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Harvesting Solar Energy by Means of Charge-Separating Nanocrystals and Their Solids

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Negatively Charged Excitons in CdSe Nanoplatelets.

Elena V Shornikova¹, Dmitri R Yakovlev^1,2, Louis Biadala³

¹Experimentelle Physik 2 , Technische Universität Dortmund , 44221 Dortmund , Germany.

|January 22, 2020

Summary

The low-energy emission line in CdSe nanoplatelets originates from negatively charged excitons (trions), not neutral excitons. This finding clarifies their optical properties and potential applications.

Keywords:

CdSe nanoplatelet Colloidal nanocrystal charged exciton high magnetic fields trion

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Seeded Synthesis of CdSe/CdS Rod and Tetrapod Nanocrystals

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Area of Science:

Materials Science
Condensed Matter Physics
Nanotechnology

Background:

Colloidal semiconductor nanoplatelets (NPLs) exhibit unique optical properties.
The origin of low-energy emission in CdSe NPLs is debated.
Understanding exciton dynamics is crucial for optoelectronic applications.

Purpose of the Study:

To experimentally determine the origin of the low-energy emission line in CdSe NPLs.
To investigate the properties of neutral excitons and negatively charged excitons (trions) in CdSe NPLs.
To elucidate the factors influencing trion binding energy and surface spin interactions.

Main Methods:

Low-temperature photoluminescence spectroscopy (down to 1.5 K).
High magnetic field measurements (up to 60 T).
Time-resolved emission dynamics and spin polarization studies.
Photocharging dynamics analysis.

Main Results:

The low-energy emission line is definitively assigned to the recombination of negatively charged excitons (trions).
Trions exhibit significantly lower sensitivity to surface spins compared to neutral excitons.
Trion binding energy in 3-monolayer CdSe NPLs reaches 30 meV, enhanced by dielectric effects.
Photocharging dynamics confirm the trion assignment and spectral variations.

Conclusions:

The low-energy emission in CdSe NPLs originates from trions.
Dielectric confinement and environmental factors significantly enhance trion binding energy.
CdSe NPLs offer a promising platform for studying exciton physics with potential for novel optoelectronic devices.