Session Chair: Husam N Alshareef, King Abdullah University of Science & Technology
4:00pm - 4:30pm Invited
Self‐organizing Hybrid Inks for Transparent, Flexible and Printed Electronics
Leibniz Institut for New Materials, Germany
It is easy to evoke structured metal and semiconductor layers that are optically transparent and mechanically flexible. Regular meshes of sub‐micron metal lines are expected to combine flexibility, low haze, and minimal extinction. But their fabrication is challenging: percolation must be ensured throughout the macroscopic film. The required line widths imply cumbersome and often costly procedures. Dense meshes are problematic for conventional microfabrication. In this talk, I will discuss how colloidal interactions and electrically active ligands can be used to form conductive superstructures with nanoscale features, hierarchical structures, and useful material properties from dispersed nanoparticles. Our goal is to split patterning into hierarchical levels. At the lowest level of hierarchy, small features emerge due to spontaneous assembly of interacting nanoparticles in the ink. As an example, I will show that ultrathin gold nanowires agglomerate into bundles that are inherently percolating. They can be spun into hierarchical wires or printed into continuous meshes. Higher levels of hierarchy can be structured by techniques such as Inkjet printing. I will discuss Inkjet‐compatible inks of spherical particles that are coated with conductive polymers. They provide colloidal stabilization in the dispersion and bridge nanometer‐sized gaps between individual inorganic cores after drying. Structure formation in self‐organizing inks is due to a combination of hydrodynamic, colloidal, and supramolecular interactions. I will discuss strategies for their analysis and modeling towards more detailed process design and simulation.
4:30pm - 5:00pm Invited
Flexible Electro-Thermochromic Devices Composed of Transparent Electrodes and Printable Hydrogels
Yang ZHOU1, Michael LAYANI2, Yi LONG1, Shlomo MAGDASSI2
1Nanyang Technological University, Singapore; 2The Hebrew University of Jerusalem, Israel
Due to the increase significantly increasing of urban heat island (UHI) and global warming, the rising demand for comfortable living and working environments have a serious impact on the electricity consumption of the building sector increasing considerably the peak and the total electricity demand. Correspondingly, numerous researches have been conducted to understand the UHI phenomenon and reduce the demand on air-conditioning systems. These researches have brought about innovative designs and technologies such as “Green Buildings” and “Smart Windows”. Electrochromic and thermochromic materials are the most promising material applied in solar energy saving green buildings and smart windows.
We have shown a new approach to fabricate high efficiency and flexible electro-thermochromic devices. The device consists of a transparent conductive heater is composed of metallic NPs which self-assemble into grid or honeycomb structures and printable PNIPAm-Si-Al hydrogel. This new device has extremely high flexibility that can be bended over 90 degrees and recover, which can be used for multi-shaped smart windows. The high electrical efficiency is benefited from PNIPAm-Si-Al gel, which can contact directly to the the transparent conductive heater without shortcut. Since the viscosity of the gel is relatively high, a dispensing system equipped with a controllable syringing rate and X-Y-Z movement. The dispenser system will be used to deposit the PNIPAm-Si-Al gel in predefined desired locations forming patterns of "blinds" and different geometries. The solar modulating ability is 73.5%, which is higher than the best reported thermochromic materials. The PNIPAm-Si-Al gel hydrogel films used enable fabrication of devices with up to 75% contrast, depending on the film thickness and the applied voltage.
5:30pm - 5:45pm Oral
Photoactive Molecular Modification of ITO Surfaces: The Role of Surface Electronics in Organic Photovoltaic Devices
Iris VISOLY-FISHER1, Hela SASSON1, Yulia FURMANSKY1, Fedor A. PRUDNOV2, Pavel A. TROSHIN2, Nurit ASHKENASY1
1Ben-Gurion University of the Negev, Israel; 2Institute of Problems of Chemical Physics, Russian Academy of Sciences, Russian Federation
Controlling charge transfer at transparent conductive oxide/ conductive polymer junctions is of special importance for organic photovoltaic (OPV) devices, organic light emitting diodes (OLEDs) and light-activated organic field effect transistors (OFETs). Indium-tin-oxide (ITO)/ conductive polymer junctions are shown herein to exhibit photoconductance under UV illumination due to photo-induced decrease of an electron barrier at the ITO-polymer interface by discharging of ITO surface states, related to the adsorption of oxygen species. ITO surface modification by photo-active porphyrin adsorption is shown to sensitize the ITO/ conductive polymer junctions by extending the photoconductance to the visible range, to which ITO is transparent. This process is ascribed to discharging of ITO surface states by recombination with photo-generated holes in the photo-excited molecules.
Molecules known to passivate such surface states were found to affectively perform as electron transporting layer in “inverted” OPV devices. However, only porphyrins supporting the existence of charged surface states and the associated electron transfer barrier were found to be able to replace PEDOT:PSS and perform as hole transporting layer in “normal” configuration OPV cells, indicating the role that surface states play in OPV operation. These works demonstrate the versatility and efficiency of utilizing photo-active molecular layers in functional photoresponsive interfaces.
5:45pm - 6:00pm Oral
Electronic Properties of In2O3(111) Investigated by Scanning Tunneling Spectroscopy
Holger EISELE1, Robert ZIELINSKI1, Celina SCHULZE1, Andrea LENZ1, Zbigbiew GALAZKA2
1Technical University of Berlin, Germany; 2Leibniz Institute for Crystal Growth (IKZ), Germany
The high electrical conductivity in combination with optical transparency makes In2O3 promising as cover material for optoelectronic devices like solar cells, flat-panel displays, or light emitting diodes. Nevertheless, the high electrical conductivity in such wide-band gap materials is not clear, up to now. Recently, the origin of the electrical conductivity has been discussed intensively and studied in order to reach better efficiency for device operation. Scanning tunneling microscopy and spectroscopy (STM/STS) is a powerful tool to get information about the structural and electronic properties at the atomic scale that may be useful for understanding and controlling of the material properties. In this contribution, we present our results of a cleaved In2O3(111) surface, measured by STM and STS. Here, a semiconducting bulk In2O3 single crystal grown from the melt was used. It was cleaved in situ at a base pressure below 1×10-8 Pa.
The atomically resolved STM images show a flat cleavage surface with monoatomic steps. The contrast within every surface unit cell is composed of a triangular substructure of unoccupied electronic states. Scanning tunneling spectra show intrinsic electronic states within the bulk band gap, the latter being determined to 2.7 eV with respect to the valence band minimum. The band gap states may contribute to electrical conductivity in In2O3. The Fermi level is energetically pinned at the surface, approximately 0.4 eV below the conduction band minimum, which shows the absence of intrinsic electron accumulation at this surface as long as it is stoichiometric and clean. This is consistent with the recent photemmission studies, carried out of the same bulk In2O3 crystals. However, the surface electron accumulation layer was also observed in the same bulk In2O3 crystals when cleaved in air.
This project was supported by the Leibniz Association, Leibniz Science Campus GraFOx, project C2-6.
6:00pm - 6:15pm Oral
Challenges to Transparency Tuning by Wrinkling of Sputtered Indium Tin Oxide Thin Film
Milan SHRESTHA1,2, Deyuan WEI1, Gih-Keong LAU1
1Nanyang Technological University, Singapore; 2Singapore Centre for 3D Printing (SC3DP), Nanyang Technological University, Singapore
Recently, a novel type of smart window is developed based on the tunable elastomeric optical diffuser, which has nanometric thin films of indium tin oxide (ITO) wrinkled as compliant electrodes of variable transparency. It appears ‘opaque’ with the elastomeric surfaces wrinkled; it becomes clear when its surfaces are flattened. Voltage-induced dielectric elastomer expansion provides a simple means to unfold and flatten the initially wrinkled surfaces. Despite its brittle nature, the wrinkled ITO thin film can unfold and maintains electrical continuity below a 5% radial compression strain. However, the unfolding close to its flat state risks causing a net tensile stretch and thus cracking the thin film. This practically limits the working range of such smart window to tune the transparency. This work investigates the voltage-induced cracking and its effect on the wrinkling and transparency tuning of a 50nm thick ITO thin films, which were DC sputtered on acrylic elastomer membrane (VHB4910). The freshly deposited ITO thin films on VHB are flat and clear. A 2.5% compression for the first time makes the ITO thin film ‘opaque’, but its unfolding close to the flat state causes the thin film crack. The cracked ITO thin films have fewer wrinkles (longer wavelength) formed under the same compression and thus does not conceal as much as the crack-free ones do. The cracks significantly degrade the transparency tunability of such elastomer optical diffuser. Hence, there is a strong need for tougher transparent conductive oxides to make the wrinkling and unfolding long-life for the smart window application.