Efficiency enhancement of organic light emitting diodes by NaOH surfacetreatment of the ITO anode

Organic light emitting diodes (OLEDs) based on tris-(8-idroxyquinoline)aluminum (Alq3) with enhanced efficiency are reported here. This is obtained by improving the charge carrier balance, through a preliminaryNaOH surface treatment of the indium tin oxide (ITO) anode, in order to decrease its work function and, consequently, reduce the hole injection. The obtained devices exhibit a 1.36% external quantum efficiency and a 1.2 lm/W power efficiency at a current density of 60 mA/cm2. These values are more than double as compared with those of identical reference devices fabricated without the preliminary NaOH surface treatment.