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Electrochemical Charging Effect on the Optical Properties of InP/ZnSe/ZnS Quantum Dots


Semiconductor quantum dot (QD) has been spotlighted as a key emissive material for the next generation light-emitting diodes (LEDs). This paper presents the investigation of the electrochemical charging effect on the absorption and emission of the InP/ZnSe/ZnS QDs with different mid-shell thicknesses. Bleach in the absorption spectra of the QDs was observed during the electrochemical charging, which is caused by 1Se (or 1Sh) state filling when the electron (or hole) was injected into the InP core. Additional charges also reduced the photoluminescence (PL), however, the PL quenching was greatly mitigated as the mid-shell thickness increased. The temperature-dependent and time-resolved PL measurements reveal that the major cause for the PL reduction under electrochemical charging is the acoustic phonon-assisted Auger recombination. It has been known that the Auger recombination in the QDs even under highly photo-excited condition can be suppressed when the QDs have spatial distribution of charge carriers in the large volume. Here, we found that the Auger recombination in the QDs with thick mid-shell could be also reduced under the electrochemically charged condition, indicating that the QD with larger volume could be more stable emitter in the charge injecting devices such as LEDs. Furthermore, we estimated the negative and positive trion Auger recombination rate constants, respectively, via electrochemical charging. They cannot be revealed by normal spectroscopic methods, including transient absorption spectroscopy and PL lifetime. The negative trion Auger rate constants decrease as the mid-shell thickness increases, while the positive trion Auger rate constants are not heavily reliant on the mid-shell thickness.

Small 2020, 2003542