Hot-electron transfer from the semiconductor domain to the metal domain in CdSe@CdS{Au} nano-heterostructures

Abstract

Semiconductor-metal hybrid nanostructures are recognized as great materials due to their high level of light-induced charge separation, which has direct relevance in photocatalysis and solar energy conversion. To understand the mechanism of charge separation processes, hybrid CdSe@CdS{Au} nano-heterostructures containing Au nanoparticles (NPs) with different sizes were synthesized, and the ultrafast charge-transfer dynamics were monitored using femtosecond transient absorption spectroscopy. Steady-state optical absorption studies suggest the formation of charge-transfer complexes between core shell nanocrystals (NCs) and Au NPs. Steady-state and time-resolved luminescence spectroscopy suggest electron transfer from the photo-excited CdSe@CdS core shell QDs NCs to the Au NPs within the heterostructure. The ultrafast interfacial electron-transfer dynamics in the heterostructures were monitored by femtosecond transient absorption spectroscopy. The results revealed that both hot and thermalized electrons are transferred from the core shell QDs to the metal NPs with time constants of 150 and 300 fs, respectively. Hot-electron transfer from QDs to Au NPs was found to take place predominantly in the heterostructures depending on the sizes of the metal NPs. The photo-degradation of rhodamin B in the presence of the CdSe@CdS{Au} heterostructures under visible-light radiation suggests that the hot electrons in the heterostructures play a major role in photocatalytic degradation.

Correlating Charge‐Carrier Dynamics with Efficiency in Quantum‐Dot Solar Cells: Can Excitonics Lead to Highly Efficient Devices?

“…This spectral broadening up to about 800 nm can be attributed to both semiconductor‐to‐metal CT transitions and/or metal‐to‐semiconductor CT transitions depending on the nature of the excitation . The emission due to CdSe is completely quenched in the Au/CdSe HNCs due to photoinduced electron transfer from CdSe to the Au nanoparticles as shown in Figure A . The time‐resolved emission‐decay measurements also confirm the electron transfer process (Figure B).…”

“…Also, broad positive photoinduced absorption appeared in the TA spectra on the longer wavelength side after 1S bleaching due to increased electron density in the Au domain (Figure ) . The electron‐transfer time from CdSe to the Au NPs was obtained from the growth of the photoinduced absorption signal and is approximately 225 fs . This positive signal decays, forming a bleach signal which does not recover in the 1 ns window, signifying the formation of a long‐lived charge‐separated state.…”

Hot Charge Carriers in Quantum Dots: Generation, Relaxation, Extraction, and Applications

“…The other area where the hot charge carriers are getting much attention is photocatalysis . It has been reported that the hot electron is much better photocatalyst as compared to thermal electron and also better suited for redox reactions . This has been demonstrated by Moon et al .…”

“…Hot charge carriers in semiconductor quantum dots (QDs) play a key role in several applications such as solar energy harvesting, photocatalysis, detection of toxic gases, and synthesis of various important chemicals . Starting from generation; their relaxation and extraction from QDs follow numerous steps and the efficiency of each step determines the net effect of hot charge carriers in different devices and applications .…”

Direct Correlation of Excitonics with Efficiency in a Core–Shell Quantum Dot Solar Cell

“…Type II arrangement core-shell semiconductor formsa long-livedc harges eparated state after photoexcitation, in which the electrons and holes are localized in shell and core, respectively,a nd the photoexcited electron can easily be transferred to the metal oxide. [12,22] Changing the thickness of the shell QD often changes the type II structure to quasi type II structure andv ice versa. [21] Bisquert and co-workers have reported the PCE efficiency of about 7.17 %b yt ypeIIZ nTe/CdSe core-shell, which absorbsi nN IR region of the solars pectrum.…”