Thermosetting Polyurethane Resins as Low-Cost, Easily Scalable, and Effective Oxygen and Moisture Barriers for Perovskite Solar Cells.

Long-term stability of perovskite solar cells (PSCs) is one of the main issues to be solved for forthcoming commercialization of this technology. In this work, thermosetting polyurethane (PU)-based resins are proposed as effective encapsulants for perovskite solar cells to prevent degradation caused by both moisture and oxygen. Application consists of drop-casting the precursor mixture directly over the devices followed by in situ polymerization, avoiding the use of other adhesives. PUs are cost-effective, lightweight, thermal, and light-stable materials whose mechanical, chemical, and physical properties can be easily tuned by thoughtful choice of their precursor. Encapsulated PSCs show extremely good stability when stored under ambient light (maximum, 1000 lux), controlled humidity (28-65%), and temperature (18-30 °C) by retaining 94% of the initial power conversion efficiency after 2500 h (4 months), whereas control devices lose 90% of their performance after 500 h (T80 = 37 h); once stored according to ISOS-D-1, PU-protected devices showed T80 > 1200 h. Encapsulated devices are stable even when immersed in pure water. The demonstration of PUs as promising solution-processed encapsulant materials for PSCs can pave the way for these to become a cost-effective encapsulation route alternative for future industrialization of this technology.

Synthesis, Physicochemical Characterization, and Interaction with DNA of Long-Alkyl-Chain Gemini Pyridinium Surfactants.

Pyridinium gemini surfactants with hexadecyl chains linked to nitrogen atoms and a tuned aliphatic spacer that bridges the two pyridinium polar heads in 2,2'-positions have been synthesized and characterized. A multitechnique approach allowed us to study the aggregation behavior, using conductivity, surface tension, and fluorescence. Graphs of the specific conductivity (κ) versus the surfactant molar concentration (C), and graphs of the molar conductivity (Λ) versus C0.5 suggest pre-aggregation phenomena of these amphiphiles at very low concentration. The trends of Amin as a function of the spacer length confirm the hypothesis of a conformational change of the molecule with four methylene groups as spacer owing to stacking interactions between the two pyridinium rings mediated by the counterion. Moreover, the trends of Amin and counterion binding (ß) suggest that the spacer must be longer than eight carbon atoms to fold efficiently toward the micellar core. The opportunity to tune the surfactant structure and aggregation properties make those surfactants-particularly the long-chain ones for which the DNA complexing ability was shown by means of atomic force microscopy (AFM) imaging-desirable candidates for gene-delivery experiments.

Rationalization of dye uptake on titania slides for dye-sensitized solar cells by a combined chemometric and structural approach.

A model photosensitizer (D5) for application in dye-sensitized solar cells has been studied by a combination of XRD, theoretical calculations, and spectroscopic/chemometric methods. The conformational stability and flexibility of D5 and molecular interactions between adjacent molecules were characterized to obtain the driving forces that govern D5 uptake and grafting and to infer the most likely arrangement of the molecules on the surface of TiO2. A spectroscopic/chemometric approach was then used to yield information about the correlations between three variables that govern the uptake itself: D5 concentration, dispersant (chenodeoxycholic acid; CDCA) concentration, and contact time. The obtained regression model shows that large uptakes can be obtained at high D5 concentrations in the presence of CDCA with a long contact time, or in absence of CDCA if the contact time is short, which suggests how dye uptake and photovoltaic device preparation can be optimized.

Roll-to-roll atmospheric plasma treatment: a green and efficient process to improve the hydrophilicity of a PET surface.

Poly(ethylene terephthalate) (PET) fibers are widely used in various fields owing to their good physical properties and chemical resistance, but PET hydrophobicity heavily compromises its use in many applications. Wet-chemical treatments are often required to induce hydrophilicity, but these can damage the polymer matrix and produce large volumes of liquid wastes. Atmospheric-pressure glow-discharge plasma (APGDP) is an alternative and ecofriendly method to obtain similar or better results with polymeric materials, compared to wet-chemical treatments. The hydrophilic behavior of PET samples is investigated after a roll-to-roll APGDP treatment by varying the plasma gas mixture, gas fluxes, and electrode temperatures. The reactive species formed in the plasma chamber are characterized by optical emission spectroscopy. The induced surface functionalization and roughness are characterized by contact-angle measurements, atomic force microscopy, and UV/Vis absorbance of a probe dye.