Highly efficient p-i-n-type organic light emitting diodes on ZnO:Al substrates

Aluminum doped zinc oxide (ZAO) is presented in this letter as an alternative transparent electrode: optimized ZAO films offer excellent parameters for organic light emitting diodes (OLEDs). The ZAO films are applied to various p-i-n-type OLEDs. By using green phosphorescent molecules in a double emitter structure, very high efficiencies were obtained, namely, 54.6 cd/A and 61.5 lm/W for 100 cd/m(2) at 2.78 V. Additionally, white OLEDs on ZAO demonstrated pure white emission independent of the luminance and high efficiencies of 12.6 cd/A and 14.5 lm/W for 100 cd/m(2) at 2.6 V, which is comparable to indium-tin-oxide based white OLEDs.