Single-layer polymer light-emitting diodes are fabricated using poly (9, 9'-dioctylfluorene)-co-benzothiadiazole (F8BT) as the emissive layer in contact with metal oxide injection layers ITO/ZnO/Cs(2)CO(3)/F8BT/MoO(3)/Au. Luminous efficiencies of up to 23 cd A(-1) are achieved for polymer layer thicknesses near 1 mu m.