The effects of (i) aquaregia-treatment of the indium tin oxide (ITO) substrate anode and (ii) a controlled Al2O3 buffer between the emitting layer (EML) and the Al cathode layer on the behavior of efficient vacuum evaporated multilayer organic light-emitting diodes (LEDs) is described. The organic layers include hole transporting layers (HTLs) such as '3-armed star' 4,4',4"- tris(N-(3-methoxyphenyl)-N-phenylamine-triphenylamine) and triphenyl diamine, and the EMLs consist either of green- emitting 8-tris-hydroxyquinoline aluminum (Alq3) or blue-emitting amino oxadiazole fluorene. While the aquaregia treatment enhances the performance, the optimized treatment depends on the HTL. This observation implies that the enhancement is due not only to contact area effects. Similarly, an Al2O3 layer of suitable thickness also enhances the current injection and EL output significantly. This enhancement is believed to be due to increased charge carrier density near the HTL/EML interface which results from removal of the intrinsic organic/Al interface gap states which trap injected carriers and quench singlet excitons nonradiatively.