As a revolutionary material, hybrid halide perovskites can greatly improve the solar conversion efficiency of solar cells. In this work, a first-principles theoretical study is performed to investigate the role of methylammonium (MA) rotation in the MAPbX3 (X = I, Br, and Cl) perovskites. To provide a full understanding of the MA rotation, we report electronic and optical properties in different rotational angles and modes. Our results evidence that rotation of MA with R z and R x modes causes substantial changes in band structure, density of states, partial density of states, electron density, dielectric function, and absorption spectra. We also showed that these changes are deeply affected by cation–cation (MA–Pb) and cation–anion (MA–X) interactions. Furthermore, the halogens of MAPbX3 were changed to iodide, bromide, and chloride anions to study the inorganic–organic interactions inside the MAPbX3 in detail. Interestingly, we conclude that the rotational modes, location, and orientation of organic cation can be used as an efficient tool to control the band gap, static dielectric constant, and absorption edge of the optical spectra. Our results providing useful and accurate insight into the behavior of MA embedded in inorganic octahedra are in good agreement with experimental data being used in photovoltaic applications.

The solubility of hydrogen sulfide (H2S) in a mixed solvent containing (19.5 to 35.5) mass percent of N-methyldiethanolamine (MDEA), (0 to 11.6) mass percent of piperazine (PZ), (0 to 10) mass percent of sulfolane (SFL), and water at temperatures of (313.15 to 353.15) K and H2S partial pressures of up to about 2 MPa is reported. To determine the absorption of H2S, the density of the solutions in the corresponding temperature range was measured using a vibrating-tube densimeter. The results show that H2S solubility decreases with increasing temperature and increases with partial pressure of H2S. In addition, increasing PZ concentration can enhance the absorption capacity of MDEA, as a benchmark alkanolamine, in aqueous and mixed aqueous sulfolane solutions in the low-loading region. A thermodynamic model based on the extended Debye–Hükel theory, namely Deshmukh-Mather model for the liquid phase, combined with the Peng-Robinson equation of state for the gas phase, was applied to correlate the H2S solubility data obtained. The average absolute deviation of the correlated data from the experimental data is 6.5%, which implies good correlative accuracy of the thermodynamic model employed in this work.

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