Two fluorescent molecules with an alkynylanthracene core and pyrene end‐cappers have been synthesized and fully characterized. Carbazole moieties are introduced into one molecule at the C9 position of the fluorene linkages to enhance the hole‐transport ability of the molecule and to reduce intermolecular interactions. Both compounds exhibit high thermal stabilities and narrow energy bandgaps. Single‐layer polymer light‐emitting diodes (PLEDs) based on poly(9,9‐dioctylfluorene) (PFO) doped with the synthesized compounds exhibit excellent performance. A PLED with 0.2 % of dopant 7 had a high luminance efficiency of 10.7 ± 0.3 cd A–1 as well as a brightness of 1400 cd m–2 at a current density of 13 mA cm–2, and a low turn on voltage (3.1 V) at a brightness of 10 cd m–2. A maximum brightness of 20 500 ± 1400 cd m–2 at 7 V was also measured. The high efficiency of the device's performance is attributed to the good electron and hole trapping ability of the dopants, which possess suitable energy levels as compared to those of PFO.
Interface and its engineering are critical to achieve efficient organic light-emitting diodes (OLEDs). In this presentation, we would like to present a new type of electron transport layer (ETL) based on metal oxide between emissive layer and metal electrode. The metal oxide synthesized by sol-gel process and can be solution processed on top of the emissive layer. The efficiency of OLEDs based on green polyfluorene polymer has found increased significantly, from 15 lumen/watt to 19 lumen/watt compared with our previous cathode structure of Cs 2 CO 3 /Al. The electrochemical properties and electronic structure of the ETL, and energy alignment at the interface are examined to understand the function of this ETL and the contribution to the improvements for device performances. We will present the details of the analysis and the composition of the materials in the presentation.
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