Bright and Efficient, Non‐Doped, Phosphorescent Organic Red‐Light‐Emitting Diodes

Abstract

Ir(III) metal complexes with formula [(nazo)2Ir(Fppz)] (1), [(nazo)2Ir(Bppz)] (2), and [(nazo)2Ir(Fptz)] (3) [(nazo)H = 4‐phenyl quinazoline, (Fppz)H = 3‐trifluoromethyl‐5‐(2‐pyridyl) pyrazole, (Bppz)H = 3‐t‐butyl‐5‐(2‐pyridyl) pyrazole, and (Fptz)H = 3‐trifluoromethyl‐5‐(2‐pyridyl) triazole] were synthesized, among which the exact configuration of 1 was confirmed using single‐crystal X‐ray diffraction analysis. These complexes exhibited bright red phosphorescence with relatively short lifetimes of 0.4–1.05 μs in both solution and the solid‐state at room temperature. Non‐doped organic light‐emitting diodes (OLEDs) were fabricated using complexes 1 and 2 in the absence of a host matrix. Saturated red electroluminescence was observed at λmax = 626 nm (host‐emitter complex 1) and 652 nm (host‐emitter complex 2), which corresponds to coordinates (0.66,0.34) and (0.69,0.31), respectively, on the 1931 Commission Internationale de l'Eclairage (CIE) chromaticity diagram. The non‐doped devices employing complex 1 showed electroluminance as high as 5780 cd m–2, an external quantum efficiency of 5.5 % at 8 V, and a current density of 20 mA cm–2. The short phosphorescence lifetime of 1 in the solid state, coupled with its modest π–π stacking interactions, appear to be the determining factors for its unusual success as a non‐doped host‐emitter.

Homoleptic Tris(Pyridyl Pyrazolate) IrIII Complexes: En Route to Highly Efficient Phosphorescent OLEDs

“…[18] Note that the N(8) atom of 4 a shows the shortest IrÀN bond length of 2.010(6) , which is due to the increased interaction at this pyrazolate site and less competition (in view of the bonding) from its trans-isoquinolinyl group, and the latter shows the longest Ir À N(1) length of 2.073(5) of all Ir À N interactions.…”

Molecular hosts for triplet emitters in organic light-emitting diodes and the corresponding working principle

“…By attaching sterically hindered t-butyl units to the C-3 and C-6 positions of both carbazole moieties in CBP (7), while preserving the characteristics of the wide band-gap and high triplet energy, a more morphologically stable material (T g = 175 °C), ttbCBP (8) (Figure 6), was obtained [30]. Devices based on ttbCBP (8) show efficiencies of 8.3% (28.8 cd/A, 16.4 lm/W) for green from Ir(ppy) 3 (3), and 9.8% (6.7 cd/A, 3.0 lm/W) for red from Ir(piq) 3 (5). Hybridizing the 9,9′-spirobifluorene function group with two carbazole units can also afford the thermally stable material (T g = 151 °C) CFL (9) (Figure 6) [63].…”

“…Non-doped PhOLEDs for blue [3], green [4,5], orange [6], and red [7,8] were demonstrated. However, those devices usually face the problem of luminescence quenching from the condensed state of emitters.…”

Recent progress in the use of fluorescent and phosphorescent organic compounds for organic light-emitting diode lighting

“…Moreover, since phosphorescent materials that include heavy atoms cannot be used by themselves in devices, the usage of host materials is essential although some phosphorescence materials were applied to an OLED device as nondoped emitters. 38 This section of the article reviews not only dopant materials used for emission, but also host materials used for the generation of phosphorescence.…”