The opto-electronic properties of single layer light emitting devices containing the polymer poly [2-(2-ethylhexyloxy)-5-methoxy-1,4-phenylenevinylene] and different electron transport materials are reported. Two oxadiazole derivatives and three oxadiazoles containing a pyridine unit have been used as electron transport materials. The effects of layer thickness and annealing on the device efficiencies are described. An external quantum efficiency of 0.1% was obtained for a 255-nm-thick device incorporating 20% of 3,5-bis[2-(4-tert-butylphenyl)-1,3,4-oxadiazol-5-yl]pyridine.