Inkjet-Printed Quantum Dot Light-Emitting Diodes with an Air-Stable Hole Transport Material

High-efficiency quantum dot light-emitting diodes (QLEDs) were fabricated using inkjet printing with a novel cross-linkable hole transport material <i>N</i>,<i>N</i>′-(9,9′-spirobi­[fluorene]-2,7-diylbis­[4,1-phenylene])­bis­(<i>N</i>-phenyl-4′-vinyl-[1,1′-biphenyl]-4-amine) (SDTF). The cross-linked SDTF film has excellent solvent resistance, high thermal stability, and the highest occupied molecular orbital (HOMO) level of −5.54 eV. The inkjet-printed SDTF film is very smooth and uniform, with roughness as low as 0.37 nm, which is comparable with that of the spin-coated film (0.28 nm). The SDTF films stayed stable without any pinhole or grain even after 2 months in air. All-solution-processed QLEDs were fabricated; the maximum external quantum efficiency of 5.54% was achieved with the inkjet-printed SDTF in air, which is comparable to that of the spin-coated SDTF in a glove box (5.33%). Electrical stabilities of both spin-coated and inkjet-printed SDTF at the device level were also investigated and both showed a similar lifetime. The study demonstrated that SDTF is very promising as a printable hole transport material for making QLEDs using inkjet printing

Configuration effect of novel bipolar triazole/carbazole-based host materials on the performance of phosphorescent OLED devices

<p id="sp0010"> A series of structurally isomeric carbazole/triazole (TAZ)-based bipolar host materials <strong class="boldFont">1</strong>&ndash;<strong class="boldFont">4</strong> were designed and synthesized. These new materials were found to exhibit wide energy gaps (<em>E</em>_g: 3.29&ndash;3.52&nbsp;eV), high triplet energies (<em>E</em>_T: 2.56&ndash;2.76&nbsp;eV), high thermal stability (<em>T</em>_d: 426&ndash;454&nbsp;&deg;C), high glass-transition temperatures (<em>T</em>_g: 116&ndash;156&nbsp;&deg;C) and excellent film-forming property. Green and blue emitting devices with <em>fac</em>-tris(2-phenylpyridine)iridium (Ir(ppy)₃) and iridium(III) bis(4,6-(di-fluorophenyl)pyridinato-<em>N</em>,C^2&prime;)picolinate (FIrpic) as phosphorescent dopants have been fabricated. The measurements of turn-on voltages, efficiencies and luminance suggested that the practice of combining carbazole&rsquo;s high triplet energy and excellent hole-transporting ability with TAZ&rsquo;s electron-transporting ability at the molecular level was effectively translated into better performance at the device level. The molecular structure of compound <strong class="boldFont">4</strong> is well-correlated with its efficiencies, which (32.7 and 21.1&nbsp;cd/A for green and blue devices, respectively) were the best among the four materials.</p> <!--VALIDHTML--> <hr /

Embedded Ag/Ni Metal-Mesh with Low Surface Roughness As Transparent Conductive Electrode for Optoelectronic Applications

Metal-mesh is one of the contenders to replace indium tin oxide (ITO) as transparent conductive electrodes (TCEs) for optoelectronic applications. However, considerable surface roughness accompanying metal-mesh type of transparent electrodes has been the root cause of electrical short-circuiting for optoelectronic devices, such as organic light-emitting diode (OLED) and organic photovoltaic (OPV). In this work, a novel approach to making metal-mesh TCE has been proposed that is based on hybrid printing of silver (Ag) nanoparticle ink and electroplating of nickel (Ni). By polishing back the electroplated Ni, an extremely smooth surface was achieved. The fabricated Ag/Ni metal-mesh TCE has a surface roughness of 0.17 nm, a low sheet resistance of 2.1 Ω/□, and a high transmittance of 88.6%. The figure of merit is 1450, which is 30 times better than ITO. In addition, the Ag/Ni metal-mesh TCE shows outstanding mechanical flexibility and environmental stability at high temperature and humidity. Using the polished Ag/Ni metal-mesh TCE, a flexible quantum dot light-emitting diode (QLED) was fabricated with an efficiency of 10.4 cd/A and 3.2 lm/W at 1000 cd/m²

Hybrid Printing Metal-mesh Transparent Conductive Films with Lower Energy Photonically Sintered Copper/tin Ink

Abstract With the help of photonic sintering using intensive pulse light (IPL), copper has started to replace silver as a printable conductive material for printing electrodes in electronic circuits. However, to sinter copper ink, high energy IPL has to be used, which often causes electrode destruction, due to unreleased stress concentration and massive heat generated. In this study, a Cu/Sn hybrid ink has been developed by mixing Cu and Sn particles. The hybrid ink requires lower sintering energy than normal copper ink and has been successfully employed in a hybrid printing process to make metal-mesh transparent conductive films (TCFs). The sintering energy of Cu/Sn hybrid films with the mass ratio of 2:1 and 1:1 (Cu:Sn) were decreased by 21% compared to sintering pure Cu film, which is attributed to the lower melting point of Sn for hybrid ink. Detailed study showed that the Sn particles were effectively fused among Cu particles and formed conducting path between them. The hybrid printed Cu/Sn metal-mesh TCF with line width of 3.5 μm, high transmittance of 84% and low sheet resistance of 14 Ω/□ have been achieved with less defects and better quality than printed pure copper metal-mesh TCFs