We reported molecular simulations of the interactions between water, an epoxy prepolymer (DGEBA) and an hardener (IPDA) on an aluminum surface. This work proposes a comprehensive thermodynamic characterization of the adhesion process from the calculation of the different interfacial tensions. The cross-interactions between the atoms of the metal surface and the different molecules are adjusted so as to reproduce the experimental work of adhesion. Water nanodroplets on the metal surface are then simulated to predict its contact angle. Liquid-vapor surface tensions of the epoxy prepolymer (DGEBA) and hardener (IPDA) and the solid-vapor surface tension of the aluminum surface are also calculated to provide the solid-liquid interfacial tension that remains very difficult to obtain from the mechanical definition.
The radical-induced cationic frontal photopolymerization (RICFP) of fully biobased epoxy composites is successfully demonstrated. This curing strategy considerably reducess the curing time and improves the efficiency of the composite fabrication. Two different natural fibre fabrics made of cellulose and flax fibres are embedded in two epoxy matrices, one derived from vanillin (diglycidylether of vanillyl alcohol-DGEVA) and the other from petroleum (3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate-CE). After RICFP the composites are characterized by means of dynamic mechanical thermal analysis and tensile tests. The mechanical properties improved with increasing fibre content, confirming a strong adhesion between the matrix and the reinforcing fibre fabrics, which is further evidenced by scanning electron microscopy analyses of the fracture surfaces. Furthermore, these fully bio-based composites possess comparable or even higher mechanical strength compared with the corresponding epoxy composites fabricated with conventional CE resin. A promising facile route to high-performing natural fibre-biobased epoxy resin composites is presented. This article is protected by copyright. All rights reserved
The importance of electrically functional biomaterials is increasing as researchers explore ways to utilise them in novel sensing capacities. It has been recognised that for many of these materials the state of hydration is a key parameter that can heavily affect the conductivity, particularly those that rely upon ionic or proton transport as a key mechanism. However, thus far little attention has been paid to the nature of the water morphology in the hydrated state and the concomitant ionic conductivity. Presented here is an inelastic neutron scattering (INS) experiment on hydrated eumelanin, a model bioelectronic material, in order to investigate its 'water morphology'. We develop a rigorous new methodology for performing hydration dependent INS experiments. We also model the eumelanin dry spectra with a minimalist approach whereas for higher hydration levels we are able to obtain difference spectra to extract out the water scattering signal. A key result is that the physi-sorbed water structure within eumelanin is dominated by interfacial water with the number of water layers between 3-5, and no bulk water. We also detect for the first time, the potential signatures for proton cations, most likely the Zundel ion, within a biopolymer/water system. These new signatures may be general for soft proton ionomer systems, if the systems are comprised of only interfacial water within their structure. The nature of the water morphology opens up new questions about the potential ionic charge transport mechanisms within hydrated bioelectronics materials.
The feasibility of a solar-driven photoelectrochemical process to generate hydrogen fuel from metal mine polluted water while simultaneously recovering heavy metals has been explored. Electron transport from the photoanode to the cathode plays a key role in generating hydrogen (37.6 µmol h–1 cm–2 at 0.2 V RHE, 1 sun illumination), and scavenging Zn2+ ions in the form of ZnO.
Bio‐based epoxy resins are attracting widespread interest in the field of polymer thermosets as environmentally friendly building block. In the present study, the feasibility of applying UV‐curable epoxidized vegetable oils (EVOs) as anti‐corrosion coating is investigated. Rheological characterization of EVOs is carried out, and their viscosity‐shear relationship is evaluated. The cationic UV‐curing of EVOs successfully gives rise to crosslinked materials with a wide range of thermo‐mechanical properties, evaluated by differential scanning calorimetric analysis and dynamic thermal mechanical analysis. A high epoxy‐group conversion, ranging from 93% to 99%, is always obtained. The thermal stability and surface properties of the bio‐based coatings, such as, pencil hardness, adhesion, solvent resistance, and contact angle, are analyzed. Moreover, the corrosion protection effectiveness of the coatings is characterized by potentiodynamic polarization and electrochemical impedance spectroscopy measurements. In addition, field emission scanning electron microscopy is used to assess the samples morphology after corrosion tests. This paper presents a comprehensive characterization of the bio‐based thermosets obtained from three different epoxidized triglycerides; the specific application for anticorrosion coatings is investigated using electrochemical measurements. Results highlight the good corrosion protection behavior of the coatings, specifically for the formulation having the highest epoxy content; this can be correlated to the high cross‐linking density and higher glass transition temperature.
Beyond the need to find a non-toxic alternative to DiGlycidyl Ether of Bisphenol-A (DGEBA), the serious subject of non-epichlorohydrin epoxy resins production remains a crucial challenge that must be solved for the next epoxy resin generations. In this context, this study focuses on the valorization of vegetable oils (VOs) into thermoset materials by using (i) epoxidation of the VOs through the “double bonds to epoxy” synthetic route and (ii) synthesis of crosslinked homopolymers by UV or hardener-free thermal curing processes. A thorough identification, selection and physico-chemical characterization of non-edible or non-valuated natural vegetable oils were performed. Selected VOs, characterized by a large range of double bond contents, were then chemically modified into epoxides thanks to an optimized, robust and sustainable method based on the use of acetic acid, hydrogen peroxide and Amberlite® IR-120 at 55 °C in toluene or cyclopentyl methyl ether (CMPE) as a non-hazardous and green alternative solvent. The developed environmentally friendly epoxidation process allows reaching almost complete double bond conversion with an epoxy selectivity above 94% for the 12 studied VOs. Finally, obtained epoxidized vegetable oils (EVOs), characterized by an epoxy index from 2.77 to 6.77 meq. g⁻¹ were cured using either UV or hardener-free thermal curing. Both methods enable the synthesis of 100% biobased EVO thermoset materials whose thermomechanical performances were proved to linearly increase with the EVOs' epoxy content. This paper highlights that tunable thermomechanical performances (Tα from −19 to 50 °C and Tg from −34 to 36 °C) of EVO based thermoset materials can be reached by well selecting the starting VO raw materials.
The development of solution-processed photovoltaic (PV) devices for indoor applications has recently attracted widespread attention owing to their outstanding potential in harvesting energy efficiently for low-power-consumption electronic devices, such as wireless sensors and internet of things (IoTs). In particular, organic PV (OPV), perovskite PV (PPV) and quantum dot PV (QDPV) are among the most promising emerging photovoltaic technologies that have already demonstrated strong commercialisation potential for this new market, owing to their excellent yet highly tuneable optoelectronic properties to meet the demands for specific applications. In this review, we summarise the recent progress in the development of OPV, PPV and QDPV for indoor applications, showing the rapid advance in their device performance in conjunction with highly diverse materials and device designs, including semi-transparent, flexible and large-area devices. The remaining challenges of these emerging indoor PV technologies that need to be urgently addressed toward their commercialisation, including in particular their limited stability and high ecotoxicity, will be discussed in detail. Potential strategies to address these challenges will also be proposed.
For the first time, the effect of reactant structure, stoichiometry and heating rate on the reactivity of epoxidized perilla oil (EPLO) and epoxidized safflower oil (ESFO) with dicarboxylic acids (DCAs) was studied using in situ FT-IR. The epoxy content in the monomer structure was found to affect the copolymerization system’s reactivity, with epoxidized linseed oil (ELO) considered as a reference. In this study we discuss also the influence of the DCA structure on the copolymerization reactivity. Two aromatic diacids, dithiodibenzoic acid (DTBA) and diphenic acid (DPA), were studied and compared in the copolymerization of the 3 EVOs, in the presence of imidazole (IM) initiator. The kinetics of these reactions were followed by in situ FT-IR. The corresponding activation energies were calculated via different kinetic models. These data highlight the higher reactivity of the EPLO monomer and the DTBA hardener.
In this study, we investigate the underlying origin of the high performance of PM6:Y6 organic solar cells. Employing transient optoelectronic and photoemission spectroscopies, we find that this blend exhibits greatly suppressed charge trapping into electronic intra-bandgap tail states compared to other polymer/non-fullerene acceptor solar cells, attributed to lower energetic disorder. The presence of tail states is a key source of energetic loss in most organic solar cells, as charge carriers relax into these states, reducing the quasi-Fermi level splitting and therefore device VOC. DFT and Raman analyses indicate this suppression of tail state energetics disorder could be associated with a higher degree of conformational rigidity and uniformity for the Y6 acceptor. We attribute the origin of such conformational rigidity and uniformity of Y6 to the presence of the two alkyl side chains on the outer core that restricts end-group rotation by acting as a conformation locker. The resultant enhanced carrier dynamics and suppressed charge carrier trapping are proposed to be a key factor behind the high performance of this blend. Low energetic disorder is suggested to be a key factor enabling reasonably efficient charge generation in this low energy offset system. In the absence of either energetic disorder or a significant electronic energy offset, it is argued that charge separation in this system is primarily entropy driven. Nevertheless, photocurrent generation is still limited by slow hole transfer from Y6 to PM6, suggesting pathways for further efficiency improvement.
Roll-to-roll coating of all active layers is demonstrated for a P-I-N perovskite solar cell stack, using a single step perovskite ink with an acetonitrile solvent system and flexible plastic substrate. A slot-die coating roll-to-roll process with a common coating speed for all layers is developed by using appropriate length meniscus guides as part of the coating head for each ink rheology. High performance devices are demonstrated with four roll-to-roll slot-die coated layers and evaporated top electrode, the drying conditions of the perovskite layer are optimized and found to be critical to achieving good performance. Multi solvent blend systems for the electron collection layer are developed that are more industrially compatible than the commonly used chlorobenzene solvent system and make use of a gradient of solvent volatilities to give both good macro film formation and rapid drying. A stabilised power conversion efficiency of 12.2% is demonstrated, that is the highest reported to date for devices with all layers other than the top electrode deposited roll-toroll. This work demonstrates the feasibility of a roll-to-roll fabrication process for perovskite solar cells that could be transferred to a fully inline roll-to-roll process with all coating and drying stages made sequentially on one line running at a common coating speed and further demonstrates the potential to produce high efficiency photovoltaics using roll-to-roll fabrication methods.
This paper demonstrates the high reactivity and potentiality of bio‐renewably obtained cardanol‐based epoxy monomers as well as the possibility of tuning the final thermo‐mechanical properties, by changing either the epoxy content or the chemical structure of the starting photocurable resin. The reactivity of the cardanol monomers towards the cationic UV‐curing process was investigated by FT‐IR analysis and it was shown that a high epoxy group conversion was achieved. Furthermore, thermomechanical properties were investigated on crosslinked films by means of DSC and DMTA analysis. This article is protected by copyright. All rights reserved.
Perovskite solar cells with high power-per-weight have great potential to be used for aerospace applications such as satellites or high-altitude pseudo-satellites. These latter are unmanned aircrafts exclusively powered by solar energy, typically flying in the stratosphere where conditions of pressure, temperature and illumination are critically different than on earth surface. In this work, we evaluate the performance and stability of high efficiency perovskite solar cells under mimic stratospheric environment. In-situ measurements at controlled conditions of pressure, temperature and illumination were developed. We show that the cells can operate efficiently in a large range of temperatures from -50°C to +20°C, with a maximum power conversion efficiency at -20°C, which is ideal for use in the stratosphere. Besides, performances are maintained after a number of temperature cycles down to -85°C, representative of temperature variations due to diurnal cycles. An efficient encapsulation is developed, which could be critical to avoid the accelerated degradation of the cells under vacuum. Finally, a promising stability for 25 days of day-night cycles was demonstrated, which suggests that perovskite solar cells could be used to power high altitude pseudo-satellites.
The demonstration of photovoltaic devices with high power conversion efficiencies using low cost perovskite materials hints at the possibility of dramatically lowering the cost of solar energy. Key to further exploiting the potential of these materials is developing rapid processing techniques that can be used to deliver lower cost high throughput manufacture. This work details the development of low viscosity rapid drying perovskite formulations designed to give high quality solar films when slot-die coated on flexible roll-to-roll compatible substrates. A single step slot-die compatible perovskite ink based on an acetonitrile/methylamine solvent system utilizing a chloride additive is developed, resulting in large area perovskite films from slot-die coating under ambient conditions. The drying conditions for the perovskite film are optimized and fast (<10 min), low temperature (<120 °C) drying of slot-die coated films on flexible substrates are demonstrated and result in high performance devices.
In order to achieve semi-transparency in perovskite solar cells, the electrode materials must be as transparent as possible. In this work, MoOx/ITO/Ag/ITO (MoOx/IAI) thin films with high average transmittance of 79.90% between 400 nm and 900 nm were introduced as the top transparent electrode to explore its influences on optoelectronic properties of the fabricated perovskite solar cells. MoOx has been demonstrated previously as protection from sputtering damage using a conventional ITO top electrode, however it is shown here to provide protection from a sputtered IAI film that provides superior transparency and conductivity and is deposited using more favourable low temperature processing conditions. MoOx and Ag were thermally evaporated and ITO was radio-frequency magnetron sputtered at room temperature. The resulting semi-transparent solar cells showed power conversion efficiency of 12.85% (steady-state efficiency of 11.3%) along with a much-reduced degradation rate as compared to the reference device with only a Ag top electrode. With such a combination of performance and transparency, this work shows great promise in application of perovskite solar cells into window glazing products for building integrated photovoltaic applications (BIPV), powering internet of things (IoT) and combining into tandem solar cells with industrially mature photovoltaic technologies such as silicon and copper indium gallium di-selenide (CIGS).
The recent emergence of non-fullerene small molecule acceptors has reinvigorated the field of organic solar cells, already resulting in significant breakthroughs of their power conversion efficiency and discovery of remarkable new science. The stability and degradation of this class of materials and devices, on the other hand, has to date received relatively less attention. Herein, we present a critical review into the fundamentally different degradation mechanisms of non-fullerene acceptors compared to fullerene acceptors, as well as the very different roles they play upon the charge carrier generation and recombination kinetics and the resulting solar cell stability. We highlight in particular the prospect in the emergence of non-fullerene acceptors in addressing several major degradation mechanisms related to the use of fullerene acceptors, in conjunction with a number of unique degradation mechanisms that only exist in non-fullerene acceptors, which would provide an important guideline for further developments toward achieving long-term stability of organic solar cells.
Crystalline quality of the perovskite film plays a key role in improving the optoelectronic properties and performance of planar perovskite hybrid solar cells (PSCs). In this work, a methodology employing post-annealing microwave treatment (MPAT) for fine tuning the crystallization of perovskite films is proposed. It is found that microwave induced electromagnetic waves results in the dipoles and ions to vibrate at high frequency in perovskite crystals, which catalyzes Ostwald ripening process resulting in a good quality perovskite films. High quality perovskite films are obtained when subjected to MPAT of 350 watts power for 25 seconds. The resulting films in inverted solar cell architecture shown champion efficiency of 13.39%. This is significant improved performance over devices employing films without MPAT treatment (PCE=11.5%). The MPAT paves a way to prepare high quality perovskite films that is of particularly significance for manufacturing of the large area perovskite solar cells.
For applications in nanomedicine, particles need to be functionalized to prevent protein corona formation and/or aggregation. Most advanced strategies take advantage of functional polymers and assembly techniques. Nowadays there is an urgent need for coatings that are tailored according to a broad range of surfaces and that can be produced on a large scale. Herein, we synthesize monophosphonic and multiphosphonic acid based poly(ethylene glycol) (PEG) polymers with the objective of producing efficient coats for metal oxide nanoparticles. Cerium, iron, titanium, and aluminum oxide nanoparticles of different morphologies (spheres, platelets, nanoclusters) and sizes ranging from 7 to 40 nm are studied in physiological and in protein rich cell culture media. It is found that the particles coated with monofunctionalized polymers exhibit a mitigated stability over time (<1 week), whereas the multifunctionalized copolymers provide resilient coatings and long‐term stability (> months). With the latter, PEG densities in the range 0.2–0.5 nm−2 and layer thickness about 10 nm provide excellent performances. The study suggests that the proposed coating allows controlling nanomaterial interfacial properties in biological environments. Most advanced coating strategies take advantage of functional polymers and assembly techniques. This study synthesizes phosphonic acid PEGylated copolymers and succeeds in producing efficient coating agents for a wide variety of oxide nanoparticles. Stability studies in protein‐rich media show that the proposed approach allows controlling nanomaterial interfacial properties in biological environments and is appropriate for nanomedicine.
This work reports three newly developed dopant free hole transporting materials (HTMs) for perovskite solar cells. The design was based on quinacridone (QA) dye analogues with three different extending moieties, including acenaphthylene (ACE), triphenylamine (TPA) and diphenylamine (DPA). They were synthesized and fabricated successfully in mesoscopic TiO2/CH3NH3PbI3/HTM perovskite devices. Under 100 mW cm-2 AM 1.5G, the devices achieved a maximum efficiency of 18.2% for ACE-QA-ACE, 16.6% for TPA-QA-TPA and 15.5% for DPA-QA-DPA without any additives, while the reference devices with doped Spiro-OMeTAD as HTM showed a PCE of 15.2%. Notably, the unencapsulated devices based on these novel dopant-free HTMs show impressive stability in comparison with the doped Spiro-OMeTAD devices under 75% relative humidity for 30 days. These linear symmetrical HTMs pave the way to a new class of organic hole transporting materials for cost-efficient and large area applications of printed perovskite solar cells.
The role of breathing behavior in hydrated and dehydrated forms of MIL-53(Fe) is investigated here. The material can be used as an efficient electrocatalyst and photocatalyst for a hydrogen evolution reaction (HER) in an alkaline medium and the same was further tested for the degradation of organic pollutants. The as-synthesized MIL-53(Fe)/hydrated and dehydrated forms were characterized by different analytical techniques to study their structure, morphology, surface analysis, thermal, physical and chemical properties. The breathing behavior of the hydrated and dehydrated forms of MIL-53(Fe) was studied through BET surface analysis. Our results show a low onset potential (-0.155 V and -0.175 V), Tafel slope (71.6 mV per decade, 88.7 mV per decade) and a large exchange current density (1.6 × 10⁻⁴ mA cm⁻² and 2.5 × 10⁻⁴ mA cm⁻²). Hydrated and dehydrated MIL-53(Fe) degraded an RhB dye solution within 30 minutes thus proving their efficiency as efficient photocatalysts.
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