Sulfonated Styrene-(ethylene-co-butylene)-styrene/Montmorillonite Clay Nanocomposites: Synthesis, Morphology, and Properties

Sulfonated styrene-(ethylene-butylene)-styrene triblock copolymer (SSEBS) was synthesized by reaction of acetyl sulfate with SEBS. SSESB-clay nanocomposites were then prepared from hydrophilic Na-montmorillonite (MT) and organically (quaternary amine) modified hydrophobic nanoclay (OMT) at very low loading. SEBS did not show improvement in properties with MT-based nanocomposites. On sulfonation (3 and 6 weight%) of SEBS, hydrophilic MT clay-based nanocomposites exhibited better mechanical, dynamic mechanical, and thermal properties, and also controlled water–methanol mixture uptake and permeation and AC resistance. Microstructure determined by X-ray diffraction, atomic force microscopy, and transmission electron microscopy due to better dispersion of MT nanoclay particles and interaction of MT with SSEBS matrix was responsible for this effect. The resulting nanocomposites have potential as proton transfer membranes for Fuel Cell applications

Tip-functionalized carbon nanotubes under electric fields

We investigated the electronic structures of chemically modified carbon nanotube tips under electric fields using density functional calculations. Hydrogen, oxygen, and hydroxyl group-terminated nanotubes have been considered as field emitters or probe tips. In the case of the open-ended tubes, the field emission originates primarily from the dangling-bond states localized at the edge, whereas the pentagonal defects are the main source of the field emission in the capped tubes. The open-ended nanotube with a zigzag edge is an efficient field emitter because of the localized electronic states around the Fermi level and the atomic alignment of carbon-carbon bonds along with external electric fields. Tip functionalization alters the local density of states as well as the chemical selectivity of nanotubes in various ways. The correlations between atomic geometries of chemically functionalized tips and their electronic structures are further discussed. We propose that a hydrogen-terminated tube would be a promising probe tip for selective chemical imaging.open252

Collapsing shear-free perfect fluid spheres with heat flow

A global view is given upon the study of collapsing shear-free perfect fluid spheres with heat flow. We apply a compact formalism, which simplifies the isotropy condition and the condition for conformal flatness. This formalism also presents the simplest possible version of the main junction condition, demonstrated explicitly for conformally flat and geodesic solutions. It gives the right functions to disentangle this condition into well known differential equations like those of Abel, Riccati, Bernoulli and the linear one. It yields an alternative derivation of the general solution with functionally dependent metric components. We bring together the results for static and time- dependent models to describe six generating functions of the general solution to the isotropy equation. Their common features and relations between them are elucidated. A general formula for separable solutions is given, incorporating collapse to a black hole or to a naked singularity.Comment: 26 page

Efficient Carrier Multiplication in Low Band Gap Mixed Sn/Pb Halide Perovskites

Carrier multiplication (CM) generates multiple electron-hole pairs in a semiconductor from a single absorbed photon with energy exceeding twice the band gap. Thus, CM provides a promising way to circumvent the Shockley-Queisser limit of solar cells. The ideal material for CM should have significant overlap with the solar spectrum and should be able to fully utilize the excess energy above the band gap for additional charge carrier generation. We report efficient CM in mixed Sn/Pb halide perovskites (band gap of 1.28 eV) with onset just above twice the band gap. The CM rate outcompetes the carrier cooling process leading to efficient CM with a quantum yield of 2 for photoexcitation at 2.8 times the band gap. Such efficient CM characteristics add to the many advantageous properties of mixed Sn/Pb metal halide perovskites for photovoltaic applications.ChemE/Opto-electronic Material

Emergence of New Materials for Exploiting Highly Efficient Carrier Multiplication in Photovoltaics

In conventional solar cell semiconductor materials (predominantlySi)photons with energy higher than the band gap initially generate hot electrons and holes, which subsequently cool down to the band edge by phonon emission. Due to the latter process,the energy of the charge carriers in excess of the band gap is lost as heat and does not contribute to the conversion of solar to electrical power. If the excess energy is more than the band gap itcan in principle be utilized through a process known as carrier multiplication (CM) in which a single absorbed photon generates two (or more) pairs of electrons and holes. Thus, through CM the photon energy abovetwice the band gap enhancesthe photocurrentofa solar cell. In this review, we discuss recent progress in CM research in terms of fundamental understanding, emergenceof new materials for efficient CM, and CM based solar cell applications. Based on our current understanding, the CM threshold can get close to the minimal value of twice the band gap in materials where a photon induces an asymmetric electronic transition from a deeper valence band or to a higher conduction band. In addition,the material must have a low exciton binding energy and high charge carrier mobility, so that photoexcitation leads directly to the formation of free charges that can readily be extracted at external electrodes of a photovoltaic device. Percolative networks of coupled PbSe quantum dots, Sn/Pb based halide perovskites,and transition metal dichalcogenides such as MoTe2fulfill these requirements to a large extent. These findings pointtowards promising prospects for further development of new materials for highly efficient photovoltaics.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.ChemE/Opto-electronic Material

Generating Triplets in Organic Semiconductor Tetracene upon Photoexcitation of Transition Metal Dichalcogenide ReS₂

We studied the dynamics of transfer of photoexcited electronic states in a bilayer of the two-dimensional transition metal dichalcogenide ReS2 and tetracene, with the aim to produce triplets in the latter. This material combination was used as the band gap of ReS2 (1.5 eV) is slightly larger than the triplet energy of tetracene (1.25 eV). Using time-resolved optical absorption spectroscopy, transfer of photoexcited states from ReS2 to triplet states in tetracene was found to occur within 5 ps with an efficiency near 38%. This result opens up new possibilities for heterostructure design of two-dimensional materials with suitable organics to produce long-lived triplets. Triplets are of interest as sensitizers in a wide variety of applications including optoelectronics, photovoltaics, photocatalysis, and photon upconversion.ChemE/Opto-electronic Material

Generating Triplets in Organic Semiconductor Tetracene upon Photoexcitation of Transition Metal Dichalcogenide ReS₂

We studied the dynamics of transfer of photoexcited electronic states in a bilayer of the two-dimensional transition metal dichalcogenide ReS2 and tetracene, with the aim to produce triplets in the latter. This material combination was used as the band gap of ReS2 (1.5 eV) is slightly larger than the triplet energy of tetracene (1.25 eV). Using time-resolved optical absorption spectroscopy, transfer of photoexcited states from ReS2 to triplet states in tetracene was found to occur within 5 ps with an efficiency near 38%. This result opens up new possibilities for heterostructure design of two-dimensional materials with suitable organics to produce long-lived triplets. Triplets are of interest as sensitizers in a wide variety of applications including optoelectronics, photovoltaics, photocatalysis, and photon upconversion.ChemE/Opto-electronic Material