We report the improvement of the electroluminescence (EL) efficiency and the device stability of green organic light-emitting diodes (OLEDs) by doping 10-(2-benzothiazolyl)-2,3,6,7-tetramethyl-1H,5H,11H-(1)- benzopyropyrano(6,7-8-i,j)quinolizin-11-one (C545T) in the thin interfacial region of the hole transporting layer of N,N'-di(1-naphthyl) -N,N'-diphenylbenzidine (alpha-NPD) in addition to the tris(8-hydroxyquinoline) aluminum (Alq3) emitting layer. The EL efficiency of 15.7 cd/A is obtained at 10 mA/cm2, which is about 10 % higher than the device with C545T doped only in the Alq3 layer. In addition, the longer lifetime with very small driving voltage variation over time is obtained under a constant current driving. This improvement in the efficiency and stability can be attributed to the combined effect of an additional radiative recombination of electrons with holes in the C545T-doped alpha-NPD layer and the reduced transport of holes into the Alq3 emitting layer, thus lowering the generation of unstable Alq3 cationic species (Alq3+).