Browsing by Author "Paschal, Catherine"

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Guanidinium tin halide perovskites: structural, electronic, and thermodynamic properties by quantum chemical study
(Springer Nature Switzerland AG., 2021-04-17) Paschal, Catherine; Pogrebnoi, Alexander M.; Pogrebnaya, Tatiana P.
The orthorhombic phase of guanidinium tin halide perovskites C(NH2)3SnX3, X = Cl, Br, I has been studied by quantum chemical method. The lattice parameters are optimized to obtain the minimum energy using the density functional theory with the generalized gradient approximation, GGA-PBE. The Kohn–Sham electronic band structures have been computed; the materials have direct bandgaps of 3.00, 2.47, and 1.78 eV for the C(NH2)3SnCl3, C(NH2)3SnBr3, and C(NH2)3SnI3, respectively, situated at the gamma symmetry points. The projected densities of states are analyzed and the contribution of the p- and s-states of the tin and halogen atoms evaluated. For the GUASnX3 compounds, thermodynamic stability to different decomposition routes has been assessed and standard enthalpies of formation obtained.
Methylammonium tin iodide perovskite: structural, electronic and thermodynamic properties by a DFT study with different exchange–correlation functionals
(Springer Nature Switzerland AG., 2020-03-20) Paschal, Catherine; Pogrebnoi, Alexander M.; Pogrebnaya, Tatiana P.; Seriani, Nicola
Lead-free perovskites have drawn much attention of researchers in the field of electronics and photovoltaics due to the toxicity issue of the lead halide perovskites. The methylammonium tin iodide CH3NH3SnI3 amongst others has become a viable alternative due to its eco-friendliness, as well as narrower bandgap and its wider visible absorption spectrum. In this study different theoretical approaches were employed in investigating the structural, electronic and thermodynamic properties of the orthorhombic phase (O-phase) of the CH3NH3SnI3 perovskite. By using the first-principle calculations with the density functional theory, a direct bandgap was determined at gamma symmetry points with three exchange–correlation functionals: PBE 1.12 eV, PBEsol 0.98 eV, and LDA 0.46 eV. Based on the comparison of lattice constants and bandgaps with the experimental values, the best performance resulted from PBE. The decomposition of the CH3NH3SnI3 perovskite into solid state products, CH3NH3I and SnI2, was considered; the enthalpy of the reaction ΔrH° (0 K) = 37 kJ mol−1 and enthalpy of formation of the O-phase perovskite ΔfH° (CH3NH3SnI3, 0 K) = − 390 kJ mol−1 were evaluated, indicating the stability of the O-phase CH3NH3SnI3 at low temperature, in agreement with experimental findings.
Tin halide perovskites: computational modeling of structural, electronic and thermodynamic properties towards solar cell applications
(NM-AIST, 2021-07) Paschal, Catherine
In the photovoltaic field, significant attention has been drawn to lead organo-halide perovskite materials because of their higher ability to convert sun energy to electricity and relatively simple process of fabrication as compared to silicon materials. Among the issues which hinder the lead perovskites solar cells (PSCs) application, are lead toxicity and instability of the PSCs in presence of moisture and light. The tin perovskites are thought over as the foremost fitting substitute due to their comparable chemical nature and high-power conversion efficiency. In this work, the methylammonium tin iodide CH3NH3SnI3 (MASnI3) and guanidinium tin halides C(NH2)3SnX3 (GUASnX3), X = Cl, Br, I, are considered; the electronic, structural as well as thermodynamic properties of the perovskites’ orthorhombic phase (O-phase) have been investigated using various theoretical DFT approaches. For the MASnI3, a direct band gap has been proved; in gamma symmetrical point of the band structure, the band gap value Eg is computed using three different exchange-correlation (XC) functionals: LDA 0.46 eV, PBEsol 0.98 eV and for PBE 1.12 eV; the best result has been obtained with the PBE which follows from the comparison of the computed Eg and lattice parameters with available experimental data. The enthalpy of the decomposition reaction of the MASnI3 into the solid-state materials, SnI2 and CH3NH3I, with reaction enthalpy, ΔrH°(0 K) = 37 kJ mol–1 , and enthalpy of formation ΔfH°(CH3NH3SnI3, 0 K) = –390 kJ mol–1 , have been evaluated showing the stability of the O-phase perovskite at low temperature. For the guanidinium-tin perovskites GUASnX3, the lattice parameters are optimized using the GGA PBE functional. Computations of the materials’ band structures was carried out, and band gaps at the gamma symmetry points were obtained: 3.00, 2.47 and 1.78 eV for the C(NH2)3SnCl3, C(NH2)3SnBr3 and C(NH2)3SnI3, respectively. The projected state densities are visualized, and the s-and p-states contribution of the halogens and tin to valence and conduction bands of the perovskites assessed. For the GUASnX3 compounds, the thermodynamic stability to different decomposition routes is examined, the standard enthalpies of formation are obtained: –673 (GUASnCl3), –541 (GUASnBr3), and –401 kJ mol–1 (GUASnI3). The interface between the hole transport material Cu2O and perovskite MASnI3 has been built and analyzed; the predicted binding energy shows strong binding between the two layers.