RESUMEN
The incorporation of chiral molecules (A) in materials based on hybrid ABX3 perovskites has opened new paths to tune the optoelectronic properties of perovskites through the transfer of chirality to the inorganic BX framework. However, our atomistic understanding of the role of chemical BX composition in the magnitude of the chirality transfer is far from complete. In this study, we use density functional theory calculations and the experimental Ruddlesden-Popper chiral (R-/S-NEA)2PbBr4 structure (R-/S-NEA = R-/S-1-(1-naphthyl)ethylammonium) to investigate the effects induced by chemical substitution of Pb by Ge or Sn and Br by Cl or I on the transfer of chirality and physical-chemical properties. We have observed that different enantiomers result in opposing orientations of octahedral tiltings within the inorganic framework, thus transferring chirality to the inorganic structure. The tilts are greater in perovskites based on Pb and decrease in the sequence of Cl to Br to I, as a consequence of the decrease in the halide electronegativity that weakens the interactions between X and the -N+H3 group of the NEA chiral cation. The chirality transfer is also evident in the Rashba-Dresselhaus effects on the electronic band structure, in which we found magnitudes directly correlated to the trends of octahedra tilting. The band offsets of substitutions B and X are predominantly influenced by their natural atomic energy levels, while organic molecules play a pivotal role in modulating the ionic potential and electron affinity in systems containing light atoms. The band gap values range from 1.91 up to 3.77 eV, with chirality and anion electronegativity providing significant tuning effects on whether the band gaps are direct or indirect.
RESUMEN
Two-dimensional (2D) chalcogenides have attracted great interest from the scientific community due to their intrinsic physical-chemical properties, which are suitable for several technological applications. However, most of the reported studies focused on particular compounds and composition, e.g., MoS2, MoSe2, WS2, and WSe2. Thus, there is an increased interest to extend our knowledge on 2D chalcogenides. Here, we report a density functional theory (DFT) screening of 2D coinage-metal chalcogenides (MQx), whereM= Cu, Ag,Q= S, Se, Te,x= 0.5, 1.0, 1.5, 2.0, with the aim to improve our atomistic understanding of the physical-chemical properties as a function of cation (M), anion (Q), and composition (x). Based on 258 DFT calculations, we selected a set of 22 stableMQxmonolayers based on phonons analyses, where we identified 9 semiconductors (7 AgQxand 2 CuQx), with band gaps from 0.07 eV up to 1.67 eV, while the remaining systems have a metallic character. Using all 258 systems, we found a logarithmic correlation between the average weighted bond lengths and effective coordination number of cations and anions. As expected, the monolayer cohesive energies increase with the radius of theQspecies (i.e., from S to Te). Furthermore, an increase in the anion size diminishes the work function for nearly allMQxmonolayers, which can be explained by the nature of the electronic states at the valence band maximum.