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

The optoelectronic properties of type-II CdSe/CdTe colloidal nanoplatelets (NPLs) charged with neutralexcitons (X0) have been intensively investigated in the last years.Motivated by the recent experimental progress, here we useeffective mass simulations to study the effect of charging core/crown NPLs with a few extra electrons or holes. Emission spectraare calculated for charged excitons (Xn, withn=2ton=-3) andbiexcitons (XX). The strong Coulomb interactions within theplatelet 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 tunableoscillator strength. For biexcitons, the binding energy can be tunedfrom nearly nonbonding to strongly antibonding (similar to 40 meV) by modulating the core/crown area ratio. We conclude that thenumber of excess carriers injected into type-II NPLs is a versatile degree of freedom to modulate the optoelectronic properties.