High transmittance Er doped ZnO thin films as electrodes for organic light-emitting diodes

Transparent conducting oxides (TCO) have attracted great attention since the first demonstration in 1907 by Baedeker. TCO thin films with high transparency and electrical conductivity have been widely used in optoelectronic devices, such as thin-film transistors, perovskite solar cells and light emitting diodes (LEDs). Er doped ZnO films exhibit higher optical transparency (~95 %) than other reported metal elements doped ZnO TCO thin films. The effect of Er doping concentration on photoelectric properties of ErZO thin films was investigated in the range of 0-2.0 wt.%. The Er impurity substitutes the Zn site and Er_Zn serves as charge donor in the ZnO crystal structure, thus resulting in the improvement of n-type conductivity as compared with intrinsic ZnO thin films. The optimized ErZO thin films present the low resistivity of 3.4×10⁻⁴ Ω/cm, high carrier concentration of 5.9×10²⁰ /cm³ and high visible optical transmittance (~93%) when the Er content is 1.0 wt.%. The ErZO thin films were used as transparent anodes to fabricate organic light-emitting diodes (OLEDs). Impressively, with the ErZO as anode, the current efficiency of the OLEDs device can reach as high as 86.5 cd/A, which was increased by 14% when compared with the reference OLEDs device (76.0 cd/A) using ITO as anode.