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

Abstract 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/m2 and high external electroluminescence (EL) quantum efficiencies of 3.4–4.1% at ∼100 A/m2. 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.