Electro‐active oligomers containing pendent carbazolyl or indolyl groups as host materials for OLEDs

Oligoethers containing electroactive carbazolyl, indolyl or 2‐phenylindolyl fragments were synthesized and characterized by NMR spectroscopy, elemental analysis and gel permeation chromatography. The oligomers represent amorphous materials of high thermal stability with glass transition temperatures of 107–161°C. The electron photoemission spectra of layers of the synthesized oligomers showed ionization potentials of 5.9–5.95 eV. Some of the derivatives were tested as host materials in phosphorescent OLEDs with iridium(III) [bis(4,6‐difluorophenyl)‐pyridinato‐N,C2′]picolinate as the guest. The device based on oligomer containing carbazolyl fragments exhibited the best overall performance with a turn‐on voltage of 3.5 V, maximum power efficiency of 4.1 lm/W and maximum brightness of 937 cd/m². © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Polylactide‐perylene derivative for blue biodegradable organic light‐emitting diodes

In this work we demonstrate, for the first time, the use of polylactic acid (PLA) as a biodegradable host matrix for the construction of the active emissive layer of organic light‐emitting diode (OLED) devices for potential use in bioelectronics. In this preliminary study, we report a robust synthesis of two fluorescent PLA derivatives, pyrene‐PLA ( AH10 ) and perylene‐PLA ( AH11 ). These materials were prepared by the ring opening polymerisation of l ‐lactide with hydroxyalkyl‐pyrene and hydroxyalkyl‐perylene derivatives using 1,8‐diazabicyclo[5.4.0]undec‐7‐ene as catalyst. OLEDs were fabricated from these materials using a simple device architecture involving a solution‐processed single‐emitting layer in the configuration ITO/PEDOT:PSS/PVK:OXD‐7 (35%): AH10 or AH11 (20%)/TPBi/LiF/Al (ITO, indium tin oxide; PEDOT:PSS, poly(3,4‐ethylenedioxythiophene) doped with poly(styrenesulfonic acid); PVK, poly(vinylcarbazole); OXD‐7, (1,3‐phenylene)‐bis‐[5‐(4‐tert‐butylphenyl)‐1,3,4‐oxadiazole]; TPBi, 2,2′,2″‐(1,3,5‐benzenetriyl)tris(1‐phenyl‐1H‐benzimidazole)). The turn‐on voltage for the perylene OLED at 10 cd m^–2 was around 6 V with a maximum brightness of 1200 cd m^–2 at 13 V. The corresponding external quantum efficiency and device current efficiency were 1.5% and 2.8 cd A^–1 respectively. In summary, this study provides proof of principle that OLEDs can be constructed from PLA, a readily available and renewable bio‐source. © 2020 The Authors. Polymer International published by John Wiley & Sons Ltd on behalf of Society of Industrial Chemistry.     

Stress behavior of electrodeposited copper films as mechanical supporters for light emitting diodes

Thick copper films electrodeposited on vertically structured GaN-based LEDs play a critical role in supporting thin GaN multi-layers mechanically after laser lift-off (LLO) of the sapphire substrate. The intrinsic stress of electrodeposited copper was measured from the change in the substrate's curvature using a modified Stoney equation. 150-μm thick copper supporters showed very low intrinsic stress of 4-28 MPa (tensile stress), which developed during copper electrodeposition on Au seed. The stress generation was attributed to nuclei coalescence and formation of grain boundaries of which volume increased with the applied current density. The preferential texture plane of thick copper supporters was (2 2 0) at high current densities, while copper films thinner than 1 μm was strongly oriented along (1 1 1) plane. Various seed metals such as Cu, Ni, Au, Ag, and Al were employed to observe the influence of seed material on the stress of copper supporters. The effect of wetting agent on the stress of copper supporters was also monitored in the concentration range of 0.1-1.5 g/L of sodium lauryl sulfate (SLS).     

Synthesis and characterization of ortho-twisted asymmetric anthracene derivatives for blue organic light emitting diodes (OLEDs)

New ortho-twisted asymmetric anthracene derivatives have been synthesized and characterized. The anthracene derivatives show good thermal stability with high glass transition temperatures and a pure blue emission with a narrow full width at half maximum in a film state (λ_max = 454 nm with 71 nm for 2-(2-methylnaphtathalene-1-yl)-9,10-di(naphthalene-2-yl)anthracene and λ_max = 445 nm with 60 nm for 2-(biphenyl-2-yl)-9,10-di(naphthalene-2-yl)anthracene). A multi-layered device using 2-(2-methylnaphtathalene-1-yl)-9,10-di(naphthalene-2-yl)anthracene as an emitting material exhibits a maximum quantum efficiency of 3.61% (power efficiency of 2.15 lm/W, current efficiency of 3.55 cd/A) and blue Commission Internationale de l’Eclairage chromaticity coordinates (x = 0.15, y = 0.13). A fabricated device using 2-(biphenyl-2-yl)-9,10-di(naphthalene-2-yl)anthracene as an emitting material exhibits a maximum quantum efficiency of 3.7% (power efficiency of 2.11 lm/W, current efficiency of 3.55 cd/A) and a blue Commission Internationale de l’Eclairage chromaticity coordinates (x = 0.15, y = 0.12).