Ultrafast Spectroelectrochemistry Reveals Photoinduced Carrier Dynamics in Positively Charged CdSe Nanocrystals
(2021) In Journal of Physical Chemistry C 125(26). p.14332-14337- Abstract
Extra charges in semiconductor nanocrystals are of paramount importance for their electrically driven optoelectronic and photovoltaic applications. Optical excitations of such charged nanocrystals lead to rapid recombinationviaan Auger process, which can deteriorate the performance of the corresponding devices. While numerous articles report trion Auger processes in negatively charged nanocrystals, optical studies of well-controlled positive charging of nanocrystals and detailed studies of positive trions remain rare. In this work, we used electrochemistry to achieve positive charging of CdSe nanocrystals, so-called quantum dots (QDs), in a controlled way. Femtosecond transient absorption spectroscopy was applied forin situinvestigation... (More)
Extra charges in semiconductor nanocrystals are of paramount importance for their electrically driven optoelectronic and photovoltaic applications. Optical excitations of such charged nanocrystals lead to rapid recombinationviaan Auger process, which can deteriorate the performance of the corresponding devices. While numerous articles report trion Auger processes in negatively charged nanocrystals, optical studies of well-controlled positive charging of nanocrystals and detailed studies of positive trions remain rare. In this work, we used electrochemistry to achieve positive charging of CdSe nanocrystals, so-called quantum dots (QDs), in a controlled way. Femtosecond transient absorption spectroscopy was applied forin situinvestigation of the charge carrier dynamics after optical excitation of the electrochemically charged QD assembly on TiO2. We observe that without bias (i.e., neutral QDs), sub-picosecond hot carrier cooling is followed by multiple phases of the dynamics corresponding to electron injection and transfer to the TiO2. Positive charging first leads to activation of the hole traps close to the valence band maximum, which opens a rapid recombination channel of the optical excitation. A further increase in the positive bias interrupts the electron injection to TiO2, and if nanocrystals are positively charged, it leads to Auger relaxation in a few hundred picosecond timescale. This study represents a step toward the understanding of the effect of positive charging on the performance of semiconductor nanocrystals under conditions which closely mimic their potential applications.
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- author
- Honarfar, Alireza ; Chabera, Pavel LU ; Lin, Weihua LU ; Meng, Jie ; Mourad, Hassan LU ; Pankratova, Galina LU ; Gorton, Lo LU ; Zheng, Kaibo LU and Pullerits, Tõnu LU
- organization
- publishing date
- 2021-07-08
- type
- Contribution to journal
- publication status
- published
- subject
- in
- Journal of Physical Chemistry C
- volume
- 125
- issue
- 26
- pages
- 6 pages
- publisher
- The American Chemical Society (ACS)
- external identifiers
-
- scopus:85110283947
- ISSN
- 1932-7447
- DOI
- 10.1021/acs.jpcc.1c02729
- language
- English
- LU publication?
- yes
- id
- 66c3594a-4743-436e-adc9-e531e2a7c95e
- date added to LUP
- 2021-09-07 15:19:38
- date last changed
- 2023-11-08 18:47:56
@article{66c3594a-4743-436e-adc9-e531e2a7c95e,
abstract = {{<p>Extra charges in semiconductor nanocrystals are of paramount importance for their electrically driven optoelectronic and photovoltaic applications. Optical excitations of such charged nanocrystals lead to rapid recombinationviaan Auger process, which can deteriorate the performance of the corresponding devices. While numerous articles report trion Auger processes in negatively charged nanocrystals, optical studies of well-controlled positive charging of nanocrystals and detailed studies of positive trions remain rare. In this work, we used electrochemistry to achieve positive charging of CdSe nanocrystals, so-called quantum dots (QDs), in a controlled way. Femtosecond transient absorption spectroscopy was applied forin situinvestigation of the charge carrier dynamics after optical excitation of the electrochemically charged QD assembly on TiO<sub>2</sub>. We observe that without bias (i.e., neutral QDs), sub-picosecond hot carrier cooling is followed by multiple phases of the dynamics corresponding to electron injection and transfer to the TiO<sub>2</sub>. Positive charging first leads to activation of the hole traps close to the valence band maximum, which opens a rapid recombination channel of the optical excitation. A further increase in the positive bias interrupts the electron injection to TiO<sub>2</sub>, and if nanocrystals are positively charged, it leads to Auger relaxation in a few hundred picosecond timescale. This study represents a step toward the understanding of the effect of positive charging on the performance of semiconductor nanocrystals under conditions which closely mimic their potential applications.</p>}},
author = {{Honarfar, Alireza and Chabera, Pavel and Lin, Weihua and Meng, Jie and Mourad, Hassan and Pankratova, Galina and Gorton, Lo and Zheng, Kaibo and Pullerits, Tõnu}},
issn = {{1932-7447}},
language = {{eng}},
month = {{07}},
number = {{26}},
pages = {{14332--14337}},
publisher = {{The American Chemical Society (ACS)}},
series = {{Journal of Physical Chemistry C}},
title = {{Ultrafast Spectroelectrochemistry Reveals Photoinduced Carrier Dynamics in Positively Charged CdSe Nanocrystals}},
url = {{http://dx.doi.org/10.1021/acs.jpcc.1c02729}},
doi = {{10.1021/acs.jpcc.1c02729}},
volume = {{125}},
year = {{2021}},
}