High efficiency molecular organic light-emitting diodes based on silole derivatives and their exciplexes

Here, we report the performance of molecular organic light-emitting diodes (MOLEDs) using novel fluorescent silole derivatives as highly efficient blue and green-emitting organic materials. Three silole derivatives, namely 2,5-di-(3-biphenyl)-1,1-dimethyl-3,4-diphenylsilacyclopentadiene (PPSPP), 9-silafluorene-9-spiro-1'-(2',3',4',5'-tetraphenyl)-1' H-silacyclopentadiene (ASP) and. 1,2-bis(1-methyl-2,3,4,5,-tetraphenylsilacyclopentadienyl)ethane (2PSP), with high solid-state photoluminescence (PL) quantum yields of 0.85, 0.87 and 0.94, respectively, were used as emissive materials. Another high electron mobility silole derivative, 2,5-bis(2',2"-bipyridin-6-yl)-1,1-dimethyl-3,4-diphenylsilacyclopentadiene (PyPySPyPy), was used as the electron transport material. MOLEDs using these siloles as emitters and N,N'-diphenyl-N,N'-(2-napthyl)-(1,1'-phenyl)-4,4'-diamine (NPB) or N,N'-diphenyl-N,N'-bis(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine (TPD) as the hole transport material show low operating voltages of 4-4.5 V at a luminance of 100 cd/m(2) and high external electroluminescence (EL) quantum efficiencies of 3.4-4.1% at similar to100 A/m(2). MOLEDs based on PPSPP and PyPySPyPy exhibit red-shifted EL spectra which are assigned to exciplexes formed at the interface between the hole transporting layer NPB or TPD and the PPSPP or PyPySPyPy light-emitting layer, respectively. (C) 2003 Elsevier B.V. All rights reserved.