We report on efficient molecular organic light-emitting diodes (MOLEDs) composed of novel silole derivatives as an electron transporting layer and an emissive layer. The silole derivative, 2,5-bis(2′,2″-bipyridin-6-yl)-1,1-dimethyl-3,4-diphenylsilacyclopentadiene, used for the electron transport layer exhibits fast electron mobility of 2×10−4 cm2/V s at 0.64 MV/cm measured by the time-of-flight technique. Another silole derivative, 1,2-bis(1-methyl-2,3,4,5-tetraphenyl silacyclopentadienyl)ethane, used for an emissive layer exhibits blue-green fluorescence with an absolute quantum yield of 97±3% in the solid state. The devices using silole derivatives show a very low operating voltage, an external electroluminescence quantum efficiency (ηEL) of 4.8 %, and luminous power efficiency of 9 lm/W at a brightness of 100 cd/m2. This value of ηEL is the best efficiency achieved for MOLED using undoped emissive and carrier transport layers and is close to the theoretical limit for a device using a fluorescent emitter. © 2002 American Institute of Physics.