Ferroelectricity Driven by Orbital Resonance of Protons in CH3NH3Cl and CH3NH3Br

The β and γ phases of methylammonium chloride CH3NH3Cl and methylammonium bromide CH3NH3Br are identified to be ferroelectric via pyroelectric current and dielectric constant measurements. The magnetic susceptibility also exhibits...

Strong Viscosity Increase in Aqueous Solutions of Cationic C22-Tailed Surfactant Wormlike Micelles

The viscoelastic properties and structure parameters have been investigated for aqueous solutions of wormlike micelles of cationic surfactant erucyl bis(hydroxyethyl) methylammonium chloride with long C22 tail in the presence inorganic salt KCl. The salt content has been varied to estimate linear to branched transition conditions due to screening of the electrostatic interaction in the networks. The local cylindrical structure and low electrostatic repulsion was obtained by SANS data. The drastic power law dependencies of rheological properties on surfactant concentrations were obtained at intermediate salt content. Two power law regions of viscosity dependence were detected in semi-dilute solutions related to “unbreakable” and “living” micellar chains. The fast contour length growth with surfactant concentration demonstrated that is in good agreement with theoretical predictions.

Strong Viscosity Increase in Aqueous Solutions of Cationic C22-Tailed Surfactant Wormlike Micelles

The viscoelastic properties and structure parameters have been investigated for aqueous solutions of wormlike micelles of cationic surfactant erucyl bis(hydroxyethyl) methylammonium chloride with long C22 tail in the presence inorganic salt KCl. The salt content has been varied to estimate linear to branched transition conditions due to screening of the electrostatic interaction in the networks. The local cylindrical structure and low electrostatic repulsion was obtained by SANS data. The drastic power law dependencies of rheological properties on surfactant concentrations were obtained at intermediate salt content. Two power law regions were detected in semi-dilute solutions related to “unbreakable” and “living” micellar chains. The fast contour length growth with surfactant concentration was demonstrated that is in good agreement with theoretical predictions.

Compositional Engineering of FAPbI3 Perovskite Added MACl with MAPbBr3 or FAPbBr3

Many attempts have been made to stabilize α-phase formamidinium lead iodide (α-FAPbI3) using mixed cations or anions with MA+, FA+, Br− and I−. A representative method is to stably produce α-FAPbI3 by adding methylammonium lead (MAPbBr3) to the light absorption layer of a perovskite solar cell and using methylammonium chloride (MACl) as an additive. However, in the perovskite containing MA+ and Br−, the current density is lowered due to an unwanted increase in the bandgap; phase separation occurs due to the mixing of halides, and thermal stability is lowered. Therefore, in this study, in order to minimize the decrease in the composition ratio of FAPbI3 and to reduce MA+, the addition amount of MACl was first optimized. Thereafter, a new attempt was made to fabricate FAPbI3 perovskite by using formamidinium lead bromide (FAPbBr3) and MACl together as phase stabilizers instead of MAPbBr3. As for the FAPbI3-MAPbBr3 solar cell, the (FAPbI3)0.93(MAPbBr3)0.07 device showed the highest efficiency. On the other hand, in the case of the FAPbI3-FAPbBr3 solar cell, the (FAPbI3)0.99(FAPbBr3)0.01 solar cell with a very small FAPbBr3 composition ratio showed the highest efficiency with fast photovoltaic performance improvement and high crystallinity. In addition, the FAPbI3-FAPbBr3 solar cell showed a higher performance than the FAPbI3-MAPbBr3 solar cell, suggesting that FAPbBr3 can sufficiently replace MAPbBr3.

Enhancement of Perovskite Solar-Cell Efficiency Using FAPbBr3/I3 with Methylammonium Chloride

Organic/inorganic metal halide formamidinium lead iodide (FAPbI3) perovskites exhibit excellent optical properties, a suitable band gap, a wide light-absorption range, and superior electron-hole mobility. However, it is difficult to fabricate high-quality α-phase FAPbI3 film due to the relatively easy formation of the more stable δ-FAPbI3 (hexagonal structure). To overcome this, in this study, formamidinium lead bromide (FAPbBr3) was used to induce the synthesis of stable α-phase FAPbI3. The resulting light-absorbing layer was composed of (FAPbI3)0.95 (FAPbBr3)0.05, but δ-phase FAPbI3 could be still observed. To suppress the formation of δ-phase FAPbI3 , methylammonium chloride (MACl) was added to the (FAPbI3)0.95 (FAPbBr3)0.05 precursor solution. At an optimal MACl content of 40 mol%, perovskites with improved crystallinity and large crystallite size could be fabricated, resulting in a perovskite solar-cell efficiency of 18.204%.