A highly efficient wide-band-gap host material for blue electrophosphorescent light-emitting devices

Abstract

We report on an efficient wide-band-gap host material for blue electrophosphorescence devices, namely, 1,2-trans-di-9-carbazolylcyclobutane (DCz). Photophysical studies show that lower-energy excimer formation between the carbazole units can be efficiently suppressed in a DCz film, thus maintaining its high triplet-state energy and inducing an exothermic energy transfer from DCz to iridium(III)bis[(4,6-difluorophenyl)-pyridinato-$N,C^{2\prime }$ ]picolinate (FIrpic). Electrophosphorescent devices comprising a FIrpic:DCz emitting layer exhibit a superior performance with a maximum external quantum efficiency of 9.8%, a maximum luminance efficiency of $21.5\mathrm{cd}∕\mathrm{A}$ , and a maximum power efficiency of $15.0\mathrm{lm}∕\mathrm{W}$ at $0.01\mathrm{mA}∕{\mathrm{cm}}^2$ .