Scattering from supramacromolecular structures

We study theoretically the scattering imprint of a number of branched supramacromolecular architectures, namely, polydisperse stars and dendrimeric, hyperbranched structures. We show that polydispersity and nature of branching highly influence the intermediate wavevector region of the scattering structure factor, thus providing insight into the morphology of different aggregates formed in polymer solutions.Comment: 20 pages, 8 figures To appear in PR

Triplet Exciton Generation in Bulk-Heterojunction Solar Cells based on Endohedral Fullerenes

Organic bulk-heterojunctions (BHJ) and solar cells containing the trimetallic nitride endohedral fullerene 1-[3-(2-ethyl)hexoxy carbonyl]propyl-1-phenyl-Lu3N@C80 (Lu3N@C80-PCBEH) show an open circuit voltage (VOC) 0.3 V higher than similar devices with [6,6]-phenyl-C[61]-butyric acid methyl ester (PC61BM). To fully exploit the potential of this acceptor molecule with respect to the power conversion efficiency (PCE) of solar cells, the short circuit current (JSC) should be improved to become competitive with the state of the art solar cells. Here, we address factors influencing the JSC in blends containing the high voltage absorber Lu3N@C80-PCBEH in view of both photogeneration but also transport and extraction of charge carriers. We apply optical, charge carrier extraction, morphology, and spin-sensitive techniques. In blends containing Lu3N@C80-PCBEH, we found 2 times weaker photoluminescence quenching, remainders of interchain excitons, and, most remarkably, triplet excitons formed on the polymer chain, which were absent in the reference P3HT:PC61BM blends. We show that electron back transfer to the triplet state along with the lower exciton dissociation yield due to intramolecular charge transfer in Lu3N@C80-PCBEH are responsible for the reduced photocurrent

Air-Stable and Flexible Photodiode for X-Rays Detection Based on a Hybrid Perovskite Active Layer and Organic Interlayers

Solution-processed organic and hybrid semiconductor materials have great potential for ionizing radiation direct detection, as they combine high sensitivity, low-power consumption, and flexibility. There is, however, an open challenge related to the stability in ambient/operational conditions of this class of devices. In this work, an air-stable, solution-processed and flexible X-ray detector is reported, based on the integration of hybrid perovskite and organic thin films used as active layer and functional interlayers, respectively. The diode architecture and the engineering of the interface between the hybrid perovskite and the organic hole transporting material (solvent-modified poly(3,4-ethylenedioxythiophene):polystyrene sulfonate) is the key to achieve enhanced detector's air stability and performance. The unencapsulated flexible device, measured in air and in passive operation (0 V), shows a limit-of-detection of 0.37 +/- 0.04 mu Gy s-1 and a sensitivity as high as 5.2 mu C Gy(-1) cm(-2), which is retained within 25% after 42 days exposure to ambient conditions

Stereoisomeric Homo- and Hetero-Binuclear Iridium(III) Complexes with 3-Oxidopicolinate Bridging Ligand and Their Application in OLEDs

The small and simple 3-hydroxypyridine-2-carboxylic acid (Hpic-OH) is explored as asymmetric bridging ligand for the synthesis of neutral binuclear cyclometalated iridium(III) complexes. Once fully deprotonated the picO2– ligand can act as ancillary ligand toward two iridium centers adopting both the N^O– and O^O– chelation modes. To tune the energy of the excited states within such binuclear complexes, the 2-(2,4-difluorophenyl)pyridine (Hdfppy) and the 2-phenylbenzothiazole (Hpbtz) are used as cyclometalating ligands to respectively obtain both blue- or orange-emissive homo-cyclometalated complexes (BB and YY, with formula [Ir(dfppy)2]2(picO) and [Ir(pbtz)2]2(picO), respectively). Moreover, for the first time, short-bridged hetero-cyclometalated binuclear complexes are also obtained (BY and YB, with formula [Ir(dfppy)2](picO)[Ir(pbtz)2] and [Ir(pbtz)2](picO)[Ir(dfppy)2]). Depending on the reciprocal arrangement of the cyclometalating ligands on the two sides of the small picolinate bridge, two couples of diastereoisomers are obtained and efficiently separated, as proved by combined NMR and DFT studies. The reported binuclear complexes are highly emissive with photoluminescence quantum yields (PLQYs) up to 67%, which are comparable to those of their mononuclear analogues (B and Y). Due to the full reversibility of their redox processes, all the complexes are also tested in solution-processed organic light-emitting diodes, providing unique OLEDs based on hetero-binuclear cyclometalated iridium(III) complexe

Compositional boundary layers trigger liquid unmixing in a basaltic crystal mush

Abstract: The separation of immiscible liquids has significant implications for magma evolution and the formation of magmatic ore deposits. We combine high-resolution imaging and electron probe microanalysis with the first use of atom probe tomography on tholeiitic basaltic glass from Hawaii, the Snake River Plain, and Iceland, to investigate the onset of unmixing of basaltic liquids into Fe-rich and Si-rich conjugates. We examine the relationships between unmixing and crystal growth, and the evolution of a nanoemulsion in a crystal mush. We identify the previously unrecognised role played by compositional boundary layers in promoting unmixing around growing crystals at melt-crystal interfaces. Our findings have important implications for the formation of immiscible liquid in a crystal mush, the interpretations of compositional zoning in crystals, and the role of liquid immiscibility in controlling magma physical properties

Detailed study of N,N'-(diisopropylphenyl)- terrylene-3,4:11,12-bis(dicarboximide) as electron acceptor for solar cells application

We report on terrylene-3,4:11,12-bis(dicarboximide) (TDI) as electron acceptor for bulk-heterojunction solar cells using poly(3-hexyl thiophene) (P3HT) as complementary donor component. Enhanced absorption was observed in the blend compared to pure P3HT. As shown by the very efficient photoluminescence (PL) quenching, the generated excitons are collected at the interface between the donor and acceptor, where they separate into charges which we detect by photoinduced absorption and electron-spin resonance (ESR). Time-of-flight (TOF) photoconductivity measurements reveal a good electron mobility of 10-3 cm2 V-1 s-1 in the blend. Nevertheless, the photocurrent in solar cells was found to be surprisingly low. Supported by the external quantum efficiency (EQE) spectrum as well as morphological studies by way of X-ray diffraction and atomic force microscopy, we explain our observation by the formation of a TDI hole blocking layer at the anode interface which prevents the efficiently generated charges to be extracted.Comment: Original research article, 9 pages, 10 figures, 1 tabl

Multiscale Self-Assembly of Silicon Quantum Dots into an Anisotropic Three-Dimensional Random Network

Multiscale self-assembly is ubiquitous in nature but its deliberate use to synthesize multifunctional three-dimensional materials remains rare, partly due to the notoriously difficult problem of controlling topology from atomic to macroscopic scales to obtain intended material properties. Here, we propose a simple, modular, noncolloidal methodology that is based on exploiting universality in stochastic growth dynamics and driving the growth process under far-from-equilibrium conditions toward a preplanned structure. As proof of principle, we demonstrate a confined-but-connected solid structure, comprising an anisotropic random network of silicon quantum-dots that hierarchically self-assembles from the atomic to the microscopic scales. First, quantum-dots form to subsequently interconnect without inflating their diameters to form a random network, and this network then grows in a preferential direction to form undulated and branching nanowire-like structures. This specific topology simultaneously achieves two scale-dependent features, which were previously thought to be mutually exclusive: good electrical conduction on the microscale and a bandgap tunable over a range of energies on the nanoscale. © 2016 American Chemical Society