Biexcitons are bound in CsPbBr3 Perovskite Nanocrystals

TL;DR

This study uses molecular dynamics simulations to analyze exciton and biexciton binding energies in CsPbBr3 nanocrystals, revealing that biexcitons are indeed bound, with size-dependent effects and lattice contributions thoroughly examined.

Contribution

It provides the first detailed computational evidence that biexcitons are bound in CsPbBr3 nanocrystals, considering complex lattice and electronic interactions.

Findings

Biexcitons are bound in CsPbBr3 nanocrystals.

Polaron formation reduces exciton binding energies.

Size and lattice effects influence binding energies.

Abstract

We study the energetics of quasi-particle excitations in CsPbBr3 perovskite nanocrystals using path integral molecular dynamics simulations. Employing detailed molecular models, we elucidate the interplay of anharmonic lattice degrees of freedom, dielectric confinement, and electronic correlation on exciton and biexciton binding energies over a range of nanocrystal sizes. We find generally good agreement with some experimental observations on binding energies, and additionally explain the observed size dependent Stokes shift. The explicit model calculations are compared to simplified approximations to rationalize the lattice contributions to binding. We find that polaron formation significantly reduces exciton binding energies, whereas these effects are negligible for biexciton interactions. While experimentally, the binding energy of biexcitons is uncertain, based on our study we conclude that biexcitons are bound in CsPbBr3.