luminance while the OLEDs with the mixture of Ag NPs and PEDOT:PSS at various ratios demonstrate stable EL spectrum. The influence of localized surface plasmon resonance (LSPR) from Ag NPs in the different structures on the EL efficiency and spectrum is discussed in details.