Effects 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.The schematic structure of the phosphorescent blue light OLED with Ag NPs incorporated is ITO/(Ag NPs/PEDOT:PSS)or(Ag NPs:PEDOT:PSS)/NPB(30nm)/TCTA(5nm)/TCTA:TPBi:Firpic(20nm)/TmPYPB(35nm)/LiF(0.6nm)/Al.The OLED with the structures of Ag NPs beneath the HIL exhibit the optimal power efficiency of 43 lm/w(EQE of 31%)at the brightness of 1000 cd/m2 compared to that of 15 lm/w(EQE 13%)for the control device without Ag NPs incorporated.It can be attributed to the localized surface plasma resonance(LSPR)effect due to the metal nanoparticles,which improves the transport of carrier,reduces the exciton quenching,and improves the device performance.Meanwhile,the emitting light is varied from sky-blue to green blue.Such color tuning effect from the Ag NPs can be attributed to the the strong LSPR.In addition,the device with the mixture of Ag nanoparticles and PEDOT:PSS as hole injection layer has been studied,and tremendous influence of the Ag NPs volume ratio on the PE has been observed and the ratio of 1:3(Ag NPs/PEDOTP:PSS)is proved to be optimal with power efficiency of 35 1m/w(EQE of 25%)at the brightness of 1000 cd/m2.The reason is that the metal nanoparticles,on the one hand,will cause uneven interface and result in serious current leakage,reduce the carrier transport,on the other hand increases the carrier transport due to the LSPR effect.Therefore,the mixing ratio of Ag nanoparticles and PEDOT:PSS is vital for the device with the mixture of Ag nanoparticles and PEDOT:PSS as hole injection layer(HIL).Meanwhile,the devices with the mixture of Ag NPs and PEDOT:PSS as HIL are capable to maintain their color stability due to the relatively weak LSPR effect.