High efficiency p-i-n organic light-emitting diodes with a novel n-doping layer

This study demonstrated p-i-n organic light-emitting diodes (OLEDs) incorporating a novel n-doping transport layer which is comprised of cesium iodide (CsI) doped into tris-(8-hydroxyquinoline) aluminum (Alq(3)) as n-doping electron transport layer (n-ETL) and a p-doping hole transport layer (p-HTL) which includes molybdenum oxide (MoO3) doped into 4,4',4 ''-tris[2-naphthyl(phenyl)amino] triphenylamine (2-TNATA). The device with a 15 wt.% CsI-doped Alq(3) layer shows a turn on voltage of 2.4 V and achieves a maximum power efficiency of to 4.67 lm/W as well, which is significantly improved compared to these (3.6 V and 3.21 lm/W. respectively) obtained from the device with un-doped Alq(3). This improvement is attributed to an increase in the number of electron carriers in the transportation layer leading to an efficient charge balance in the emission zone. A possible mechanism behind the improvement is discussed based on X-ray photoelectron spectroscopy (XPS). (C) 2010 Elsevier Ltd. All rights reserved.