Plasma damage-free sputtering of indium tin oxide cathode layers for top-emitting organic light-emitting diodes

Abstract

We report on plasma damage-free sputtering of an indium tin oxide (ITO) cathode layer, which was grown by a mirror shape target sputtering (MSTS) technique, for use in top-emitting organic light-emitting diodes (TOLEDs). It is shown that OLEDs with ITO cathodes deposited by MSTS show much lower leakage current (9.2×10−5mA∕cm2) at reverse bias of −6V as compared to that (1×10−1–10−2mA∕cm2 at −6V) of OLEDs with ITO cathodes grown by conventional dc magnetron sputtering. Based on high-resolution electron microcopy, x-ray diffraction, and scanning electron microscopy results, we describe a possible mechanism by which plasma damage-free ITO films are grown and their application for TOLEDs.

Fully Solution-Processed Semitransparent Organic Solar Cells with a Silver Nanowire Cathode and a Conducting Polymer Anode

“…1 ITO, however, suffers from several drawbacks that limit its viability as a TCE for next-generation optoelectronics, including high cost, poor performance on plastic substrates, and a tendency to crack when flexed. 2,3 Potential solution-processable alternatives to ITO include carbon nanotubes, 4,5 graphene, [6][7][8][9] conducting polymers, 10,11 and metal nanowires [12][13][14][15] Single-Walled Carbon Nanotubes (SWCNTs) are attractive TCE materials due to their high intrinsic conductivity and mechanical durability but, owing to large inter-tube resistances, their reported performance characteristics are significantly worse than ITO. The need for aggressive acid treatments to induce p-type doping of semiconducting tubes and the non-permanent nature of the doped state are also problematic.…”

Transparent conductive electrodes of mixed TiO2−x–indium tin oxide for organic photovoltaics

“…It has been documented in published literature that ITO films grown by conventional sputtering process possess mostly a columnar structure which results in rougher surface. 12 In our case, ITO films with a nominal thickness of 150 nm show roughness of higher root-mean-square (RMS) and peak-to-valley (PTV) values than those of mixed TiO 2Àx -ITO layers. The typical RMS roughness of ITO and TiO 2Àx -ITO over a 5 lm  5 lm scan is 3.89 and 2.40 nm, respectively.…”

“…This results in better interfaces needed for some applications. For example, smoother electrode-polymer interfaces in organic electronics lead to reduction in leakage current 11,12 and subsequently a better device performance. In our test bed based on organic photovoltaic (OPV) device, the use of TiO 2Àx also improves the optical absorption of photoactive blend layers of poly (3-hexylthiophene) (P3HT) and [6,6]-phenyl C 61 butyric acid methyl ester (PCBM) when compared to ITO-based devices.…”

Get it white: color-tunable AC/DC OLEDs

“…This intermediate electrode must be transparent and therefore must be made either of a thin metal layer (,15 nm) or from indium tin oxide. 10 However, the deposition of indium tin oxide can be problematic due to sputter-induced damage to the organic material underneath, 11 whereas metal films absorb a significant amount of light and introduce additional micro-cavity effects. [12][13][14] Hence, the device development of highly efficient color-tunable OLEDs remains experimentally challenging: the color-tunable OLEDs that have been reported thus far demonstrate relatively modest efficiencies (,10% external quantum efficiency (EQE), ,10 lm W 21 ), despite the use of phosphorescent emitter systems.…”