A study of light-emitting diodes constructed with copolymers having cyclohexyl thiophene and hexyl thiophene units

We report visible light emission from a diode made from copolymers of 3-alk ylthiophenes. These chemically synthesized copolymers exhibit improved elec troluminescence and quantum efficiencies compared to poly (3-cyclohexylthio phene). Good solubility of copolymers allows the fabrication of the light e mitting diodes by spin-cast polymer film. The devices emit greenish-blue li ght in wavelength region of 550-580 nm, which is easily visible in poorly l ighted room. The quantum efficiencies are in the range of 0.002 to 0.01% (p hotons per electron) at room temperature; which are significantly higher th an corresponding values for poly(3-cyclohexylthiophene) based light emittin g diodes. The charge carrier mobility in the device is found to be 5.6 x 10 (-4) cm(2)/Vs. (C) 2000 John Wiley & Sons, Inc.