Transparent organic light-emitting diodes consisting of a metal oxide multilayer cathode

Abstract

The authors have developed a semitransparent, multilayered cathode of indium tin oxide (ITO)/Ag/tungsten oxide (WO3) for transparent organic light-emitting diodes. The device showed a weak negative differential resistance (NDR), until the operating voltage of 8V was reached. NDR was due to the resonant tunneling by both the quantum barrier and quantum well. The silver oxide (Ag2O) on the Ag metal was confirmed by x-ray photoelectron spectroscopy, and the energy levels of Ag2O were quantized due to the quantum size effect and this produced the resonant tunneling channels. The device using ITO∕Ag∕WO3 with a LiF∕Al bilayer was superior to those devices which only used ITO or WO3, mainly because the out coupling was enhanced by employing a WO3 material, which is much more transparent than ITO.

Effect of thermal annealing on the performance of WO 3 –Ag–WO 3 transparent conductive film

“…3 shows the sheet resistances of the as-prepared and annealed WAW films. The as-prepared WAW film is very conductive (about 6.55 Ω/sq), which is consistent with other literature [13]. The sheet resistance monotonously increases with the increase of annealing temperature.…”

“…These tri-layer films possess the following advantages: very low resistivity comparable to metal electrodes, high optical transparency in the visible wavelength region, relatively lower thickness, and superior flexibility [2,[8][9][10]. Among them, WO 3 -Ag-WO 3 (WAW) tri-layer film has been extensively demonstrated as transparent electrode for organic light emission diode, solar cell, and thin film transistor owing to its advantage of thermal evaporation fabrication process compatibility (avoiding sputter damage in the ITO case) [11][12][13][14]. Particularly, WAW film can act both as transparent electrode and electrochromatic coating [15], which may greatly reduce the fabrication cost of electrochromatic devices.…”

Optical and Electrical Properties of Oxide Multilayers

“…It is interesting to note that the total resistance of the OMO multilayer structure was consistent with the parallel-connected resistance of the top/ bottom oxide layer and metal layer. This model can be used to define the resistivity on the OMO multilayer as follows [14]: (1) where R oxide_t and R oxide_b are the resistances of the top and bottom oxide layers, respectively. The total resistivity of the a-IGZO/ Ag/a-IGZO thin film was the dominant property according to the thickness of the Ag layer, and this could be mainly attributed to: (1) the thickness of the top and bottom oxide layers being fixed during the change in the Ag thickness; (2) the main current path occurred through the Ag layer due to lower resistivity for Ag than for the oxide layer.…”

Transparent oxide/metal/oxide trilayer electrode for use in top-emitting organic light-emitting diodes

“…[10][11][12][13][14] While these electrodes have typically been deposited using e-beam deposition and therefore require additional processing steps and chambers apart from traditional thermal evaporation, Yook et al have shown that such a structure can be thermally evaporated as well, which integrates into the fabrication of small molecule organic devices and has less potential to damage the underlying layers. 12 Typically the metal used has been Ag, while the oxide layers have run the gamut from ITO to WO 3 to ZnO.…”