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Electron relaxation in the CdSe quantum dot - ZnO composite: prospects for photovoltaic applications

View Article: PubMed Central - PubMed

ABSTRACT

Quantum dot (QD)-metal oxide composite forms a “heart” of the QD-sensitized solar cells. It maintains light absorption and electron-hole separation in the system and has been therefore extensively studied. The interest is largely driven by a vision of harvesting the hot carrier energy before it is lost via relaxation. Despite of importance of the process, very little is known about the carrier relaxation in the QD-metal oxide composites. In order to fill this gap of knowledge we carry out a systematic study of initial electron dynamics in different CdSe QD systems. Our data reveal that QD attachment to ZnO induces a speeding-up of transient absorption onset. Detailed analysis of the onset proves that the changes are caused by an additional relaxation channel dependent on the identity of the QD-ZnO linker molecule. The faster relaxation represents an important factor for hot carrier energy harvesting, whose efficiency can be influenced by almost 50%.

No MeSH data available.


Changes in TA onset rates and amplitudes after deposition of QDs on SiO2 and ZnO.(a-b) TA onset rates difference (panel a) and amplitudes ratio (panel b) for QD-SiO2 (blue symbols) and QD-ZnO (red symbols) samples. The QDs in solution serve as a reference sample. (c) Comparison between different linker molecules. Different red symbols correspond to sets of measurements on different batches of samples with the same parameters.
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f5: Changes in TA onset rates and amplitudes after deposition of QDs on SiO2 and ZnO.(a-b) TA onset rates difference (panel a) and amplitudes ratio (panel b) for QD-SiO2 (blue symbols) and QD-ZnO (red symbols) samples. The QDs in solution serve as a reference sample. (c) Comparison between different linker molecules. Different red symbols correspond to sets of measurements on different batches of samples with the same parameters.

Mentions: We used the isolated QDs in solution as our reference sample and calculated difference in the relaxation rates observed in the other two samples (see Figure 5a). We start our discussion for relatively low excess energies (energy above the QD bandgap) close to 0.4 eV, where we mostly excite 1Se electron state and states energetically close. Here it is expected to observe very little or no HET. We would therefore expect to obtain for all samples a similar TA onset rate. This is, however, not the case, because already here the onset for QD-ZnO is faster by about 2 ps−1.


Electron relaxation in the CdSe quantum dot - ZnO composite: prospects for photovoltaic applications
Changes in TA onset rates and amplitudes after deposition of QDs on SiO2 and ZnO.(a-b) TA onset rates difference (panel a) and amplitudes ratio (panel b) for QD-SiO2 (blue symbols) and QD-ZnO (red symbols) samples. The QDs in solution serve as a reference sample. (c) Comparison between different linker molecules. Different red symbols correspond to sets of measurements on different batches of samples with the same parameters.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5384232&req=5

f5: Changes in TA onset rates and amplitudes after deposition of QDs on SiO2 and ZnO.(a-b) TA onset rates difference (panel a) and amplitudes ratio (panel b) for QD-SiO2 (blue symbols) and QD-ZnO (red symbols) samples. The QDs in solution serve as a reference sample. (c) Comparison between different linker molecules. Different red symbols correspond to sets of measurements on different batches of samples with the same parameters.
Mentions: We used the isolated QDs in solution as our reference sample and calculated difference in the relaxation rates observed in the other two samples (see Figure 5a). We start our discussion for relatively low excess energies (energy above the QD bandgap) close to 0.4 eV, where we mostly excite 1Se electron state and states energetically close. Here it is expected to observe very little or no HET. We would therefore expect to obtain for all samples a similar TA onset rate. This is, however, not the case, because already here the onset for QD-ZnO is faster by about 2 ps−1.

View Article: PubMed Central - PubMed

ABSTRACT

Quantum dot (QD)-metal oxide composite forms a “heart” of the QD-sensitized solar cells. It maintains light absorption and electron-hole separation in the system and has been therefore extensively studied. The interest is largely driven by a vision of harvesting the hot carrier energy before it is lost via relaxation. Despite of importance of the process, very little is known about the carrier relaxation in the QD-metal oxide composites. In order to fill this gap of knowledge we carry out a systematic study of initial electron dynamics in different CdSe QD systems. Our data reveal that QD attachment to ZnO induces a speeding-up of transient absorption onset. Detailed analysis of the onset proves that the changes are caused by an additional relaxation channel dependent on the identity of the QD-ZnO linker molecule. The faster relaxation represents an important factor for hot carrier energy harvesting, whose efficiency can be influenced by almost 50%.

No MeSH data available.