Enhanced Light Emission through Symmetry Engineering of Halide Perovskites

Abstract

Metal-halide perovskites (MHPs) have attracted tremendous attention as active materials in optoelectronic devices. For light-emitting diode (LED) applications, nanostructuring of MHPs is considered to be inevitable, but its light-enhancement mechanism is still elusive because the particle (or grain) size is often beyond the quantum confinement regime. As motivated by the experimental finding that the nanostructuring can change the preferred crystalline symmetry from the orthorhombic phase to the high-symmetric cubic phase, we here investigated the carrier dynamics in various polymorphic phases of CsPbBr3 using ab initio quantum dynamics simulation. We found that the cubic phase shows a smaller inelastic phonon scattering than the orthorhombic phase; the suppression of the octahedral tilt minimizes the longitudinal Br fluctuation and helps disentangle the A-site cation dynamics from the nonadiabatic carrier dynamics. We thus anticipate that our present work will offer a material design principle to enhance the quantum yield of MHPs via symmetry engineering, which will help develop highly luminescent LED technology based on MHPs.

Nonadiabatic Molecular Dynamics with Extended Density Functional Tight-Binding: Application to Nanocrystals and Periodic Solids

“…Furthermore, in this work, we adopt the neglect of back-reaction approximation (NBRA) pioneered by Prezhdo et al − and further adopted by many researchers modeling NA dynamics in nanoscale systems. − According to the NBRA, the electronic evolution does not affect the nuclear evolution, whereas the latter (on the ground electronic state) parametrically affects the corresponding vibronic Hamiltonian. This approach cannot properly describe the thermal equilibrium because it does not take the derivative couplings into account and there is no feedback between quantum and classical parts of the system.…”

“…Nonadiabatic molecular dynamics (NA-MD) is a powerful computational technique that can model NA processes and describe the excited-state dynamics in various materials. NA-MD simulations have been successfully utilized in predicting the photochemistry and photophysics of molecular systems − and nanoscale materials. − These simulations have been widely used to gain insights into NA processes in solar cells, − light-emitting diodes, and chemical reactions. − However, due to the highly demanding computational costs, the NA-MD simulations of solid-state and nanoscale systems are often limited to a few hundred atoms. Simulation of realistic nanostructures, comparable to those studied experimentally is still computationally expensive, primarily due to the demanding costs of the underlying electronic structure calculations and their unfavorable scalability with the system size.…”

“…NA-MD simulations have been successfully utilized in predicting the photochemistry and photophysics of molecular systems 1−9 and nanoscale materials. 10−36 These simulations have been widely used to gain insights into NA processes in solar cells, 10−31 light-emitting diodes, 32 and chemical reactions. 33−36 However, due to the highly demanding computational costs, the NA-MD simulations of solid-state and nanoscale systems are often limited to a few hundred atoms.…”

Dependence of Electron–Hole Recombination Rates on Charge Carrier Concentration: A Case Study of Nonadiabatic Molecular Dynamics in Graphitic Carbon Nitride Monolayers

“…Nonadiabatic (NA) molecular dynamics (MD) provides valuable insights into excited state dynamics in many classes of solar energy materials such as light-harvesting systems, − light-emitting diodes, and photocatalytic materials. − The efficiency of photoinduced processes such as charge carrier injection, relaxation, and electron–hole (e–h) recombination in these materials can be described using NA-MD simulations. Although such calculations have provided multiple insights into the functioning of solar energy materials, − ,,,− ,, helped rationalize numerous experiments, ,,,,− and revealed valuable trends, ,− the direct connection of the obtained computational results with the experimental observations and measurements remains a challenge.…”

“…Nonadiabatic (NA) molecular dynamics (MD) provides valuable insights into excited state dynamics in many classes of solar energy materials such as light-harvesting systems, 1−18 light-emitting diodes, 19 and photocatalytic materials. 20−22 The efficiency of photoinduced processes such as charge carrier injection, relaxation, and electron−hole (e−h) recombination in these materials can be described using NA-MD simulations.…”