Molecular dynamics study of formamidine decomposition in gas and solution phases via free energy curves from ab initio interaction potentials

Triiodide Attacks the Organic Cation in Hybrid Lead Halide Perovskites: Mechanism and Suppression

Molecular I2 can be produced from iodide-based lead perovskites under thermal stress; triiodide, I3 - , is formed from this I2 and I- . Triiodide attacks protic cation MA+ - or FA+ -based lead halide perovskites (MA+ , methylammonium; FA+ , formamidinium) as explicated through solution-based nuclear magnetic resonance (NMR) studies: triiodide has strong hydrogen-bonding affinity for MA+ or FA+ , which leads to their deprotonation and perovskite decomposition. Triiodide is a catalyst for this decomposition that can be obviated through perovskite surface treatment with thiol reducing agents. In contrast to methods using thiol incorporation into perovskite precursor solutions, no penetration of the thiol into the bulk perovskite is observed, yet its surface application stabilizes the perovskite against triiodide-mediated thermal stress. Thiol applied to the interface between FAPbI3 and Spiro-OMeTAD ("Spiro") prevents oxidized iodine species penetration into Spiro and thus preserves its hole-transport efficacy. Surface-applied thiol affects the perovskite work function; it ameliorates hole injection into the Spiro overlayer, thus improving device performance. It helps to increase interfacial adhesion ("wetting"): fewer voids are observed at the Spiro/perovskite interface if thiols are applied. Perovskite solar cells (PSCs) incorporating interfacial thiol treatment maintain over 80% of their initial power conversion efficiency (PCE) after 300 h of 85 °C thermal stress.

A computational model of the glycine tautomerization reaction in aqueous solution

A theoretical study of the internal proton transfer reaction of glycine (Gly) in aqueous solution was performed by means of steered molecular dynamics (SMD) simulation with solute-solvent interaction potentials derived from AMBER van der Waals parameters and QM/MM electrostatic charges in solution. Thermodynamic calculations and the analysis of the solvation structure, dynamic properties, and vibrational spectra associated with the species involved in the tautomerization process were performed. The results obtained for the Gibbs free energy activation and reaction (ΔG(≠) =5.28 kcal mol⁻¹ and ΔG(R)=-6.65 kcal mol⁻¹), the solute-solvent interaction energy of the different glycine structures, and the hydrogen-bond lifetimes are in agreement with previous studies. These hydrations drive an increase in the diffusion coefficient and a decrease in the time of reorientation when the process takes place in the direction Z-Gly → TS-Gly → N-Gly. The vibrational spectrum associated with the normal modes of the bridge hydrogen atoms shows the N-H stretching at ν(s)=3,470 cm⁻¹ and ν(as)=3,470 cm⁻¹, the O-H stretching at 3,205 cm⁻¹, and the NHO bending at about 1,400 cm⁻¹, in agreement with previously reported data.

Amide-imide tautomerism of acetohydroxamic acid in aqueous solution: quantum calculation and SMD simulations

The kinetics and the thermodynamics of the amide-imide tautomerizations of acetohydroxamic acid in aqueous solution are studied from a theoretical point of view.