Recent work in structure–processing relationships of polymer semiconductors have demonstrated the versatility and control of thin-film microstructure offered by meniscus-guided coating (MGC) techniques. Here, we analyze the qualitative and quantitative aspects of solution shearing, a model MGC method, using coating blades augmented with arrays of pillars. The pillars induce local regions of high strain rates—both shear and extensional—not otherwise possible with unmodified blades, and we use fluid mechanical simulations to model and study a variety of pillar spacings and densities. We then perform a statistical analysis of 130 simulation variables to find correlations with three dependent variables of interest: thin-film degree of crystallinity and transistor field-effect mobilities for charge-transport parallel (μpara) and perpendicular (μperp) to the coating direction. Our study suggests that simple fluid mechanical models can reproduce substantive correlations between the induced fluid flow and important performance metrics, providing a methodology for optimizing blade design.

Recent studies have shown spray-pyrolysis is a low-cost, simple and efficient technique for deposition of metal oxide semiconductors (such as zinc oxide) as the active layer of thin-film transistors (TFTs). However, to allow the translation from laboratory scale to industry the reproducibility of such method needs to be evaluated. We present herein a representative study concerning the reproducibility and uniformity of spray-coated ZnO TFTs using several devices, from different production batches, following the same fabrication protocol. We demonstrate that it is possible to obtain transistors with high performance and reproducibility by controlling the most relevant deposition factors, corroborated by a low deviation rate (below 10%) from the characteristic TFT parameters (mobility in saturation, threshold voltage and on/off ratio), which is compatible to commonly available commercial electronic devices.

Wide-bandgap oxide semiconductors have received significant attention as they can produce devices with high output and breakdown voltage. p-Type conductivity control is essential to realize bipolar devices. Therefore, as a rare wide-bandgap p-type oxide semiconductor, NiO (3.7 eV) has garnered considerable attention. In view of the heterojunction device with Ga2O3 (4.5–5.0 eV), a p-type material with a large bandgap is desired. Herein, we report the growth of a Ni1-xMgxO thin film, which has a larger bandgap than NiO, on α-Al2O3 (0001) substrates that was developed using the mist chemical vapor deposition method. The Ni1-xMgxO thin films epitaxially grown on α-Al2O3 substrates showed crystallographic orientation relationships identical to those of NiO thin films. The Mg composition of Ni1-xMgxO was easily controlled by the Mg concentration of the precursor solution. The Ni1-xMgxO thin film with a higher Mg composition had a larger bandgap, and the bandgap reached 3.9 eV with a Ni1-xMgxO thin film with x = 0.28. In contrast to an undoped Ni1-xMgxO thin film showing insulating properties, the Li-doped Ni1-xMgxO thin film had resistivities of 101–105 Ω∙cm depending on the Li precursor concentration, suggesting that Li effectively acts as an acceptor.

We report the development of a sensitive and a label-free electrochemical immunosensing platform for the detection of cardiac biomarker troponin I (cTnI) using tungsten trioxide nanorods (WO3 NRs). The low-temperature hydrothermal technique was employed for the controlled synthesis of WO3 NRs. Thin films of 3-aminopropyltriethoxy saline (APTES)-functionalized WO3 NRs were deposited on indium tin oxide (ITO)-coated glass substrate (0.5 cm × 1 cm) using electrophoretic deposition technique. The covalent immobilization of cTnI antibody onto functionalized WO3 NRs electrode was accomplished using EDC-NHS [1-(3-(dimethylamino)-propyl)-3-ethylcarbodiimide hydrochloride and N-hydroxysulfosuccinimide] chemistry. The structural and morphological characterizations of WO3 NRs and functionalized WO3 NRs were studied using X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, and electrochemical techniques. The impedimetric response study of the proposed immunosensor demonstrates high sensitivity [6.81 KΩ mL·cm2)] in a linear detection range of 0.01–10 ng/mL. The excellent selectivity, good reproducibility, and long-term stability of the proposed immunosensing platform indicate WO3 NRs as a suitable platform for the development of a point-of-care biosensing device for cardiac detection.

We have shown that molecular imprinting (MI) technology can be used to produce sensitive, robust, cost-effective biosensing systems with a real-time electrochemical readout that can be utilized for point of care diagnostics. Real time detection of biomarkers is essential when rapid, critical decisions need to be made, such as in situations where public health is threatened. Our biosensor has high sensitivity compared to standard methods like ELISA, and results are obtained within minutes, using inexpensive, accessible potentiometric readout technology. These biosensors utilize surface molecular imprinting of a self-assembling monolayer of hydroxy-terminated alkanethiol chains which form a crystalline ‘lock-and-key’ structure around a target analyte, allowing the sensors to detect and differentiate between bio-macromolecules of similar size and shape with high selectivity and sensitivity. The sensors are extremely versatile and able to detect a diverse range of molecules of varied chemical composition and structure. To fully exploit the sensors’ advantages, especially in remote, economically disadvantaged areas, it is important to quantify their durability and reusability. Biosensor chips were created to test the viability of hemoglobin detection and to evaluate the potential for sensor reusability when washed after detection testing. The successful readsorption of hemoglobin even after washing, accompanied by cyclic voltammetry data indicating the preservation of the SAM, indicate that these biosensors are reusable, significantly augmenting the device’s value. Potential applications include the analysis of complex chemical and biological processes such as stem cell differentiation and on-the-spot detection of diseases such as Zika.

Thin films of Cu2ZnSnS4 have been synthesized through solution chemistry. The correlation between film morphology and the ratio of cations (copper, zinc and tin) and the amount of monoethanolamine (MEA) in solution has been investigated. The stoichiometric ratio of cations resulted in films comprised of fine grains (∼165 nm) with large crystals (∼ 1 − 2μm) spread over its surface. The films corresponding to copper poor and zinc rich solutions were comprised of grains having uniform size (∼300 nm). The addition of MEA to precursor solutions resulted in a significant drop of pinholes in the films, however, at the same time grain size decreases to 50 − 200 nm range depending on the amount of MEA present in the precursor solution.

Ternary Sn-Sb-S thin films with remarkable optical, electrical and structural properties were developed by chemical bath deposition. Tin and antimony chlorides and thioacetamide were used as tin, antimony, and sulfur ion sources, respectively, while tartaric acid was used as a complexing agent. XRD analysis of as-deposited films showed a combination of binary phases of SnS, Sn2S3, and Sb2S3, while after thermal treatment in nitrogen at 400 °C, the films became crystalline showing well-defined reflections of the ternary SnSb2S4. The heating also influenced the morphology, compactness, and thickness of the films. On the other hand, all the films showed an absorption coefficient higher than 104 cm-1, while the optical band gap of the as-deposited film decreased from 1.49 to 1.37 eV after heating at 400 °C. In addition, the photoconductivity of the films prior to heating was of 10-9 Ω-1 cm-1, while after that at 400 °C was of 10-7 Ω-1 cm-1. The evaluation of the ternary film in solar cells gave an open-circuit voltage Voc of 448 mV and short-circuit current density of Jsc of 2.4 mA/cm2.

Formation of a low barrier back contact plays a critical role in improving the photoconversion efficiency of the CdTe solar cells. Incorporating a buffer layer to minimize the band bending at the back of the CdTe device can significantly lower the barrier for the hole current, improving open circuit voltage (VOC) and the fill factor. Over the past years, researchers have incorporated the both ZnTe and Te as buffer layers to improve CdTe device performance. Here we compare device performance using these two materials as buffer layers at the back of CdTe devices. We show that using Te in contact to CdTe results in higher performance than using ZnTe in contact to the CdTe. Low temperature current density-voltage measurements show that Te results is a lower barrier with CdTe than ZnTe, indicating that Te has better band alignment, resulting in less downward bending in the CdTe at the back interface, than ZnTe does.

Wearable and bio-implantable health monitoring applications require flexible memory devices that can be used to locally store body vitals prior to transmission or to support local data processing in distributed smart systems. In recent years, non-volatile resistive random access memories composed of oxide-based insulators such as hafnium oxide and niobium pentoxide have attracted a great deal of interest. Unfortunately, hafnium and niobium are not low-cost materials and may also present health challenges. In this work, we have explored the alternative of using titanium dioxide as the insulating oxide using a low-cost solution-phase deposition process. Aqueous sol deposited thin films were deposited on standard RCA-cleaned commercial thermal silicon dioxide (500 nm) wafer (500 µm). Patterned bottom contacts Cr/Au (∼200/300 Å) using shadow masks were deposited on the substrate using successive DC sputtering, and thermal evaporation, respectively at 5 X 10-6 Torr. A sol was prepared using titanium (IV) butoxide as precursor hydrolysed under water and ethanol to form a colloidal solution (sol) at 50°C under constant stirring. Powder X-Ray Diffraction (PXRD) scans of calcined (from sol at 750°C) nanoparticles show a mixture of anatase and rutile phases, confirming the composition of the material. The sol was slowly cooled to room temperature before being spin coated at low rotational speeds on to the substrate in multiple steps involving several spin coating and drying steps to form a uniform film. Top contacts (Ag) of thickness (∼500 Å) were deposited on the sol-deposited thin films using thermal evaporation. The resulting devices were coated with a thick layer of polydimethylsiloxane (PDMS) using a 10:1 ratio of base elastomer and curing agent respectively. After drying the PDMS, resistance measurements were carried out. A high resistance state was detected prior to electroforming in the air at ∼5 MΩ which remains nearly unchanged (∼4.3 MΩ) when dipped in a ∼7.4 pH phosphate buffer solution (equivalent to human blood’s pH (reference average value ∼7.4 pH)). Unencapsulated devices (UM1) were further characterized in air using a Keithley 4200-SCS semiconductor parameter analyzer in dual sweep mode to observe repeatable hysteresis behavior with a large difference between trace and retrace R-V characteristics (∼50±3% over a pristine device), which compares favorably with recent data in the literature on high-performance sputtered TiO2 memristors. Unchanged retention ratio using biocompatible device materials and encapsulation suggests that these devices can be used for biomedical implantable sensor electronics.

In the synthesis of metallic nanocrystals (NCs) using a high-temperature colloidal approach, the competition between deposition and diffusion of “free atom (or clusters)” plays an important role as it can direct the morphology of NCs during their evolution. This competition is closely associated with some dynamic conditions such as heat and mass transfer. Stirring speed and ramp rate of heating are two factors that greatly impact the heat and mass transfer processes and consequently determine the morphology of the products but rarely discussed in most synthetic protocols. Herein, we study the syntheses of Pt-M (M = Ni, Fe) NCs as model reactions, showing that a low stirring speed and high ramp rate of heating result in ununiform pod-like NCs, whereas the inverse conditions promote NCs in a uniform shape. This observation can be plausibly explained using a competition mechanism between the deposition and diffusion of the newly reduced atoms during a stage of the NC’s growth.

We report the synthesis and photovoltaic characterization of four novel polymers based on poly({4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl}{3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl}) (PTB7) incorporating various numbers of photocrosslinkable n-octyl chloride sidechains (PTB-Cl). These polymers showed similar optoelectronic properties to PTB7 and readily cross-linked in the form of thin films after deep-UV exposure. Photolithography with micrometer-scale patterning is demonstrated. PTB-Cls exhibit similar PV performances to PTB7 and lightly cross-linked PTB-Cls showed stable high photoconversion efficiencies after prolonged thermal treatment. However, it is found that a high-degree cross-linking is needed to prevent the formation of PCBM crystallites at high annealing temperatures even though the PV performance is stabilized with a much lower degree of cross-linking. This implies that the complete prevention of PCBM crystallite formation is not necessary to affect the stabilization of PV devices against excessive heat.

The apparent diffusion coefficients of La, Nd, Eu, Dy, Er, and Lu in compacted bentonites were investigated at various bicarbonate concentrations. The apparent diffusion coefficients of these lanthanides tended to decrease with increasing dry density. At bicarbonate concentrations below 0.25 M, lanthanum had the largest diffusion coefficient (ca. 10-13 m2/s) at 1.0 Mg/m3, and the diffusion coefficient decreased with increasing atomic number. On the other hand, at bicarbonate concentrations above 0.25 M, lutetium had the largest diffusion coefficient, and the diffusion coefficient decreased with decreasing atomic number. In particular, lanthanum and neodymium had diffusion coefficients below 10-14 m2/s, even at 1.0 Mg/m3. The diffusion coefficient of europium was around 10-13 m2/s at 1.0 Mg/m3 and was influenced less by the bicarbonate concentration. The diffusion coefficient of lutetium increased from 2 × 10-14 to 10-12 m2/s as the bicarbonate concentration was increased to 1.0 M. The concentration of carbonate ion in the pore water of bentonite is estimated to be much lower than that in solutions in contact with bentonite from the viewpoints of solubility and chemical species of lanthanides.

We report single-shot transient absorption (SSTA) measurements of an organic film of 3,3’-Diethyloxatricarbocyanine iodide (DOTCI). In SSTA, the pump-probe time delay is spatially encoded by using a tilted pump pulse. Translation of the sample during SSTA measurements averages over any spatial heterogeneity in the film. We demonstrate that exciton dynamics measured with the single-shot technique agrees with traditional transient absorption measurements of the same film. A signal-to-noise ratio of ∼40 is achieved in 10 s. The ability to measure exciton dynamics in organic films will enable future SSTA measurements of exciton dynamics during the molecular aggregation events that result in film formation.

Pb-based organometal halide perovskite solar cells have passed the threshold of 20 % power conversion efficiency (PCE). However, the main issues hampering commercialization are toxic Pb contained in these cells and their instability in ambient air. Therefore, great attention is devoted to replace Pb by Sn or Bi, which are less harmful and - in the case of Bi - also expected to yield enhanced stability. In literature, the most efficient hybrid organic-inorganic methylammonium bismuth iodide (MBI) perovskite solar cells reach PCE up to 0.2 %. In this work, we present spin-coated MBI perovskite solar cells and highlight the impact of the concentration of the perovskite solution on the layer morphology and photovoltaic (PV) characteristics. The solar cells exhibit open-circuit voltages of 0.73 V, which is the highest value published for this type of solar cell. The PCE increases from 0.004 % directly after processing to 0.17 % after 48 h of storage in air. 300 h after exposure to air, the cells still yield 56 % of their peak PCE and 84 % of their maximum open-circuit voltage.

Tungsten oxide based micro and nanostructures as well as their 2-D integrated counterparts with appropriate surface modifications such as sensitization, coating of other semiconductors or growth of functional groups have been examined to enhance supercapacitance and sensing capabilities. With the goal of investigation of these changes, the electrochemical capacitance behavior of newly prepared nano and micro-structured tungsten oxide coated substrates were examined. The utilization of WO3 based sensors to differentiate edible colorant and toxic pigments, was also explored. The systematic electrochemical analysis and comparative study of selected colorants was done in order to establish a roadmap to detect model organic compounds for better preventive action.

High quality active layers for hybrid organic-inorganic perovskite solar cells are essential for achieving maximum device performance. However, perovskite active layers in solar cells are frequently prepared with unoptimized processes that lead to layers of inferior quality. This is often the case when research focuses on other aspects of the solar cell device, such as device design and architecture, carrier transport layers, electrodes, interlayers, etc. In this study, a single-step spin-coating method was used to prepare semi-crystalline PbI2(DMSO) complex films via evaporation-induced self-assembly. These optimized intermediate films were then used to form homogeneous methylammonium lead iodide (MAPbI3) perovskite films of optimum thickness (ca. 400 nm) with uniform surface coverage, good crystallinity, high purity, and grain sizes up to one micron, by employing a sequential deposition process involving intramolecular exchange between the PbI2(DMSO) complex film and a methylammonium iodide (MAI) layer deposited on top of it. We found that for certain ranges of MAI concentration, the formation of optimal-quality perovskite active layers was independent of MAI concentration, so long as MAI deposition occurred at specific corresponding spin speeds. Planar p-i-n perovskite solar cells comprising the optimized active layers were fabricated, and they exhibited negligible hysteresis and a maximum power conversion efficiency (PCE) of 16.72%, without any additional compositional and interfacial engineering. The latter can be used in the future to further enhance the PCE. These findings demonstrate the importance of an optimized perovskite active layer for reproducibly fabricating high-efficiency planar p-i-n photovoltaic devices. Additionally, the simplicity of the PbI2(DMSO) complex film preparation and the versatility of the MAI deposition with this fabrication method further enhances the potential of this material for large-scale processing.

Graphene quantum dots (GQDs) are zero-dimensional material with characteristics derived from functionalized graphene precursors are graphene sheets a few nanometers in the lateral dimension having a several-layer thickness. Combining the structure of graphene with the quantum confinement and edge effects, GQDs possess unique chemical behavior and physical properties. Intense research activity in GQDs is attributed to their novel phenomena of charge transport and light absorption and photoluminescence excitation. The optical transitions are known to be available up to 6 eV in GQDs, applicable for ultraviolet photonics and optoelectronics devices, biomedical imaging capabilities and technologies. We present facile hydrothermal and solvothermal methods for synthesizing homogenous dispersed and uniform sized GQDs with a strong greenish and violet blue emission peaks at ∼10-14% yield. This approach enabled a large-scale production of aqueous GQD dispersions without the need for chemical stabilizers. The structure and emission mechanism of the GQDs have been studied by combining extensive characterization techniques and rigorous control experiments. We further demonstrate the distinctive advantages of such GQDs as high-performance photodetectors (PDs). Here we also report high-efficient photocurrent (PC) behaviors consisting of multilayer GQDs sandwiched between monolayer graphene sheets. It is conceivable that the observed unique PD characteristics proved to be dominated by tunneling of charge carriers which occurs through the multiple energy states within the bandgap of GQDs, based on bias-dependent variation of the band profiles. This results in novel dark current and PC behaviors. The external quantum efficiency (η) is predicted to be 47% at applied potential 2 V. These findings highlight rich photophysics and comparable performance of graphene/graphene oxide hybrids opening up potential applications as optoelectronic devices.

We report a 6,13-Bis(triisopropylsilylethynyl)-pentacene (TIPS-pentacene) solution-processed high-voltage organic thin film transistor (HVOTFT) with a large breakdown voltage of |VDS| > 450 V, a three-fold increase from previous results. An offset channel architecture and an organosilane-based self-assembled monolayer (SAM) treatment were used to achieve large breakdown voltages. Solution-processed HVOTFTs will enable novel high-voltage and flexible applications. Reliability of the HVOTFT under high-field stress was studied in the context of threshold and onset to conduction voltages.

Recently, an epoch-making printing technology called “SuPR-NaP (Surface Photo-Reactive Nanometal Printing)” that allows easy, high-speed, and large-area manufacturing of ultrafine silver wiring patterns has been developed. Here we demonstrate low-voltage operation of organic thin-film transistors (OTFTs) composed of printed source/drain electrodes that are produced by the SuPR-NaP technique. We utilize an ultrathin layer of perfluoropolymer, Cytop, that functions not only as a base layer for producing patterned reactive surface in the SuPR-NaP technique but also as an ultrathin gate dielectric layer of OTFTs. By the use of 22 nm-thick Cytop gate dielectric layer, we successfully operate polycrystalline pentacene OTFTs below 2 V with negligible hysteresis. We also observe the improvement of carrier injection by the surface modification of printed silver electrodes. We discuss that the SuPR-NaP technique allows the production of high-capacitance gate dielectric layers as well as high-resolution printed silver electrodes, which provides promising bases for producing practical active-matrix OTFT backplanes.

The deposition of uniform, reproducible and compact Sb2S3 thin films were obtained by chemical bath deposition using tartaric acid as a complexing agent. It was found that the thickness of the films increases with the pH of the solution, reaching values of 130 and 170 nm for pH values of 9.5 and 10, respectively. XRD, as well as Raman analysis, showed amorphous Sb2S3 films formed directly from the chemical bath, which crystallized into stibnite after a thermal treatment in N2 with crystallite sizes between 31 and 39 nm. On the other hand, the optical band gap of the Sb2S3 films decreased with an increase in pH, with values of 1.82-2.03 eV for the crystalline ones. An n-type photo-conductivity of 10-6 Ω-1 cm-1 was obtained for the heated films. The evaluation of these films for solar cell applications using CdS as the window layer gave a Voc of 656 mV and a Jsc of 2.66 mA/cm2 under AM1.5G radiation.