(2,2′-Binaphthyl-6,6′-diyl)bis(diphenylphosphine oxide) as a potentially simple and efficient electron-transport layer for stable organic light-emitting diodes

The synthesis of organic electron-transport materials (ETMs) for organic light-emitting diodes (OLEDs) has been intensely pursued. Herein we report an organic phosphinyl compound (2,2'-Binaphthyl-6,6'-diyl)bis(diphenylphosphine oxide) (BiNa-BiDPO) with concise synthesis and purification. BiNa-BiDPO is thermally stable up to ca. 415 degrees C and exhibits distinct glass transition with a T-g of 112 degrees C after being cooled from the melt. Upon further heating, no crystallization or melting is observed. Ultraviolet photoemission spectroscopy studies reveal that E-HOMO approximate to -6.12 eV for the new compound. Consequently, the LUMO level was roughly estimated as -2.77 eV based on the onset of the film absorption spectrum. BiNa-BiDPO possesses a higher electron mobility of 1.6-8.4 x 10(-5) cm(2) V-1 s(-1) at E = 2-5 X 10(5)V cm(-1) relative to a common ETM 1,3,5-tris(N-phenylbenzimidazolyl)benzene (TPBi), thus providing better OLED efficiency with lower working voltage. Moreover the OLED devices involving BiNa-BiDPO as the electron-transport layer showed a half life-time of 172 h at an initial luminance of ca. 1000 cd m(-2), driven at a constant current density, in contrast with the TPBi device with a shortened t(1/2) of 93 h. Further device engineering as well as molecular design may provide enhanced device durability. (C) 2015 Elsevier B.V. All rights reserved.