Ink Deposition Research Articles

Fuel Cell Electrodes Based on Functional Meso-Structured Arrays

State-of-the-art fuel cell catalyst layers consist of a random mixture of functional components (catalyst, ionomer, and pore) that are formed in an uncontrolled ink deposition process. The random nature of these structures makes it difficult to optimize the functional domains and hence causes severe mass transport limitations during high-power operation, resulting in a loss in performance and requiring that the fuel cell be oversized to maintain an acceptable level of performance. The ionomer binder adds an additional transport resistance and becomes significant at lower Pt loadings [1]. Decreasing this transport resistance would remove the main barrier to low-cost, ultra-high power density fuel cells. Rational design of the electrode structure in PEFCs could improve performance and reduce cost. By separating the different electrode functions into discrete electrode elements, each element can be optimized for specific functions. Arranging these optimized discrete elements in a controlled, low-tortuosity array configuration enables transport limitations to be reduced or eliminated. We have demonstrated this approach through fabrication of freestanding arrays of vertically-oriented ionomer channels with different aspect ratios, and incorporation of these channels into fuel cell electrodes where they serve as non-tortuous proton-transport highways (Figure 1). Providing effective proton transport through these low-tortuosity percolating highways allows the catalyst domain to have a lower ionomer/catalyst ratio, reducing transport resistance. Proof of concept was demonstrated by achieving a 15% increase in performance with channels with an aspect ratio of 8. Further work is underway to increase channel aspect ratio and improve integration of channels with surrounding catalyst layer, leading to further transport improvements and increases in performance. Fig. 1. Left: freestanding array of ionomer channels. Right: catalyst layer incorporating ionomer channels. References N. Nonoyama, S. Okazaki, A. Z. Weber, Y. Ikogi, and T. Yoshida, J. Electrochem. Soc., 158, B416 (2011). Acknowledgments This research is supported by DOE Fuel Cell Technologies Office, through the Fuel Cell Performance and Durability (FC-PAD) Consortium. Figure 1

Dynamics of Cellulose Nanocrystal Alignment during 3D Printing.

The alignment of anisotropic particles during ink deposition directly affects the microstructure and properties of materials manufactured by extrusion-based 3D printing. Although particle alignment in diluted suspensions is well described by analytical and numerical models, the dynamics of particle orientation in the highly concentrated inks typically used for printing via direct ink writing (DIW) remains poorly understood. Using cellulose nanocrystals (CNCs) as model building blocks of increasing technological relevance, we study the dynamics of particle alignment under the shear stresses applied to concentrated inks during DIW. With the help of in situ polarization rheology, we find that the time period needed for particle alignment scales inversely with the applied shear rate and directly with the particle concentration. Such dependences can be quantitatively described by a simple scaling relation and qualitatively interpreted in terms of steric and hydrodynamic interactions between particles at high shear rates and particle concentrations. Our understanding of the alignment dynamics is then utilized to estimate the effect of shear stresses on the orientation of particles during the printing process. Finally, proof-of-concept experiments show that the combination of shear and extensional flow in 3D printing nozzles of different geometries provides an effective means to tune the orientation of CNCs from fully aligned to core-shell architectures. These findings offer powerful quantitative guidelines for the digital manufacturing of composite materials with programmed particle orientations and properties.

CL‐20 based Explosive Ink of Emulsion Binder System for Direct Ink Writing

AbstractAn emulsion is a multiphase dispersion system in which one or more liquids are dispersed in the form of particles in another immiscible liquid. Emulsion method has been applied for preparation of binder system via oil in water (O/W) emulsions. The formulation contains: 40 g 12 % a solution of polyvinyl alcohol (PVA) in water, 15 g 7.5 % a solution of Viton A (vinylidene hexafluoropropene copolymer) in ethyl acetate, 0.25 g sodium dodecyl sulfate (SDS) and 0.25 g Tween‐80.The emulsion as a binder system, sub‐micro CL‐20 (prepared by the ball milling method) as the body explosives to prepared CL‐20 based explosive ink (CL‐20 88 % concentration). Deposition of explosive inks via DIW technology and its properties were characterized. The results showed that the composite has fewer internal defects and low impact sensitivity, the crystal type has no change, critical detonation size is around 1×0.17 mm and detonation velocity is 8079 m/s.

Custom tailoring of conductive ink/substrate properties for increased thin film deposition of poly(dimethylsiloxane) films

The creation of more robust biocompatible printed electronics devices requires an understanding of interactions between conductive inks and substrates to achieve desired printing and functional properties. In this study, we present a water-based conductive ink that can provide a readily achieved thin film deposition on a highly hydrophobic surface such as poly(dimethylsiloxane) (PDMS). We also show that surface treatments with atmospheric plasma can be utilized to tailor the surface energy of hydrophobic substrates to improve the deposition of inks not custom made for such applications. By using a tailored Ag nano-particle ink, we have successfully printed conductive traces onto a hydrophobic (PDMS) substrate without any surface modification. It was also shown that when introducing atmospheric plasma treatment to the PDMS substrate prior to printing with the tailored ink poor printing resulted. The proposed mechanism for the cause of this poor wetting and deposition is an adverse interaction between the ink and PDMS surface caused by surface oxidation resultant of plasma treatment. The results show that the generally accepted rule that a difference between the substrate and ink surface energy of 10 mN/m for good print quality does not necessarily hold true in the case of functional printing.

High-Throughput Activity and Performance Screening Methods for PGM-Free Catalysts

Platinum is widely used as the catalyst in polymer electrolyte fuel cells (PEFCs) due to its high catalytic activity and stability. However, the high cost of this precious metal is one of main barriers to widespread commercialization of PEFCs in automotive and stationary applications. Many research efforts have focused on reducing this cost barrier by either decreasing the platinum loading by developing more active Pt-based catalysts, such as nanostructured alloys, or by developing platinum group metal-free (PGM-free) catalysts based on earth-abundant materials, such as iron, cobalt, carbon, and nitrogen [1-4]. The overall approach of this project is to accelerate the development of PGM-free catalysts by developing high-throughput materials synthesis, characterization, and performance evaluation methodologies. A multi-channel flow double electrode (m-CFDE) cell, based on previous work by M. Watanabe’s group [5], has recently been designed and tested for the simultaneous screening of the catalytic activity of multiple samples in an aqueous environment [6]. An automated robotic catalyst ink dispensing system has been developed for precise deposition of nano-liter ink droplets across the m-CFDE glassy carbon electrodes (1 mm × 3 mm). The nano-liter injector with exchangeable micro-tips deposits the electrode ink onto the tiny surface glassy carbon at a precise injection speed. The removable electrode plugs of the m-CFDE cell are fixed on a numerically-controlled XY table to uniformly distribute the PGM-free catalyst across the glassy-carbon electrode. This automated deposition stage provides better reproducibility and uniform distribution over the conventional hand deposition using micropipettes as is typically utilized for ink deposition for rotating disk electrode measurements. In the performance evaluation aspect, a commercial combinatorial membrane-electrode assembly (MEA) test system has been further developed and utilized to simultaneously evaluate the fuel cell performance of 25 electrodes with different catalyst and ionomer-to-carbon ratios. The automated electrode deposition system in combination with a custom-designed heated vacuum table mounted on the XY table has also been used to make a catalyst-coated membrane (CCM) with 25 segmented electrodes. The results of application of this high-throughput methodology to a promising class of PGM-free catalysts will be discussed. Acknowledgements This work was supported by the U.S. Department of Energy, Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office under the auspices of the Electrocatalysis Consortium (ElectroCat). Argonne National Laboratory is managed for the U.S Department of Energy by the University of Chicago Argonne, LLC, under contract DE-AC-02-06CH11357.

On the Preparation and Testing of Fuel Cell Catalysts Using the Thin Film Rotating Disk Electrode Method

We present a step-by-step tutorial to prepare proton exchange membrane fuel cell (PEMFC) catalysts, consisting of Pt nanoparticles (NPs) supported on a high surface area carbon, and to test their performance in thin film rotating disk electrode (TF-RDE) measurements. The TF-RDE methodology is widely used for catalyst screening; nevertheless, the measured performance sometimes considerably differs among research groups. These uncertainties impede the advancement of new catalyst materials and, consequently, several authors discussed possible best practice methods and the importance of benchmarking. The visual tutorial highlights possible pitfalls in the TF-RDE testing of Pt/C catalysts. A synthesis and testing protocol to assess standard Pt/C catalysts is introduced that can be used together with polycrystalline Pt disks as benchmark catalysts. In particular, this study highlights how the properties of the catalyst film on the glassy carbon (GC) electrode influence the measured performance in TF-RDE testing. To obtain thin, homogeneous catalyst films, not only the catalyst preparation, but also the ink deposition and drying procedures are essential. It is demonstrated that an adjustment of the ink's pH might be necessary, and how simple control measurements can be used to check film quality. Once reproducible TF-RDE measurements are obtained, determining the Pt loading on the catalyst support (expressed as Pt wt%) and the electrochemical surface area is necessary to normalize the determined reaction rates to either surface area or Pt mass. For the surface area determination, so-called CO stripping, or the determination of the hydrogen underpotential deposition (Hupd) charge, are standard. For the determination of the Pt loading, a straightforward and cheap procedure using digestion in aqua regia with subsequent conversion of Pt(IV) to Pt(II) and UV-vis measurements is introduced.

On the Preparation and Testing of Fuel Cell Catalysts Using the Thin Film Rotating Disk Electrode Method.

We present a step-by-step tutorial to prepare proton exchange membrane fuel cell (PEMFC) catalysts, consisting of Pt nanoparticles (NPs) supported on a high surface area carbon, and to test their performance in thin film rotating disk electrode (TF-RDE) measurements. The TF-RDE methodology is widely used for catalyst screening; nevertheless, the measured performance sometimes considerably differs among research groups. These uncertainties impede the advancement of new catalyst materials and, consequently, several authors discussed possible best practice methods and the importance of benchmarking.The visual tutorial highlights possible pitfalls in the TF-RDE testing of Pt/C catalysts. A synthesis and testing protocol to assess standard Pt/C catalysts is introduced that can be used together with polycrystalline Pt disks as benchmark catalysts. In particular, this study highlights how the properties of the catalyst film on the glassy carbon (GC) electrode influence the measured performance in TF-RDE testing. To obtain thin, homogeneous catalyst films, not only the catalyst preparation, but also the ink deposition and drying procedures are essential. It is demonstrated that an adjustment of the ink's pH might be necessary, and how simple control measurements can be used to check film quality. Once reproducible TF-RDE measurements are obtained, determining the Pt loading on the catalyst support (expressed as Pt wt%) and the electrochemical surface area is necessary to normalize the determined reaction rates to either surface area or Pt mass. For the surface area determination, so-called CO stripping, or the determination of the hydrogen underpotential deposition (Hupd) charge, are standard. For the determination of the Pt loading, a straightforward and cheap procedure using digestion in aqua regia with subsequent conversion of Pt(IV) to Pt(II) and UV-vis measurements is introduced.

Porous silicon film formation from silicon-nanoparticle inks: The possibility of effects of van der Waals interactions on uniform film formation

Porous Si films were formed on electrically insulative, semiconductive, and conductive substrates by depositing aqueous and nonaqueous Si nanoparticle inks. In this study, we focused on whether the Si ink deposition resulted in the formation of uniform porous Si films on various substrates. As a result of the experiments, we found that the inks showing better substrate wettabilities did not necessarily result in more uniform film formation on the substrates. This implies that the ink-solvent wettability and the nanoparticle–substrate interactions play important roles in the uniform film formation. As one of the interactions, we discussed the influence of van der Waals interactions by calculating the Hamaker constants. The calculation results indicated that the uniform film formation was hampered when the nanoparticle surface had a repulsive van der Waals interaction with the substrate.

Inkjet printing of specular holograms based on a coffee-ring effect concave structure

The proposed method for creating specular holograms on a variety of surface materials is based on creating a three-dimensional surface microstructure by controllable ink deposition.

Homogeneous and highly controlled deposition of low viscosity inks and application on fully printable perovskite solar cells

The fully printed, hole-transporter-free carbon perovskite solar cell structure incorporating a triple mesoscopic layer has emerged as a possible frontrunner for early industrialisation. It is an attractive structure because it can be fabricated by the simple sequential screen printing and sintering of titania, zirconia, and carbon. The device is finalised by manual dropping of a perovskite precursor solution onto the carbon which subsequently infiltrates. This stage in device fabrication is inhomogeneous, ineffective for large areas, and prone to human error. Here we introduce an automated deposition and infiltration system using a robotic dispenser and mesh which delivers the perovskite precursor uniformly to the carbon surface over a large area. It has been successfully used to prepare perovskite solar cells with over 9% efficiency. Cells, prepared by this robotic mesh deposition, showed comparable performance to reference cells, made by standard drop deposition, confirming this approach to be effective and reliable. X-ray diffraction and Raman spectroscopy were used to confirm the uniformity of the deposition over a large area.

Digital Aerosol Jet Printing for the Fabrication of Terahertz Metamaterials

AbstractIn this paper the use of aerosol jet printing as a fabrication and rapid prototyping method for terahertz metamaterials is presented. Since this technique combines the very precise deposition of metallic inks with line widths down to 10 µm and the use of digitally generated tool paths, it is highly suitable for fabricating arbitrary 2D microstructures for terahertz applications. The fabrication of a metamolecule composed of four closed ring resonators with two different radii on conventional polyester foil is shown. Furthermore, the metamaterials are characterized thoroughly using microscopic images, confocal microscopy, and terahertz time‐domain spectroscopy, which demonstrate impressively the suitability of this fabrication technology for terahertz applications. For an additional validation the experimentally gathered data with numerical simulations are compared.

Paper‐based Electrochemical Devices Coupled to External Graphene‐Cu Nanoparticles Modified Solid Electrode through Meniscus Configuration and their Use in Biological Analysis

AbstractThis paper demonstrates, for the first time, the use of paper‐based electrochemical devices coupled to external solid working electrodes. The paper‐based electrochemical cells were fabricated using inexpensive and largely available office paper, according to a simple protocol that consists on the creation of hydrophobic barriers using paraffinized paper and preheated metal stamp. The counter and reference electrodes were integrated to the paper platform through the deposition of carbon and silver inks, respectively. The electrochemical paper analytical device (ePAD) was coupled to external glassy carbon rod electrode modified with reduced graphene oxide doped with Cu nanoparticles through meniscus configuration. The analytical usefulness of this electrochemical approach was demonstrated through the simultaneous determination of paracetamol and caffeine in biological samples. The analytes were successfully quantified in real urine samples and limits of detection of 24.6 nM (paracetamol) and 36.1 nM (caffeine) were obtained. The paper platform showed good stability (RSD of 1.07 % for the peak currents and 1.43 % for the peak potentials) and satisfactory performance. The use of solid electrodes coupled to paper electrochemical devices, firstly demonstrated here, opens new possibilities for the utilization of ePADs in electrochemistry and electroanalytical chemistry and offers advantages such as the extremely reduced consumption of reagents and the minimal generation of wastes.

An Economical Half-Cell and Modified Rotating Disk Electrode for Electrochemical Characterizations of Fuel Cell Catalyst-Coated Membranes and Gas Diffusion Electrodes

Common methods of fuel cell electrocatalyst characterization, in particular the oxygen reduction reaction (ORR) catalysts, include thin-film RDE and PEMFC measurements using fuel cell test stations. The former is generally available in many electroanalytical labs, however, ink deposition on RDE tips and limited solubility of oxygen in the electrolyte lead to testing environments which are quite different from those of fuel cell hardwares. The latter option requires fuel cell hardware and an appropriate test station which are expensive and not widely accessible by many labs. We present two approaches in order to bridge the gap between these methods: 1) a modified RDE tip which accepts catalyst-coated membranes (CCMs), thus eliminating the potential issues of catalyst ink deposition and the associated variabilities, and 2) a low-cost half-cell setup which allows fuel cell-like current densities (~ 1 A cm-2) to be obtained using gaseous oxygen feed. The novel RDE tip has been tested with Pt foil and commercial CCMs in 0.1 M HClO4 at room temperature (20°C) and good agreements with polycrystalline Pt and H2/O2 fuel measurements have been obtained, respectively. In addition, CCM degradation tests, using an accelerated degradation test protocol (ADT) with potential cycling, have been performed and the loss of Pt and Pt surface area have been quantified. With the half-cell setup, constant current polarizations with IR drop measurement at each step were found to provide a simple, reproducible method of measuring catalyst performance using an optimal electrolyte concentration of 1.0 M HClO4. Accurate ORR activity of commercial GDEs/CCMs and good agreement with measurements made in fuel cell hardware have been obtained with the half-cell setup. Both of these approaches are low cost (< $1000 USD) and can be implemented in a typical electroanalytical lab. Cells designs and results of ORR experiments with both approaches will be presented. Figure 1

Meso-Structured Array Electrode for Polymer Electrolyte Fuel Cells

Current state-of-the-art fuel cell cathodes rely on high loading of platinum (Pt) or Pt-alloy on high surface area carbon supports mixed with Nafion. The cost of the high Pt loading is still a hindrance to the commercialization of polymer electrolyte fuel cells (PEFCs) 1. The electrode structure consists of a random aggregation of the functional components (catalyst, ionomer, and pore space) that are formed in an uncontrolled ink deposition process. The random nature of these structures makes it difficult to optimize the functional domains and hence causes severe mass transport limitations during high-power operation, resulting in a loss in performance and requiring a higher loading and active area of Pt to maintain an acceptable level of performance. The ionomer binder adds an additional transport resistance and becomes significant at lower Pt loadings2. Decreasing this transport resistance would remove a significant barrier to low-cost, ultra-high power density fuel cells. Rational design of the electrode structure in PEFCs could improve performance and reduce cost. However, in current state-of-the-art fuel cells, each unit volume of electrode contains a random mix of components that must simultaneously provide catalytic activity, water transport, O2transport, electronic conductivity, and protonic conductivity. Since each unit must provide all functions, units cannot be optimized for individual functions. By separating the different electrode functions into discrete electrode elements, each element can be optimized for specific functions as shown in Figure 1a. Arranging these optimized discrete elements in a controlled, low-tortuosity configuration enables transport limitations to be reduced or eliminated. In previous work, Middlemen et al. showed under optimal conditions oriented catalyst layer structure can be fabricated but didn’t present any electrochemical evaluation 3. Komini Babu et al. fabricated vertically oriented Nafion nanofibers and deposited Pt via vapor deposition 4. The Nafion nanofiber electrode showed increase in performance compared to Pt sputtered on Nafion 115 electrode but lower in performance to Pt/C based electrode. In this work, we propose an alternate electrode structure to enable good transport behavior and high cell performance through controlled deposition of electrode components in an optimized, organized structural configuration. Figure 1b shows the SEM image of Nafion nanofibers for proton transport, fabricated by solution casting on a porous template. Providing effective proton transport through these low-tortuosity percolating highways allows the catalyst domain to have a lower ionomer/catalyst ratio, reducing transport resistance. Acknowledgments This research is supported by DOE Fuel Cell Technologies Office, through the Fuel Cell Performance and Durability (FC-PAD) Consortium; Fuel Cells program manager: Dimitrios Papageorgopoulos.

A laser curable palladium complex ink used for fabrication of copper pattern on polyimide substrate

Abstract A simple and efficient approach for selective metallization of polyimide (PI) substrate has been developed in this work. A heat curable Pd complex ink consists of Pd salt, pH sensitive monomer N, N-dimethyl-dimethylaminoethyl methacrylate (DMAEMA), trimethylolpropane triacrylate (TMPTA), and tert-butyl peroxybenzoate (TBPB) is utilized to promote the adhesion between the Cu coating and PI substrate. After heating the spin-coated ink on PI and successive electroless deposition (ELD) of copper, a layer of copper with excellent adhesion is formed on PI substrate. The effects of this ink on catalyzing the ELD of copper and the mechanism for the enhancement of the adhesion between flexible PI substrate and copper layer are investigated by XPS and FT-IR. The copper coating plated by this method has a low resistivity (about 13.6 × 10 − 6 Ω cm) and satisfied endurance of bending. Moreover, we also demonstrate that the copper patterns can be prepared easily by integration of laser-direct patterning of the spin-coated ink and electroless Cu deposition, which is fast and effective strategy for fabricating circuit patterns on the plastic substrate.

PDMS Deposition for Optical Devices by Dip‐Pen Nanolithography

Dip‐pen nanolithography (DPN) is a low‐cost, versatile bench‐top method for directly patterning materials on surfaces with sub‐50 nm resolution; it involves the use of a cantilever tip to transfer a selected ink onto various surfaces to create predefined patterns. Many parameters may influence DPN quality, due to the variety of deposited and surface materials and the chemical interactions between them. DPN tip deposition of liquid inks is not yet well understood, due to the lack of thorough study of the various parameters that need to be controlled in order to achieve uniform patterning. In this research, the printing of polydimethylsiloxane (PDMS) lines and the control of their physical dimensions are investigated; the applied parameters are different humidity levels, n‐hexane dilution proportions and different tip velocities. Numerous experiments accompanied by atomic force microscope measurements are conducted in order to derive a recommended recipe for the required dimensions of the printable lines. A practical aspect of the research is to assess the potential of the application of DPN for the fabrication of various optical devices, such as gratings and waveguides. In order to validate the theoretical results, PDMS printing over silicon is used to successfully produce an optical diffraction grating. image

Direct Growth of Carbon Nanofibers on Nickel Foam and Its Application As Electrochemical Supercapacitor Electrodes

Carbon nanofibers (CNF) are useful for many applications such as polymer reinforcement, electrochemical devices like sensors, batteries, and supercapacitors. The most common method of producing them is by catalytic chemical vapor deposition (CVD) or by electrospinning. CNF growth using CVD is a single step process, unlike electro spinning which requires an additional carbonization step at higher temperatures. In CVD the catalyst is either incorporated directly onto the substrate or introduced with the feed gases. This adds extra cost and set limits to the design of the systems used for the CNF growth process, particularly in cases where porous structures are envisioned. In supercapacitors, the electrode material is most often painted or deposited with an ink of carbon particles. Directly growing the carbon nanomaterial from the supporting surface would eliminate this step and allow complex geometries. It would also help in achieving a higher capacitance by removing the requirement of a binder material and eliminate the occurrence of agglomeration of the active material inherent in the ink deposition process. Another advantage is the higher conductivity of CNF compared to the commonly used active carbon material. With CNF growing directly of the current collector, the addition of conductive carbon black can possibly be eliminated. Finally, an increase access of the electrolyte to the electrode can be expected due to the natural 3-D nano-architecture formed by the CNF. On the other hand, the micro-scale 3-D structure of nickel foams have been the most sought after substrates (current collectors) in the battery and supercapacitor research as they offer more surface area for the deposition of the required active material, together with being non-corrosive in alkali medium. CNF grown directly on Ni-foams are thus expected to extend the performances of supercapacitor electrodes. In this work, we have found a novel method of growing dense CNF on nickel foam. Cyclic voltammetry, galvanotactic charge discharge, and electrochemical impedance spectroscopy was made to electrochemically characterize these CNF/Ni-foam supercapacitor electrodes. When tested as a supercapacitor electrode in 6M KOH, our directly grown CNF gives a good aerial capacitance of about 60 mF/cm2 and an energy density of 16 mWh/m2. We believe this nickel foam with CNF to be very useful in supercapacitors and batteries in decreasing the resistance of the electrochemical device and provide additional surface area.

Selective Conversion from p-Type to n-Type of Printed Bottom-Gate Carbon Nanotube Thin-Film Transistors and Application in Complementary Metal-Oxide-Semiconductor Inverters.

The fabrication of printed high-performance and environmentally stable n-type single-walled carbon nanotube (SWCNT) transistors and their integration into complementary (i.e., complementary metal-oxide-semiconductor, CMOS) circuits are widely recognized as key to achieving the full potential of carbon nanotube electronics. Here, we report a simple, efficient, and robust method to convert the polarity of SWCNT thin-film transistors (TFTs) using cheap and readily available ethanolamine as an electron doping agent. Printed p-type bottom-gate SWCNT TFTs can be selectively converted into n-type by deposition of ethanolamine inks on the transistor active region via aerosol jet printing. Resulted n-type TFTs show excellent electrical properties with an on/off ratio of 106, effective mobility up to 30 cm2 V-1 s-1, small hysteresis, and small subthreshold swing (90-140 mV dec-1), which are superior compared to the original p-type SWCNT devices. The n-type SWCNT TFTs also show good stability in air, and any deterioration of performance due to shelf storage can be fully recovered by a short low-temperature annealing. The easy polarity conversion process allows construction of CMOS circuitry. As an example, CMOS inverters were fabricated using printed p-type and n-type TFTs and exhibited a large noise margin (50 and 103% of 1/2 Vdd = 1 V) and a voltage gain as high as 30 (at Vdd = 1 V). Additionally, the CMOS inverters show full rail-to-rail output voltage swing and low power dissipation (0.1 μW at Vdd = 1 V). The new method paves the way to construct fully functional complex CMOS circuitry by printed TFTs.

Low band‐gap CuIn(S,Se)2 thin film solar cells using molecular ink with 9.5% efficiency

Vacuum free, solution based routes to the preparation of chalcopyrite absorbers for solar cells promise options in device design and manufacturing that are not provided by the standard vacuum based approaches. In order to fully exploit these options, the precursor should contain neither nanoparticles nor hazardous chemicals, and it should be stable under ambient conditions. In this contribution we report on CuIn(S,Se)2 thin film preparation based on spin coating of an air stable molecular ink containing metal chlorides and thiourea in organic solvents. Several key parameters directly influencing the performance of the resulting solar cells have been identified. Wetting of the glass/Mo substrate has been adjusted by varying the concentration of ethylene glycol butyl ether in the ink. Before annealing in Ar/Se at atmospheric pressure, several cycles of ink deposition and drying can be used to increase the thickness of the precursor stack. Careful balancing of ink concentration, number of precursor deposition cycles, and annealing temperature profile will transform the multi‐layer precursor into a sufficiently thick, continuous, large grained film as required for high quantum efficiency, and good red response of the cells. These optimizations aimed at high photo current have already led to an efficiency of 9.5%.

Gradient and Patterned Protein Films Stabilized via Nanoimprint Lithography for Engineered Interactions with Cells.

Protein-based biomaterials provide versatile scaffolds for generating functional surfaces for biomedical applications. However, tailoring the functional and biological properties of protein films remains a challenge. Here, we describe a high-throughput method to designing stable, functional biomaterials by combining inkjet deposition of protein inks with a nanoimprint lithography based methodology. The translation of the intrinsically charged proteins into functional materials properties was demonstrated through controlled cellular adhesion. This modular strategy offers a rapid method to produce customizable biomaterials.