Defining the topological influencers and predictive principles to engineer the band structure of halide perovskites

Abstract

Complex quantum coupling phenomena of halide perovskites are examined through ab-initio calculations and exact diagonalization of model Hamiltonians to formulate a set of fundamental guiding rules to engineer the bandgap through strain. The bandgap tuning in halides is crucial for photovoltaic applications and for establishing non-trivial electronic states. Using CsSnI3 as the prototype material, we show that in the cubic phase, the bandgap reduces irrespective of the nature of strain. However, for the tetragonal phase, it reduces with tensile strain and increases with compressive strain, while the reverse is the case for the orthorhombic phase. The reduction can give rise to negative bandgap in the cubic and tetragonal phases leading to normal to topological insulator phase transition. Also, these halides tend to form a stability plateau in a space spanned by strain and octahedral rotation. In this plateau, with negligible cost to the total energy, the bandgap can be varied in a range of 1eV. Furthermore, we present a descriptor model for the perovskite to simulate their bandgap with strain and rotation. Analysis of band topology through model Hamiltonians led to the conceptualization of topological influencers that provide a quantitative measure of the contribution of each chemical bonding towards establishing a normal or topological insulator phase. On the technical aspect, we show that a four orbital based basis set (Sn-{s,p} for CsSnI3) is sufficient to construct the model Hamiltonian which can explain the electronic structure of each polymorph of halide perovskites.

Strain-driven topological quantum phase transition in (pseudo)cubic (mixed)-Cs/MA/FA halide perovskites

“…Nevertheless, if we tune certain external parameters such as those mentioned above, a topological phase can be realized in halide perovskites. 31 This is consistent with the recent theoretical calculations that compressive strain can drive these materials into the topological insulator region. 30 At a critical value of strain, a phase transition takes place, transforming a normal insulator to a topological insulator (NI-TI).…”

Strain Engineering of Low‐Dimensional Materials for Emerging Quantum Phenomena and Functionalities

“…As a result, the bandgap decreases and subsequently becomes negative at a critical strain leading to the band inversion and the phase transition from normal insulator to topological insulator. [ 305 ] In addition to low energy surface states, switchable polarization can contribute to novel device functionalities. Ferroelectric topological insulators (FETI) have hardly been realized despite the possibilities CsPbI 3 can possess ferroelectric properties along with topological states under appropriate strain engineering.…”

Electronic Structure and Optoelectronic Properties of Halide Double Perovskites: Fundamental Insights and Design of a Theoretical Workflow

“…In the last couple of decades, organic and inorganic halide single perovskites (HSPs) of the formula ABX 3 (e.g., CsPbI 3 ) have gained enormous research attention as they demonstrate promising optoelectronic properties , for solar cell applications and nontrivial topological quantum phases. The latter brings the dimension of orbitronics , and topotronics. − At the same time, there appears to be a large number of disadvantages associated with this class of compounds. The most significant one is the lack of stability upon prolonged exposure to light and heat.…”