Preparation Of White Organic Light Emitting Device Based On Localized Surface Plasmon Resonance Of Au Nanoparticles

The study investigates the effect of Au NPs on the electroluminescence(EL)of blue and white organic light emitting diodes(OLED),and detailed discussion regarding the responsible mechanism is performed.For the blue OLED with the blue thermally activated delayed fluorescence(TADF)emitter DMAC-DPS(B)as the neat emission layer(EML),the effects of the location and concentration of Au NPs on the EL performance have been studied.Through the comparison of the EL performance of blue OLED with the Au NPs inserted between indium tin oxide(ITO)and PEDOT:PSS hole injection layer(HIL)(A/P),with the mixture of Au NPs and PEDOT:PSS at volume ratio of 1:2 as HIL(A-2P),and without Au NPs(W/A),the beneficial effect of the localized surface plasmon resonance(LSPR)of Au NPs on the EL performance via the enhancement of carriers transport and excitons radiative decaying has been confirmed.Moreover,the EL performance of the blue OLED with the A/P structure is superior to that of the A-2P structure,indicating that the LSPR effect of Au NPs is capable to impose beneficial influence on the EL behavior only in the effective range between excitons and Au NPs.Furthermore,white OLED(WOLED)incorporating Au NPs beneath PEDOT:PSS HIL and employing neat blue DMAC-DPS(B)and green 4CzIPN(G)TADF emission layer(EML)together with sandwiched ultrathin red phosphorescence Ir(piq)2(acac)(R)layer have been fabricated and the effects of LSPR of the Au NPs and EML thickness on the EL performance are investigated.It is found that EML thickness imposes vital influence on the EL performance of the WOLED and the WOLED with the embedded Au NPs and simple EML structure with optimal thickness of G(15nm)/R(0.3nm)/B(15nm)demonstrate maximum power efficiency(PE),external quantum efficiency(EQE)and color rendering index(CRI)around 11.73 lm/w,10.51%and 94,respectively,obviously superior to those of the WOLED without Au NPs(the maximum PE,EQE and CRI are 6.86 1m/w,4.7%,80,respectively),indicating the achievement of balance between EL efficiency and CRI by carefully adjustment of EML thickness with the presence of Au NPs.Moreover,the decaying dynamics including the delay fluorescence(DF),prompt fluorescence(PF),phosphorescence(PH)and energy transferring inside G(15 nm)/R(0.3 nm)/B(15 nm)EML with and without embedded Au NPs is discussed in details.Especially the green and red light emission is dramatically enhanced leading to enormous improvement of CRI,which can be ascribed to the remarkable enhancement of energy transferring inside G(15 nm)/R(0.3 nm)/B(15 nm)EML proved by the much shortened decaying lifetime at 475 and 550 nm from transient photoluminescence(PL)decaying testing.Almost double enhancement of the total fluorescence efficiency(including PF and DF)at 550 nm can be obtained with the assistance of LSPR from the Au NPs,which increase from 23.85%to 49.82%and 15.22%to 28.86%for the respective EML of G(15 nm)/B(15 nm)and G(15 nm)/R(0.3 nm)/B(15 nm).The study provides an easy way to utilize the LSPR of Au NPs together with simple neat TADF and phosphorescent EML to develop high quality WOLEDs.