Masataka Yashima

Highly Efficient Green Organic Light-Emitting Diodes Containing Luminescent Three-Coordinate Copper(I) Complexes

A series of highly emissive three-coordinate copper(I) complexes, (dtpb)Cu(I)X [X = Cl (1), Br (2), I (3); dtpb =1,2-bis(o-ditolylphosphino)benzene], were synthesized and investigated in prototype organic light-emitting diodes (OLEDs). 1-3 showed excellent photoluminescent performance in both degassed dichloromethane solutions [quantum yield (Φ) = 0.43-0.60; lifetime (τ) = 4.9-6.5 μs] and amorphous films (Φ = 0.57-0.71; τ = 3.2-6.1 μs). Conventional OLEDs containing 2 in the emitting layer exhibited bright green luminescence with a current efficiency of 65.3 cd/A and a maximum external quantum efficiency of 21.3%.

Highly efficient green organic light-emitting diodes containing luminescent tetrahedral copper(I) complexes

A series of highly emissive sublimable copper(I) complexes with tetrahedral geometries, Cu(dppb)(pz2Bph2) 1, Cu(dppb-F)(pz2Bph2) 2, and Cu(dppb-CF3)(pz2Bph2) 3 [dppb = 1,2-bis(diphenylphosphino)benzene, dppb-F = 1,2-bis[bis(3,5-difluorophenyl)phosphino]benzene, and dppb-CF3 = 1,2-bis[bis[3,5-bis(trifluoromethyl)phenyl]phosphino]benzene, pz2Bph2− = diphenyl-bis(pyrazol-1-yl)borate], were synthesized and investigated as luminescent guest molecules in prototype organic light-emitting diodes. Thermogravimetric analysis of 1–3 under vacuum revealed that introduction of F or CF3 substituents to the meta positions of the four peripheral phenyl groups in the dppb skeleton increased the ability of the copper(I) complexes to be sublimed. 1–3 exhibited strong green emission in amorphous films at 293 K with maximum emission wavelengths of 523–544 nm, quantum yields of 0.50–0.68, and decay times of 3.6–8.2 μs. Molecular orbital calculations indicated that the origin of green phosphorescence from 1–3 was a mixture of σ → π* and π → π* transitions. Conventional bottom-emitting devices with three-layer structures containing 1–3 produced bright green luminescence with maximum external quantum efficiencies of 11.9, 16.0, and 17.7% for 1, 2 and 3, respectively.

11.2: Novel Fluorene-Based Blue Emitters for High Performance OLEDs

High performance new blue-emitting host-dopant systems, which consist of pyrene-substituted fluorene hosts such as DPYFL01 and diarylamino-substituted origo(fluorenylene)s represented by BDT3FL as dopants, have been developed. The new host material,DPYFL01 showed high electron-mobility with 1×10−3 cm2/Vs. A device using DPYFL01 demonstrated blue emission (CIE: x, y = 0.15–0.16, 0.20–0.21) with high power efficiency of 4.5 lm/W at 200 cd/m2. The use of 20%BDT3FL inDPYFL01 resulted in deep-blue emission (CIE: 0.15, 0.15) while keeping high power efficiency of 4.6 lm/W at 3.1 V. The device-structure optimization together with the use of an additional host,C-H01 afforded deep-blue emission (CIE: 0.15, 0.14) and higher power efficiency of 4.9 lm/W and external quantum efficiency of 3.9 % at 4.3 mA/cm2 with 200 cd/m2. Lifetime of the optimized device using 10 %BDT3FL was estimated to be over 10,000 hour at an initial luminance of 200 cd/m2.