A single anionic conductor (SAC) was employed to improve the hole injection properties in an Al anode/SAC/poly[2-methoxy-5-(2'-(ethyl-hexyloxy)-1,4-phenylenevinylene) emissive layer/indium tin oxide cathode device. The SAC possesses an excellent hole-injection property, because of ionic space charge accumulation near the anode by the good chain segmental motion of the soft block in the polymer chains of the SAC. Thus, a balanced injection of an electron-hole pair can be achieved to greatly improve the quantum efficiency.