Achieving high solar-to-hydrogen (STH) efficiency concomitant with long-term durability using low-cost, scalable photo-absorbers is a long-standing challenge. Here we report the design and ...fabrication of a conductive adhesive-barrier (CAB) that translates >99% of photoelectric power to chemical reactions. The CAB enables halide perovskite-based photoelectrochemical cells with two different architectures that exhibit record STH efficiencies. The first, a co-planar photocathode-photoanode architecture, achieved an STH efficiency of 13.4% and 16.3 h to t
, solely limited by the hygroscopic hole transport layer in the n-i-p device. The second was formed using a monolithic stacked silicon-perovskite tandem, with a peak STH efficiency of 20.8% and 102 h of continuous operation before t
under AM 1.5G illumination. These advances will lead to efficient, durable, and low-cost solar-driven water-splitting technology with multifunctional barriers.
Aptamers, due to their small size, strong target affinity, and ease of chemical modification, are ideally suited for molecular detection technologies. Here, we describe successful use of aptamer ...technology in a consumer device for the detection of peanut antigen in food. The novel aptamer-based protein detection method is robust across a wide variety of food matrices and sensitive to peanut protein at concentrations as low as 12.5 ppm (37.5 µg peanut protein in the sample). Integration of the assay into a sensitive, stable, and consumer friendly portable device will empower users to easily and quickly assess the presence of peanut allergens in foods before eating. With many food reactions occurring outside the home, the type of technology described here has significant potential to improve lives for children and families.
Photoelectrochemical (PEC) water splitting, which utilizes sunlight and water to produce hydrogen fuel, is potentially one of the most sustainable routes to clean energy. One challenge to success is ...that, to date, similar materials and devices measured in different labs or by different operators lead to quantitatively different results, due to the lack of accepted standard operating procedures and established protocols for PEC efficiency testing. With the aim of disseminating good practices within the PEC community, we provide a vetted protocol that describes how to prepare integrated components and accurately measure their solar-to-hydrogen (STH) efficiency (η
STH
). This protocol provides details on electrode fabrication, η
STH
test device assembly, light source calibration, hydrogen evolution measurement, and initial material qualification by photocurrent measurements under monochromatic and broadband illumination. Common pitfalls in translating experimental results from any lab to an accurate STH efficiency under an AM1.5G reference spectrum are discussed. A III–V tandem photocathode is used to exemplify the process, though with small modifications, the protocol can be applied to photoanodes as well. Dissemination of PEC best practices will help those approaching the field and provide guidance for comparing the results obtained at different lab sites by different groups.
Charge trapping and storage in polymer dielectrics can be harnessed to control semiconductor devices. Organic transistor (OFET) gate insulators affect bias stress and threshold voltage (V th), and ...charging them can preset the operating voltages and control bias stress. We describe a chemical design and film fabrication procedure for construction of stacks of polystyrene (PS) layers, each with arbitrary concentrations of potentially chargeable functional groups. Thermal cross-linking of benzocyclobutene subunits ensures layer integrity while keeping the layers free of polar functionality and small molecule byproducts. Neutron reflectivity (NR), scanning electron microscopy, and atomic force microscopy (AFM) showed that individual layer thicknesses varied systematically with polymer concentration in deposition solutions, and interfacial thicknesses ranged from 1.5 to 4 nm, independent of layer thickness, demonstrating formation of distinct layers with minimal roughness or intermixing. The PS-based materials were used as the sole gate dielectrics for pentacene OFETs. We compared V th before and after charging. Increased bias stress stability as evidenced by reduced V th shift was seen in devices with trilayer dielectrics with substituted PS as the middle layer compared to a dielectric made from unsubstituted PS. On the other hand, increased V th shift was seen in many devices with bilayer dielectrics made with substituted PS as the top layer. We attribute the decreased V th shift seen in trilayer devices to an increased dielectric polarization of the substituted PS in the middle layer that countered the charge trapping effect in the top layer. This demonstration establishes a method for utilizing vertical charge patterns for various electronics applications.
The conformational equilibrium of 3-(dimethylazinoyl)propanoic acid (DMAPA, azinoyl = N+(O−) has a weak pH-dependence in D2O, with a slight preference for trans in alkaline solutions. The acid ...ionization constants of the protonated amine oxide and carboxylic functional groups as determined by NMR spectroscopy were 7.9 × 10−4 and 6.3 × 10−6, respectively. The corresponding value of K 1/K 2 of 1.3 × 102 is not deemed large enough to provide experimental NMR evidence for a significant degree of intramolecular hydrogen bonding in D2O. Conformational preferences of DMAPA are mostly close to statistical (gauche/trans = 2/1) in other protic solvents, e.g., alcohols. However, the un-ionized form of DMAPA appears to be strongly intramolecularly hydrogen-bonded and gauche in aprotic solvents.
Organic electronics have attracted increasing interest during the past decade due to their potential applications in transparent, large-area, printable, and stretchable devices. Solution based ...material deposition considerably reduces processing costs, and allows the use of non-standard substrates in device design. Many organic electronic device parameters are controlled by interfacial as well as bulk properties. Organic donor-acceptor junctions are relevant to organic photovoltaics (OPVs) as well as organic light emitting diodes (OLEDs). In an OPV, interfacial potentials between the hole transporting (donor) organic semiconductor (OSC) and electron transporting OSC (acceptor) lead to separation and recombination of electrons and holes. The mechanisms behind interfacial potential formation in organic donor-acceptor junctions are not fully understood and are an active area of study. In this thesis, the interfacial potential was measured, and interface and bulk contributions were separated by fabricating lateral organic donor-acceptor junctions both with and without a gap between the donor and acceptor materials. Contact between the donor and acceptor materials increases the interfacial potential beyond that calculated from bulk values. This can be explained through differences in electron affinity of the donor and acceptor, and also by differences in the delocalization of molecular orbitals (MOs) of the two OSC films. Greater delocalization of MOs allows for electron donation to adjacent molecules, a surprising result in organic electronics. In addition, the effect of the substrate on the potential was examined. The field is persistently negative on the acceptor side when the junction is made on a SiO2 substrate. When Al2Oi3, a substrate with higher dielectric constant, is used, the field decreases in one case, and reverses in the other. For organic field effect transistors (OFETs), the instability of switching voltages is an interface-dominated issue which causes the device left on to turn off over time, referred to as bias stress. Bias stress, caused by charges trapped at the dielectric/OSC interface, can be quantified by a shift in the threshold voltage (Vth) of the device. This thesis discusses localizing trapped charges in an OFET dielectric to control bias stress and operating voltages. By changing numbers and positions of trapped charges in the dielectric, the voltage at which the OFET turns on can be defined, and by pre-populating interfacial traps before running the device, bias stress may be reduced. In this thesis, charging of bilayer and trilayer dielectrics made from in-house synthesized ‘chargeable’ substituted polymers was studied. There was greater stabilization of trapped charges at the dielectric/OSC interface in chargeable polymers adjacent to the OSC, indicating charging occurs through an interface-driven mechanism. However, when they were encapsulated such that the chargeable polymer was situated between two layers of unsubstituted polymer, there was less response to charging than in the fully unsubstituted control. This reduction in bias stress susceptibility could stem from the bulk dielectric polarization of the chargeable layer, which counteracts the charge trapping mechanism at the dielectric/OSC interface.
Lateral organic field-effect transistors (OFETs), consisting of a polystyrene (PS) polymer gate material and a pentacene organic semiconductor (OSC), were electrically polarized from bias stress ...during operation or in a separate charging step, and investigated with scanning Kelvin probe microscopy (SKPM) and current–voltage determinations. The charge storage inside the polymer was indicated, without any alteration of the OFET, as a surface voltage with SKPM, and correlated to a threshold voltage (V T) shift in the transistor operation. The SKPM method allows the gate material/OSC interface of the OFET to be visualized and the surface voltage variation between the two gate material interfaces to be mapped. The charge distribution for three samples was derived from the surface voltage maps using Poisson’s equation. Charge densities calculated this way agreed with those derived from the V T shifts and the lateral gate-OSC capacitance. We also compared the behavior of two other polymers with PS: PS accepted the most static charge in its entire volume, poly(2-trifluoromethylstyrene) (F-PS) had the most stability to bias stress, and poly(methyl methacrylate) (PMMA) showed the most leakage current and least consistent response to static charging of the three polymers. This work provides a clear demonstration that surface voltage on a working OFET gate material can be related to the quantity of static charge responsible for bias stress and nonvolatility in OFETs.
Metal oxide-based transistors can be fabricated by low-cost, large-area solution processing methods, but involve a trade-off between low processing temperature, facile charge transport and ...high-capacitance/low-voltage transistor gates. We achieve these simultaneously by fabricating zinc oxide and sodium-incorporated alumina (SA) thin films with temperature not exceeding 200 to 250 °C using aqueous and combustion precursors, respectively. X-ray reflectivity shows a compositionally distinct SA boundary layer forming near the substrate and that a portion of the SA is chemically removed during the subsequent semiconductor deposition. Improved etch resistance and reduced dielectric leakage was obtained when (3-glycidoxypropyl) trimethoxysilane was included in the SA precursor.
PDF
