An Indium‐Free Anode for Large‐Area Flexible OLEDs: Defect‐Free Transparent Conductive Zinc Tin Oxide

Abstract

Flexible large‐area organic light‐emitting diodes (OLEDs) require highly conductive and transparent anodes for efficient and uniform light emission. Tin‐doped indium oxide (ITO) is the standard anode in industry. However, due to the scarcity of indium, alternative anodes that eliminate its use are highly desired. Here an indium‐free anode is developed by a combinatorial study of zinc oxide (ZnO) and tin oxide (SnO 2 ), both composed of earth‐abundant elements. The optimized Zn–Sn–O (ZTO) films have electron mobilities of up to 21 cm 2 V −1 s −1 , a conductivity of 245 S cm −1 , and <5% absorptance in the visible range of the spectrum. The high electron mobilities and low surface roughness (<0.2 nm) are achieved by producing dense and void‐free amorphous layers as confirmed by transmission electron microscopy. These ZTO layers are evaluated for OLEDs in two anode configurations: i) 10 cm 2 devices with ZTO/Ag/ZTO and ii) 41 cm 2 devices with ZTO plus a metal grid. The ZTO layers are compatible with OLED processing steps and large‐area white OLEDs fabricated with the ZTO/grid anode show better performance than those with ITO/grid anodes. These results confirm that ZTO has the potential as an In‐free and Earth‐abundant alternative to ITO for large‐area flexible OLEDs.