Blue top-emitting organic light-emitting devices based on wide-angle interference enhancement and suppression of multiple-beam interference

Blue top-emitting organic light-emitting devices (TEOLEDs) based on blue phosphor iridium (III) bis[(4,6-difluorophenyl)-pyridinato-N,C2′] picolinate (FIrpic) are demonstrated. Instead of using microcavity effects to obtain the blue top emission in conventional reports, the blue emission with a good chromaticity is achieved in this paper through the suppression of the multiple-beam interference by introducing a 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline light outcoupling layer onto the semitransparent Sm/Ag cathode. The electroluminescent performances of the blue emission is further improved based on the effective carrier transport and the consideration of the wide-angle interference at the emission peak of FIrpic with a maximum luminance of 8029 cd/m2 and a luminous efficiency of 4.02 cd/A achieved at 14 V and 10 V, respectively. With a polarizer on the top cathode, a high pixel contrast ratio of 113:1 is realized under an ambient illumination of 140 lx and a pixel brightness of 1000 cd/m2.

The EL spectra of devices A, B, and C under the current density of 1 mA/cm2. Inset: normalized EL spectra of devices A, B, and C at the same current density of 1 mA/cm2, and the measured PL spectra of the blue phosphor FIrpic in a solid film state.Figure optionsDownload as PowerPoint slideResearch highlights
► The blue top-emitting organic light-emitting devices are obtained by using a BCP layer as a light outcoupling layer onto the semitransparent top metal cathode.
► With an optimized BCP thickness of 35 nm, a low reflectivity of the top Sm/Ag cathode is achieved with desirable suppression of multiple-beam interference in devices.
► We can improve the blue electroluminescent performance by satisfying wide-angle interference at the emission peak of FIrpic.
► The pixel contrast ratio is obviously improved by using the BCP light outcoupling layer together with a polarizer.