Graded Al-doped ZnO layers, constituted by a mesoporous forest-like system evolving into a compact transparent conductor, were synthesized by Pulsed Laser Deposition with different morphologies to study the correlation with functional properties. Morphology was monitored by Scanning Electron Microscopy images and by measuring the resulting surface roughness. Its effects on electrical conductivity – especially carrier mobility, which significantly decreases with increasing roughness – allow to discuss the limitations in conduction mechanisms. Significant changes in light scattering capability due to variations in morphology are also investigated and discussed to study the correlation between morphology and functional properties.

We demonstrated nanostructured, ITO-free anodes in flexible OLEDs using a combination of a composite organic-inorganic UV nanoimprint resist and a conductive, transparent polymer layer. Flexible OLEDs with grating anodes were fabricated on polycarbonate substrates. The nanoimprint resist was blended with 30% TiO2 nanoparticles in order to achieve a sufficient refractive index contrast to the polymer anode. It was periodically structured with a 370-nm period linear photonic crystal structure. PEDOT:PSS was spin-coated on as a polymer anode and structured in an oxygen plasma treatment. For OLED demonstration an organic emission layer (PPV-derivative “Super Yellow”) and a metal cathode (LiF/Al) were deposited. We observed successful waveguide mode extraction both in electroluminescence and photoluminescence for flat and bend substrates. The waveguide mode extraction angle varied slightly under bending. The combination of an inorganic-organic composite material with a conductive polymer transparent electrode is promising for improving the performance of ITO-free, flexible OLEDs.

Graphene is a strong contender as a material to replace indium tin oxide as the transparent conductor of choice for electronic applications due to its exceptional electrical and optical properties. In this work, we present a study of graphene oxide (GO) films produced by inkjet-printing. The printed GO films are reduced using hydriodic acid (HI) and acetic acid vapour at low temperature. The reduced GO (rGO) films displayed good optical and electrical properties with a sheet resistance 6.8 kΩ/□ at a transmittance of 80%. In addition, we show that the conductivity of rGO films is related to both the size of individual GO sheets in the ink and the thickness of printed films. The rGO films using large size GO sheets displayed a thickness-independent conductivity of ∼ 4 × 104 S/m, while the rGO films using small size GO sheets showed a thickness-independent conductivity of ∼ 1.7 × 104 S/m. These properties are comparable to graphene films produced by solvent exfoliation. In summary, we demonstrate a scalable and potentially low-cost technique to produce rGO transparent films and a route to improve the conductivity of rGO films by controlling size of GO sheets in the ink.

Cambrios has developed a transparent conductor material based on silver nanowires which can be used to replace the ITO layer in organic photovoltaics (OPV) device and in organic light-emitting devices (OLED).

After being deposited from a liquid suspension by conventional coating or printing methods onto a transparent substrate, these nanowires form a transparent conducting network. The sheet resistance of the resulting film is determined by the density of the nanostructures and can thus be easily controlled during the coating process.

The elimination of the ITO layer also results in a reduced microcavity effect and thus has a positive impact on the optical performance for OLED lighting devices.

This paper will focus on the use of this material as an ITO replacement for OLED devices for lighting applications and for OPV devices. The performance of ITO-free OPV and OLED devices with a nanowire anode will be discussed. We also will present the optical performance data of OLED lighting devices which show the implications of a reduced microcavity effect. In addition, we will show lifetime data for these devices which demonstrate the viability of this technology.

Generally, indium-tin-oxides (ITO) thin film is prepared by the sputtering process with ITO target, but only 20% of ITO yielded from the target is deposited on the substrate. Namely, about 80% ITO is exhausted by the deposition elsewhere far from the substrate. The recycling process is limited so that ca 20% ITO of the starting target is lost without any recovery. Even if the recycling of ITO has been carried out in this process, we should prepare ITO target of 5 times more than apparent use of ITO on film. If we change it to printing process from the sputtering, the reduction in ITO use is expected as ca. 50%, considering the increase in film thickness by printing. Our target technology also includes ITO nanoink for the project. As a result, monodispersed ITO nanoparticles (NPs) with a cubic shape were fabricated by using quaternary ammonium hydroxide-assisted metal hydroxide organogels. These NPs have perfect uniformity in size with beautiful shape, and perfect single crystalline structure including Sn. As we were attempted to make thin film with ITO nanoink, it was successfully fabricated below 200 nm in thickness and the resistivity was drastically decreased below 1.0 x 10-3 Ω cm after heat treatments. GZO nanoink as substitute of ITO has also been developed.

We have developed a low cost and convenient approach to fabricate ITO-comparable transparent electrodes by using solution process of silver nanowires mixed with poly peroxotitanic acid (PPT) gel. The PPT gel is applied to connect the dispersed silver nanowires to preserve its high conductivity while remaining transparency and reducing surface roughness of the transparent electrode. The silver nanowires were synthesized via a modified polyol method, and the PPT gels were prepared by sol-gel method in appropriate concentrations. After applying the PPT gels, the sheet resistance of the transparent electrodes was improved from 192 Ω/□ to 44.7 Ω/□ with a transmittance of 81 %. And the roughness (RMS) was decreased from 106.3 nm to 48.1 nm. The PPT gel also improved the reliability of the proposed electrodes, which the conductivity was remained after general atmospheric storage of 6 months. We also demonstrate an Alq3 based OLED with the proposed transparent electrodes.

Thin films of pure aluminum doped ZnO and with addition of nitrogen, oxygen and hydrogen have been prepared by magnetron sputtering. The spectral absorption coefficient close to the band gap energy has been determined by spectrophotometry and analyzed regarding band tailing and creation of defect bands. We found, that an improvement of Raman crystallinity under O2- rich growth conditions is not accompanied by a suppression of band tailing as expected. An additional absorption feature evolves for layers grown in N2 containing atmosphere. Doping with hydrogen attenuates sub-band gap absorption.

ITO samples were sputtered at room temperature by ion assisted dual ion beam sputtering using atomic or molecular oxygen. The electrical properties appear to depend on the oxygen flow rate during deposition and the resistivity decreases for samples sputtered at a higher oxygen flow rate (1-5 sccm). The resistivity is lowest at an oxygen flow rate of 4 sccm. The average absorption in the visible part of the spectrum also decreases as a function of the oxygen flow rate and is lower for samples sputtered with atomic oxygen. The figure of merit, i.e. the ratio of the conductivity versus the average absorption in the visible range, increases for higher oxygen flow rates and is typically 20-60% higher for samples sputtered using an atomic oxygen assist beam.

Aluminum doped ZnO (AZO) has been deposited on (100), (110) and (111) oriented n-type Si and on fused silica by atomic layer deposition (ALD). The films have been post deposition annealed in the temperature range 200-500 οC. The AZO films have been characterized by X-ray diffraction (XRD), Hall and transmittance measurements. Circular diodes have been fabricated from the AZO/Si structures and characterized by current-voltage (IV) and deep level transient spectroscopy (DLTS). The AZO films form Schottky junctions with the Si substrates for all the crystallographic orientations. It is established that after post deposition annealing the structure AZO/n-Si (110) is distinguished as the system with largest rectification.