Chemical mapping of excitons in halide double perovskites
Nano Letters American Chemical Society 23:17 (2023) 8155-8161
Abstract:
Halide double perovskites comprise an emerging class of semiconductors with tremendous chemical and electronic diversity. While their band structure features can be understood from frontier-orbital models, chemical intuition for optical excitations remains incomplete. Here, we use ab initio many-body perturbation theory within the GW and the Bethe–Salpeter equation approach to calculate excited-state properties of a representative range of Cs2BB′Cl6 double perovskites. Our calculations reveal that double perovskites with different combinations of B and B′ cations display a broad variety of electronic band structures and dielectric properties and form excitons with binding energies ranging over several orders of magnitude. We correlate these properties with the orbital-induced anisotropy of charge-carrier effective masses and the long-range behavior of the dielectric function by comparing them with the canonical conditions of the Wannier–Mott model. Furthermore, we derive chemically intuitive rules for predicting the nature of excitons in halide double perovskites using computationally inexpensive density functional theory calculations.Correction to "Zwitterions in 3D Perovskites: Organosulfide-Halide Perovskites".
Journal of the American Chemical Society 145:25 (2023) 14164
A regularized second-order correlation method from Green's function theory
J. Chem. Theory Comput. 2023, 19, 13, 3915–3928
Abstract:
We present a scalable single-particle framework to treat electronic correlation in molecules and materials motivated by Green’s function theory. We derive a size-extensive Brillouin-Wigner perturbation theory from the single-particle Green’s function by introducing the Goldstone self-energy. This new ground state correlation energy, referred to as Quasi-Particle MP2 theory (QPMP2), avoids the characteristic divergences present in both second-order Møller–Plesset perturbation theory and Coupled Cluster Singles and Doubles within the strongly correlated regime. We show that the exact ground state energy and properties of the Hubbard dimer are reproduced by QPMP2 and demonstrate the advantages of the approach for larger Hubbard models where the metal-to-insulator transition is qualitatively reproduced, contrasting with the complete failure of traditional methods. We apply this formalism to characteristic strongly correlated molecular systems and show that QPMP2 provides an efficient, size-consistent regularization of MP2.
Understanding the Degradation of Methylenediammonium and Its Role in Phase-Stabilizing Formamidinium Lead Triiodide.
Journal of the American Chemical Society American Chemical Society (ACS) 145:18 (2023) 10275-10284
Abstract:
Formamidinium lead triiodide (FAPbI<sub>3</sub>) is the leading candidate for single-junction metal-halide perovskite photovoltaics, despite the metastability of this phase. To enhance its ambient-phase stability and produce world-record photovoltaic efficiencies, methylenediammonium dichloride (MDACl<sub>2</sub>) has been used as an additive in FAPbI<sub>3</sub>. MDA<sup>2+</sup> has been reported as incorporated into the perovskite lattice alongside Cl<sup>-</sup>. However, the precise function and role of MDA<sup>2+</sup> remain uncertain. Here, we grow FAPbI<sub>3</sub> single crystals from a solution containing MDACl<sub>2</sub> (FAPbI<sub>3</sub>-M). We demonstrate that FAPbI<sub>3</sub>-M crystals are stable against transformation to the photoinactive δ-phase for more than one year under ambient conditions. Critically, we reveal that MDA<sup>2+</sup> is not the direct cause of the enhanced material stability. Instead, MDA<sup>2+</sup> degrades rapidly to produce ammonium and methaniminium, which subsequently oligomerizes to yield hexamethylenetetramine (HMTA). FAPbI<sub>3</sub> crystals grown from a solution containing HMTA (FAPbI<sub>3</sub>-H) replicate the enhanced α-phase stability of FAPbI<sub>3</sub>-M. However, we further determine that HMTA is unstable in the perovskite precursor solution, where reaction with FA<sup>+</sup> is possible, leading instead to the formation of tetrahydrotriazinium (THTZ-H<sup>+</sup>). By a combination of liquid- and solid-state NMR techniques, we show that THTZ-H<sup>+</sup> is selectively incorporated into the bulk of both FAPbI<sub>3</sub>-M and FAPbI<sub>3</sub>-H at ∼0.5 mol % and infer that this addition is responsible for the improved α-phase stability.Minimal molecular building blocks for screening in quasi-two-dimensional organic–inorganic lead halide perovskites
Nano Letters American Chemical Society 23:9 (2023) 3796-3802
Abstract:
Layered hybrid organic–inorganic lead halide perovskites have intriguing optoelectronic properties, but some of the most interesting perovskite systems, such as defective, disordered, or mixed perovskites, require multiple unit cells to describe and are not accessible within state-of-the-art ab initio theoretical approaches for computing excited states. The principal bottleneck is the calculation of the dielectric matrix, which scales formally as O(N4). We develop here a fully ab initio approximation for the dielectric matrix, known as IPSA-2C, in which we separate the polarizability of the organic/inorganic layers into minimal building blocks, thus circumventing the undesirable power-law scaling. The IPSA-2C method reproduces the quasi-particle band structures and absorption spectra for a series of Ruddlesden–Popper perovskites to high accuracy, by including critical nonlocal effects neglected in simpler models, and sheds light on the complicated interplay of screening between the organic and inorganic sublattices.