Sublimed C60 for efficient and repeatable perovskite-based solar cells.

Thermally evaporated C60 is a near-ubiquitous electron transport layer in state-of-the-art p-i-n perovskite-based solar cells. As perovskite photovoltaic technologies are moving toward industrialization, batch-to-batch reproducibility of device performances becomes crucial. Here, we show that commercial as-received (99.75% pure) C60 source materials may coalesce during repeated thermal evaporation processes, jeopardizing such reproducibility. We find that the coalescence is due to oxygen present in the initial source powder and leads to the formation of deep states within the perovskite bandgap, resulting in a systematic decrease in solar cell performance. However, further purification (through sublimation) of the C60 to 99.95% before evaporation is found to hinder coalescence, with the associated solar cell performances being fully reproducible after repeated processing. We verify the universality of this behavior on perovskite/silicon tandem solar cells by demonstrating their open-circuit voltages and fill factors to remain at 1950 mV and 81% respectively, over eight repeated processes using the same sublimed C60 source material. Notably, one of these cells achieved a certified power conversion efficiency of 30.9%. These findings provide insights crucial for the advancement of perovskite photovoltaic technologies towards scaled production with high process yield.

Acute Otitis Externa: Rapid Evidence Review.

Acute otitis externa is an inflammatory condition that affects the external ear canal. It is usually of rapid onset and is generally caused by bacterial infection. The primary bacterial infections are Pseudomonas aeruginosa and Staphylococcus aureus. Acute otitis externa presents with pain (otalgia), redness, and swelling of the canal. It is more common in children and young adults. Tenderness on movement of the pinna or tragus is the classic finding. Analgesics and topical antibiotics are the mainstays of therapy. Topical medications include acetic acid 2%, aminoglycosides, polymyxin B, and quinolones with and without corticosteroids. There is no evidence that any one preparation is clinically superior to another, and the choice of treatment is based on factors such as cost, whether the tympanic membrane is intact, and patient adherence. Oral antibiotics are indicated only if evidence of cellulitis occurs outside of the ear canal or if associated conditions such as immunocompromise, diabetes mellitus, or conditions that would not allow for the use of topical treatment are found. Duration of topical treatment is usually seven to 10 days. Keys to prevention include avoiding injury to the ear canal and keeping it free of water.

Wavy graphene sheets from electrochemical sewing of corannulene.

The presence of non-hexagonal rings in the honeycomb carbon arrangement of graphene produces rippled graphene layers with valuable chemical and physical properties. In principle, a bottom-up approach to introducing distortion from planarity of a graphene sheet can be achieved by careful insertion of curved polyaromatic hydrocarbons during the growth of the lattice. Corannulene, the archetype of such non-planar polyaromatic hydrocarbons, can act as an ideal wrinkling motif in 2D carbon nanostructures. Herein we report an electrochemical bottom-up method to obtain egg-box shaped nanographene structures through a polycondensation of corannulene that produces a new conducting layered material. Characterization of this new polymeric material by electrochemistry, spectroscopy, electron microscopy (SEM and TEM), scanning probe microscopy, and laser desorption-ionization time of flight mass spectrometry provides strong evidence that the anodic polymerization of corannulene, combined with electrochemically induced oxidative cyclodehydrogenations (Scholl reactions), leads to polycorannulene with a wavy graphene-like structure.

Nearly exclusive growth of small diameter semiconducting single-wall carbon nanotubes from organic chemistry synthetic end-cap molecules.

The inability to synthesize single-wall carbon nanotubes (SWCNTs) possessing uniform electronic properties and chirality represents the major impediment to their widespread applications. Recently, there is growing interest to explore and synthesize well-defined carbon nanostructures, including fullerenes, short nanotubes, and sidewalls of nanotubes, aiming for controlled synthesis of SWCNTs. One noticeable advantage of such processes is that no metal catalysts are used, and the produced nanotubes will be free of metal contamination. Many of these methods, however, suffer shortcomings of either low yield or poor controllability of nanotube uniformity. Here, we report a brand new approach to achieve high-efficiency metal-free growth of nearly pure SWCNT semiconductors, as supported by extensive spectroscopic characterization, electrical transport measurements, and density functional theory calculations. Our strategy combines bottom-up organic chemistry synthesis with vapor phase epitaxy elongation. We identify a strong correlation between the electronic properties of SWCNTs and their diameters in nanotube growth. This study not only provides material platforms for electronic applications of semiconducting SWCNTs but also contributes to fundamental understanding of the growth mechanism and controlled synthesis of SWCNTs.

Electron transfer in a supramolecular associate of a fullerene fragment.

Herein, we investigate the association of a fullerene fragment, hemifullerene C30H12, with an electron-donating bowl-shaped tetrathiafulvalene derivative (truxTTF). UV/Vis titrations and DFT calculations support formation of the supramolecular complex, for which an association constant of log Ka = 3.6±0.3 in CHCl3 at room temperature is calculated. Remarkably, electron transfer from truxTTF to C30H12 to form the fully charge-separated species takes place upon irradiation of the associate with light, constituting the first example in which a fullerene fragment mimics the electron-accepting behavior of fullerenes within a supramolecular complex.

Corannulene and its penta-tert-butyl derivative co-crystallize 1:1 with pristine C60-fullerene.

The first X-ray structural determinations of pristine fullerene C(60), cocrystallized 1:1 with corannulene and with its pentaalkyl-substituted derivative, 1,3,5,7,9-penta-tert-butyl-corannulene, have now been achieved.

A short, rigid, structurally pure carbon nanotube by stepwise chemical synthesis.

The inaccessibility of uniform-diameter, single-chirality carbon nanotubes (CNTs) in pure form continues to thwart efforts by scientists to use these ultrathin materials in innovative applications that could revolutionize nanoscale electronics. Stimulated by the challenge to address this long-standing problem, we and other organic chemists have envisioned a new production strategy involving the controlled elongation of small hydrocarbon templates, such as hemispherical nanotube end-caps, prepared by bottom-up chemical synthesis; the diameter and rim structure encoded in the template would dictate the diameter and chirality of the resulting CNT. Toward that objective, a short [5,5] CNT has now been synthesized by stepwise chemical methods. This C(50)H(10) geodesic polyarene has been isolated, purified, crystallized, and fully characterized by NMR spectroscopy, UV-vis absorption spectroscopy, high resolution mass spectrometry, and X-ray crystallography.

Highly charged supramolecular oligomers based on the dimerization of corannulene tetraanion.

The supramolecular dimerization of tetraanionic corannulene is utilized as a self-assembly motif for the construction of highly charged, buckybowl-based supramolecular oligomers. Oligomers of up to 7 units (3900 g mol(-1)) of reduced dicorannulenic monomers are identified and characterized by various NMR techniques, and the reversibility of their assembly is established through the concentration dependence of their molecular weight and the effect of monofunctional chain-stoppers.

Aromatic pi-systems more curved than C(60). The complete family of all indenocorannulenes synthesized by iterative microwave-assisted intramolecular arylations.

Syntheses and X-ray crystal structures are reported for all seven members of the indenocorannulene family, comprising indenocorannulene, both isomers of diindenocorannulene, both isomers of triindenocorannulene, tetraindenocorannulene, and pentaindenocorannulene. With each additional indenoannulation, the pyramidalization of the trigonal carbon atoms at the hub of the corannulene increases. Five of the seven indenocorannulenes contain carbon atoms at the hub that are actually more pyramidalized than the carbon atoms of C(60). This work demonstrates, for the first time, that extended pi-systems with curvatures exceeding those of the most curved stable fullerenes and carbon nanotubes can be prepared by ordinary laboratory methods in solution, without recourse to high-temperature gas phase methods, such as flash vacuum pyrolysis. This proof of principle presages the days when scientists will be able to synthesize isomerically pure fullerenes and single-chirality nanotubes by well-understood, controlled chemical methods. Pentaindenocorannulene, itself, represents an attractive precursor to the C(5v) end-cap of an all-carbon, single-walled, "armchair" [5,5]nanotube.

Electrochemical and theoretical investigation of corannulene reduction processes.

The voltammetric generation of corannulene anions was investigated over a large range of experimental conditions comprising either "traditional" electrochemical solvents, such as dimethylformamide, acetonitrile, and tetrahydrofuran, or "unconventional" solvents, such as liquid ammonia, liquid methylamine, or liquid dimethylamine, and several different supporting electrolytes. Strong ion pairing effects were found to dominate the electrochemical generation of corannulene higher anions, and through the suitable choice of the solvent/electrolyte system, we observed, for the first time, the reversible electrochemical generation of up to the triply reduced corannulene. The standard potentials obtained experimentally compared rather well with the theoretical values calculated by ab initio and density functional methods, in which solvation and ion pairing effect were explicitly taken into account. In particular, the calculations considered the effect of the electrolyte cation size on ion pairing in order to rationalize the occurrence of the third reduction within the experimental potential window.

Bicorannulenyl: stereochemistry of a C40H18 biaryl composed of two chiral bowls.

The bicorannulenyl molecule is composed of two chiral bowls tethered by a single bond in a helical fashion. This simple combination of two chiral motifs gives rise to rich dynamic stereochemistry, where 12 conformers interconvert through bowl inversions and central bond rotation, and enantiomerizations occur via multistep processes. Interestingly, 8 out of 10 transition states are chiral, giving rise to mostly chiral enantiomerization pathways, where the molecule changes chirality without passing through an achiral conformation. However, analysis of the stereochemical landscape by DFT calculations and variable temperature NMR spectroscopy reveals that the energetically most favorable enantiomerization pathway passes through one of the two achiral transition states. Single-crystal X-ray diffraction corroborates the DFT results and provides information on packing modes of bicorannulenyl molecules in the solid state that have not been seen previously for other buckybowls.

X-ray and density functional theory structural study of 1,3,5,7,9-penta-tert-butylcorannulene, C40H50.

The first X-ray structural characterization of an alkyl-substituted corannulene, namely, 1,3,5,7,9-penta-tert-butylcorannulene (C40H50), has been accomplished. The addition of bulky tert-butyl groups to the corannulene core flattens the bowl and affects the solid-state packing. The presence of two enantiomers, in addition to positional disorder of the C40H50 bowls in the solid-state structure, has prevented the acquisition of accurate geometric parameters of this open geodesic polyarene. Therefore, DFT calculations have been used to describe its molecular geometry and to access bond lengths, bond angles, and a bowl depth.

Ball-and-socket stacking of supercharged geodesic polyarenes: bonding by interstitial lithium ions.

Unprecedented supramolecular stacks of highly reduced geodesic pi-systems were prepared by the reduction of the derivatized fullerenes Me(5)C(60)H and Ph(5)C(60)H and corannulene with lithium metal (R(5)C(60)(5)(-)/Cor(4)(-)/9Li(+)). The host--guest assemblies form because of the enhanced electrostatic interactions between the lithium cations and the anionic moieties, in addition to the structural compatibility between the curved hydrocarbons. The high stability of these new supramolecular assemblies (heterodimers) enables the introduction of another organization motif to the system. This is achieved by using tethered corannulenes as host molecules, which leads to the formation of tethered bis-heterodimers ((Me(5)C(60)(5)(-)/Cor(4)(-))(2)(CH(2))(8)/18Li(+)).