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Organic-inorganic trihalide perovskites have become one of hotspots in the field of photoelectric functional materials. Based on first-principles calculations within density functional theory, we analyzed the changes of the electronic structure of the perovskite MAPbBr3 under different pressures. We found that the band gap of compressed perovskite MAPbBr3 exhibits a significant red-shift under a relatively mild pressure of ∼ 1.877 GPa and becomes larger under higher pressure. This can be semiquantitatively explained by the effects of hydrogen bonding between organic MA cation and bromine framework. These effects drive rotations of PbBr6 octahedral in order to fit the local environment. Results of Bader analysis under different pressures suggest that Coulomb interaction driven by charge transfer leads to movement of the amine end of MA cation towards Br atoms and alters the predominant Pb-Br-Pb bond angle. Given that, compressed perovskite MAPbBr3 exhibits notable band gap changes. Our results provide an efficient and clean approach to optimize photovoltaic properties of organic-inorganic trihalide perovskites. [ABSTRACT FROM AUTHOR]

Abstract: The effect of B/Ti mass ratio on grain refining of the low-titanium aluminum produced by electrolysis was investigated by adding AlB master alloy to the melt of the low-titanium aluminum. The results show that the addition of titanium by electrolysis is an effective way of grain refining of aluminum, and addition of boron to the melt of the low-titanium aluminum can further increase the grain refining efficiency. And the best grain refining efficiency is obtained when the B/Ti mass ratio is 1:10. However, when the B/Ti mass ratio is 1:2.22 (the stoichiometric value for TiB2), the grain refining efficiency vanishes almost completely. It means that all of the solute titanium atoms in the melt of the low-titanium aluminum react with boron atoms that come from AlB master alloy to form TiB2 particles, and TiB2 particles have not grain refining ability. The grain refining efficiency seems to increase with addition of more boron to the melt after the B/Ti mass ratio exceeds 1:2.22. But the grain refining efficiency is very poor, and similar to that of pure Al refined by AlB master alloy. It further shows that TiB2 particles do not participate in grain refining, and that the excess boron atoms in the melt also cannot turn TiB2 particles into the effective nuclei for aluminum as the solute titanium atoms do. [Copyright &y& Elsevier]