Abstract: Organic light emitting diodes (OLEDs) incorporating an n-doping transport layer comprised of 8-hydroxy-quinolinato lithium (Liq) doped into 4’7- diphyenyl-1,10-phenanthroline (BPhen) as ETL and a p-doping transport layer that includes tetrafluro-tetracyano-quinodimethane (F4- TCNQ) doped into 4,4′,4" -tris (3-methylphenylphenylamono) triphenylamine (m-MTDATA) are demonstrated.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 are improved significantly after introducing an n-doping (BPhen:33wt% Liq) layer as an electron transport layer (ETL) and a p-doping layer composed of m-MTDATA and F4- TCNQ as a hole transport layer (HTL).Compared with the control device (without doping),the current efficiency and power efficiency of the most efficient device (device C) are 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 efficient charge balance in the emission zone.

Key words: p-i-n,  n-doping, current efficiency, electron transport, conductivity