Stability and Electronic Properties of Rocksalt (CdO)_n, (SrO)_n, and (BaO)_n Nanoparticles

Abstract

The low-lying isomeric structures in the shapes of hexagonal prisms and cuboids for (MO) n , M = Cd, Sr, and Ba for n ≤ 45 were explored using density functional theory. The rocksalt cuboid structures are found to be the lowest energy isomers for (MO) n for almost all sizes. Among the cuboid isomers, the particles in approximate aspect ratio of 1:1:1 are found to be most energetically favorable for particles of the same size. Density functional theory exchange-correlation functionals for predicting the stability of the (MO) n particles at the cluster and bulk limits were benchmarked against correlated molecular orbital theory. A fragment-based structure–energy relationship model was used to predict the particle position-related surface energy density and size-related particle aspect ratio transitions for rocksalt (MO) n nanoclusters. The critical sizes at which transitions of the particle aspect ratio may occur for the rocksalt particles were predicted. Linear correlations were found between the ionization potentials of the metal and the highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) gap of the rocksalt (MO) n nanoclusters. We found that the stability of the (MO) n structure is predominantly determined by the particle size and aspect ratio and is slightly affected by the intrinsic dipole moment. Aspects of the electronic structure including HOMO and LUMO energies and the HOMO–LUMO gap are less sensitive to the particle size and aspect ratio than to the intrinsic dipole moment, which is indicated by the parity sums of the atom counts of the edges. In terms of the parity sums, rocksalt (MO) n nanoclusters can be classified into three types with distinct electronic structures. The intrinsic longitudinal dipole moment of type-2 (parity sum = 2) (MO) n particles correlates with a decrease in the first excitation energy with increased particle length. The implications of the (MO) n nanoclusters in photochemistry were explored. The (CdO) n nanoclusters exhibit suitable electronic structures to be utilized in photocatalytic and photovoltaic applications.

Causes and Solutions of Recombination in Perovskite Solar Cells

“…c) Energy level diagram showing carrier transport and injection. Adapted with permission . Copyright 2018, American Chemical Society.…”

“…C60 was reported to have similar passivation effect for defects in perovskite films . When considering the good hole conductivity of CuI and the complexation of thiourea with Pb 2+ , Ye et al first synthesized the novel p‐type conductor Cu(thiourea)I [Cu(Tu)I] and then incorporated it into perovskite precursor solution for inverted PSCs, which delivered high PCE of 20.0%. Such an encouraging result was related to shallower trap state energy level in Cu(Tu)I‐incorporated perovskite film (0.25−0.35 eV) than pristine film (0.35−0.45 eV).…”

“…For the purpose of improving stability of PSCs, inorganic HTMs were suggested as alternative to organic HTMs . Among the commonly used inorganic HTMs, the device based on room temperature solution‐processed CuSCN HTM demonstrated a promising PCE over 20% .…”

Multifunctional Chemical Linker Imidazoleacetic Acid Hydrochloride for 21% Efficient and Stable Planar Perovskite Solar Cells

“…However, high‐temperature sintering process (usually over 500 °C) required for preparing mesoporous TiO 2 films complicates device fabrication and increases energy consumption and thus device cost, which is incompatible with the fabrication of flexible PSCs. In order to overcome the above issues, low‐temperature normal1b,4 and inverted planar PSCs were developed considering the long carrier diffusion length of commonly utilized perovskite compositions …”

Size and shape effects on the stability, electronic structure, and Raman spectroscopy of (SrO)n nanoclusters

“…The alkaline earth metal oxides (AEMO) are usually found as closed‐shell isostructural cubic lattice in the bulk form. In the cluster form, these systems have the same structural shape as the bulk‐sized crystal [19–25]. This characteristic can be explored to understand the influence of the size and shape of the clusters on the Raman spectroscopy, circumventing the theoretical difficulties to predict the ground state geometry presented above.…”