Oxide-Metal-Oxide Layers for Flexible and See-Through Electronics

Abstract

Transparent electrode (TE) is a key component in many modern electronic devices. While it has been heavily dominated by indium tin oxides (ITOs), various process- or material-related constraints in next-generation devices such as flexible displays and see-through electronic devices often require an alternative TE technology to be developed. In general, transparent electrodes to be used with these emerging devices should fulfill the following requirements: (i) their sheet resistance should be as low as possible; (ii) TEs themselves should be compatible with pre- or post-processing used during the fabrication of devices of interest; (iii) their deposition should be mild enough not to damage layers underneath; and (iv) for flexible devices, TEs should also possess an excellent flexibility with sufficiently high onset strain for bending-induced crack formation. In fact, one of the major reasons to develop ITO-alternatives is because ITO forms crack at a relatively low strain (typically around 1.5% or less). In addition, TEs should be able to provide optical properties required by a given application. In many cases, high transmittance is generally desired; in case of light-emitting or photovoltaic devices, however, a certain range of reflectance (at the expense of transmittance) may be preferred for a cavity resonance effect for wide color gamut or for efficiency enhancement. Therefore, ability to tune transmittance (reflectance) in a wide range could be highly useful to cope with desired specifications of various applications. In this talk, oxide-metal-oxide (OMO) or dielectric-metal-dielectric (DMD) layers are introduced as a versatile TE that can fulfill all the requirements mentioned above and, moreover, can easily tune its transmittance/ reflectance for the required optical characteristics. Highly flexible organic light-emitting diodes (OLEDs), transparent thin-film transistors, efficient see-through solar cells are introduced as representative examples. Subtle but significant effect of the refractive index of oxide layers is also discussed to reveal its versatile potential.