High power efficiency phosphorescent poly(dendrimer) OLEDs

Doping-Free Phosphorescent and Thermally Activated Delayed Fluorescent Organic Light-Emitting Diodes with an Ultra-Thin Emission Layer

We report the electroluminescence (EL) characteristics of blue ultra-thin emissive layer (U-EML) phosphorescent (PH) organic light-emitting diodes (OLED) and thermally activated delayed fluorescence (TADF) OLED. A variety of transport layer (TL) materials were used in the fabricated OLEDs. The well-known FIrpic and DMAC-DPS were used with a thickness of 0.3 nm, which is relatively thicker than the optimal thickness (0.15 nm) of the blue phosphorescent ultra-thin emissive layer to ensure sufficient energy transfer. While FIrpic showed overall high efficiency in various TLs, DMAC-DPS exhibited three times lower efficiency in limited TLs. To clarify/identify low efficiency and to improve the EL, the thickness of DMAC-DPS was varied. A significantly higher and comparable efficiency was observed with a thickness of 4.5 nm, which is 15 times thicker. This thickness was oriented from the TADF itself, which reduces quenching in a triplet-triplet annihilation compared to the PH process. The thinner optimal thickness compared with ~30 nm of fluorescent OLEDs suggests that there still is quenching taking place. We expect that the efficiency of TADF U-EML OLEDs can be enhanced through further research on controlling the exciton quenching using multiple U-EMLs with spacers and a novel material with a high energy transfer rate (ΔES-T).

Enhancement of the electroluminescence properties of iridium-complexes by decorating the ligand with hole-transporting carbazole dendrons

Iridium-complexes decorating with carbazole dendrons exhibit an improved hole-transporting capability and OLED devices with brightness of 16 170 cd m⁻², maximum luminous efficiency of 13.59 cd A⁻¹ and maximum EQE of 4.36%.

Iridium(III)-Complexed Polydendrimers for Inkjet-Printing OLEDs: The Influence of Solubilizing Steric Hindrance Groups

With the great success of organic light-emitting diodes (OLEDs) based on thermal evaporation techniques, the development of printable materials for inkjet-printing high-performance OLEDs is particularly attractive yet challenging. In this paper, a set of printable Ir(III)-complexed polydendrimers, poly[bis[2-(2,4-difluorophenyl)-4-(4-((2-ethylhexyl)oxy)phenyl)pyridine][1-ethyl-5-phenyl-3-propyl-1H-1,2,4-triazole] iridium(III)] (PIr-D1) and poly[bis[2-(2,4-difluorophenyl)-4-(4-((2-ethylhexyl)oxy)-2,6-dimethylphenyl)pyridine][1-methyl-5-phenyl-3-propyl-1H-1,2,4-triazole] iridium(III)] (PIr-D2), were designed and synthesized via ring-opening metathesis polymerization (ROMP). As a comparison, the iridium precursor complexes bis[2-(2,4-difluorophenyl)-4-(4-((2-ethylhexyl)oxy)phenyl)pyridine][1-methyl-5-phenyl-3-propyl-1H-1,2,4-triazole]iridium(III) (Ir-D1) and bis[2-(2,4-difluorophenyl)-4-(4-((2-ethylhexyl)oxy)-2,6-dimethylphenyl)pyridine][1-methyl-5-phenyl-3-propyl-1H-1,2,4-triazole] iridium(III) (Ir-D2) and the core structure bis[2-(2,4-difluorophenyl)pyridine] [1-methyl-5-phenyl-3-propyl-1H-1,2,4-triazole] iridium(III) (Ir-D0) were also synthesized and the corresponding OLEDs were fabricated. Compared with the dendritic iridium complexes Ir-D1 and Ir-D2, the resulting polydendrimers PIr-D2 and PIr-D2 showed enhanced film-forming properties, good thermal stability, and attractive ink rheological characteristics with a suitable viscosity for inkjet-printing. Promising device performance has been achieved for the resulting polydendrimers by both spin-coating and inkjet-printing, showing low driving voltages and relatively high current efficiencies and brightnesses. The results suggest that the construction of polydendritic Ir(III) complexes is an attractive design strategy for exploring efficient printable light-emitting materials for inkjet-printing high-performance OLEDs.

High-efficiency, solution-processed, multilayer phosphorescent organic light-emitting diodes with a copper thiocyanate hole-injection/hole-transport layer

Copper thiocyanate (CuSCN) is introduced as a hole-injection/hole-transport layer (HIL/HTL) for solution-processed organic light-emitting diodes (OLEDs). The OLED devices reported here with CuSCN as HIL/HTL perform significantly better than equivalent devices fabricated with a PEDOT:PSS HIL/HTL, and solution-processed, phosphorescent, small-molecule, green OLEDs with maximum luminance ≥10 000 cd m(-2) , maximum luminous efficiency ≤50 cd A(-1) , and maximum luminous power efficiency ≤55 lm W(-1) are demonstrated.