Ligand-Assisted Charge-Transfer Mechanism: The Case of CdSe/Cysteine/MoS₂ Heterostructures

Linker-Assisted Assembly of Ligand-Bridged CdS/MoS2 Heterostructures: Tunable Light-Harvesting Properties and Ligand-Dependent Control of Charge-Transfer Dynamics and Photocatalytic Hydrogen Evolution

“…Notably, our TCSPC and transient absorption data together reveal that electron transfer is fastest and most efficient specifically in CdS-cys- MoS 2 heterostructures, which is consistent with a recent computational study by Zhang and co-workers that revealed that the coordination of cys to both cadmium chalcogenide QDs and MoS 2 creates a charge-transfer state that promotes interfacial electron transfer. 16 Our results thus provide experimental evidence that cys is a particularly optimal ligand to mediate the attachment of cadmium chalcogenides to MoS 2 for excited-state charge separation via electron transfer. More generally, our results reveal that charge-transfer mechanisms underpinning photocatalysis can be tuned systematically by varying the properties of linker ligands in LAA-derived heterostructures.…”

“…We hypothesized (a) that incorporating presynthesized colloidal CdS QDs into heterostructures would afford improved control over the bandgap and first-excitonic absorption onset of CdS, as well as the energetic offsets at the CdS/MoS 2 interface that drive excited-state charge separation; (b) that excited-state electron transfer dynamics and yields could be tuned systematically by varying the properties of linker molecules; and (c) that ligand-dependent charge-transfer dynamics would, in turn, influence the photocatalytic reactivity of the heterostructures. We envisioned cysteine as a particularly promising linker given its propensity to facilitate the transfer of excited charge carriers from QDs to semiconductors. ,,, Indeed, a recent first-principles time-dependent density functional theory study by Zhang and co-workers revealed that the hybridization of states from CdSe, cys , and MoS 2 promotes rapid and efficient bridge-mediated electron transfer . We discovered that rate constants of CdS-to-MoS 2 electron transfer indeed varied systematically, by nearly 3 orders of magnitude, with the length and properties of linking ligands, with cysteine and 3-mercaptopropionic acid facilitating the fastest electron transfer.…”

“…We and others have recently reported on heterostructured photocatalysts consisting of semiconductor quantum dots (QDs) interfaced with MoS 2 nanosheets. − MoS 2 , monolayers of which absorb sunlight unusually efficiently, is an earth-abundant catalyst for the hydrogen evolution reaction (HER) or the reduction of H + to H 2 . Electrons in the conduction band of MoS 2 are positioned such that HER is thermodynamically favorable at low overpotentials, and sulfur edge sites are catalytically active. − Photocatalyst constructs can thus be created by interfacing MoS 2 with molecules or materials that absorb efficiently in the solar spectrum and that have appropriate excited-state potentials to transfer excited electrons to MoS 2 . ,, QDs are attractive light harvesters to interface with MoS 2 owing to their large molar absorption coefficients, size- and composition-dependent band-edge energetics, and surface-localized electronic states that can be exploited in interfacial charge transfer. − Moreover, QDs can be interfaced with hole-accepting materials to enable an oxidation half-reaction complementary to HER. ,,− …”

“…In analogy with results for cys-bridge heterostructures, metallic radical molecular orbitals are expected to renormalize the HOMO/ LUMO gap, thus affording a (ligand-dependent) direct pathway for carrier transport. 16 The lower Faradaic efficiencies for reductive HER than oxidative HER suggest that another reduction half-reaction competed with the reduction of H + . Finally, intrigued by the photoelectrochemical HER performance of CdS-L-MoS 2 heterostructures, we sought to determine whether they could promote redox photocatalysis in the absence of an applied potential, counter electrode, or external circuit.…”

Engineering the synthesized colloidal CuInS2 passivation layer in interface modification for CdS/CdSe quantum dot solar cells

“…3 Quantum dot (QD) sensitizers as a core part of QDSCs have become an important research direction, including size-dependent quantum dots, 4 alloyed QDs, 5 co-sensitization QDs, 6,7 and ion-doped QDs. 8 Currently, various QDs have been investigated, such as CdS, 4,9 CdSe, 10 PbS, 6,11,12 SnSe 13 and Sb 2 S 3 . 14 In cadmium sulfide materials, nanocomposite CdS/CdSe QD sensitizers form a step-like energy band structure, so that the photogenerated carriers can be better arranged on the photoanode, thus reducing recombination loss.…”