DOI: https://doi.org/10.29363/nanoge.incnc.2021.021
Publication date: 8th June 2021
It is well known that the optoelectronic properties of colloidal nanoplatelets are largely set by the strong electron-hole Coulomb attraction, which is enabled by the dielectric confinement and 2D geometry, and gives rise to large exciton binding energies or giant oscillator strength, to name a few effects.[1,2]
Much less is known about the role of electron-electron or hole-hole repulsions. Naturally, the same conditions that lead to strong attractions in nanoplatelets, should lead to strong repulsions as well. In combination with the weak lateral confinement, such repulsions can trigger severe electronic correlations, which are found neither in nanocrystals (owing to the strong confinement) nor in bulk (owing to the weak Coulomb interaction).
In this work, we explore theoretically the opportunities of exploting Coulomb repulsions to engineer the band structure of colloidal nanoplatelets. We study type-I and type-II CdSe-based nanoplatelets charged with up to 4 electrons or holes. Several remarkable phenomena are then predicted
1) The giant oscillator strength effect, present for neutral excitons, vanishes for trions.
2) Addition energies exceeding 100 meV are required to introduce extra charges in the nanoplatelets, which implies that carriers can be injected electrochemically one-by-one at room temperature
3) High electron spin states are populated even at low temperatures, which provides multi-electron platelets with an enhanced magnetic moment and paramagnetic response.
4) In type-II core/crown nanoplatelets, large and reversible changes in the emission intensity and energy (~100 meV) can be achieved when switching from X2+ to X3- excitonic species.
5) Biexciton binding energies are highly tunable depending on the lateral dimensions of the platelet, from highly repulsive (40 meV) to neutral (~0 meV).
It is concluded that the charging of nanoplatelets with a few interacting electrons or holes is a promising route to develop novel magnetic and optical functionalities.
Financial support from MINECO, project CTQ2017-83781-P is gratefully acknowledged.
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