Highly Charged Excitons and Biexcitons in Type-II Core/Crown Colloidal Nanoplatelets

Abstract

The optoelectronic properties of type-II CdSe/CdTe colloidal nanoplatelets (NPLs) charged with neutral excitons (X0) have been intensively investigated in the last years. Motivated by the recent experimental progress, here we use effective mass simulations to study the effect of charging core/crown NPLs with a few extra electrons or holes. Emission spectra are calculated for charged excitons (Xn, with n = 2 to n = -3) and biexcitons (XX). The strong Coulomb interactions within the platelet lead to a number of remarkable properties. For excitons, varying the number of excess charges gives rise to band gap red- and blue-shifts spanning over 100 meV and widely tunable oscillator strength. For biexcitons, the binding energy can be tuned from nearly nonbonding to strongly antibonding (∼40 meV) by modulating the core/crown area ratio. We conclude that the number of excess carriers injected into type-II NPLs is a versatile degree of freedom to modulate the optoelectronic properties.