We demonstrate p-i-n organic light-emitting diodes (OLEDs) incorporating an n-doping transport layer which comprises 8-hydroxy-quinolinato lithium (Liq) doped into 4'7-diphyenyl-1,10-phenanthroline as ETL and a p-doping transport layer which includes tetrafluro-tetracyano-quinodimethane (F(4)-TCNQ) doped into 4,4',4 ''-tris(3-methlphenylphenylamono) triphenylamine (m-MTDATA). In order to examine the improvement in the Conductivity of transport layers, hole-only and electron-only devices are fabricated. The current and power efficiency of organic light-emitting diodes have been improved significantly after introducing a novel n-doping (Bphen: 33 wt% Liq) layer as an electron transport layer (ETL) and a p-doping layer composed of n-MTDATA and F(4)-TCNQ as a hole transport layer (HTL). Compared with the control device (without doping), the current efficiency and power efficiency of Device C (most efficient) is enhanced by approximately 51% and 89%, respectively, while driving voltage is reduced by 29%. This improvement is attributed to the improved conductivity of the transport layers that leads to the efficient charge balance in the emission zone. (c) 2008 Published by Elsevier B.V.