Humidity Sensing Applications of Lead-Free Halide Perovskite Nanomaterials.

Over the past decade, perovskite-based nanomaterials have gained notoriety within the scientific community and have been used for a variety of viable applications. The unique structural properties of these materials, namely good direct bandgap, low density of defects, large absorption coefficient, high sensitivity, long charge carrier lifetime, good selectivity, acceptable stability at room temperature, and good diffusion length have prompted researchers to explore their potential applications in photovoltaics, light-emitting devices, transistors, sensors, and other areas. Perovskite-based devices have shown very excellent sensing performances to numerous chemical and biological compounds in both solid and liquid mediums. When used in sensing devices, Perovskite nanomaterials are for the most part able to detect O2, NO2, CO2, H2O, and other smaller molecules. This review article looks at the use of lead-free halide perovskite materials for humidity sensing. A complete description of the underlying mechanisms and charge transport characteristics that are necessary for a thorough comprehension of the sensing performance will be provided. An overview of considerations and potential recommendations for the creation of new lead-free perovskite nanostructure-based sensors is presented.

Pushing the Limits of Flexibility and Stretchability of Solar Cells: A Review.

Emerging forms of soft, flexible, and stretchable electronics promise to revolutionize the electronics industries of the future offering radically new products that combine multiple functionalities, including power generation, with arbitrary form factor. For example, skin-like electronics promise to transform the human-machine-interface, but the softness of the skin is incompatible with traditional electronic components. To address this issue, new strategies toward soft and wearable electronic systems are currently being pursued, which also include stretchable photovoltaics as self-powering systems for use in autonomous and stretchable electronics of the future. Here recent developments in the field of stretchable photovoltaics are reviewed and their potential for various emerging applications are examined. Emphasis is placed on the different strategies to induce stretchability including extrinsic and intrinsic approaches. In the former case, engineering and patterning of the materials and devices are key elements while intrinsically stretchable systems rely on mechanically compliant materials such as elastomers and organic conjugated polymers. The result is a review article that provides a comprehensive summary of the progress to date in the field of stretchable solar cells from the nanoscale to macroscopic functional devices. The article is concluded by discussing the emerging trends and future developments.

Capturing Mobile Lithium Ions in a Molecular Hole Transporter Enhances the Thermal Stability of Perovskite Solar Cells.

A thermally stable perovskite solar cell (PSC) based on a new molecular hole transporter (MHT) of 1,3-bis(5-(4-(bis(4-methoxyphenyl) amino)phenyl)thieno[3,2-b]thiophen-2-yl)-5-octyl-4H-thieno[3,4-c]pyrrole-4,6(5H)-dione (coded HL38) is reported. Hole mobility of 1.36 × 10-3 cm2 V-1 s-1 and glass transition temperature of 92.2 °C are determined for the HL38 doped with lithium bis(trifluoromethanesulfonyl)imide and 4-tert-butylpyridine as additives. Interface engineering with 2-(2-aminoethyl)thiophene hydroiodide (2-TEAI) between the perovskite and the HL38 improves the power conversion efficiency (PCE) from 19.60% (untreated) to 21.98%, and this champion PCE is even higher than that of the additive-containing 2,2',7,7'-tetrakis(N,N-di-p-methoxyphenylamine)-9,9'-spirobifluorene (spiro-MeOTAD)-based device (21.15%). Thermal stability testing at 85 °C for over 1000 h shows that the HL38-based PSC retains 85.9% of the initial PCE, while the spiro-MeOTAD-based PSC degrades unrecoverably from 21.1% to 5.8%. Time-of-flight secondary-ion mass spectrometry studies combined with Fourier transform infrared spectroscopy reveal that HL38 shows lower lithium ion diffusivity than spiro-MeOTAD due to a strong complexation of the Li+ with HL38, which is responsible for the higher degree of thermal stability. This work delivers an important message that capturing mobile Li+ in a hole-transporting layer is critical in designing novel MHTs for improving the thermal stability of PSCs. In addition, it also highlights the impact of interface design on non-conventional MHTs.

A Ladder-like Dopant-free Hole-Transporting Polymer for Hysteresis-less High-Efficiency Perovskite Solar Cells with High Ambient Stability.

Perovskite solar cells (PSCs) have received high attention in the past few years due to their terrific photovoltaic performance and potentially low production cost. However, the use of hole transport materials (HTMs) with hygroscopic dopants, which cause the inevitable instability of device performance, has hampered commercialization. Herein, a dopant-free polymeric HTM with functional aromatic rings was used to optimize the HTM/perovskite interface and employed in a planar n-i-p configuration. Poly(1,4-(2,5-bis((2-butyloctyloxy)phenylene)-2,7-(5,5,10,10-tetrakis(4-hexylphenyl)-5,10-dihydro-s-indaceno[2,1-b:6,5-b']dithiophene)) (IDTB) co-polymer constructed with indaceno[1,2-b:5,6-b']dithiophene and bis(alkyloxy)benzene units adopts an S⋅⋅⋅O intramolecular bond linked ladder-like planar conjugated polymer backbone. Without any dopant, the hole mobility of IDTB is in the same order of magnitude as a doped 2,2',7,7'-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9'-spirobifluorene (spiro-OMeTAD). Also, the hydrophobic nature of IDTB facilitated the long-term stability of the perovskite underneath. The unencapsulated PSC devices made of IDTB-based HTM achieved a power conversion efficiency of 19.38 % with a high moisture stability, retaining above 80 % of initial power conversion efficiency at 65 % relative humidity for more than 10 days. The superior passivation effect to perovskite surface made a hysteresis of 0.44 % was almost the least reported for regular planar undoped polymer HTM PSCs.

Conducting and Stretchable PEDOT:PSS Electrodes: Role of Additives on Self-Assembly, Morphology, and Transport.

The addition of dimethylsulfoxide and Zonyl into poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) can be combined to achieve excellent electrical, optical, and mechanical properties. We demonstrate that it is possible to produce highly transparent conducting electrodes (FoM > 35) with low Young's modulus and high carrier density. We investigated the relationship between the transport properties of PEDOT:PSS and the morphology and microstructure of these films by performing Hall effect measurement, atomic force microscopy, and grazing incidence wide-angle X-ray scattering (GIWAXS). Our analysis reveals the distinctive impact of the two additives on the PEDOT and PSS components in the solid-state PEDOT:PSS films. Both additives induce fibrillar formation in the film, and the combination of the two additives only enhances the fibrillary nature and the aggregations of both PEDOT and PSS components of the film. In situ GIWAXS allows to time-resolve the morphology evolution. Our analysis reveals the influence of additives on the aggregation and self-assembly behaviors of the PEDOT and PSS components. Aggregation occurs during the transition from wet to dry film, which is observed exclusively during the thermal annealing step of the as-cast hydrated film. These results indicate that the additives directly influence the self-assembly behaviors of PEDOT and PSS during the ink-to-solid phase transformation of the hydrated film, which occurs primarily during the initial seconds of post-deposition thermal annealing.

Triphenylamine-Thienothiophene Organic Charge-Transport Molecular Materials: Effect of Substitution Pattern on their Thermal, Photoelectrochemical, and Photovoltaic Properties.

Two readily accessible thienothiophene-triphenylamine charge-transport materials have been synthesized by simply varying the substitution pattern of the triphenylamine groups on a central thienothiophene π-linker. The impact of the substitution pattern on the thermal, photoelectrochemical, and photovoltaic properties of these materials was evaluated and, based on theoretical and experimental studies, we found that the isomer in which the triphenylamine groups were located at the 2,5-positions of the thienothiophene core (TT-2,5-TPA) had better π-conjugation than the 3,6-isomer (TT-3,6-TPA). Whilst the thermal, morphological, and hydrophobic properties of the two materials were similar, their optoelectrochemical and photovoltaic properties were noticeably impacted. When applied as hole-transport materials in hybrid perovskite solar cells, the 2,5-isomer exhibited a power-conversion efficiency of 13.6 %, much higher than that of its 3,6-counterpart (0.7 %) under the same standard conditions.

Recent advances on organic blue thermally activated delayed fluorescence (TADF) emitters for organic light-emitting diodes (OLEDs).

The design of highly emissive and stable blue emitters for organic light emitting diodes (OLEDs) is still a challenge, justifying the intense research activity of the scientific community in this field. Recently, a great deal of interest has been devoted to the elaboration of emitters exhibiting a thermally activated delayed fluorescence (TADF). By a specific molecular design consisting into a minimal overlap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) due to a spatial separation of the electron-donating and the electron-releasing parts, luminescent materials exhibiting small S1-T1 energy splitting could be obtained, enabling to thermally upconvert the electrons from the triplet to the singlet excited states by reverse intersystem crossing (RISC). By harvesting both singlet and triplet excitons for light emission, OLEDs competing and sometimes overcoming the performance of phosphorescence-based OLEDs could be fabricated, justifying the interest for this new family of materials massively popularized by Chihaya Adachi since 2012. In this review, we proposed to focus on the recent advances in the molecular design of blue TADF emitters for OLEDs during the last few years.

Characterizing the Intrinsic Fluorescence Properties of Historical Painting Materials: The Case Study of a Sixteenth-Century Mesoamerican Manuscript.

Ultraviolet visible (UV-Vis) fluorescence spectroscopy is widely used to study polychrome objects and can help to identify the nature of certain materials when they present specific fluorescent properties. However, given the complexity of the stratified and heterogeneous materials under study, the characterization of an intrinsic fluorescence related to a given constituent (a pigment or a binder composing a paint layer for example) is not straightforward, and the recorded raw data need to be corrected for a number of effects that can influence the detected spectral distribution. The application of standard correction procedures to experimental fluorescence data gathered on the polychromatic surface of the Codex Borbonicus, a 16th-century Aztec manuscript, is described. The results are confronted to an alternate new methodology that is based on the hypothesis of transparent non-scattering paint layers. This second approach allows to establish more clearly the material origin of the detected emission and to discriminate apparent fluorescence (emitted by the substrate and transmitted through the paint layers) from actual intrinsic emission generated by the coloring materials under study. The results show that most of the various emission profiles detected in the paint layers of the manuscript actually originate from a unique fluorophore (composing the substrate) and should not be used to characterize the coloring materials.

Novel Carbazole Skeleton-Based Photoinitiators for LED Polymerization and LED Projector 3D Printing.

Radical chemistry is a very convenient way to produce polymer materials. Here, an application of a particular photoinduced radical chemistry is illustrated. Seven new carbazole derivatives Cd1-Cd7 are incorporated and proposed as high performance near-UV photoinitiators for both the free radical polymerization (FRP) of (meth)acrylates and the cationic polymerization (CP) of epoxides utilizing Light Emitting Diodes LEDs @405 nm. Excellent polymerization-initiating abilities are found and high final reactive function conversions are obtained. Interestingly, these new derivatives display much better near-UV polymerization-initiating abilities compared to a reference UV absorbing carbazole (CARET 9H-carbazole-9-ethanol) demonstrating that the new substituents have good ability to red shift the absorption of the proposed photoinitiators. All the more strikingly, in combination with iodonium salt, Cd1-Cd7 are likewise preferred as cationic photoinitiators over the notable photoinitiator bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (BAPO) for mild irradiation conditions featuring their remarkable reactivity. In particular their utilization in the preparation of new cationic resins for LED projector 3D printing is envisioned. A full picture of the included photochemical mechanisms is given.

Visible-light active conducting polymer nanostructures with superior photocatalytic activity.

The development of visible-light responsive photocatalysts would permit more efficient use of solar energy, and thus would bring sustainable solutions to many environmental issues. Conductive polymers appear as a new class of very active photocatalysts under visible light. Among them poly(3,4-ethylenedioxythiophene) (PEDOT) is one of the most promising conjugated polymer with a wide range of applications. PEDOT nanostructures synthesized in soft templates via chemical oxidative polymerization demonstrate unprecedented photocatalytic activities for water treatment without the assistance of sacrificial reagents or noble metal co-catalysts and turn out to be better than TiO2 as benchmark catalyst. The PEDOT nanostructures exhibit a narrow band gap (E = 1.69 eV) and are characterized by excellent ability to absorb light in visible and near infrared region. The novel PEDOT-based photocatalysts are very stable with cycling and can be reused without appreciable loss of activity. Interestingly, hollow micrometric vesicular structures of PEDOT are not effective photocatalysts as compared to nanometric spindles suggesting size and shape dependent photocatalytic properties. The visible-light active photocatalytic properties of the polymer nanostructures present promising applications in solar light harvesting and broader fields.

Conducting polymer nanostructures for photocatalysis under visible light.

Visible-light-responsive photocatalysts can directly harvest energy from solar light, offering a desirable way to solve energy and environment issues. Here, we show that one-dimensional poly(diphenylbutadiyne) nanostructures synthesized by photopolymerization using a soft templating approach have high photocatalytic activity under visible light without the assistance of sacrificial reagents or precious metal co-catalysts. These polymer nanostructures are very stable even after repeated cycling. Transmission electron microscopy and nanoscale infrared characterizations reveal that the morphology and structure of the polymer nanostructures remain unchanged after many photocatalytic cycles. These stable and cheap polymer nanofibres are easy to process and can be reused without appreciable loss of activity. Our findings may help the development of semiconducting-based polymers for applications in self-cleaning surfaces, hydrogen generation and photovoltaics.

Panchromatic Photopolymerizable Cationic Films Using Indoline and Squaraine Dye Based Photoinitiating Systems.

The photoinitiating abilities of indoline and squaraine dyes (D102 and SQ02) incorporated in multicomponent systems for the cationic polymerization of an epoxide or a vinyl ether have been investigated. The polymerizable films exhibit a panchromatic character as revealed by their photosensitivity to a halogen lamp (370-800 nm); household LED bulbs centered at 462 nm (blue), 514 nm (green), 591 nm (yellow), and 630 nm (red); and laser diodes at 457, 473, 532, and 635 nm. SQ02 is particularly efficient in the 520-700 nm range, while D102 exhibits a good efficiency in the 400-580 nm region. The radical photopolymerization of an acrylate can also be observed particularly at 635 nm or upon a halogen lamp. The photochemical mechanisms are studied by steady state photolysis, fluorescence, cyclic voltammetry, electron spin resonance spin trapping, and laser flash photolysis techniques.

Iridium(III) soft salts from dinuclear cationic and mononuclear anionic complexes for OLED devices.

Two iridium(III) soft salts based on ion-paired dinuclear cationic and mononuclear anionic complexes were designed and investigated as phosphorescent emitters for solution processed OLEDs. New dinuclear cationic complexes were prepared with two different bridging ligands, a carbazole and a phenylene spacer. Best devices were designed with the soft salt bearing a carbazole moiety.

Labeling of fibronectin by fluorescent and paramagnetic nanoprobes for exploring the extracellular matrix: bioconjugate synthesis optimization and biochemical characterization.

In this study, fibronectin-nanoparticles bioconjugates are developed and characterized. Multilabeled nanoparticles are composed of a core of the rare-earth oxide Gd(2)O(3):Tb(3+), capped with a set of Rhodamine B isothiocyanate encapsulated in a silica matrix and functionalized by a carboxylated polyethylene glycol shell. These nanoparticles are stabilized in aqueous solution and are found to contain about 400 carboxyl groups on their surface. Nanoparticle bioconjugation with highly purified human plasma fibronectin (Fn) is mediated by 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide and N-hydroxysuccinimide, resulting in an amide linkage between the carboxylic acid-terminated surface of the nanoparticle and the primary amine of Fn. The bioconjugation temperature and pH are optimized. The Local structure and global conformation of fibronectin-nanoparticle bioconjugates (FnNP*) are studied by fluorescence spectroscopy and enzymatic sites accessibility. Protein biochemical functionalities are globally conserved, and the protein is actually labeled. Elaboration of such complexes provides a promising bimodal contrasting agent for in vivo imaging.

Elaboration of nanohybrid materials by photopolymerisation of 3,4-ethylenedioxythiophene on TiO2.

A method for the elaboration of a heterojunction composed on n-type inorganic semiconducting nanoparticles, TiO(2), and a p-type organic semiconducting polymer poly(3,4-ethylene dioxythiophene) by UV illumination is described.

Functionalization of luminescent aminated particles for facile bioconjugation.

For labeling proteins (streptavidin and fibronectin) by luminescent aminated nanoparticles, an interesting strategy that requires neither activation nor chemical pre- or post-treatment was explored. Because biomolecules are easily rendered luminescent after reaction with organic dyes carrying isothiocyanate moiety, phenylene diisothiocyanate (DITC) was used for covalently binding proteins onto luminescent hybrid gadolinium oxide nanoparticles whose ability to combine imaging and therapy was recently demonstrated.

Characterization limits of a polymer adsorbed under a monolayer by GIXD measurements.

The study of interactions between a polyelectrolyte (sodium polystyrene sulfonate, PSSt) or its water-soluble monomer (SSt) at different concentrations and a monolayer of dioctadecyldimethylammonium bromide (DODA) has been investigated. The monolayer phase behavior and structure at the air-water interface were studied by surface pressure-area isotherms and grazing incidence X-ray diffraction measurements. DODA molecules organize following a rectangular unit cell in all three subphases (pure water, water containing SSt or PSSt). The presence of polyelectrolytes in the subphase decreases, on one hand, the tilt angle and the mean area per molecule in the condensed phase, revealing a higher 2D density in this state, and, on the other hand, the amount of organized matter.

In vitro denaturation-renaturation of fibronectin. Formation of multimers disulfide-linked and shuffling of intramolecular disulfide bonds.

It is well established that fibronectin into extracellular matrix undergoes repeated tensions applied by cells, resulting into dramatic structural changes which reflect its elastic properties. However, there is currently no study reporting with precision the consequences of this elasticity on fibronectin structure and conformation. In the present work, we investigated fibronectin structural and conformational reorganization in vitro through a denaturation-renaturation approach. The similarities and differences between "refolded fibronectin" and "native fibronectin" were investigated using various spectroscopic methods, hydrodynamic characterization, molecular imaging and biochemical characterization. In the refolded form, secondary structure elements as well as local tyrosine and tryptophan environment are identical compared to the native form. Interestingly, some differences in global tertiary structure organization and molecular conformation were observed. These differences are due to the reactivity of the two free cysteines, which are buried in the native state but become accessible during the unfolding process. First, oxidation of these residues leading to the formation of intermolecular disulfide bonds results in formation of stabilized multimer. Second, some illegitimate intramolecular disulfide bonds are formed. The presence of iodoacetamide, the sulfhydryl alkylating agent, during the unfolding-refolding process prevents all these events. This study clearly demonstrates that, under near physiological conditions, competitive renaturation pathways occur, involving free cysteines in either multimer formation or intermolecular shuffling of disulfide bonds. These findings might have important implications for future studies and be helpful to develop a deeper understanding of fibronectin morphology.

Urea-induced sequential unfolding of fibronectin: a fluorescence spectroscopy and circular dichroism study.

Fibronectin (FN) is an extracellular matrix (ECM) protein found soluble in corporal fluids or as an insoluble fibrillar component incorporated in the ECM. This phenomenon implicates structural changes that expose FN binding sites and activate the protein to promote intermolecular interactions with other FN. We have investigated, using fluorescence and circular dichroism spectroscopy, the unfolding process of human fibronectin induced by urea in different ionic strength conditions. At any ionic strength, the equilibrium unfolding data are well described by a four-state equilibrium model N <= => I(1) <= =>I(2) <= => U. Fitting this model to experimental values, we have determined the free energy change for the different steps. We found that the N <= => I(1) transition corresponds to a free energy of 10.5 +/- 0.4 kcal/mol. Comparable values of free energy change are generally associated with a partial unfolding of the type III domain. For the I(1) <= => I(2) transition, the free energy change is 7.6 +/- 0.4 kcal/mol at low ionic strength but is twice as low at high ionic strength. This result is consistent with observations indicating that the complete unfolding of the type III domain from partially unfolded forms necessitates about 5 kcal/mol. The third step, I(2) <= => U, which leads to the complete unfolding of fibronectin, corresponds to a free energy change of 14.4 +/- 0.9 kcal/mol at low ionic strength whereas this energy is again twice as low under high ionic strength conditions. This hierarchical unfolding of fibronectin, as well as the stability of the different intermediates controlled by ionic strength demonstrated here, could be important for the understanding of activation of the matrix assembly.