Binding energy of polaronic trions and biexcitons in CsPbBr 3 nanocrystals

The effect of polaron formation on the ground state of excitons, trions, and biexcitons confined in ${\mathrm{CsPbBr}}₃$ nanocrystals is studied in the framework of effective mass Hamiltonians, using a Haken-like (Bajaj) potential for carrier-phonon coupling. The binding energy of trions agrees well with that observed in experiments, with position-dependent dielectric screening playing a significant role. For biexcitons, however, neither polaronic effects, nor dielectric confinement, nor electronic correlations---here accounted for with a variational quantum Monte Carlo method---suffice to explain the large binding energies reported by single nanocrystal spectroscopy experiments. This result reinforces the hypothesis that biexcitons polarize the perovskite lattice differently from excitons and trions.