In this paper, the pore filling of spiro‐OMeTAD (2,2′,7,7′‐tetrakis‐(N,N‐di‐p‐methoxyphenylamine)9,9′‐spirobifluorene) in mesoporous TiO2 films is quantified for the first time using XPS depth profiling and UV–Vis absorption spectroscopy. It is shown that spiro‐OMeTAD can penetrate the entire depth of the film, and its concentration is constant throughout the film. We determine that in a 2.5‐µm‐thick film, the volume of the pores is 60–65% filled. The pores become less filled when thicker films are used. Such filling fraction is much higher than the solution concentration because the excess solution on top of the film can act as a reservoir during the spin coating process. Lastly, we demonstrate that by using a lower spin coating speed and higher spiro‐OMeTAD solution concentration, we can increase the filling fraction and consequently the efficiency of the device.

CsPbF3 is the only experimentally synthesized ABF3 fluoride perovskite with a polar ground state. We use CsPbF3 as a guide in our search for rules to rationally design new ABX3 polar fluorides and halides from first-principles and as a model compound to study the interactions of lone pairs, octahedral rotations, and A- and B-site driven ferroelectricity. We find that the lone pair cation on the B-site serves to stabilize a polar ground state, analogous to the role of lone pair cations on the A-site of oxide perovskites. However, we also find that the lone pair determines the pattern of nonpolar structural distortions, rotations of the PbF6 octahedra, that characterize the lowest energy structure. This result is remarkable since rotations are typically associated with bonding preferences of the A-site cation (here Cs(+)), whereas the Pb(2+) cation occupies the B site. We show that the coordination requirements of the A-site cation and the stereoactivity of the B-site lone pair cation compete or cooperate via the anionic displacements that accompany polar distortions. We consider the generalizability of our findings for CsPbF3 and how they may be extended to the oxide perovskites as well as to the organic-inorganic hybrid halide perovskite photovoltaics.

The search for materials displaying a large magnetoelectric effect has occupied researchers for many decades. The rewards could include not only advanced electronics technologies, but also fundamental insights concerning the dielectric and magnetic properties of condensed matter. In this article, we focus on the magnetoelectric effect in transition metal oxides and review the manner in which first-principles calculations have helped guide the search for (and increasingly, predicted) new materials and shed light on the microscopic mechanisms responsible for magnetoelectric phenomena.

Eighteen Pt-M binary (M = Sn, Ta, W, Mo, Ru, Fe, In, Pd, Hf, Zn, Zr, Nb, Sc, Ni, Ti, V, Cr, Rh) thin film composition spreads were deposited at low M concentrations using magnetron sputtering and screened for methanol and ethanol electrooxidation activity using a fluorescence assay. Characterization of these thin films was performed using high energy X-ray diffraction and X-ray fluorescence. The electrochemical fluorescence assay revealed highest activity in the films with M = Sn, Zn, In, Fe, and Ru. Pt-M (M = Sn, Zn, In) showed highest activity at concentrations below 5 atom-% with a high fraction of Pt fcc(111) texturing and Pt-Fe showing the best activity at 10 atom-% Fe. On the other hand, the best (most negative) fluorescence onset potential in the Pt-Ru system was observed at a concentration of 35 atom-% Ru with only slight texturing of the film. To explore the potential origins of the observed catalytic activity, preliminary calculations on the d-band center shift with alloying were performed for bulk concentrations of up to 30 atom-% for Fe and 16 atom-% for M = Sn, Zn.Fuel cells present a promising energy conversion technology that is not limited by the Carnot cycle efficiency. Fuel cell efficiencies can reach up to 80-90% whereas a typical Carnot engine can only reach a maximum efficiency of 45-50%. 1 Fuel cells, in principle, could provide higher efficiency, an environmentally friendly form of energy conversion and high power/energy density. While the ideal system is a hydrogen-oxygen proton exchange membrane fuel cell (PEMFC), transportation, storage, and widespread availability of hydrogen is challenging due to the required high pressures and low volumetric energy density when compared to other fuels. Methanol, ethanol, and other small organic molecules (SOMs) have the advantage of higher volumetric energy densities, easier transportation, and diversity of availability from biosources. 2 Present limitations for widespread deployment of fuel cells are the cathode and anode materials which are expensive, easily poisoned, and show degradation over time. For methanol and ethanol oxidation, the process is more complicated than in the case of hydrogen, since the carbon in the fuel must be oxidized to CO 2 for maximal efficiency. The catalyst must also exhibit high catalytic activity for fuel oxidation with minimal poisoning. Platinum is the most commonly used catalyst, but it is readily poisoned with even low (ppm) levels of CO. As CO stands as a general and ubiquitous intermediate in the oxidation of SOMs, different catalysts must be used/found. Many materials have been investigated as anode catalysts for the oxidation of methanol, ethanol, and ethylene glycol, including alloys, 3 intermetallics, 4 nonPt containing materials (carbides, nitrides, oxides), 5 and core-shell structures. 6 For the cathode case, Strasser et al. reported improved activity for oxygen reduction with a Pt shell and a Pt-Cu alloyed core when compared to Pt alone. 6a They also considered the improved activity to be a result of the...

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