Stable and efficient blue fluorescent organic light-emitting diode by blade coating with or without electron-transport layer

Abstract

Multi-layer small-molecule blue fluorescent organic light-emitting diode (OLED) is fabricated by blade coating. The emission layer is based on a mixed host of 1-(7-(9,90-bianthracen-10-yl)-9,9-dioctyl-9H-fluoren- 2-yl) pyrene (PT-404) and electron-transport material 2,7-Bis(diphenylphosphoryl)-9,90 -spirobifluorene (SPPO13), and the blue guest emitter is 4-40-(1E, 10E)-2,20-(naphthalene-2,6-diyl) bis(ethane-2,1diyl) bis(N, N-bis(4-hexyl-Phenyl) aniline) (Blue D). A hole-transport layer of Poly-(9, 9-dioctylfluorenyl2, 7-diyl)-co-(4, 4-(N-(4-sec-butylphenyl)) diphenylamine) (TFB) is added on top of PEDOT: PSS anode. The electrons are blocked away from TFB by a layer of pure host emission layer of PT-404 between TFB and the mixed ehost emission layer. For the devicewith the electron transport layer of Tris(8-hydroxyquinolinato) aluminum (Alq3) blade-coated over the emission layer the efficiency and lifetime at initial brightness of 500 cd m(-2) are 7.5 cd A(-1) and 150 h for Alq3/CsF/Al cathode. When the Alq3/CsF/Al is replaced by simply CsF/Al over the mixed-host emission layer the efficiency and lifetime are 6.4 cd A(-1) and 300 h (2 times longer than that of the Alq3/CsF/Al cathode). The lifetime depends on the electron-hole balance tuned by the mixed-host blending ratio as well as the electron injection from the cathode. This work shows good stability is possible for all-solution-processed blue OLED. (C) 2017 Published by Elsevier B.V.