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Neonatal mice exhibit natural heart regeneration after myocardial infarction (MI) on postnatal day 1 (P1), but this ability is lost by postnatal day 7 (P7). Cardiac biomechanics intricately affect long-term heart function, but whether regenerated cardiac muscle is biomechanically similar to native myocardium remains unknown. We hypothesized that neonatal heart regeneration preserves native left ventricular (LV) biomechanical properties after MI. C57BL/6J mice underwent sham surgery or left anterior descending coronary artery ligation at age P1 or P7. Echocardiography performed 4 weeks post-MI showed that P1 MI and sham mice (n = 22, each) had similar LV wall thickness, diameter, and ejection fraction (59.6% vs 60.7%, p = 0.6514). Compared to P7 shams (n = 20), P7 MI mice (n = 20) had significant LV wall thinning, chamber enlargement, and depressed ejection fraction (32.6% vs 61.8%, p ex vivo, and the multiaxial lenticular stress-strain relationship was tracked. While LV tissue modulus for P1 MI and sham mice were similar (341.9 kPa vs 363.4 kPa, p = 0.6140), the modulus for P7 MI mice was significantly greater than that for P7 shams (691.6 kPa vs 429.2 kPa, p = 0.0194). We conclude that, in neonatal mice, regenerated LV muscle has similar biomechanical properties as native LV myocardium.

Bacterial infections remain a leading threat to global health because of the misuse of antibiotics and the rise in drug-resistant pathogens. Although several strategies such as photothermal therapy and magneto-thermal therapy can suppress bacterial infections, excessive heat often damages host cells and lengthens the healing time. Here, a localized thermal managing strategy, thermal-disrupting interface induced mitigation (TRIM), is reported, to minimize intercellular cohesion loss for accurate antibacterial therapy. The TRIM dressing film is composed of alternative microscale arrangement of heat-responsive hydrogel regions and mechanical support regions, which enables the surface microtopography to have a significant effect on disrupting bacterial colonization upon infrared irradiation. The regulation of the interfacial contact to the attached skin confines the produced heat and minimizes the risk of skin damage during thermoablation. Quantitative mechanobiology studies demonstrate the TRIM dressing film with a critical dimension for surface features plays a critical role in maintaining intercellular cohesion of the epidermis during photothermal therapy. Finally, endowing wound dressing with the TRIM effect via in vivo studies in S. aureus infected mice demonstrates a promising strategy for mitigating the side effects of photothermal therapy against a wide spectrum of bacterial infections, promoting future biointerface design for antibacterial therapy. National Research Foundation (NRF) Accepted version This work was financially supported by the NTU-Northwestern Institute for Nanomedicine and the National Research Foundation, Prime Minister’s Office, Singapore, under the NRF Investigatorship (NRF-NRFI2017-07).

Atomic layer deposited titanium dioxide (ALD-TiO2) has emerged as an effective protection layer for highly efficient semiconductor anodes which are normally unstable under the potential and pH conditions used to oxidize water in a photoelectrochemical cell. The failure modes of silicon anodes coated with an Ir/IrO x oxygen evolution catalyst layer are investigated, and poor catalyst/substrate adhesion is found to be a key factor in failed anodes. Quantitative measurements of interfacial adhesion energy show that the addition of TiO2 significantly improves reliability of anodes, yielding an adhesion energy of 6.02 ± 0.5 J/m2, more than double the adhesion energy measured in the absence of an ALD-TiO2 protection layer. These results indicate the importance of catalyst adhesion to an interposed protection layer in promoting operational stability of high efficiency semiconducting anodes during solar-driven water splitting.

Sputter-processed oxide films are typically annealed at high temperature (activation process) to achieve stable electrical characteristics through the formation of strong metal-oxide chemical bonds. For instance, indium-gallium-zinc oxide (IGZO) films typically need a thermal treatment at 300 °C for ≥1 h as an activation process. We propose an open-air plasma treatment (OPT) to rapidly and effectively activate sputter-processed IGZO films. The OPT effectively induces metal-oxide chemical bonds in IGZO films at temperatures as low as 240 °C, with a dwell time on the order of a second. Furthermore, by controlling the plasma-processing conditions (scan speed, distance a between plasma nozzle and samples, and gas flow rate), the electrical characteristics and the microstructure of the IGZO films can be easily tuned. Finally, OPT can be utilized to implement a selective activation process. Plasma-treated IGZO thin-film transistors (TFTs) exhibit comparable electrical characteristics to those of conventionally thermal treated IGZO TFTs. Through in-depth optical, chemical, and physical characterizations, we confirm that OPT simultaneously dissociates weak chemical bonds by UV radiation and ion bombardment and re-establishes the metal-oxide network by radical reaction and OPT-induced heat.

Tsai et al . (Reports, 6 April 2018, p. 67) report a uniform light-induced lattice expansion of metal halide perovskite films under 1-sun illumination and claim to exclude heat-induced lattice expansion. We show that by controlling the temperature of the perovskite film under both dark and illuminated conditions, the mechanism for lattice expansion is in fact fully consistent with heat-induced thermal expansion during illumination.

Entanglements between polymer chains are responsible for the strength and toughness of polymeric materials. When the chains are too short to form entanglements, the polymer becomes weak and brittle. Here we show that molecular bridging of oligomers in molecular-scale confinement can dramatically toughen materials even when intermolecular entanglements are completely absent. We describe the fabrication of nanocomposite materials that confine oligomer chains to molecular-scale dimensions and demonstrate that partially confined unentangled oligomers can toughen materials far beyond rule-of-mixtures estimates. We also characterize how partially confined oligomers affect the kinetics of nanocomposite cracking in moist environments and show that the presence of a backfilled oligomeric phase within a nanoporous organosilicate matrix leads to atomistic crack path meandering in which the failure path is preferentially located within the matrix phase.

An important aspect of the biomechanical behaviour of the stratum corneum (SC) is the drying stresses that develop with water loss. These stresses act as a driving force for damage in the form of chapping and cracking. Betasitosterol is a plant sterol with a structure similar to cholesterol, a key component in the intercellular lipids of the outermost layer of human skin, the SC. Cholesterol plays an important role in stabilizing the SC lipid structure, and altered levels of cholesterol have been linked with SC barrier abnormalities. Betasitosterol is currently applied topically to skin for treatment of wounds and burns. However, it is unknown what effect betasitosterol has on the biomechanical barrier function of skin. Here, by analysing the drying stress profile of SC generated during a kinetics of dehydration, we show that betasitosterol, in combination with two emollient molecules, isocetyl stearoyl stearate (ISS) and glyceryl tri-2-ethylhexanoate (GTEH), causes a significant modulation of the drying stress behaviour of the SC by reducing both the maximal peak stress height and average plateau of the drying stress profile. Raman spectra analyses demonstrate that the combination of betasitosterol with the two emollients, ISS and GTEH, allows a high water retention capacity within the SC, while the lipid conformational order by increasing the amount of trans conformers. Our study highlights the advantage of combining a biomechanical approach together with Raman spectroscopy in engineering a suitable combination of molecules for alleviating dryness and dry skin damage.

xtending photovoltaic (PV) module lifetimes beyond 30 years is a goal of significant priority. A challenge that must first be addressed, however, is the development of a predictive reliability model that captures the synergy of terrestrial stressors on module degradation, particularly at encapsulant interfaces. Using a metrology designed specifically for PV modules, a comprehensive study of the widely used ethylene vinyl acetate encapsulant was performed in which encapsulant adhesion was evaluated as a function of environmental stressors (UV exposure, temperature, and humidity) for modules aged both under accelerated lab and internationally located field conditions for months to nearly 3 decades. Mechanical and chemical characterization methods are combined with fundamental polymer reaction engineering to unravel the degradation processes active at the molecular scale that lead to encapsulant delamination. An analytical and modular model framework is put forward enabling the prediction of long‐term PV module durability, starting from fundamental principles at the molecular level and explicitly accounting for bond rupture events in the bulk encapsulant and at the encapsulant interfaces. Successful parameter tuning to adhesion data indicates a dominant occurrence of deacetylation, β‐scission, and hydrolytic depolymerization, respectively. The model contributes to the longstanding challenge of predicting module lifetimes in any geographic location while minimizing time‐consuming and costly aging studies. Supporting Information

Ultrathin nanowires with3 nm diameter have long been sought for novel properties that emerge from dimensional constraint as well as for continued size reduction and performance improvement of nanoelectronic devices. Here, we report on a facile and large-scale synthesis of a new class of electrically conductive ultrathin core-shell nanowires using benzenethiols. Core-shell nanowires are atomically precise and have inorganic five-atom copper-sulfur cross-sectional cores encapsulated by organic shells encompassing aromatic substituents with ring planes oriented parallel. The exact nanowire atomic structures were revealed via a two-pronged approach combining computational methods coupled with experimental synthesis and advanced characterizations. Core-shell nanowires were determined to be indirect bandgap materials with a predicted room-temperature resistivity of ∼120 Ω·m. Nanowire morphology was found to be tunable by changing the interwire interactions imparted by the functional group on the benzenethiol molecular precursors, and the nanowire core diameter was determined by the steric bulkiness of the ligand. These discoveries help define our understanding of the fundamental constituents of atomically well-defined and electrically conductive core-shell nanowires, representing significant advances toward nanowire building blocks for smaller, faster, and more powerful nanoelectronics.

We report on a sustainable route to protective nanocomposite coatings, where one of the components, nanocellulose fibrils, is derived from trees and the glass matrix is an inexpensive sol-gel organic-inorganic hybrid of zirconium alkoxide and an epoxy-functionalized silane. The hydrophilic nature of the colloidal nanocellulose fibrils is exploited to obtain a homogeneous one-pot suspension of the nanocellulose in the aqueous sol-gel matrix precursors solution. The mixture is then sprayed to form nanocomposite coatings of a well-dispersed, random in-plane nanocellulose fibril network in a continuous organic-inorganic glass matrix phase. The nanocellulose incorporation in the sol-gel matrix resulted in nanostructured composites with marked effects on salient coating properties including optical transmittance, hardness, fracture energy, and water contact angle. The particular role of the nanocellulose fibrils on coating fracture properties, important for coating reliability, was analyzed and discussed in terms of fibril morphology, molecular matrix, and nanocellulose/matrix interactions.

Phenyl-C61-butyric acid methyl ester (PCBM) is universally used as the electron-transport layer (ETL) in the low-cost inverted planar structure of perovskite solar cells (PeSCs). PCBM brings tremendous challenges in upscaling of PeSCs using industry-relevant methods due to its aggregation behavior, which undermines the power conversion efficiency and stability. Herein, we highlight these, seldom reported, challenges with PCBM. Furthermore, we investigate the potential of nonfullerene indacenodithiophene (IDT)-based molecules by employing a commercially available variant, 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3- d:2',3'- d']- s-indaceno[1,2- b:5,6- b'] dithiophene (ITIC), as a PCBM replacement in ambient-processed PeSCs. Films fabrication by laboratory-based spin-coating and industry-relevant slot-die coating methods are compared. Although similar power-conversion efficiencies are achieved with both types of ETL in a simple device structure fabricated by spin-coating, the nanofibriller morphology of ITIC compared to the aggregated morphology of PCBM films enables improved mechanical integrity and stability of ITIC devices. Upon slot-die coating, the aggregation of PCBM is exacerbated, leading to significantly lower power-conversion efficiency of devices than spin-coated PCBM as well as slot-die-coated ITIC devices. Our results clearly indicate that IDT-based molecules have great potential as an ETL in PeSCs, offering superior properties and upscaling compatibility than PCBM. Thus, we present a short summary of recently emerged nonfullerene IDT-based molecules from the field of organic solar cells and discuss their scope in PeSCs as electron or hole-transport layer.

A well-known but heretofore uncharacterized failure mechanism in multijunction photovoltaic cells involves the development of cracks in the top cell directly adjacent to metal gridline structures. In this study, we systematically explore the potential evolution of stress, grain size, roughness, and hardness of metal gridlines during thermal cycling as it pertains to top cell cracking behavior. We discover that although top cells are found to crack after many cycles, this is not due to an accumulation of stress or damage, but rather a progression of strain hardening within the metal gridlines due to cyclic plastic deformations, quantified as an increase in hardness of as much as 57%. Furthermore, optical and topological characterization reveals morphology changes at the gridlines’ top surfaces, lending some insight to commonly observed bus bar wire-bonding issues. Ultimately this suite of characterization techniques not only reveals the underlying behavior leading to gridline-induced top cell cracking failures in multijunction photovoltaics, but also suggests a route forward for the development of improved gridline materials.

We report on the fabrication of transparent, conductive, mechanically robust electrode composites of poly(triarylamine) (PTAA) doped with different concentrations of carbon nanotubes (CNTs) or graphene nanoplatelets (GNPs). Additionally, the effects of nanofiller surface modification with amines were characterized by comparing the transparency, conductivity, and mechanical properties to composites with unmodified nanofillers. The optimization of the concentrations and fabrication parameters resulted in films with high transparency, improved electrical conductivity, and superior mechanical properties. Amine-functionalized nanofillers more readily dispersed into the matrix, and the addition of 1 wt% amine-CNTs resulted in a composite film with a conductivity of 1.1 S cm− 1 and a transparency of 90–95% in the visible spectrum at a sub-100 nm thickness. At low doping concentrations, composites with amine-functionalized nanofillers exhibited a 100% increase in fracture energy compared to composites with unmodified nanofillers, an effect attributed to increased plasticity of the doped polymer. These findings have applications in many electronic devices that utilize organic semiconducting layers, such as organic light emitting diodes and perovskite photovoltaics.

The performance of perovskite solar cells has rapidly increased above 22%, and their environmental stability is also progressing. However, the mismatch in thermal expansion coefficients and low fracture energy of layers in perovskite solar cells raise a concern as to whether devices can withstand mechanical stresses from temperature fluctuations. We measured the fracture energy of a perovskite film stack, which was shown to produce 23.6% efficiency when incorporated in a monolithic perovskite-silicon tandem. We found that the fracture energy increased by a factor of two after 250 standardized temperature cycles between −40 °C and 85 °C and a factor of four after laminating an encapsulant on top of the stack. In order to observe how the increased mechanical stability translated from film stacks to device performance and reliability, we carried out a comparative study of perovskite solar cells packaged between glass and two commonly used encapsulants with different elastic moduli. We demonstrated that solar cells encapsulated with a stiffer ionomer, Surlyn, severely decreased in performance with temperature cycling and delaminated. However, the solar cells encapsulated in softer ethylene vinyl acetate withstood temperature cycling and retained over 90% of their initial performance after 200 temperature cycles. This work demonstrates a need for an encapsulant with a low elastic modulus to enable mechanical stability and progress toward 25 year operating lifetime.

We demonstrate a scalable atmospheric plasma route to rapidly form efficient and mechanically robust photoactive metal halide perovskite films in open air at linear deposition rates exceeding 4 cm s−1. Our plasma process uses clean dry air to produce a combination of reactive energetic species (ions, radicals, metastables, and photons) and convective thermal energy to rapidly convert the perovskite precursor solution after spray-coating. Such high energy species dissociate the precursor and superheat the solvent, quickly and efficiently curing the perovskite film. Synchrotron X-ray radiation enabled in situ wide angle X-ray scattering (WAXS) measurements with high time resolution. The ultrafast crystallization kinetics are governed by rapid nucleation and growth during the plasma exposure, followed by continued grain growth during cooling. We deposit pinhole-free, robust CH3NH3PbI3 films with a ten-fold increase in fracture toughness, a key metric for reliability. Planar devices exhibited remarkably consistent performance with 15.7% power conversion efficiency (PCE) without hysteresis and an improved open-circuit voltage (VOC). This excellent performance is attributed to lower defect densities, as measured by external quantum efficiency, steady-state and time-resolved photoluminescence. Large-area devices were made with a strip of 10 samples, and a 13.4% average PCE was measured on a total of 2.4 cm2 electrode area.

We demonstrate molecular design strategies for engineering the deformation rate sensitivity and fracture resistance of organic-inorganic hybrid films in moist environment. Hybrids with intimate mixing of inorganic and organic molecular networks were synthesized with an epoxy-functionalized silane, (3-glycidoxypropyl) trimethoxysilane and an acetate-stabilized zirconium alkoxide, tetra-n-propoxyzirconium. The highly confined non-hydrolysable organic molecular network connectivity was systematically manipulated by tuning the epoxy ring opening polymerization reaction and the incorporation of carbon bridges of selected lengths. By investigating the corresponding time-dependent crack growth in moist environments, new insights into the fundamental molecular-scale relaxation and cracking mechanisms of the hybrids are provided. These processes were found to be impacted by the confined organic network connectivity which results in significant changes in the deformation rate sensitivity and fracture resistance. With increasing non-hydrolysable organic network connectivity, mechanical behavior that varied from almost perfectly elastic to increasingly viscoelastic could be obtained in a controlled fashion. The related resistance to cracking in moist environments was found to be significantly improved. These findings provide a basis for the rational design of functional hybrids with precisely defined mechanical properties.

We demonstrate the deposition of mechanically robust UV-absorbing nanocomposite coatings with a newly developed dual-source deposition method involving ultrasonic spraying and open-air plasma deposition. Nanoparticles and the coating matrix are independently deposited which eliminates difficulties associated with preparing composites with high mass fraction of well-dispersed nanoparticles in the matrix. Nanocomposite coatings containing different concentrations of silica, ceria, and both titania and ceria nanoparticles were successfully deposited with good nanoparticle dispersity, high transparency over the visible range, effective absorption in the UV wavelength, and enhanced mechanical properties. Moreover, films were successfully deposited on several substrates including polycarbonate to demonstrate the low processing temperature of this dual-source deposition method. Coatings with different nanoparticle concentrations and film thicknesses were systematically studied in terms of their surface morphology, optical properties and mechanical properties. Accelerated photostability testing of the UV-absorbing nanocomposites demonstrates significantly enhanced performance compared to existing coatings with either a polymeric matrix or organic UV-absorbers.

Hydration of the outermost layer of human skin, the stratum corneum (SC), affects barrier function, physical appearance, and sensory perception of skin. Water loss, ubiquitously associated with dry skin conditions, results in the development of mechanical tensile stresses that lead to the perception of skin tightness and provide a driving force for damage in the form of chapping or cracking. Restorative moisturizing formulations contain molecular components that counteract the effects of water loss. However, the quantitative connection between water loss and SC mechanical behavior together with a predictive model has remained elusive. We develop a diffusional-based mechanics model that accurately predicts the SC mechanical behavior during hydration or dehydration over a wide range of ambient humidity conditions and presence of moisturizing ingredients. The model was validated with published studies including SC water diffusion, quantitative Raman spectroscopy, and mechanical property and stress characterization. The roles of mobile and partially bound water states are included together with one humectant and three cosmetic emollient molecules commonly used in moisturizing formulations. The model accurately predicts the effects of moisture content and moisturizer ingredients on SC mechanical behavior and provides a quantitative predictive capability that can be employed in the design of efficacious treatments.

A low-temperature, open-air plasma process to deposit amorphous SnOx thin films as an electron-transport layer in a planar-heterojunction n−i−p perovskite solar cell is reported. Open-air plasma processing is a scalable, low capital expenditure technique capable of manufacturing-scale production without enclosures or vacuum pumps. The technique provides flexibility to tune SnOx film composition and properties by adjusting several easily accessible processing parameters. In this study, we demonstrate large area SnOx thin film deposition on substrates up to 100 cm2. The SnOx films are deposited using monobutyltin trichloride as the chemical precursor and formed without any post-annealing, which has the potential for lowering costs as an in-line process. The film exhibits low surface roughness, excellent optical transmission of greater than 90 % across the visible regime, and low electrical resistivity of 13.3 Ω*m, which is multiple orders of magnitude lower than previously reported values of amorphous SnO2 thin films. The film is then incorporated into a planar perovskite solar cell with a power conversion efficiency of 11.8 %. These factors suggest that open-air plasma-deposited SnOx thin films can potentially be compatible with low-cost and large-scale fabrication of organohalide lead perovskite solar cells and modules.

Thermal interface materials (TIMs) are essential for managing heat in modern electronics, and nanocomposite TIMs can offer critical improvements. Here, we demonstrate thermally conductive, mechanically compliant TIMs based on dense, vertically aligned copper nanowires (CuNWs) embedded into polymer matrices. We evaluate the thermal and mechanical characteristics of 20–25% dense CuNW arrays with and without polydimethylsiloxane infiltration. The thermal resistance achieved is below 5 mm2 K W–1, over an order of magnitude lower than commercial heat sink compounds. Nanoindentation reveals that the nonlinear deformation mechanics of this TIM are influenced by both the CuNW morphology and the polymer matrix. We also implement a flip–chip bonding protocol to directly attach CuNW composites to copper surfaces, as required in many thermal architectures. Thus, we demonstrate a rational design strategy for nanocomposite TIMs that simultaneously retain the high thermal conductivity of aligned CuNWs and the mechanical...

Delamination of encapsulant materials from PV cell surfaces often appears to originate at regions with metallization. Using a fracture mechanics based metrology, the adhesion of EVA encapsulant to screen printed silver metallization was evaluated. At room temperature, the fracture energy, Gc [J/m2], of the EVA/silver interface (952 J/m2) was ∼70% lower than that of the EVA/AR coating $(> \mathbf{2900}\ \mathbf{J}/\mathbf{m}^{\mathbf{2}})$ and ∼60% lower than that of the EVA to the surface of cell (2265 J/m2). After only 300 hours of damp heat aging, the adhesion energy of the silver interface dropped to and plateaued at ∼50-60 J/m2, while that of the EVA/AR coating and EVA/cell remained mostly unchanged. Elemental surface analysis showed that the EVA separates from the silver in a purely adhesive manner, indicating that bonds at the interface were likely displaced in the presence of humidity and chemical byproducts at elevated temperature, which in part accounts for the propensity of metallized surfaces to delaminate in the field.

Adhesively bonding composite components is a reliable alternative to conventional joining processes that minimizes part weight and reduces fabrication costs. Regarding performance and reliability, of particular interest is developing adherend surface treatments that enhance adhesion of the joint interfaces in aggressive chemical environments. Using fracture mechanics-based adhesion metrologies, critical and subcritical crack growth were evaluated for several peel-ply-treated, adhesively bonded composite joints. Fracture toughness, Gc, and corresponding failure modes were evaluated for specimens constructed using two different bonding processes (co-bonding and secondary bonding) and four different peel ply treatments. Environmentally assisted crack growth was evaluated as a function of time in several environments: humid, high temperature humid, and hydraulic fluid immersion. It is shown that humid environments accelerate crack growth rates, da/dt, relative to the strain energy release rate, G. This effect was amplified at elevated temperatures and further amplified in the presence of hydraulic fluid.

The width-tapered cantilever beam method is used to quantify the debond energy (adhesion) of encapsulant and backsheet structures of 32 modules collected from the field. The collected population of modules contains both those that have remained intact and those with instances of either or both encapsulant and backsheet delamination. From this survey, initial threshold values (an adhesion value above which a module should remain intact throughout its lifetime) for encapsulant and backsheet interfaces are proposed. For encapsulants this value is ∼ $160\,{\text{J}\text{/}\text{m}}^{2}$ and for backsheets ∼ $10\,{\text{J}\text{/}\text{m}}^{2}$ . It is expected that these values will continue to be refined and evolve as the width-tapered cantilever beam method gets adopted by the PV industry, and that they may aid in the future improvement of accelerated lifetime tests and the development of new, low-cost materials.

In this work, we exploit a confinement-induced molecular synthesis and a resulting bridging mechanism to create confined polyimide thermoset nanocomposites that couple molecular confinement-enhanced toughening with an unprecedented combination of high-temperature properties at low density. We describe a synthesis strategy that involves the infiltration of individual polymer chains through a nanoscale porous network while simultaneous imidization reactions increase the molecular backbone stiffness. In the extreme limit where the confinement length scale is much smaller than the polymer's molecular size, confinement-induced molecular mechanisms give rise to exceptional mechanical properties. We find that polyimide oligomers can undergo cross-linking reactions even in such molecular-scale confinement, increasing the molecular weight of the organic phase and toughening the nanocomposite through a confinement-induced energy dissipation mechanism. This work demonstrates that the confinement-induced molecular bridging mechanism can be extended to thermoset polymers with multifunctional properties, such as excellent thermo-oxidative stability and high service temperatures (350 °C).

An asymmetric elastic modulus is a recently discovered and unexpected property of hybrid molecular materials that has significant implications for their underlying thermomechanical reliability. Elastic asymmetries are inherently related to terminal groups in the molecular structure, which limit network connectivity. Terminal groups sterically interact to stiffen the network in compression, while they disconnect the network and interact significantly less in tension. Here we study the importance of terminal group molecular weight and size (OH, methyl, vinyl, and phenyl) on the resulting elastic asymmetries and find that increasing the terminal group size actually leads to even larger degrees of asymmetry. As a result, we develop a molecular design criterion to predict how molecular structure affects the mechanical properties, a vital step toward integrating hybrid molecular materials into emerging nanotechnologies.

Organic solar cells subjected to environmental stressors such as heat, moisture, and UV radiation can undergo significant mechanical degradation, leading to delamination of layers and device failure. This paper reports the effect these stressors have on the mechanical integrity of active layers and interfaces as measured by subcritical debonding tests, and the in situ evolution of defects and fracture processes is characterized. At elevated temperatures below 50 °C in inert conditions, significant device weakening was observed, an effect we attributed to a temperature-induced P3HT:PCBM delamination mechanism from the underlying ZnO. At 50 °C in ambient conditions with UV exposure—selected to better simulate real-world environments—devices were more resistant to fracture because of an interfacial strengthening effect from increased hydrogen bonding where UV-induced Zn(OH) 2 formation reinforced the interface with P3HT:PCBM. This photoinduced hydroxylation mechanism was determined from a decrease in the Zn/O ratio with increased UVA or UVB exposure, and hydroxylation was shown to directly correlate with the resistance to fracture in devices.

Similar to organoammonium cations that template the well-studied layered perovskites, organosulfonium cations template the layered Pb–Br hybrid (tms)4Pb3Br10 (1; tms = (CH3)3S+). Upon ultraviolet excitation, this colorless, organic-inorganic hybrid exhibits broad red/near-infrared photoluminescence (PL) with a massive Stokes shift of ca. 1.7 eV. A suite of PL measurements suggests that the broad emission is an intrinsic property of the material. We ascribe this emission to radiative recombination of self-trapped excitons in the inorganic sublattice, which features both face- and corner-sharing Pb–Br octahedra. We further demonstrate that complex sulfonium-based cations can expand this family of lead-halide hybrids while maintaining the broad, Stokes-shifted PL. The use of more exotic main-group cations affords an exciting opportunity for synthetic chemists to expand the phase-space of semiconducting hybrids with unusual properties for potential applications in optoelectronics.

The mechanical properties of organic electronic materials and interfaces play a central role in determining the manufacturability and reliability of flexible and stretchable organic electronic devices. The synergistic effects of mechanical stress and deformation, together with other operating parameters such as temperature and temperature cycling, and exposure to solar radiation, moisture, and other environmental species are particularly important for longer-term device stability. We review recent studies of basic mechanical properties such as adhesion and cohesion, stiffness, yield behavior, and ductility of organic semiconducting materials, and their connection to underlying molecular structure. We highlight thin-film metrologies to probe the mechanical behavior, including when subjected to simulated operational conditions. We also report on strategies for improving reliability through interface engineering and tailoring material chemistry and molecular structure. These studies provide insights into how these metrologies and metrics inform the development of materials and devices for improved reliability.

The relative insensitivity of the optoelectronic properties of organometal trihalide perovskites to crystallographic defects and impurities has enabled fabrication of highly-efficient perovskite solar cells by scalable solution-state deposition techniques well suited to low-cost manufacturing. Fracture analyses of state-of-the-art devices, however, have revealed that both the perovskite active layer and adjacent carrier selective contacts are mechanically fragile—a major obstacle to technological maturity that stands to significantly compromise their thermomechanical reliability and operational lifetimes. We report a new concept in solar cell design, the compound solar cell (CSC), which addresses the intrinsic fragility of these materials with mechanically reinforcing internal scaffolds. The internal scaffold effectively partitions a conventional monolithic planar solar cell into an array of dimensionally scalable and mechanically shielded individual perovskite cells that are laterally encapsulated by the surrounding scaffold and connected in parallel via the front and back electrodes. The CSCs exhibited a significantly increased fracture energy of ∼13 J m−2—a 30-fold increase over previously reported planar perovskite (∼0.4 J m−2)—while maintaining efficiencies comparable to planar devices. Notably, the efficiency of the microcells formed within the scaffold is comparable to planar devices on an area-adjusted basis. This development is a significant step in demonstrating robust perovskite solar cells to achieve increased reliability and service lifetimes comparable to c-Si, CIGS, and CdTe solar cells.

Solution-processed organic semiconducting materials feature prominently in modern optoelectronic devices, especially where low-cost and flexibility are specific goals, such as perovskite solar cells. Their intrinsic solubility, poor cohesion and lack of adhesion to underlying substrates, however, curtail their scope of application and durability. To overcome this, a mechanically stiff, light-activated, tetra-azide cross-linking agent, 1,3,5,7-tetrakis-(p-benzylazide)-adamantane (TPBA), has been developed to transform solution processed organic polymers into solvent-resistant and mechanically tough films. The use of 3-azidopropyltrimethoxysilane (AzPTMS) has been developed as a light-activated adhesion promotor, enabling mechanical testing of toughened, cross-linked polymers. Lithium bis(trifluoromethane)sulfonimide (LiTFSI) doped poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine, poly(triaryl amine) (PTAA), a hole-transporting material used in perovskite solar cells, has been selected as a candidate system for demonstrating the utility of TPBA to transform a fragile and highly-soluble hole-transporting organic semiconductor into a mechanically tough and solvent-resistant semiconducting composite. TPBA enables the solvent resistance and mechanical toughness of PTAA to be tuned without compromising the electronic functionality of the semiconducting material. While increasing the fracture toughness of PTAA by over 300%, TPBA cross-linking also enables fabrication of perovskite solar cells with increased photovoltaic efficiencies in n–i–p and p–i–n geometries, and promotes adhesion of the doped polymer to the perovskite layer, mitigating interfacial device failure.

We report on submicron organosilicate barrier films produced rapidly in air by a scalable spray plasma process that improves both the stability and efficiency of perovskite solar cells. The plasma is at sufficiently low temperature to prevent damage to the underlying layers. Oxidizing species and heat from the plasma improve device performance by enhancing both interfacial contact and the conductivity of the hole transporting layer. The thickness of the barrier films is tunable and transparent over the entire visible spectrum. The morphology and density of the barrier are shown to improve with the addition of a fluorine-based precursor. Devices with submicron coatings exhibited significant improvements in stability, maintaining 92% of their initial power conversion efficiencies after more than 3000 h in dry heat (85 °C, 25% RH) while also being resistant to degradation under simulated operational conditions of continuous exposure to light, heat, and moisture. X-ray diffraction measurements performed while heating showed the barrier film dramatically slows the formation of PbI2. The barrier films also are compatible with flexible devices, exhibiting no signs of cracking or delamination after 10 000 bending cycles on a 127 μm substrate with a bending radius of 1 cm.

Low-cost solar technologies such as perovskite solar cells are not only required to be efficient, but durable too, exhibiting chemical, thermal and mechanical stability. To determine the mechanical stability of perovskite solar cells, the fracture resistance of a multitude of solution-processed organometal trihalide perovskite films and cells utilizing these films were studied. The influence of stoichiometry, precursor chemistry, deposition techniques, and processing conditions on the fracture resistance of perovskite layers was investigated. In all cases, the perovskites offered negligible resistance to fracture, failing cohesively below 1.5 J/m2. The solar cells studied featured these perovskites and a variety of organic and inorganic charge transporting layers and carrier-selective contacts. These ancillary layers were found to significantly influence the overall mechanical stability of the perovskite solar cells and were repeatedly the primary source of mechanical failure, failing at values below those measured for the isolated fragile perovskite films. A detailed insight into the nature of perovskite and perovskite solar cell fracture is presented and the influence of grain size, device architecture, deposition techniques, environmental variables, and molecular additives on these fracture processes is reported. Understanding the influence of materials selection, deposition techniques and processing variables on the mechanical stability of perovskite solar cells is a crucial step in their development.

Concentrator photovoltaic (CPV) modules operate in extreme conditions, including enhanced solar flux, elevated operating temperature, and frequent thermal cycling. Coupled with active environmental species such as oxygen and moisture, the operating conditions pose a unique materials challenge for guaranteeing operational lifetimes of greater than 25 years. Specifically, the encapsulants used in the optical elements are susceptible to environmental degradation during operation. For example, the interfaces must remain in contact to prevent optical attenuation and thermal runaway. We developed fracture mechanics based metrologies to characterize the adhesion of the silicone encapsulant and its adjacent surfaces, as well as the cohesion of the encapsulant. Further, we studied the effects of weathering on adhesion using an outdoor concentrator operating in excess of 1100 times the AM1.5 direct irradiance and in indoor environmental chambers with broadband ultraviolet (UV) irradiation combined with controlled temperature and humidity. We observed a sharp initial increase in adhesion energy followed by a gradual decrease in adhesion as a result of both outdoor concentrator exposure and indoor UV weathering. We characterized changes in mechanical properties and chemical structures using XPS, FTIR, and DMA to understand the fundamental connection between mechanical strength and the degradation of the silicone encapsulant. We developed physics based models to explain the change in adhesion and to predict operational lifetimes of the materials and their interfaces.

Introduction: Neonatal mice exhibit natural heart regeneration after myocardial infarction (MI) until postnatal day 7 (P7). Whether this regenerated muscle is similar biomechanically to native myocardium remains unknown. We hypothesized that neonatal heart regeneration preserves native left ventricular (LV) biomechanical properties after MI. Methods: C57BL/6J mice (n=58) underwent sham surgery or left anterior descending coronary artery ligation on postnatal day 1 (P1) or P7. After 4 weeks, echocardiography was performed. The explanted anterolateral LV wall was mounted for lenticular hydrostatic deformation testing (Fig 1A-B) and pressurized to 130 mmHg with 37°C saline to impart a homogeneous stress load. Surface strain was tracked to calculate a multiaxial composite tissue modulus. Data are expressed as mean±SEM. Results: P1 MI and sham mice (n=14, each) had similar post-MI LV wall thickness (0.61±0.05 cm vs 0.66±0.03 cm, p=0.39), end-diastolic diameter (3.14±0.10 cm vs 3.05±0.12 cm, p=0.57), and ejection fraction (58.2±4.1% vs 55.2±4.4%, p=0.63). P7 MI mice (n=14) had significant LV wall thinning (0.40±0.04 cm vs 0.71±0.02 cm, p Conclusion: In a neonatal mouse MI model, regenerated LV muscle has similar biomechanical properties as native LV muscle.

The effect of tuning molecular weight (Mn) in poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) to increase both mechanical properties of the film and electrical properties of perovskite solar...

Understanding how photovoltaic (PV) module backsheet polymers age and degrade in response to environmental stresses is important for designing polymers that can maintain their structural integrity after decades of outdoor use. X-ray scattering is a powerful technique for exploring backsheet polymer structure at the angstrom- (wide-angle, WAXS) and nanometer- (small-angle, SAXS) length-scales. We present the use of SAXS and WAXS to study pristine and aged polymer backsheets. The structural insight from these techniques can be used to compare the degradation induced by accelerated testing with the degradation seen in field-aged PV materials.

The impact of sunscreen formulations on the barrier properties of human skin are often overlooked leading to formulations with components whose effects on barrier mechanical integrity are poorly understood. The aim of this study is to demonstrate the relevance of carrier selection and sunscreen photostability when designing sunscreen formulations to protect the biomechanical barrier properties of human stratum corneum (SC) from solar ultraviolet (UV) damage. Biomechanical properties of SC samples were assayed after accelerated UVB damage through measurements of the SC's mechanical stress profile and corneocyte cohesion. A narrowband UVB (305–315 nm) lamp was used to expose SC samples to 5, 30, 125, and 265 J cm−2 in order to magnify damage to the mechanical properties of the tissue and characterize the UV degradation dose response such that effects from smaller UV dosages can be extrapolated. Stresses in the SC decreased when treated with sunscreen components, highlighting their effect on the skin prior to UV exposure. Stresses increased with UVB exposure and in specimens treated with different sunscreens stresses varied dramatically at high UVB dosages. Specimens treated with sunscreen components without UVB exposure exhibited altered corneocyte cohesion. Both sunscreens studied prevented alteration of corneocyte cohesion by low UVB dosages, but differences in protection were observed at higher UVB dosages indicating UV degradation of one sunscreen. These results indicate the protection of individual sunscreen components vary over a range of UVB dosages, and components can even cause alteration of the biomechanical barrier properties of human SC before UV exposure. Therefore, detailed characterization of sunscreen formulation components is required to design robust protection from UV damage., Highlights • UV light increases stress and reduces cohesion of stratum corneum (SC) to impair barrier function. • The sunscreen carrier (glyceryl tri-2-ethylhexanoate) has marked effects on SC stress and cohesiveness regardless of UV. • Accelerated UV damage tests on treated SC shows octyl methoxycinnamate sunscreen loses photoprotection with large exposure. (Fourth bullet): The same tests show dioctyl 4-methoxybenzylidenemalonate sunscreen protects SC mechanical properties with large exposure.

Objective Solar ultraviolet (UV) radiation is ubiquitous in human life and well known to cause skin damage that can lead to harmful conditions such as erythema. Although sunscreen is a popular form of protection for some of these conditions, it is unclear whether sunscreen can maintain the mechanical barrier properties of skin. The objective of this study was to determine whether in vitro thin-film mechanical analysis techniques adapted for biological tissue are able to characterize the efficacy of commonly used UV inhibitors and commercial sunscreens to protect the biomechanical barrier properties of stratum corneum (SC) from UV exposure. Methods The biomechanical properties of SC samples were assayed through measurements of the SC's drying stress profile and delamination energy. The drying stresses within SC were characterized from the curvature of a borosilicate glass substrate onto which SC had been adhered. Delamination energies were characterized using a double-cantilever beam (DCB) cohesion testing method. Successive DCB specimens were prepared from previously separated specimens by adhering new substrates onto each side of the already tested specimen to probe delamination energies deeper into the SC. These properties of the SC were measured before and after UV exposure, both with and without sunscreens applied, to determine the role of sunscreen in preserving the barrier function of SC. Results The drying stress in SC starts increasing sooner and rises to a higher plateau stress value after UVA exposure as compared to non-UV-exposed control specimens. For specimens that had sunscreen applied, the UVA-exposed and non-UV-exposed SC had similar drying stress profiles. Additionally, specimens exposed to UVB without protection from sunscreen exhibited significantly lower delamination energies than non-UV-exposed controls. With commercial sunscreen applied, the delamination energy for UV-exposed and non-UV-exposed tissue was consistent, even up to large doses of UVB. Conclusion In vitro thin-film mechanical analysis techniques can readily characterize the effects of SC's exposure to UV radiation. The methods used in this study demonstrated commercial sunscreens were able to preserve the biomechanical properties of SC during UV exposure, thus indicating the barrier function of SC was also maintained.

Photovoltaic modules are designed to operate for decades in terrestrial environments. However, mechanical stress, moisture, and ultraviolet radiation eventually degrade protective materials in modules, particularly their adhesion properties, eventually leading to reduced solar cell performance. Despite the significance of interfacial adhesion to module durability, currently there is no reliable technique for characterizing module adhesion properties. We present a simple and reproducible metrology for characterizing adhesion in photovoltaic modules that is grounded in fundamental concepts of beam and fracture mechanics. Using width-tapered cantilever beam fracture specimens, interfacial adhesion was evaluated on relevant interfaces of encapsulation and backsheet structures of new and 27-year-old historic modules. The adhesion energy, Gc [J/m2], was calculated from the critical value of the strain energy release rate, G, using G = βP2, where β (a mechanical and geometric parameter of the fracture specimen) and P (the experimentally measured critical load) are constants. Under some circumstances where testing may result in cracking of brittle layers in the test specimen, measurement of the delamination length in addition to the critical load was necessary to determine G. Relative to new module materials, backsheet adhesion was 95% and 98% lower for historic modules that were exposed (operated in the field) and unexposed (stored on-site, but out of direct sunlight), respectively. Encapsulation adhesion was 87–94% lower in the exposed modules and 31% lower in the unexposed module. The metrology presented here can be used to improve module materials and assess long-term reliability. Copyright © 2016 John Wiley & Sons, Ltd.

The stability of roll-to-roll processed organic photovoltaic modules having an inverted structure and incorporating polyethylenimine–ethoxylate (PEIE) as the electron-selective layer was investigated. Large-area modules were fabricated on ITO-coated PET substrates using roll-to-roll coating and printing methods. Modules were encapsulated with commercially-available ultra-high gas/vapor barrier films by employing new encapsulation protocols developed during this work. The operational lifetime of modules on storage in an environmental chamber at ambient temperature and relative humidity of 35 °C and 50%, respectively, and under continuous simulated AM1.5G illumination was found to increase by more than three orders of magnitude upon encapsulation. The chemical stability of the PEIE films under these storage conditions was also studied. Fracture tests were conducted on modules exposed to the same storage conditions to investigate the effects on inter- and intra-layer adhesion and cohesion. An increase in adhesive strength was found for the exposed devices indicating an absence of any substantial mechanical degradation of the deposited layers for the exposure conditions used during this work. The results described here demonstrate the potential utility of commercially-available PEIE as a convenient and effective organic electron-selective layer for the fabrication of durable roll-to-roll processed organic solar cell devices.

We discuss the development of a new composite dual cantilever beam (cDCB) thin-film adhesion testing method, which enables the quantitative measurement of adhesion on the thin and fragile substrates used in multijunction photovoltaics. In particular, we address the adhesion of several 2- and 3-layer antireflective coating systems on multijunction cells. By varying interface chemistry and morphology through processing, we demonstrate the marked effects on adhesion and help to develop an understanding of how high adhesion can be achieved, as adhesion values ranging from 0.5 J/m2 to 10 J/m2 were measured. Damp heat (85 °C/85% RH) was used to invoke degradation of interfacial adhesion. We demonstrate that even with germanium substrates that fracture relatively easily, quantitative measurements of adhesion can be made at high test yield. The cDCB test is discussed as an important new methodology, which can be broadly applied to any system that makes use of thin, brittle, or otherwise fragile substrates.

We demonstrate the deposition of transparent organosilicate protective bilayer coatings on poly methyl methacrylate (PMMA) substrates with different carbon chain length dipodalsilane precursors using atmospheric plasma deposition in ambient air. The bottom adhesive layer was a hybrid organosilicate coating deposited using either only carbon bridge organosilicate precursor or accompanied with a ring structure 1,5-cyclooctadiene precursor. The top layer was a dense silica coating with high elastic modulus and hardness deposited with only carbon bridge precursor. The adhesion energy of bottom layer increased with increasing carbon bridge length of precursors while the density, hardness, and elastic modulus of top hard layer decreased. The deposited bilayer structure showed ∼3 times the adhesion energy and four times the elastic modulus of commercial polysiloxane sol–gel coatings.

Within their first days of life, newborns' skin undergoes various adaptation processes needed to accommodate the transition from the wet uterine environment to the dry atmosphere. The skin of newborns and infants is considered as a physiological fragile skin, a skin with lower resistance to aggressions. Fragile skin is divided into four categories up to its origin: physiological fragile skin (age, location), pathological fragile skin (acute and chronic), circumstantial fragile skin (due to environmental extrinsic factors or intrinsic factors such as stress) and iatrogenic fragile skin. Extensive research of the past 10 years have proven evidence that at birth albeit showing a nearly perfect appearance, newborn skin is structurally and functionally immature compared to adult skin undergoing a physiological maturation process after birth at least throughout the first year of life. This article is an overview of all known data about fragility of epidermis in 'fragile populations': newborns, children and adolescents. It includes the recent pathological, pathophysiological and clinical data about fragility of epidermis in various dermatological diseases, such as atopic dermatitis, acne, rosacea, contact dermatitis, irritative dermatitis and focus on UV protection.

Quantitative characterization techniques based on fracture mechanics were proposed and used to examine the interface strength in multilayered structures. Novel in situ micro-fracture testing for nanolayers inside a Scanning Electron Microscope (SEM) is developed to observe fracture evolution during bending deformation of nanolayered films. Other quantitative technique on interface fracture mechanics has been the 4-point bending or double cantilever beam bending methods. In this paper we will discuss about these two techniques and their applications. In particular, the Double Cantilever Beam bending test method using Delaminator v8.2 Adhesion testing system has been used to quantify the adhesion strength between the Solar PV backsheet and encapsulant. The environmental conditions in tropical countries makes the photovoltaics components vulnerable to salt mist and water vapour as well as acid penetration. Under moisture condition, the hydrolysis reaction of water vapour with backsheet materials release acetic acid, causing delamination and further corrosion of the encapsulant and inter-metallic connectors on solar cells by the salt mist leading to electrical shorts, heat accumulation and fire. Understanding the interface strength between these two materials and its degradation with typical environments in tropical and near-ocean regions is instrumental to enable robust and reliable solar PV technology for such regions.

The role of thermal cycling of inverted P3HT:PCBM-based polymer solar cells is reported. We found that thermal cycling between −40 °C and 85 °C up to 200 cycles had no significant effect on solar cell efficiency and mechanical integrity. On the contrary, the solar cells exhibited a slight increase in fracture resistance, similar to that reported for a post-electrode deposition thermal annealing at 85 °C. Gc increased from 2.6 J/m2 for our control solar cells to a sustained maximum value of 4.0 J/m2 after 25 thermal cycles. Surface analysis on the fractured samples revealed the formation of an intermixed layer between P3HT:PCBM and PEDOT:PSS, causing the debond path to change from adhesive between P3HT:PCBM and PEDOT:PSS to meandering through the intermixed layer. A kinetic analysis was used to model the effect of thermal cycling on the Gc values of polymer cells. The model revealed for cycling between −40 °C and 85 °C that 25 cycles are needed to reach the maximum Gc, which is consistent with our experimental results. After 5 thermal cycles, the effects of heating and cooling have little impact on the mechanical stability of polymer solar cells.

We explore the structure–property relationships in hybrid organosilicate glasses that form a special class of materials for use in advanced interconnects to improve their mechanical reliability by exploiting the structural characteristics most effectively. Our results show that hybrid organosilicate glasses that are hyperconnected and derived from organic linkers with optimal molecular geometry lead to exceptional elastic and fracture properties. Using molecular dynamics simulations and the min-cut algorithm that is based on a novel graph theory approach, we demonstrate the choice of hyperconnected and cyclic planar organic linkers, such as the 1,3,5-benzene ring, significantly increases the bulk modulus and total fracture bond density, which is directly correlated with fracture energy.

Unlike existing silicon, CIGS, and multi-junction cells that exhibit remarkable mechanical durability, perovskite solar cells have been shown to delaminate when subjected to the mechanical loads that occur during processing and field exposures, limiting their potential as a reliable solar technology. Mechanical reinforcement is thus essential for durable and reliable perovskite technologies. A recent strategy to overcome the thermomechanical fragility of perovskite solar cells is to extrinsically shield them by introducing reinforcing scaffolds which partition the cell into many distinct microcells, but improvements in mechanical stability coincide with a reduced device efficiency due to parasitic absorption by the scaffold. We address this reduced efficiency by integrating concentrating immersion-lens arrays (CILAs) into scaffold-reinforced solar cells. These scaffolds are lithographically patterned by a maskless process, in which ultraviolet light is used to pattern the scaffolds through the CILAs, ensuring self-alignment and optical contact with the microcells. This process creates mm-scale scaffold patterns with a line edge roughness of 17.5 ± 4.3 µm and line width roughness of 26.4 ± 8.5 µm. Perovskite devices are deposited into the microcells, and during operation, light is concentrated into the microcells and away from the insulating scaffolds, resulting in mechanically resilient solar cells with efficiencies comparable to planar devices. The devices with the strongest lenses—i.e., lower radius of curvature—recover up to 89 ± 15% of photocurrent and 91 ± 29% power conversion efficiency that would have been otherwise lost to parasitic absorption. Ray-tracing simulations of the CILAs also demonstrate passive tracking of incident light which is critical for optimal power output as the sun moves across the sky during the day. In these simulations, devices with CILAs showed improved passive tracking compared to devices without CILAs out to 60° off-normal. The UV stability of CILAs are experimentally verified through aging tests which show no change in their mechanical integrity after 1000 h of UV exposure. The simplicity of the fabrication process and the efficiency of the resulting scaffolded devices show that a lens-integrated scaffold-reinforced structure is a potential pathway to high-performance, robust, commercially viable perovskite solar cells.