Film thickness influence of dual iridium complex ultrathin layers on the performance of nondoped white organic light-emitting diodes

Using a blue iridium complex phosphorescent dye of bis[(4,6-diflourophenyl)-pyridinato-N,C2′)](picolinato) iridium(III) (FIrpic) and a yellow iridium complex phosphorescent dye of bis[2-(4-tertbutylphenyl)benzothiazolato-N,C2,]iridium (acetylacetonate) [(t-bt)2Ir(acac)] as dual ultrathin layers, nondoped white organic light-emitting diodes (WOLEDs) were fabricated. By optimizing the thickness of ultrathin layers, the influence of FIrpic and (t-bt)2Ir(acac) dual ultrathin layers on the performance of WOLEDs was studied. The results showed that a stable pure white light emission was obtained with a maximum current efficiency of 11.08 cd/A and a power efficiency of 6.21 lm/W. The Commissions Internationale De L’ Eclairage (CIE) coordinates at (0.33, 0.33) were observed at 9 V bias and showed a very slight variation of (±0.01, ±0.01) in a wide range of voltages. The high power efficiency and stable electroluminescence spectra were attributed to the excitons confined effectively in the recombination zone by the charge trapping effect of dual phosphorescent ultrathin layers.

Research highlights
► We fabricated the nondoped WOLEDs using dual phosphorescent ultrathin layers.
► Stable white light with the CIE of (0.33, 0.33) was achieved at 9 V.
► Device performance was improved by optimizing thicknesses of ultrathin layers.
► The performance was attributed to the excitons confined in the recombination zone.