Realizing high color-stability in tetra-chromatic white organic light-emitting diodes by strict manipulation of red emissive layer

Abstract

Tetra-chromatic (Blue–Green–Red–Orange) white organic light-emitting diodes (WOLEDs) with superior color stability was demonstrated. Strong carrier trapping effects of red dyes cause significant color shift in multi-color WOLEDs. The high color stability here is attributed to the decrease of red dye trapping sites and enhancement of effective energy transfer to red dye while maintaining appropriate exciton concentration near red dye. As luminance increased from 1000 to 10 000 cd m−2, variations in Commission Internationale de L’Eclairage are merely (0.007, 0.007). Furthermore, this color-stable WOLED achieved a color rendering index close to 90 simultaneously. Our work shows the manipulation of red dye is crucial for achieving superior color stability in multi-color WOLEDs.

Realizing the stable spectrum in four-chromatic white organic light-emitting diodes by controlling the positions of various emitters in the bipolar interlayer

“…In multi-EML WOLEDs based on unipolar interlayers, the exciton recombination zone is generally at a narrow interface [13], while the mixed bipolar interlayer is beneficial to obtain a wide exciton recombination zone and allows the excitons to be uniformly distributed throughout all the ultrathin EMLs which is of great significance to improve the spectral stability [14]. Red emission is an integral component of high-quality white light, however, maintaining high spectral stability in multi-EML WOLED with the red EML is a challenge [15]. In a previous work [16], we have demonstrated three-chromatic WOLEDs (Blue-Orange-Green), ITO/MoO 3 (5 nm)/TCTA (35 nm)/FIrpic (0.5 nm)/TCTA: TmPyPB (1:4, 3 nm)/Ir(ppy) 2 (acac) (0.2 nm)/TCTA: TmPyPB (1:4, 3 nm)/PO-01 (0.1 nm)/TmPyPB (40 nm)/LiF (1 nm)/Al (100 nm), exhibited superior spectral stability with the ∆CIEs of (0.001, 0.001) as the luminance increased from 1000 cd m −2 to 10 000 cd m −2 .…”

Pseudo-Tris(heteroleptic) Red Phosphorescent Iridium(III) Complexes Bearing a Dianionic C,N,C′,N′-Tetradentate Ligand

“… 12 In contrast, increasing the conjugation of the heterocycle by fused aromatic rings gives rise to a red shift. 13 According to this, we decided to replace the phenylpyridine unit of the tetradentate ligand of complex D with a phenylisoquinoline group in the search for red emitters with the structural rigidity of the latter. Furthermore, we wished to investigate how the rigidity of the tetradentate ligand predetermines the stereochemistry of the [6tt′ + 3b] compound when an orthometalated 2-phenylpyridine is employed as a 3b ligand, what isomers can be obtained, and under what experimental conditions.…”

“…In this context, it should be mentioned that the presence of fluorine substituents at the phenyl group of an orthometalated 2-phenylpyridine usually produces a blue shift with regard to the unsubstituted chromophore, , although their use is limited by issues involving partial defluorination during the OLED assembly . In contrast, increasing the conjugation of the heterocycle by fused aromatic rings gives rise to a red shift . According to this, we decided to replace the phenylpyridine unit of the tetradentate ligand of complex D with a phenylisoquinoline group in the search for red emitters with the structural rigidity of the latter.…”