Hybridized electronic states between CdSe nanoparticles and conjugated organic ligands: A theoretical and ultrafast photo-excited carrier dynamics study

Abstract

Formation of densely packed thin films of semiconductor nanocrystals is advantageous for the exploitation of their unique optoelectronic properties for real-world applications. Here we investigate the fundamental role of the structure of the bridging ligand on the optoelectronic properties of the resulting hybrid film. In particular, we considered hybrid films formed using the same CdSe nanocrystals and two organic ligands that have the same bidentate dithiocarbamate binding moiety, but differ in their bridging structures, one bridged by ethylene, the other by phenylene that exhibits conjugation. Based on the results of photo-excited carrier dynamics experiments combined with theoretical calculations on the electronic states of bridged CdSe layers, we show that only the phenylene-based ligand presents a strong hybridization of the molecular HOMO state with CdSe layers, that is a marker of formation of an effective bridge. We argue that this hybridization spread favors the hopping of photo-excited carriers between nanocrystals, which may explain the reported larger photo-currents in phenylene-based hybrid films than those observed in ethylene-based ones. [Figure not available: see fulltext.

Multilayers of Carbodithioate and Sulfide-Linked CdSe Nanocrystals: Progressive Increase of Exciton Delocalization

“…In fact, we found that PDTC-based multilayers have a Δ E g∞ n of 48 meV (Table ), that means an increase of the exciton delocalization of 0.59 nm. This result is also supported by previously reported theoretical calculations . They have shown that the dithiocarbamate causes hybridization of the PDTC HOMO state with the CdSe-NCs layers, favoring charge delocalization over two layers, the first step to have a good photoconductor layer as the PDTC-based multilayered system is reported to be .…”

“…This result is also supported by previously reported theoretical calculations. 3 They have shown that the dithiocarbamate causes hybridization of the PDTC HOMO state with the CdSe-NCs layers, favoring charge delocalization over two layers, the first step to have a good photoconductor layer as the PDTC-based multilayered system is reported to be. 2 On the other hand, ΔE g∞n for EDTC-based multilayers is 30 meV lower than the one of PDTC-based ones (Table 2) with an apparent increase of the exciton radius of just 0.2 nm.…”

“…In a previous work, we found that multilayered hybrid films realized by the alternation of CdSe-NCs and bi-functionalized linkers bearing a dithiocarbamate moiety with ethylene or phenylene as spacers [disodium 1,2ethylene-bis(dithiocarbamate) (EDTC) and 1,4-phenylenebis-(dithiocarbamate) (PDTC), respectively, in Chart 1] have shown promising photoconductive properties, 2 which were supported by photoexcited carrier dynamic experiments combined with theoretical calculations. 3 These latter studies show that the dithiocarbamate anchoring group causes the hybridization of the highest occupied molecular orbital (HOMO) state with the CdSe-NCs layers, which may favor the delocalization of the charge carriers through the layers.…”

Electrochemical Characterization of CdSe Monolayers Modified with Glycosilated Molecules

“…In this respect hybrid systems obtained by the integration of CdSe‐NCs and organic molecules are promising materials because they combine the properties of both components with the advantage of being more flexible and more resistant against oxidative degradation. Along these lines, the photoconductive properties of mono‐multilayers obtained by the alternation of CdSe‐NCs and organic molecules were largely investigated and electrochemical measurements were proposed as a novel approach, for the determination of CdSe‐NCs mass coverage in monolayers . In fact, CdSe‐NCs monolayers undergo in organic medium a sharp and irreversible oxidation process at 1.2 V vs SCE and corresponding to the passage of two electrons per CdSe unit .…”

Ultrafast spectroscopy studies of carrier dynamics in semiconductor nanocrystals

“…However, the field has most recently begun to expand and apply ultrafast spectroscopy to non-Cd-based and/or more complex In particular, cesium lead halide (CsPbX 3 ) and other perovskite nanocrystals have recently gained popularity for their enhanced efficiencies in quantum dot photovoltaics and high photoluminescence quantum yields and have garnered great interest in understanding their fundamental excitonic properties (Boehme et al, 2020;Carroll et al, 2021;Dai et al, 2021;Qin et al, 2021;Socie et al, 2021). Doped nanocrystal systems have also sparked interest (Dutta et al, 2018) as well as hybrid systems such as multilayered CdSe nanocrystals bridged with bidentate dithiocarbamate ligands (Virgili et al, 2018). Beyond the zerodimensional nanocrystals which are the focus of this review, and even one-dimensional nanomaterials such as nanorods which we briefly highlighted, recent work has also begun to explore two-dimensional materials and even composites of two-dimensional materials such as nanoplatelets of CdSe, CsPbX 3 , and graphene oxide, among other materials (Das et al, 2019;Ghosh et al, 2020).…”