Infrared Quantum Dots

Sargent, Edward H.

doi:10.1002/adma.200401552

Cited by 508 publications

(383 citation statements)

References 32 publications

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“…Sulfur (99.999%, S) and PbCl 2 (99.999%) were purchased from AlfaAesar. Methanol (MeOH), butanol (BuOH), and toluene were all of quality "for synthesis"; concentrated (65%) nitric acid (HNO 3 ) was of quality "normatom ultrapure". These products were ordered from VWR.…”

Section: Methodsmentioning

confidence: 99%

Size-Dependent Optical Properties of Colloidal PbS Quantum Dots

et al. 2009

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We quantitatively investigate the size-dependent optical properties of colloidal PbS nanocrystals or quantum dots (Qdots) by combining-the Qdot absorbance spectra with detailed elemental analysis of the Qdot suspensions. At high energies, the molar extinction coefficient epsilon increases With the Not volume d(3) and agrees with theoretical calculations using the Maxwell-Garnett effective medium theory and bulk values for the Qdot dielectric function. This demonstrates that quantum confinement has no influence on E in this spectral range, and it provides an accurate method to calculate the Qdot concentration. Around the band gap, epsilon only increases with d(1.3), and values are comparable to the epsilon of PbSe Qdots. The data are related to the oscillator strength f(if) of the band gap transition and results agree well with theoretical tight-binding calculations, predicting a linear dependence of f(if) on d. For both PbS and PbSe Qdots, the exciton lifetime tau is calculated from f(if). We find values ranging between 1 and 3 mu s, in agreement with experimental literature data from time-resolved luminescence spectroscopy. Our results provide a thorough general framework to calculate and understand the optical properties of suspended colloidal quantum dots. Most importantly, it highlights the significance of the local field factor in these systems

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Section: Methodsmentioning

confidence: 99%

Size-Dependent Optical Properties of Colloidal PbS Quantum Dots

et al. 2009

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“…To the best of our knowledge, the present study is the first using a noninjection-based approach to produce PbSe NCs. First, our noninjection approach adapted the "traditional" method (1) shown by eq 1. Typically, a reaction was carried out in ODE, with Pb(OA) 2 and TOPSe as Pb and Se precursors, respectively.…”

Section: ' Results and Discussionmentioning

confidence: 99%

“…1 Semiconductor lead selenide (PbSe) is of particular appeal, with its bulk band gap in the mid-IR (0.26 eV) and large exciton Bohr radius of 46 nm, rendering extremely strong quantum confinement to its nanosized structures. 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).…”

Section: ' Introductionmentioning

confidence: 99%

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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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“…Of particular interest among these artificial nanostructures are chemically synthesized QD nanocrystals, which, like organic semiconductors, can be processed from solution and which have a broad optical response that can be tuned from the visible to the infrared by selection of the type and physical size of the nanocrystals. 1,2 The novelty of QD optoelectronic structures suggests the need for new device designs that optimally utilize their properties. In the present study we demonstrate a hybrid organic/QD PD in which the optical absorption and electrical charge transport are physically separated into different layers, enabling their independent tuning and optimization.…”

mentioning

confidence: 99%

Lateral heterojunction photodetector consisting of molecular organic and colloidal quantum dot thin films

Osedach

Geyer

et al. 2009

Applied Physics Letters

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We demonstrate a heterojunction photodetector of lateral geometry that utilizes an evaporated film of the hole-transporting molecular material N , NЈ-bis͑3-methylphenyl͒-N , NЈ-bis͑phenyl͒-9,9-spirobifluorene ͑spiro-TPD͒ as a charge transport layer and that is sensitized across visible wavelengths by a thin film of colloidal CdSe nanocrystal quantum dots ͑QDs͒. High photon-to-electron quantum conversion efficiencies are obtained at room temperature as a result of photoconductive gain. With an electric field of 3.0ϫ 10 5 V / cm applied across the electrodes, we measure the external quantum efficiency at the first QD absorption peak ͑at wavelength = 590 nm͒ to be 13%, corresponding to an internal quantum efficiency of approximately 80%. The operating mechanism of these devices is discussed, noting that the optical response is dominated by the QD absorption spectrum while the charge transport nearly exclusively takes place in the spiro-TPD.

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Infrared Quantum Dots

Cited by 508 publications

References 32 publications

Size-Dependent Optical Properties of Colloidal PbS Quantum Dots

Size-Dependent Optical Properties of Colloidal PbS Quantum Dots

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

Lateral heterojunction photodetector consisting of molecular organic and colloidal quantum dot thin films

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