Electrospray‐Assisted Fabrication of Moisture‐Resistant and Highly Stable Perovskite Solar Cells at Ambient Conditions

An electrospray deposition technique to fabricate a perovskite (CH₃NH₃PbI₃) layer for highly stable and efficient perovskite solar cells at ambient humidity (30%–50% relative humidity) conditions is demonstrated. A detailed study is conducted to determine the effect of different electrospray parameters on the device performance and to provide a mechanistic explanation of the superior stability of the films. Due to the controlled reactivity that results in the formation of a smooth perovskite film, these cells exhibit stability exceeding 4000 h, in contrast to much lower stability of those fabricated by conventional spin coating methods. Furthermore, the perovskite film deposited by electrospray methods exhibits a self‐healing behavior when exposed to moisture. The authors hypothesize the formation of an intermediate metastable phase and smooth morphology of the film as the reason for this enhanced stability. Electrospray is a scalable technique that provides precise control over the amount of material required for deposition, reducing significant material loss that occurs in conventional solution‐based methods. Overall, this work shows that stability of perovskite solar cells can be improved by fabrication using a well controlled and optimized electrospray technique, without the use of any additives or cell encapsulants.     

Co-polymerization of MTPC (methylene tri p-cresol) and m-cresol using CiP (Coprinus cinereus peroxidase) to improve the dissolution characteristics of the enzyme-catalyzed polymer

MTPC (Methylene tri p-cresol) and m-cresol were copolymerized by Coprinus cinereus peroxidase in aqueous acetone. Although MTPC did not dissolve completely in the aqueous acetone, copolymerization was achieved owing to the radical transfer between solute and solid surface. Various polymerized products with different molecular weights and hydroxyl values were synthesized depending upon reaction compositions (ratio of MTPC to m-cresol and buffer to acetone). Poly(MTPC–m-cresol), a copolymer of MTPC and m-cresol, was mixed with a diazonaphthoquinone derivative to form a new type of photoresist, a thin film of which was formed on a silicon wafer and immersed in alkaline solution (tetramethylammonium hydroxide) to measure speed of dissolution. Poly(MTPC–m-cresol), with higher hydroxyl value (over 80%), showed remarkably improved dissolution characteristics (dark loss in alkaline solution decreased by almost half), which is prerequisite for sensitive photoresist polymer.     

In Situ Preparation of Biomimetic Thin Films and Their Surface-Shielding Effect for Organisms in High Vacuum

Self-standing biocompatible films have yet to be prepared by physical or chemical vapor deposition assisted by plasma polymerization because gaseous monomers have thus far been used to create only polymer membranes. Using a nongaseous monomer, we previously found a simple fabrication method for a free-standing thin film prepared from solution by plasma polymerization, and a nano-suit made by polyoxyethylene (20) sorbitan monolaurate can render multicellular organisms highly tolerant to high vacuum. Here we report thin films prepared by plasma polymerization from various monomer solutions. The films had a flat surface at the irradiated site and were similar to films produced by vapor deposition of gaseous monomers. However, they also exhibited unique characteristics, such as a pinhole-free surface, transparency, solvent stability, flexibility, and a unique out-of-plane molecular density gradient from the irradiated to the unirradiated surface of the film. Additionally, covering mosquito larvae with the films protected the shape of the organism and kept them alive under the high vacuum conditions in a field emission-scanning electron microscope. Our method will be useful for numerous applications, particularly in the biological sciences.     

Top‐illuminated Organic Photovoltaics on a Variety of Opaque Substrates with Vapor‐printed Poly(3,4‐ethylenedioxythiophene) Top Electrodes and MoO3 Buffer Layer

Organic photovoltaics devices typically utilize illumination through a transparent substrate, such as glass or an optically clear plastic. Utilization of opaque substrates, including low cost foils, papers, and textiles, requires architectures that instead allow illumination through the top of the device. Here, we demonstrate top‐illuminated organic photovoltaics, employing a dry vapor‐printed poly(3,4‐ethylenedioxythiophene) (PEDOT) polymer anode deposited by oxidative chemical vapor deposition (oCVD) on top of a small‐molecule organic heterojunction based on vacuum‐evaporated tetraphenyldibenzoperiflanthene (DBP) and C₆₀ heterojunctions. Application of a molybdenum trioxide (MoO₃) buffer layer prior to oCVD deposition increases the device photocurrent nearly 10 times by preventing oxidation of the underlying photoactive DBP electron donor layer during the oCVD PEDOT deposition, and resulting in power conversion efficiencies of up to 2.8% for the top‐illuminated, ITO‐free devices, approximately 75% that of the conventional cell architecture with indium‐tin oxide (ITO) transparent anode (3.7%). Finally, we demonstrate the broad applicability of this architecture by fabricating devices on a variety of opaque surfaces, including common paper products with over 2.0% power conversion efficiency, the highest to date on such fiber‐based substrates.     

High‐Performance Ta2O5/Al‐Doped Ag Electrode for Resonant Light Harvesting in Efficient Organic Solar Cells

A efficient indium tin oxide (ITO)‐free transparent electrode based on an improved Ag film is designed by introducing small amount of Al during co‐deposition, producing ultrathin and smooth Ag film with low loss. A transparent electrode as thin as 4 nm is achieved by depositing the film on top of Ta₂O₅ layer, and organic solar cells based on such ultrathin electrode are built, producing power conversion efficiency over 7%. The device efficiency can be optimized by simply tuning Ta₂O₅ layer thickness external to the organic photovoltaic (OPV) structure to create an optical cavity resonance inside the photoactive layer. Therefore Ta₂O₅/Al‐doped Ag films function as a high‐performance electrode with high transparency, low resistance, improved photon management capability and mechanical flexibility.     

Direct observation of poly(3-hydroxybutyrate) depolymerase adsorbed on polyester thin film by atomic force microscopy

Poly[(R)-3-hydroxybutyrate] (PHB) depolymerases adsorbed on poly(L-lactide) (PLLA) thin film were directly observed by atomic force microscopy (AFM). A PLLA thin film of 100 nm thickness was prepared on a silicon wafer by spin-cast method. The PLLA thin film was treated at 220 degrees C and quenched to room temperature, resulting in the formation of a completely amorphous film with a smooth surface. Then, the PHB depolymerases from Pseudomonas stutzeri YM1006 and Ralstonia pickettii T1 were dispersed on the amorphous PLLA thin film. Direct AFM observation has revealed that the PHB depolymerases bind in an elliptic shape on the surface of the PLLA thin film and that a small ridge is created around each enzyme molecule. After removal of the enzymes with 40% ethanol aqueous solution, small hollows were found on the PLLA thin film. These results suggest that a PHB depolymerase interacts with polyester molecules during their adsorption to make a hollow on the substrate surface.     

Polycrystal diamond growth in a microwave plasma torch

Diamond films of different structures were deposited on quartz, WC-Co, and molybdenum substrates in a microwave plasma torch discharge in an argon-hydrogen-methane gas mixture in a sealed chamber at pressures close to atmospheric by using the chemical vapor deposition technique. Images of diamond polycrystal films and separate crystals, as well as results of Raman spectroscopy, are presented. The spectra of optical plasma radiation recorded during film deposition demonstrate the presence of intense H_α hydrogen and C₂ radical bands known as Swan bands.     

Understanding the Morphology of PTB7:PCBM Blends in Organic Photovoltaics

The structure–property relationships of PTB7‐phenyl‐C₆₁‐butyric acid methyl ester (PCBM)‐based organic photovoltaics are investigated. The morphology is investigated in an active layer setting where a multi‐length‐scale morphology is observed using a solvent additive‐assisted film processing. This multi‐length‐scale structure consists of a phase separated morphology with a characteristic length scale of ≈30 nm, which is critical for producing large currents in devices; a second length scale of ≈130 nm, arises from face‐on PTB7 crystalline aggregates. This latter morphological feature is also observed in films prepared without the use of an additive. By observing the structure formation in situ during solvent evaporation for blade coated thin films, the additive is found to promote the formation of ordered domains of the PTB7 at an earlier stage during the solvent evaporation, which is critical in the development of the final morphology. In studies on PTB7/PCBM bilayers, PCBM is found to diffuse into the PTB7 layer. However, the performance of devices prepared in this manner is low. This diffusion leads to a swelling of the PTB7 and a reduction in the crystallinity of the PTB7, reflecting the strong miscibility of PCBM with PTB7. The morphology resulting from the interdiffusion is single‐length‐scale with slightly large phase separation. This leads to devices with poor performance.     

Direct detection of isotopically labeled metabolites bound to a protein microarray using a charge-coupled device

A charge-coupled device (CCD) was used to quantitatively detect isotope-labeled ligands bound to a protein microarray. Protein microarrays with protein dots, 10-50 microm in diameter, were fabricated on an aluminized Mylar film using an electrospray deposition technique. Proteins in dots were immobilized by cross-linking in glutaraldehyde vapor. After contact with solutions of isotope-labeled metabolites, the protein microarrays were washed, dried and placed face down onto the surface of a standard B/W video CCD chip with the protective window removed. We show here that such a simple inexpensive CCD detector can be used to quantify distribution of 14C and other radioactive isotopes on microarrays.     

Doxorubicin uptake and release from microgel thin films

We report investigations on the thermally regulated uptake and release of the chemotherapeutic drug doxorubicin from microgel thin films. A spin coating, layer-by-layer (scLbL) assembly approach was used to prepare thin films composed of thermoresponsive poly(N-isopropylacrylamide-co-acrylic acid) (pNIPAm-AAc) microgels by alternatively exposing a 3-aminopropyltrimethoxysilane (APTMS) functionalized glass substrate to polyanionic pNIPAm-AAc microgels and polycationic poly(allylamine hydrochloride) (PAH). Using this method, 10, 20, and 30 microgel layer films were constructed with uniform layer buildup, as confirmed by quartz crystal microgravimetry (QCM). The films were subsequently loaded with doxorubicin by cycling the temperature of the film in an aqueous doxorubicin solution between 25 and 50 degrees C. Release characteristics were then examined using UV-vis spectroscopy, which revealed temperature-dependent release properties.     

Important parameters affecting efficiency of protein refolding by reversed micelles

Refolding of denatured RNase A as a model of inclusion bodies was performed by reversed micelles formulated with sodium di-2-ethylhexyl sulfosuccinate (AOT) in isooctane. In the novel refolding process, a solid-liquid extraction was utilized as an alternative to the ordinary protein extraction by reversed micelles based on a liquid-liquid extraction. First, the effects of operational parameters such as concentration of AOT, W(o) (= [H(2)O]/[AOT]), and pH were examined on the solubilization of solid denatured proteins into a reversed micellar solution. The solubilization was facilitated by a high AOT concentration, a high W(o) value, and a high pH in water pools. These conditions are favorable for the dispersion of the solid protein aggregates in an organic solvent. Second, the renaturation of the denatured RNase A solubilized into the reversed micellar solution was conducted by addition of glutathione as a redox reagent. A complete renaturation of RNase A was accomplished by adjusting the composition of the redox reagent even at a high protein concentration in which protein aggregation would usually occur in aqueous media. In addition, the renaturation rates were improved by optimizing water content (W(o)) and the pH of water pools in reversed micelles. Finally, the recovery of renatured RNase A from the reversed micellar solution was performed by adding a polar organic solvent such as acetone into the reversed micellar solution. This precipitation method was effective for recovering proteins from reversed micellar media without any significant reduction in enzymatic activity.     

Conducting polymer polypyrrole supported bilayer lipid membranes

Electrochemically synthesized conducting polymer polypyrrole (PPy) film on gold electrode surface was used as a novel support for bilayer lipid membranes (BLMs). Investigations by surface plasmon resonance (SPR) suggest that dimyristoyl-L-alpha-phosphatidylcholine (DMPC) and dimyristoyl-L-alpha-phosphatidyl-L-serine (DMPS) can form BLMs on PPy film surface but dimyristoyl-L-alpha-phosphatidylglycerol (DMPG) and didodecyldimethylammonium bromide (DDAB) can not do so, indicating the formation of PPy supported bilayer lipid membranes (s-BLMs) is dependent on the chemical structure of the lipids used. The self-assembly of DMPC induces a smoother topography than the PPy layer with rms roughness decreasing from 4.484 to 2.914 nm convinced by atomic force microscopy (AFM). Impedance spectroscopy measurements confirm that the deposition of BLM substantially increases the resistance of the system indicating a very densely packed BLM structures. The little change of PPy film in capacitance shows that solvent and electrolyte ions still retain within the porous PPy film after BLM deposition. Therefore, the PPy supported BLM is to some extent comparable to conventional BLM with aqueous medium retaining at its two sides. As an example and preliminary application, horseradish peroxidase (HRP) reconstituted into the s-BLM shows the expected protein activity and can transfer electron from or to the underlying PPy support for its response to electrocatalytic reduction of hydrogen peroxide in solution. Thus the system maybe possesses potential applications to biomimetic membrane studies.     

The mucous coat on gill lamellae of rainbow trout (Oncorhynchus mykiss)

The existence of a layer of mucus covering the gill lamellae of healthy rainbow trout (Oncorhynchus mykiss) was investigated. Using cryo-scanning electron microscopy, a smooth, undulating, thin layer was observed which completely covered gill filaments and lamellae, thereby obscuring epithelial microridges. After processing cryopreserved gill arches in glutaraldehyde for conventional scanning electron microscopy, the layer was no longer present and epithelial microridges were clearly visible. The identity of this layer was investigated using cryopreserved gills which were treated in one of two ways. First, gills were incubated with a rabbit antiserum to gill mucus, with normal rabbit serum, or with phosphate-buffered saline. Following fixation in glutaraldehyde and processing, only the gill tissue incubated with the mucus-specific antiserum was still covered with the smooth layer. The layer was also retained on the gills of fish anesthetized in a solution containing mucusspecific antiserum and then processes in glutaraldehyde for conventional scanning electron microscopy. The tenacious nature of the mucous layer was demonstrated by its stability following exposure to formalin and a cationic detergent. Second, the presence of this layer was confirmed on gill tissue which was cryopreserved, followed by freeze-substitution and vapor fixation, and then examined by transmission electron microscopy.     

Activation of lignin peroxidase in organic media by reversed micelles

Activation of lignin peroxidase (LIP) in an organic solvent by reversed micelles was investigated. Bis(2-ethylhexyl)sulfosuccinate sodium salt (AOT) was used as a surfactant to form a reversed micelle. Lyophilized LIP from an optimized aqueous solution exhibited no enzymatic activity in any organic solvents examined in this study; however, LIP was catalytically active by being entrapped in the AOT reversed micellar solution. LIP activity in the reversed micelle was enhanced by optimizing either the preparation or the operation conditions, such as water content and pH in water pools of the reversed micelle and the reaction temperature. Stable activity was obtained in isooctane because of the stability of the reversed micelle. The optimal pH was 5 in the reversed micellar system, which shifted from pH 3 in the aqueous solution. The degradation reaction of several environmental pollutants was attempted using LIP hosted in the AOT reversed micelle. Degradation achieved after a 1-h reaction reached 81%, 50%, and 22% for p-nonylphenol, bisphenol A, and 2,4-dichlorophenol, respectively. This is the first report on the utilization of LIP in organic media.     

The mucous coat on gill lamellae of rainbow trout (Oncorhynchus mykiss)

The existence of a layer of mucus covering the gill lamellae of healthy rainbow trout (Oncorhynchus mykiss) was investigated. Using cryo-scanning electron microscopy, a smooth, undulating, thin layer was observed which completely covered gill filaments and lamellae, thereby obscuring epithelial microridges. After processing cryopreserved gill arches in glutaraldehyde for conventional scanning electron microscopy, the layer was no longer present and epithelial microridges were clearly visible. The identity of this layer was investigated using cryopreserved gills which were treated in one of two ways. First, gills were incubated with a rabbit antiserum to gill mucus, with normal rabbit serum, or with phosphate-buffered saline. Following fixation in glutaraldehyde and processing, only the gill tissue incubated with the mucus-specific antiserum was still covered with the smooth layer. The layer was also retained on the gills of fish anesthetized in a solution containing mucusspecific antiserum and then processes in glutaraldehyde for conventional scanning electron microscopy. The tenacious nature of the mucous layer was demonstrated by its stability following exposure to formalin and a cationic detergent. Second, the presence of this layer was confirmed on gill tissue which was cryopreserved, followed by freeze-substitution and vapor fixation, and then examined by transmission electron microscopy.     

Investigating Pervaporation for In Situ Acetone Removal as Process Intensification Tool in ω-Transaminase Catalyzed Chiral Amine Synthesis

Hydrophobic pervaporation (PV), allowing for the separation of an organic component from an aqueous stream, was investigated for in situ acetone removal from a transamination reaction. A poly(dimethylsiloxane) membrane was applied in a coupled enzymatic process at 5 L scale. Among the four components, there was no loss of donor and product amines through PV which was highly desirable. However, in addition to removal of acetone, there was also an unwanted loss of acetophenone (substrate ketone) because of PV. The coupled enzyme-PV process resulted in 13% more product formation compared to the control process (where no PV was applied) after 9 h. Results from a qualitative simulation study (based on partial vapor pressures and a vapor–liquid equilibrium of the feed solution) indicated that PV might have an advantage over direct distillation strategy for selective removal of acetone from the reaction medium. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 35: e2731, 2019     

Scalable In-Plane Directional Crystallization for The Printable Hole-Conductor-Free Perovskite Solar Cell Based on The Carbon Electrode

Popular solution-processed approaches for producing the active layer of perovskite solar cells (PSCs) generally have to make compromise between crystallinity and compactness by inducing a rapid crystallization process with explosive nucleation and limited growth via removing solvent quickly. Here, a practical growth-dominated in-plane directional crystallization technique (IPDC) with a deeply retarded crystallization process for the scalable preparation of PSCs are reported. During the low-temperature annealing, a tiny chamber with a small height is built atop the wet perovskite precursor film to restrain the vertical diffusion and removal of solvent vapor. The chamber eliminates the vertical solvent vapor gradient and induce a horizonal in-plane gradient of solvent vapor pressure (SVP) toward the preset exhaust port which allows the slow escape of solvent vapor to outer space. In this way, nucleation is induced preferentially near the port and the as-formed heterogeneous nuclei then grow continuously and directionally. With IPDC, sufficient filling of perovskite with high crystallinity and obvious growth orientation is realized in non-ordered mesoporous scaffolds. An encouraging power conversion efficiency of 19.35% and 16.53% is achieved respectively for the 0.1 and 52.3-cm² printable mesoscopic hole-conductor-free PSCs with carbon electrodes.     

Structural perturbations of azurin deposited on solid matrices as revealed by trp phosphorescence

The phosphorescence emission of Cd-azurin from Pseudomonas aeruginosa was used as a probe of possible perturbations in the dynamical structure of the protein core that may be induced by protein-sorbent and protein-protein interactions occurring when the macromolecule is deposited into amorphous, thin solid films. Relative to the protein in aqueous solution, the spectrum is unrelaxed and the phosphorescence decay becomes highly heterogeneous, the average lifetime increasing sharply with film thickness and upon its dehydration. According to the lifetime parameter, adsorption of the protein to the substrate is found to produce a multiplicity of partially unfolded structures, an influence that propagates for several protein layers from the surface. Among the substrates used for film deposition, hydrophilic silica, dextran, DEAE-dextran, dextran sulfate, and hydrophobic octodecylamine, the perturbation is smallest with dextran sulfate and largest with octodecylamine. The destabilizing effect of protein-protein interactions, as monitored on 50-layer-thick films, is most evident at a relative humidity of 75%. Stabilizing agents were incorporated to attenuate the deleterious effects of protein aggregation. Among them, the most effective in preserving a more native-like structure are the disaccharides sucrose and trehalose in dry films and the polymer dextran in wet films. Interestingly, the polymer was found to achieve maximum efficacy at sensibly lower additive/protein ratios than the sugars.     

Optical Absorption Enhancement in Freestanding GaAs Thin Film Nanopyramid Arrays

Although III–V compound semiconductor multi‐junction cells show the highest efficiency among all types of solar cells, their cost is quite high due to expensive substrates, long epitaxial growth and complex balance of system components. To reduce the cost, ultra‐thin films with advanced light management are desired. Here effective light trapping in freestanding thin film nanopyramid arrays is demonstrated and multiple‐times light path enhancement is realized, where only 160 nm thick GaAs with nanopyramid structures is equivalent to a 1 μm thick planar film. The GaAs nanopyramids are fabricated using a combination of nanosphere lithography, nanopyramid metal organic chemical vapor deposition (MOCVD) growth, and gas‐phase substrate removal processes. Excellent optical absorption is demonstrated over a broad range of wavelengths, at various incident angles and at large‐curvature bending. Compared to an equally thick planar control film, the overall number of photons absorbed is increased by about 100% at various incident angles due to significant antireflection and light trapping effects. By implementing these nanopyramid structures, III–V material usage and deposition time can be significantly reduced to produce high‐efficiency, low‐cost thin film III–V solar cells.     

Long Range Surface Plasmons for Observation of Biomolecular Binding Events at Metallic Surfaces

A long range surface plasmon (LRSP) is an electromagnetic wave propagating along a thin metal film with an order of magnitude lower damping than conventional surface plasmon (SP) waves. Thus, the excitation of LRSP is associated with a narrower resonance and it provides larger enhancement of intensity of the electromagnetic field. In surface plasmon resonance (SPR) biosensors, these features allow a more precise observation of the binding of biomolecules in the proximity to the metal surface by using the (label-free) measurement of refractive index (RI) variations and by SP-enhanced fluorescence spectroscopy. In this contribution, we investigate LRSPs excited on a layer structure consisting of a fluoropolymer buffer layer, a thin gold film, and an aqueous sample. By implementing such structure in an SPR sensor, we achieved a 2.4- and 4.4-fold improvement of the resolution in the label-free and fluorescence-based detection, respectively, of the binding of biomolecules in the close proximity to the surface. Moreover, we demonstrate that the sensor resolution can be improved by a factor of 14 and 12 for the label-free and fluorescence-based detection, respectively, if the biomolecular binding events occur within the whole evanescent field of LRSP.