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Shengyi Yang

Bio: Shengyi Yang is an academic researcher from Beijing Institute of Technology. The author has contributed to research in topics: Photodetector & Quantum dot. The author has an hindex of 11, co-authored 23 publications receiving 654 citations.

Papers
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Journal ArticleDOI
TL;DR: In this paper, the off-stoichiometry effects and gram-scale production of luminescent CuInS2-based semiconductor nanocrystals, as well as their application in electroluminescence devices are reported.
Abstract: The off-stoichiometry effects and gram-scale production of luminescent CuInS2-based semiconductor nanocrystals, as well as their application in electroluminescence devices are reported. The crystal structures and optical properties of CuInS2 nanocrystals can be significantly influenced by controlling their [Cu]/[In] molar ratio. A simple model adapted from the bulk materials is proposed to explain their off-stoichiometry effects. Highly emissive and color-tunable CuInS2-based NCs are prepared by a combination of [Cu]/[In] molar ratio optimization, ZnS shell coating, and CuInS2–ZnS alloying. The method is simple, hassle-free, and easily scalable to fabricate tens of grams of nanocrystal powders with photoluminescence quantum yields up to around 65%. Furthermore, the performance of high-quality CuInS2-based NCs in electroluminescence devices is examined. These devices have lower turn-on voltages of around 5 V, brighter luminance up to approximately 2100 cd m−2 and improved injection efficiency of around 0.3 lm W−1 (at 100 cd m−2) in comparison to recent reports.

445 citations

Journal ArticleDOI
TL;DR: A solution-processed colloidal quantum dot (CQDs) photodetector with the configuration of a field-effect transistor (FET), in which the drain and source electrodes are fabricated by a shadow mask, provides an easy way to fabricate such a FET-based photodetsector with a channel length of some hundreds of micrometers by ashadow mask.
Abstract: We demonstrate a solution-processed colloidal quantum dot (CQDs) photodetector with the configuration of a field-effect transistor (FET), in which the drain and source electrodes are fabricated by a shadow mask. By blending PbS CQDs into the hybrid blend, poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methylester (PCBM), the photosensitive spectrum of the nanocomposite blend is extended into the near-infrared region. A FET-based photodetector ITO/PMMA (180 nm)/P3HT:PCBM:PbS (110 nm)/Al, in which PMMA (polymethylmethacrylate) acts as the dielectric layer and P3HT:PCBM:PbS (in weight ratio of 1:1:1) as the active layer, shows a broad spectral bandwidth, a responsivity of 0.391 mA W−1 and a specific detectivity of 1.31 × 1011 Jones are obtained at VGS = 1 V under 600 nm illumination with an intensity of 30 μW cm−2. Therefore, it provides an easy way to fabricate such a FET-based photodetector with a channel length of some hundreds of micrometers by a shadow mask.

44 citations

Journal ArticleDOI
TL;DR: A solution to suppress dark current and maintain high photocurrent by using polymethyl methacrylate doped with Au nanoparticles (NPs) as the interlayer for enhanced-performance tandem photodetectors, and the physical mechanism for the enhanced performance is presented.
Abstract: Currently, colloidal quantum dots (CQDs)-based photodetectors are widely investigated due to their low cost and easy integration with optoelectronic devices. The requirements for a high-performance photodetector are a low dark current and a high photocurrent. Normally, photodetectors with a low dark current also possess a low photocurrent, or photodetectors with reduced dark current possess a reduced photocurrent, resulting in low detectivity. In this paper, a solution to suppress dark current and maintain a high photocurrent, i.e., use of poly(methyl methacrylate) doped with Au nanoparticles (NPs) (i.e., PMMA:Au) as an interlayer for enhanced-performance tandem photodetectors, is presented. Our experimental data showed that the dark current through the tandem photodetector ITO/PEDOT:PSS/PbS:CsSnBr3/ZnO/PMMA:Au/CuSeN/PbS:CsSnBr3/ZnO/Ag is suppressed significantly; meanwhile, a high photocurrent is maintained after a PMMA:Au interlayer has been inserted between two subdetectors. The inserted PMMA:Au interlayer acts as storage nodes for electrons, reducing the dark current through the device; meanwhile, the photocurrent can be enhanced under illumination. As a result, the specific detectivity of the tandem photodetector with 35 nm PMMA:Au interlayer was enhanced significantly from 5.01 × 1012 to 2.7 × 1015 Jones under 300 μW/cm2 532 nm illumination at a low voltage of -1 V as compared to the device without a PMMA:Au interlayer. Further, the physical mechanism of enhanced performance is discussed in detail.

41 citations

Journal ArticleDOI
TL;DR: In this paper, high-gain ultraviolet (UV) photodetectors based on vertically aligned ZnO nanorods (ZnO-NRs) array as light absorption antenna were presented.

38 citations

Journal ArticleDOI
TL;DR: In this paper, a solution-processed near-infrared (NIR) photodetector based on PbSe colloidal quantum dots (CQDs) with a field effect transistor (FET) configuration was presented.
Abstract: A solution-processed near-infrared (NIR) photodetector based on PbSe colloidal quantum dots (CQDs) with a field-effect transistor (FET) configuration was presented. By blending PbSe CQDs into poly(3-hexylthiophene-2, 5-diyl) (P3HT) as active layer, the photosensitive spectrum of P3HT:PbSe nanocomposites extends into the NIR region. The responsivity and the specific detectivity of FET-based photodetector Au(gate)/PMMA (930nm)/P3HT:PbSe(55nm)/Au(source, drain) reached 500 A/W and $5.02 \times 10^{12}$ Jones, respectively, at $V_{\rm DS}=-40$ V and $V_{\rm G}=-40$ V with 40 mW/cm $^{2}$ of 980-nm laser illumination. It gets more stable due to its reverse fabrication using the dielectric layer to cover the active layer from environment air.

38 citations


Cited by
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Journal ArticleDOI
TL;DR: Carbon dots represent an emerging class of fluorescent materials and provide a broad application potential in various fields of biomedicine and optoelectronics as discussed by the authors, and the applicability of carbon dots as components of light emitting diodes, which include carbon dot based electroluminescence, optical downconversion, and hybrid plasmonic devices.

745 citations

Journal ArticleDOI
TL;DR: Recent advances in nanocrystal research related to applications of QD materials in lasing, light-emitting diodes (LEDs), and solar energy conversion are examined.
Abstract: The field of nanocrystal quantum dots (QDs) is already more than 30 years old, and yet continuing interest in these structures is driven by both the fascinating physics emerging from strong quantum confinement of electronic excitations, as well as a large number of prospective applications that could benefit from the tunable properties and amenability toward solution-based processing of these materials. The focus of this review is on recent advances in nanocrystal research related to applications of QD materials in lasing, light-emitting diodes (LEDs), and solar energy conversion. A specific underlying theme is innovative concepts for tuning the properties of QDs beyond what is possible via traditional size manipulation, particularly through heterostructuring. Examples of such advanced control of nanocrystal functionalities include the following: interface engineering for suppressing Auger recombination in the context of QD LEDs and lasers; Stokes-shift engineering for applications in large-area luminesce...

703 citations

Journal ArticleDOI
TL;DR: This review captures the synthesis, assembly, properties, and applications of copper chalcogenide NCs, which have achieved significant research interest in the last decade due to their compositional and structural versatility.
Abstract: This review captures the synthesis, assembly, properties, and applications of copper chalcogenide NCs, which have achieved significant research interest in the last decade due to their compositional and structural versatility. The outstanding functional properties of these materials stems from the relationship between their band structure and defect concentration, including charge carrier concentration and electronic conductivity character, which consequently affects their optoelectronic, optical, and plasmonic properties. This, combined with several metastable crystal phases and stoichiometries and the low energy of formation of defects, makes the reproducible synthesis of these materials, with tunable parameters, remarkable. Further to this, the review captures the progress of the hierarchical assembly of these NCs, which bridges the link between their discrete and collective properties. Their ubiquitous application set has cross-cut energy conversion (photovoltaics, photocatalysis, thermoelectrics), en...

636 citations

Journal ArticleDOI
TL;DR: The field of multinary metal chalcogenide nanocrystals has gained strongly increasing interest in the quest for novel narrow band gap semiconductors as discussed by the authors, which can be classified according to the obtained crystal structure.
Abstract: We review the field of multinary metal chalcogenide nanocrystals, which has gained strongly increasing interest in the quest for novel narrow band gap semiconductors. Small (2–4 nm) CuInS2 and CuInSe2 nanocrystals, for example, exhibit size dependent luminescence in the visible and near infrared range. Their quantum yield can exceed 50% after growth of a ZnS shell, which makes them appealing emitters for lighting, displaying and biological imaging applications. Cu2ZnSnS4 (CZTS) nanocrystals, on the other hand, can be used as solution processed absorbing materials in thin film solar cells showing high power conversion efficiencies (currently around 8–10%). These examples illustrate that multinary metal chalcogenide nanocrystals have high potential for replacing classical cadmium and lead chalcogenide quantum dots in many fields. We give an overview of the chemical synthesis methods of the different systems reported to date, classifying them according to the obtained crystal structure. Next, we discuss their photophysical properties and give a brief description of the main fields of application. Finally, we conclude by outlining current challenges and related future directions of this exponentially growing domain.

553 citations

Journal ArticleDOI
TL;DR: This efficiency is the best performance to date for QDSCs and demonstrates that it is possible to obtain comparable or even better photovoltaic performance from green CIS QDs to the toxic cadmium and lead chalcogenides QDs.
Abstract: Semiconductor quantum dots (QDs) are extremely interesting materials for the development of photovoltaic devices, but currently the present the drawback is that the most efficient devices have been prepared with toxic heavy metals of Cd or Pb. Solar cells based on “green” QDs—totally free of Cd or Pb—present a modest efficiency of 2.52%. Herein we achieve effective surface passivation of the ternary CuInS2 (CIS) QDs that provides high photovoltaic quality core/shell CIS/ZnS (CIS-Z) QDs, leading to the development of high-efficiency green QD solar cells that surpass the performance of those based on the toxic cadmium and lead chalcogenides QDs. Using wide absorption range QDs, CIS-Z-based quantum dot sensitized solar cell (QDSC) configuration with high QD loading and with the benefit of the recombination reduction with type-I core/shell structure, we boost the power conversion efficiency of Cd- and Pb-free QDSC to a record of 7.04% (with certified efficiency of 6.66%) under AM 1.5G one sun irradiation. Thi...

540 citations