Direct generation of multiple excitons in adjacent silicon nanocrystals revealed by induced absorption

Trinh, M. Tuan; Limpens, Rens; Boer, W. D. A. M. de; Schins, Juleon M.; Siebbeles, Laurens D. A.; Gregorkiewicz, T.

doi:10.1038/nphoton.2012.36

Cited by 181 publications

(212 citation statements)

References 49 publications

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“…While the particular measurement has been conducted with the excitation set to 302 nm, the EQE value turned out to be independent of the excitation wavelength. This implies that effects such as excitation-dependent trapping and the space-separated quantum cutting process frequently reported for Si NCs, 4,5,25 and leading to variation of EQE upon excitation energy, are not present in the samples investigated in this study. This indicates large NC separation precluding coupling of high energy states between NCs.…”

Section: -4mentioning

confidence: 78%

Spectroscopic investigations of dark Si nanocrystals in SiO2 and their role in external quantum efficiency quenching

Limpens

Gregorkiewicz

2013

Journal of Applied Physics

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The percentage of dark silicon nanocrystals, i.e., the nanocrystals that are not able to radiatively recombine after absorption of a photon, is investigated by combining measurements of external and internal quantum efficiencies. The study is conducted on samples prepared by co-sputtering and subsequent heat treatments. We show that the external quantum efficiency is mainly limited by the presence of dark nanocrystals, which induce losses after direct excitation and also, as we propose, by indirect excitation enabled by energy migration. The percentage of dark nanocrystals can be decreased by high quality surface passivation as a result of low-temperature annealing in ambients of O 2 and H 2 . By using a non-passivated sample as a reference, the relation between the size of a nanocrystal and its probability of being dark is studied. Larger nanocrystals are demonstrated to function more likely as dark centers. The study shows that high external quantum efficiencies of Si nanocrystal ensembles can be realized for small, well passivated Si nanocrystals under suppression of excitation diffusion. V C 2013 AIP Publishing LLC. [http://dx

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Section: -4mentioning

confidence: 78%

Spectroscopic investigations of dark Si nanocrystals in SiO2 and their role in external quantum efficiency quenching

Limpens

Gregorkiewicz

2013

Journal of Applied Physics

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“…This is concluded from previous IA experiments conducted on the same samples with similar excitation photon energies, but orders-of-magnitude lower-photon fluence (so that N abs 1). 22,23 Here, the intensity of the (monocolor NIR probing) IA signal for delay times t > 500 ps did not fully decay, giving evidence for the presence of (a small concentration of) free carriers even at longer delay times.…”

Section: B Time-resolved Investigations Of Iamentioning

confidence: 89%

Carrier dynamics in Si nanocrystals in an SiO2matrix investigated by transient light absorption

et al. 2013

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We report on investigations of optical carrier generation in silicon nanocrystals embedded in an SiO 2 matrix. Carrier relaxation and recombination processes are monitored by means of time-resolved induced absorption, using a conventional femtosecond pump-probe setup for samples containing different average sizes of nanocrystals (d NC = 2.5-5.5 nm). The electron-hole pairs generated by the pump pulse are probed by a second pulse over a broad spectral range (E probe = 0.95-1.35 or 1.6-3.25 eV), by which information on excited states is obtained. Under the same excitation conditions, we observe that the induced absorption intensity in the near-infrared range is a factor of ∼10 higher than in the visible range. To account for these observations, we model the spectral dependence of the induced absorption signal using an empirical sp 3 d 5 s * tight-binding technique, by which the spectrum can be well reproduced up to a certain threshold. For probe photon energies above this threshold (dependent on nanocrystal size), the induced absorption signal is found to feature a long-standing component, whereas the induced absorption signal for probe photon energies below this value vanishes within 0.5 ns. We explain this by self-trapping of excitons on surface-related states.

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“…Whilst MEG has been detected in a number of materials, including silicon [57][58][59], most studies focused on QDs consisting of lead chalcogenides (PbS, PbSe and PbTe) [26,41,[60][61][62]. The large Bohr radius of lead chalcogenides, relative to, for example, silicon or GaAs [59,63,64], allows strong quantum confinement effects and efficient tuning of the confinement to produce a band gap in the near-IR region (0.7-1.0 eV) [65].…”

Section: Qd Materials For Meg In Pv Devicesmentioning

confidence: 99%

“…tuning of ligand chemistry, QD shape and material) [26][27][28]. Besides the QD film designs presented here, there are other promising quantum-confined materials including indium phosphide QDs [7], (6,5) single-walled carbon nanotubes [128] and silicon QDs [58], which show high CM rates at comparably low photon energies and η MEG in a solar cell [29,31,32]. For further improvements in MEG-enhanced PV performance, a deeper understanding of the MEG photophysics is therefore necessary.…”

Section: Future Directions and Outlookmentioning

confidence: 99%

Multiple exciton generation in quantum dot-based solar cells

et al. 2017

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Multiple exciton generation (MEG) in quantumconfined semiconductors is the process by which multiple bound charge-carrier pairs are generated after absorption of a single high-energy photon. Such charge-carrier multiplication effects have been highlighted as particularly beneficial for solar cells where they have the potential to increase the photocurrent significantly. Indeed, recent research efforts have proved that more than one chargecarrier pair per incident solar photon can be extracted in photovoltaic devices incorporating quantum-confined semiconductors. While these proof-of-concept applications underline the potential of MEG in solar cells, the impact of the carrier multiplication effect on the device performance remains rather low. This review covers recent advancements in the understanding and application of MEG as a photocurrent-enhancing mechanism in quantum dot-based photovoltaics.

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Direct generation of multiple excitons in adjacent silicon nanocrystals revealed by induced absorption

Cited by 181 publications

References 49 publications

Spectroscopic investigations of dark Si nanocrystals in SiO2 and their role in external quantum efficiency quenching

Spectroscopic investigations of dark Si nanocrystals in SiO2 and their role in external quantum efficiency quenching

Carrier dynamics in Si nanocrystals in an SiO2matrix investigated by transient light absorption

Multiple exciton generation in quantum dot-based solar cells

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