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

Morales‐Masis, Monica; Dauzou, Fabien; Jeangros, Quentin; Dabirian, Ali; Lifka, Herbert; Gierth, Rainald; Ruske, Manfred; Moet, Date; Hessler‐Wyser, Aïcha; Ballif, Christophe

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 (SnO2), both composed of earth-abundant elements. The optimized Zn-Sn-O (ZTO) films have electron mobilities of up to 21 cm2 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 cm2 devices with ZTO/Ag/ZTO and ii) 41 cm2 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.

OPTICAL properties of zinc oxide; ORGANIC light emitting diodes; ELECTRICAL properties of tin oxides; ZINC tin oxide; ANODES; OPTICAL properties of indium tin oxide; ABSORPTION

Advanced Functional Materials, 2016, Vol 26, Issue 3, p384

1616-301X

Academic Journal

10.1002/adfm.201503753