Ultrahigh Hot Carrier Transient Photocurrent in Nanocrystal Arrays by Auger Recombination

Gao, Jianbo; Kidon, Lyran; Rabani, Eran; Alivisatos, A. Paul

doi:10.1021/acs.nanolett.9b02374

Cited by 16 publications

(17 citation statements)

References 32 publications

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“…One elusive structure in the field of self-assemblies of semiconducting nanocrystals is the formation of mini-band structures using colloidal nanocrystals as artificial atoms, and a very high degree of crystallinity is required to form such materials 10 . Although long range transport phenomena may occur transiently with nanocrystals capped with long alkane capping ligands at high optical excitation densities via multi-electron Auger effects 98 , the tunnelling barrier of aliphatic organic ligands generally prevents self-assemblies from achieving the couplings required. However, recent work has shown how these ligands can assist in creating structures as a template in the potential synthetic pathway for these structures 10 .…”

Section: Future Perspectivesmentioning

confidence: 99%

The role of organic ligand shell structures in colloidal nanocrystal synthesis

2022

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olloidal nanocrystals bridge the gap between molecules and bulk materials, and enable researchers to probe fundamentals of nanomaterials, surfaces and size-dependent physics 1,2 . Beyond this, they have found a variety of applications from quantum dot emitters in displays 3,4 to photovoltaics 5,6 . Their colloidal nature allows them to be dispersed into solvents for optical studies, which include single-particle measurements 7,8 and assemblies of these materials can be created to investigate collective effects and their use as artificial atoms 9,10 .Fundamentally, most colloidal nanocrystals are composites that consist of an inorganic core and an organic ligand shell. This organic ligand shell enables colloidal stability in solvents 11,12 , prevents inorganic cores from fusing 10,13 , passivates undercoordinated atoms that lead to exciton traps in quantum dots [14][15][16][17] , acts as soft matter in the assembly of artificial solids 9,10,18,19 and provides a platform for the modification of inorganic cores 15,17,20 . Beyond contributing to colloidal nanocrystals properties, they are essential in synthesis.Organic ligands mediate growth by binding to growing nanocrystal surfaces as a surfactant. The group that binds to the nanocrystal surface is referred to as the head group, and the rest of the capping ligand is referred to as the tail group 1,19,21 . Typically, in hydrophobic environments, when growth is terminated by the exhaustion of precursors or reaction quenching, these ligands form an organic shell around each nanocrystal, in which the head groups face into the nanocrystal and the organic tail groups face outward. The nature of the ligands dictates the inorganic nanocrystal surface structure 11,19,21,22 , and has been designed to promote surfaces that minimize electronic trap states in quantum dots 15,17,23,24 . A variety of head groups are used to terminate colloidal nanocrystal surfaces, such as carboxylates, amines, phosphonates, thiols and halides, and often a mixture of capping groups is used [15][16][17]20,[25][26][27][28][29][30][31][32] . The amount, type and impurities of the ligands used in nanocrystal synthesis have implications for the nanocrystal size, shape, crystal structure and stability, as well as for their optical and electronic properties 33,34 .Head groups play a critical role in the control of colloidal nanocrystal growth, and different nanocrystal shapes can be formed by manipulating head group binding. Using combinations of

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Section: Future Perspectivesmentioning

confidence: 99%

The role of organic ligand shell structures in colloidal nanocrystal synthesis

2022

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“…As compared to molecular light absorbers, QDs have the capacity to concentrate many excited charge carriers within a small volume following multiple photon absorption or charge multiplication processes, due to their large absorptivity and high density of available electronic states. , The multiexcitonic state of a QD can enable photophysical processes that are inaccessible by single-excitonic states, such as the transfer of multiple charges on ultrafast time scales , and the tunneling transport of electrons across high energy barriers . The efficient extraction of charge carriers from multiexcitonic QDs would also be particularly useful for reactions related to photocatalytic solar fuel generation, as these chemical transformations universally involve multielectron catalysis.…”

Section: Introductionmentioning

confidence: 99%

Uncovering the Role of Hole Traps in Promoting Hole Transfer from Multiexcitonic Quantum Dots to Molecular Acceptors

et al. 2020

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Understanding electronic dynamics in multi-excitonic quantum dots (QDs) is important for designing efficient systems useful in high power scenarios, such as solar concentrators and multielectron charge transfer. The multiple charge carriers within a QD can undergo undesired Auger recombination events, which rapidly annihilate carriers on picosecond timescales and generate heat from absorbed photons instead of useful work. Compared to the transfer of multiple electrons, the transfer of multiple holes has proven to be more difficult due to slower hole transfer rates. To probe the competition between Auger recombination and hole transfer in CdSe, CdS, and CdSe/CdS QDs of varying sizes, we synthesized a phenothiazine derivative, with optimized functionalities for binding to QDs as a hole accepting ligand and for spectroscopic observation of hole transfer. Transient absorption spectroscopy was used to monitor the photoinduced absorption features from both trapped holes and oxidized ligands under excitation fluences where the averaged initial number of excitons in a QD ranged from ~1 to 19. We observed fluence-dependent hole transfer kinetics that last around 100 ps longer than the predicted Auger recombination lifetimes, and the transfer of up to 3 holes per QD. Theoretical modeling of the kinetics suggests that binding of hole acceptors introduces trapping states significantly different from those in native QDs passivated with oleate ligands. Holes in these modified trap states have prolonged lifetimes, which promotes the hole transfer efficiency. These results highlight the beneficial role of hole trapping states in devising hole transfer pathways in QD-based systems under multi-excitonic conditions.

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“…18,19 Alivisatos et al reported that PbSe NC arrays exhibited a transient photocurrent with a high excitation intensity, the current obtained being 6-9 orders of magnitude higher than a dark current due to the fast tunneling process of hot carriers produced via Auger recombination of multiple excitons. 20 Zhu et al reported shape-dependent hot electron transfer of CdSe NCs, in which the transfer rate from CdSe nanorods to MV 2+ was faster than that obtained with spherical NCs. 21 Recently, instead of using binary NCs showing high toxicity, such as CdSe, CdTe, and PbS, group I-III-VI semiconductor NCs have attracted increasing attention as light-absorbing materials with practical applications.…”

Section: Introductionmentioning

confidence: 99%