Charging of colloidal nanoplatelets: effect of Coulomb repulsion on spin and optoelectronic properties

TL;DR

This paper explores how Coulomb repulsion in charged colloidal nanoplatelets influences their electronic, magnetic, and optoelectronic properties, revealing tunable emission spectra and high-spin states.

Contribution

It provides a theoretical analysis of Coulomb effects on shell filling, emission spectra, and band profiles in charged nanoplatelets, highlighting new ways to modulate their properties.

Findings

Coulomb repulsions enable addition energies above room temperature thermal energy.

Charged excitons and biexcitons exhibit multi-peaked, tunable emission spectra.

Increasing electrons in the core causes a transition from type-II to quasi-type-II band profile.

Abstract

Colloidal semiconductor nanoplatelets combine weak lateral confinement with strong Coulomb interactions, enhanced by dielectric confinement. When the platelets are charged with carriers of the same sign, this results in severe Coulomb repulsions which shape the electronic structure. To illustrate this point, the shell filling of type-I (CdSe/CdS) and type-II (CdSe/CdTe) core/crown nanoplatelets with up to 4 electrons or holes is investigated theoretically. We find that Coulomb repulsions enable addition energies exceeding room temperature thermal energy and promote the occupation of high-spin states. For charged excitons and biexcitons in CdSe/CdTe nanoplatelets, the repulsions further give rise to multi-peaked emission spectra with widely tunable (over 100 meV) energy, and a transition from type-II to quasi-type-II band profile as the number of electrons confined in the core increases. We conclude that the number of excess carriers injected in nanoplatelets is a versatile degree of freedom to modulate their magnetic and optoelectronic properties.