Optical Properties of Colloidal PbSe Nanocrystals

Du, Hui; Chen, Chialing; Krishnan, R.; Krauss, Todd D.; Harbold, Jeffrey M.; Wise, Frank W.; Thomas, M. G.; Silcox, J.

doi:10.1021/nl025785g

Cited by 469 publications

(449 citation statements)

References 28 publications

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“…2 Accordingly, colloidal PbSe QDs can be engineered to absorb and emit in a vast spectral range, spanning from ∼800 to 4000 nm with high photoluminescence (PL) emission quantum yields (QYs). [3][4][5][6][7][8] Hence, PbSe QDs are important materials for near-IR (NIR; >700 nm) and mid-IR (>2500 nm) applications, including biological imaging/labeling, 9,10 solar cells, [11][12][13][14][15][16] light-emitting devices, 17 and telecommunications. 18,19 PbSe nanocrystals (NCs) are especially attractive in the PV application, with a multiple exciton generation effect reported.…”

Section: ' Introductionmentioning

confidence: 99%

Low-Temperature Approach to High-Yield and Reproducible Syntheses of High-Quality Small-Sized PbSe Colloidal Nanocrystals for Photovoltaic Applications

Ouyang¹,

Schuurmans²,

Zhang³

et al. 2011

ACS Appl. Mater. Interfaces

106

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Small-sized PbSe nanocrystals (NCs) were syn-thesized at low temperature such as 50−80 °C with high reaction yield (up to 100%), high quality, and high synthetic reproducibility, via a noninjection-based one-pot approach. These small-sized PbSe NCs with their first excitonic absorption in wavelength shorter than 1200 nm (corresponding to size < ∼3.7 nm) were developed for photovoltaic applications requiring a large quantity of materials. These colloidal PbSe NCs, also called quantum dots, are high-quality, in terms of narrow size distribution with a typical standard deviation of ∼7−9%, excellent optical properties with high quantum yield of ∼50−90% and small full width at half-maximum of ∼130−150 nm of their band-gap photoemission peaks, and high storage stability. Our synthetic design aimed at promotion of the formation of PbSe monomers for fast and sizable nucleation with the presence of a large number of nuclei at low temperature. For formation of the PbSe monomer, our low-temperature approach suggests the existence of two pathways of Pb−Se (route a) and Pb−P (route b) complexes. Either pathway may dominate, depending on the method used and its experimental conditions. Experimentally, a reducing/nucleation agent, diphenylphosphine, was added to enhance route b. The present study addresses two challenging issues in the NC community, the monomer formation mechanism and the reproducible syntheses of small-sized NCs with high yield and high quality and large-scale capability, bringing insight to the fundamental understanding of optimization of the NC yield and quality via control of the precursor complex reactivity and thus nucleation/growth. Such advances in colloidal science should, in turn, promote the development of next-generation low-cost and high-efficiency solar cells. Schottky-type solar cells using our PbSe NCs as the active material have achieved the highest power conversion efficiency of 2.82%, in comparison with the same type of solar cells using other PbSe NCs, under Air Mass 1.5 global (AM 1.5G) irradiation of 100 mW/cm2.

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Section: ' Introductionmentioning

confidence: 99%

Low-Temperature Approach to High-Yield and Reproducible Syntheses of High-Quality Small-Sized PbSe Colloidal Nanocrystals for Photovoltaic Applications

Ouyang¹,

Schuurmans²,

Zhang³

et al. 2011

ACS Appl. Mater. Interfaces

106

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“…Lead chalcogenide CQDs ͑PbX with X = S or Se͒ have a fundamental exciton absorption peak which can be wavelength tuned from ϳ700 nm to 3 m. [6][7][8][9][10] The near-infrared wavelength window is desirable for imaging thick samples since infrared wavelength undergoes less Rayleigh scattering than visible light. Moreover, biological specimens have their weakest absorption in the 0.7-1.3 m wavelength range, the near-infrared window in biological tissue.…”

Section: Introductionmentioning

confidence: 99%

Four-wave-mixing imaging and carrier dynamics of PbS colloidal quantum dots

et al. 2010

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We demonstrate coherent multiphoton imaging of PbS colloidal quantum dots based on the detection of their transient resonant four-wave-mixing ͑FWM͒ emission under 150 fs pulsed laser excitation. Background-free imaging of PbS quantum dots in resonance with their ground-state excitonic absorption at 1.2 m wavelength is shown, with intrinsic optical sectioning and a spatial resolution better than the one-photon diffraction limit, promising for deep tissue microscopy. The four-wave-mixing efficiency is found to be resonant to the groundstate absorption maximum, which is a prerequisite for spectral multiplexing. The measured FWM dynamics is consistent with the presence of charged exciton and biexiton Auger recombination in the 10-100 ps time scale, phonon-assisted exciton thermalization in the nanosecond time scale, and excitonic recombination in the microsecond time scale.

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“…The slow relaxation is also reminiscent of the long excited-state lifetime that is observed in studies of PbSe NQDs. 36,38 Rationalization of the slow relaxation in PbSe NQDs has drawn upon consideration of the large dielectric screening correction of the optically active exciton radiative recombination rate. 36 However, the same calculation applied to InAs NQDs does not provide for a reduced rate of radiative relaxation.…”

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confidence: 99%

Carrier Multiplication in InAs Nanocrystal Quantum Dots with an Onset Defined by the Energy Conservation Limit

2007

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Carrier multiplication (CM) is a process in which absorption of a single photon produces not just one but multiple electron−hole pairs (excitons). This effect is a potential enabler of next-generation, high-efficiency photovoltaic and photocatalytic systems. On the basis of energy conservation, the minimal photon energy required to activate CM is two energy gaps (2E g ). Here, we analyze CM onsets for nanocrystal quantum dots (NQDs) based upon combined requirements imposed by optical selection rules and energy conservation and conclude that materials with a significant difference between electron and hole effective masses such as III−V semiconductors should exhibit a CM threshold near the apparent 2E g limit. Further, we discuss the possibility of achieving sub-2E g CM thresholds through strong exciton−exciton attraction, which is feasible in NQDs. We report experimental studies of exciton dynamics (Auger recombination, intraband relaxation, radiative recombination, multiexciton generation, and biexciton shift) in InAs NQDs and show that they exhibit a CM threshold near 2E g .Carrier Multiplication Thresholds in Bulk and Nanocrystalline Semiconductors. It has recently been established that carrier multiplication (CM), the production of multiple excitons following absorption of a single photon of sufficient energy, is efficient within the range of solar photon energies in semiconductor nanocrystal quantum dots (NQDs). [1][2][3][4][5][6][7][8][9] This finding is important because CM can potentially provide increased power conversion efficiency in low-cost, singlejunction photovoltaics via an enhanced photocurrent. 10,11 To obtain optimum photovoltaic power conversion efficiency using a single semiconductor material with energy gap E g , it is desirable that the CM onset energy is minimal and that the CM efficiency above the onset is as large as is allowed by energy conservation.According to energy conservation, the apparent minimal photon energy that is required to activate CM (pω CM ) is simply 2E g . However, the CM thresholds observed in bulk materials are significantly larger than this value. 12,13 In bulk semiconductors, the generally accepted mechanism for multiexciton generation is impact ionization in which a highenergy electron (or a hole) transfers its energy to a valenceband electron that is excited across the energy gap. 14 The CM threshold in this case is determined not only by conservation of energy but also by conservation of translational momentum, which increases the threshold above 2E g . For example, using a free-particle approximation 15,16 and applying both energy and momentum conservation laws, one can obtain that the CM threshold is approximately 4E g (Figure 1a).In NQDs, translational momentum conservation is relaxed. Therefore, one might expect that the CM threshold could reach the 2E g limit as defined by energy conservation. However, available experimental data indicate that pω CM is still greater than twice the energy gap in such materials. For example, in PbSe and PbS NQDs, it ...

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Optical Properties of Colloidal PbSe Nanocrystals

Cited by 469 publications

References 28 publications

Low-Temperature Approach to High-Yield and Reproducible Syntheses of High-Quality Small-Sized PbSe Colloidal Nanocrystals for Photovoltaic Applications

Low-Temperature Approach to High-Yield and Reproducible Syntheses of High-Quality Small-Sized PbSe Colloidal Nanocrystals for Photovoltaic Applications

Four-wave-mixing imaging and carrier dynamics of PbS colloidal quantum dots

Carrier Multiplication in InAs Nanocrystal Quantum Dots with an Onset Defined by the Energy Conservation Limit

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