Symposium Organizers
Philipp Stadler, Johannes Kepler University Linz
Edward (Ted) Sargent, University of Toronto
Mykhailo Sytnyk, Friedrich-Alexander-Universität Erlangen-Nürnberg
Susanna Thon, Johns Hopkins University
Symposium Support
Lake Shore Cryotronics, Inc.
LOT, Quantum Design
ED6.1: Frontiers 1D and 2D Quantum Materials
Session Chairs
Philipp Stadler
Susanna Thon
Tuesday PM, April 18, 2017
PCC North, 100 Level, Room 132 C
11:30 AM - *ED6.1.01
Dimensionality Matters—Dimensionality Effects on Optoelectronic Behavior of Semiconductor Nanocrystals
Uri Banin 1
1 , Hebrew University of Jerusalem, Jerusalem Israel
Show AbstractStudying the transition of properties of nanostructures as they develop from the zero-dimensional to the one-dimensional regime is significant for unravelling the modifications that occur in the electronic structure of the particle as its length to width aspect ratio is increased. Such understanding can lead to better design and control of the particle properties, with relevance for a wide range of technological applications. The ongoing improvements in the control of shape and morphology of nanoparticles in colloidal synthesis, which allows forming structures of similar composition but of different dimensionalities and shapes, open the way for probing such dimensionality effects. We will present several effects involving the 0D to 1D transition in colloidal semiconductor nano heterostructures of different morphologies including “sphere in a sphere”, “sphere in a rod” and “rod in a rod”. We will also discuss the effect of rod composition on the opto-electronic properties. In addition, a recently discovered new architecture of “nanorod couples” will be introduced.
Both ensemble and single particle based measurements were used to decipher these effects providing complementary viewpoints. A first dimensionality related aspect involves the modification of emission and absorption polarizations, as the dimensionality of the particles and of their cores changes. The second aspect relates to the effects of rod comopsition on color tuning, polarization and fluorescence blinking. The high quality dot-in-rod heterostructures studied and developed here are of relevance to displays and additional optoelectronic applications.
12:00 PM - ED6.1.02
The Extension of Confined-Yet-Coupled Design to 2D Semiconductors
Tyler Farnsworth 1 , Adam Woomer 1 , Jonathan Thompson 1 , Scott Warren 1 2
1 Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States, 2 Department of Applied Physical Sciences, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States
Show AbstractThe ability to control the properties of a material based on its underlying building blocks is at the core of structure-property relationships within materials science. The quantum dot solid (QDS) community has revolutionized this concept through their confined-yet-coupled design, but the implementation of these design principles to other quantum-confined systems, namely 2D materials, remains an open question. Two-dimensional materials have an interesting point of comparison to colloidal nanocrystals based on their quantum-confined, size-dependent electronic structure. Research on 2D materials has expanded rapidly, with much progress in understanding charge transport and optical absorption of individual nanoflakes and, more recently, 2D heterostructures. Despite these advances, the number of studies that investigate the interactions between quantum-confined 2D flakes that are deposited in a thick film have remained limited. Understanding the extent to which quantum-confined properties are retained or lost when 2D flakes are stacked together will be crucial for their implementation as quantum-confined solids for photovoltaic and optoelectronic applications. In this work, we demonstrate the assembly of solution-processed 2D semiconductors into quantum-confined 3D architectures. Similar to QDS, we show that these films remain quantum-confined and exhibit tunable absorption profiles that are nearly identical to that of their 2D building blocks. Characterization of these films via rocking curve XRD and conductivity measurements help to (1) elucidate the influence of stacking order and flake orientation on the quantum-confined absorption properties of these 2D solids and (2) provide evidence for a quantum-confined, yet electronically-coupled material. Our work reveals an important extension of the confined-yet-coupled design of QDS to the field of 2D semiconductors; enabling new advances in the next generation of quantum-confined solid-state materials.
12:15 PM - ED6.1.03
Near-Infrared Emitting 2D Colloidal PbS Nanoplatelets with Lateral Size Control
Ali Hossain Khan 1 , Rosaria Brescia 1 , Anatolii Polovitsyn 1 , Ilaria Angeloni 1 , Beatriz Garcia 1 , Iwan Moreels 1
1 , Istituto Italiano di Tecnologia (IIT), Genova Italy
Show AbstractLead sulphide (PbS) is a key material for quantum dot (QD) based photodetectors,1 photovoltaics,2 NIR LEDs3 and thermoelectric devices.4 Spherical PbS QDs have been well developed, yet structures confined in one dimension (2D materials) offer additional benefits such as fast photoluminescence (PL) lifetimes and higher color purity (narrower FWHM).5 However, in contrast with 0D QDs, the development of fluorescent 2D PbS nanostructures is still in progress.6-8
In this work, we discuss the synthesis of thin PbS nanoplatelets (NPLs), using a single source precursor route that is performed at temperatures of only 80-90°C. Transmission electron microscopy (TEM) and optical spectroscopy were used to monitor the growth at the different stages of the reaction. The lateral size can be controlled from 48×3.5 nm2 to 83×21 nm2 by varying the growth time. The reaction temperature, precursor concentration and capping ligands are also critical to control the length and width further. The TEM and X-ray diffraction analysis reveals that the NPLs exhibit an orthorhombic crystal structure rather than the rocksalt structure reported for bulk PbS. High resolution TEM (HRTEM) analysis on vertically standing PbS NPLs reveals a thickness of ~1.8 nm, resulting in a strongly blue shifted absorption and emission spectrum. HRTEM also shows that the extended facets are {100} planes, with lateral {010} and {001} facets. The NPLs show typical characteristics of 1D-confined structures: the PL peaks are narrow, with a full width at half maximum (FWHM) of about 50-60 nm, and have a reduced Stokes shift of only 18 nm compared to 0D QDs (with a FWHM typically greater than 100 nm, and a Stokes shift of around 100-200 nm). A tunable PL from 735 nm to 748 nm was observed for different lateral extensions, with amplitude-weighted average emission rates of 10 ns to 60 ns, about two orders of magnitude faster than 0D PbS QDs. The narrow PL spectrum, a strongly reduced Stokes shift and significantly enhanced PL decay rates all make NIR emitting PbS NPLs promising building blocks for future solution-processed photonic and opto-electronic applications.
References:
1. R. Saran, and R. J. Curry, Nat. Photon. 10, 81 (2016).
2. G. H. Kim, et al. Nano Lett. 15, 7691 (2015).
3. G. J. Supran, et al. Adv. Mater. 27, 1437 (2015).
4. M. Ibanez, et al. J. Am. Chem. Soc. 137, 4046 (2015).
5. E. Lhuillier, et al. Acc. Chem. Res. 48, 22 (2015).
6. C. Schliehe, et al. Science 329, 550 (2010).
7. H. Zhang, et al. Chem. Mater. 28, 127 (2016).
8. S. Khan, et al. Chem. Mater. 28, 5342 (2016).
12:30 PM - ED6.1.04
Nonadiabatic Dynamics in Semiconductor Nanomaterials
Dmitri Kilin 1 2 , Dayton J. Vogel 1
1 , University of South Dakota, Vermillion, South Dakota, United States, 2 C&BC, North Dakota State University, Fargo, North Dakota, United States
Show AbstractWithin photovoltaics and optoelectronic applications, pathways of energy dissipation of the generated charges following photoexcitation are of great importance. These processes can highlight charge carrier lifetimes, energy states facilitating the relaxation, radiative emission, and non-radiative relaxation. The presented work is a computational look into the application of nonadiabatic dynamics, using Redfield formalism, in MAPbI3,1 Si QD,2 and polyoxotitante clusters3 to study electronic population probability among electronic states to predict charge collection efficiency. Electronic density of states, absorption spectra, and partial change localization, among others, provide valuable insight to the specific atomic species and molecular motions that contribute the observed physical properties of a material. Synthesis of nanostructures allows fine-tuning of electronic and optical properties, resulting from quantum size effects. The increased control of the material size can lead to increased efficiency within photovoltaic and water-splitting devices. Many methods for increasing quantum efficiencies (QE) within photovoltaic and optoelectronic processes have been developed such as material interfacing, modified device architecture, and physical constraints to the photoactive material. This processes applied to small bandgap semiconductor quantum dots (QD) has achieved QE over 1. Understanding electronic relaxation mechanisms and their corresponding timescales allow for a clearer picture into which relaxation processes are of greatest importance and can be harnessed for maximum efficiency.
1. Junkman, D.; Vogel, D. J.; Han, Y.; Kilin, D. S., Ab Initio Analysis of Charge Carrier Dynamics in Organic-Inorganic Lead Halide Perovskite Solar Cells. MRS Online Proceedings Library 2015, 1776, 19-29.
2. Brown, S. L. V., D. J.; Miller, J. B. ; Inerbaev, T. M.; Anthony, R. J. ; Kortshagen, U. R.; Kilin, D. S.; Hobbie, , Enhancing Silicon Nanocrystal Photoluminescence Through Temperature and Microstructure. J. Phys. Chem. C. 2016, 120 (33), 18909–18916.
3. Vogel, D. J.; Kilin, D. S., First-Principles Treatment of Photoluminescence in Semiconductors. Journal of Physical Chemistry C 2015, 119 (50), 27954-27964.
ED6.2: Chemical Strategies in Quantum Materials
Session Chairs
Uri Banin
Mykhailo Sytnyk
Tuesday PM, April 18, 2017
PCC North, 100 Level, Room 132 C
2:30 PM - *ED6.2.01
Chemical Strategies for Nanocrystal Devices—Designing the Core and the Surface
Yuanyuan Wang 1 , Igor Fedin 1 , Margaret Hudson 1 , Dmitri Talapin 1
1 , University of Chicago, Chicago, Illinois, United States
Show AbstractSolution-based techniques often introduce a lower cost alternative to traditional semiconductor technology and push the trade-offs between performance and cost for a number of important applications, including displays, photovoltaics and electronics, just to name a few. In this contribution we discuss and compare different synthetic strategies toward nanostructured inorganic semiconductors, focusing primarily on the parameters relevant to device performance. Along these lines, semiconductor quantum dots are explored as the functional elements in printable electronics, light emitting devices, photodetectors and solar cells. All the above applications rely on efficient charge and energy transport in nanocrystal arrays. We will discuss chemical approaches to control electronic transport, doping and recombination kinetics in nanocrystal arrays. By using optimized inorganic surface chemistries, we prepared solution-processed nanocrystalline solids exhibiting electron mobility above 300 cm2/Vs and demonstrated ultrathin solar cells with 13% power conversion efficiency. Most recently, we developed new families of inorganic ligands that enable robust direct optical patterning of various types of nanocrystalline solids including metals, semiconductors, and insulators. These findings show the potential of solution-based techniques for nanocrystal-based technologies and applications.
3:00 PM - *ED6.2.02
Designed Colloidal Synthesis, Assembly and Device Applications of Chalcogenide Nanostructures
Jiwoong Yang 1 2 , Moon Kee Choi 1 2 , Kunsu Park 1 2 , Sue In Chae 1 2 , In Chung 1 2 , Dae-Hyeong Kim 1 2 , Taeghwan Hyeon 1 2
1 School of Chemical and Biological Engineering, Seoul National University, Seoul Korea (the Republic of), 2 Center for Nanoparticle Research, Institute for Basic Science (IBS), Seoul Korea (the Republic of)
Show AbstractColloidal semiconductor nanostructures have been widely studied due to their unique properties that cannot be achieved by their bulk counterparts. In this presentation, our group’s recent studies on the colloidal synthesis, assembly, and applications of chalcogenide nanocrystals will be presented. We synthesized non-toxic quantum dots such as Mn2+:ZnS and Cu-In-Se for biomedical imaging1 and solar cell applications.2,3 We developed high-resolution intaglio transfer printing methods for QDs. Using this technique we fabricate wearable quantum dot light emitting didoes (QLEDs),4,5 which can be applied to various devices such as memory device arrays based on MoS2 nanosheets.6 In addition, our recent studies on the magic-sized CdSe nanoclusters will be discussed,7,8 which play key roles in the synthesis of 2-dimensional CdSe quantum nanostructures.9-12 Finally, our efforts on designing of Bi2Te3 nanomaterials for thermo-electric application will be highlighted.13
1. Nature Mater. 2013, 12, 359.
2. ACS Nano 2015, 9, 11286.
3. Phys. Chem. Chem. Phys. 2013, 15, 20517.
4. Nature Communications 2015, 6, 7149.
5. Adv. Mater. 2016, 28, 1176.
6. Adv. Mater. 2016, DOI: 10.1002/adma.201602391
7. J. Am. Chem. Soc. 2015, 137, 12776.
8. ACS Nano 2016, 10, 7135.
9. Nature Rev. Mater. 2016, 1, 16034.
10. Nature Mater. 2010, 9, 47.
11. Angew. Chem. Int. Ed. 2011, 50, 1363.
12. J. Am. Chem. Soc. 2006, 128, 5632.
13. J. Am. Chem. Soc. 2016.
3:30 PM - ED6.2.03
Nonthermal Plasma Synthesis of Free-Standing Core/Shell Quantum Dots
Katharine Hunter 1 , Jacob Held 1 , Andre Mkhoyan 1 , Uwe Kortshagen 1
1 , University of Minnesota, Minneapolis, Minnesota, United States
Show AbstractIn this work, we present an enabling approach to the synthesis of free-standing core/shell nanocrystals using an all gas-phase method in a low-pressure nonthermal plasma. This plasma approach allows for the generation and investigation of core/shell nanocrystals inaccessible through traditional solution-based processes. Through in-flight control of epitaxial shell thickness in the gas-phase, we demonstrate the ability to tune nanocrystal optoelectronic properties beyond size variation alone. This approach is tailored towards the incorporation of materials requiring high synthesis temperatures (e.g. group IV semiconductors – Si and Ge) in heterostructured quantum dots. Our plasma synthesis approach provides control over nanocrystal size and epitaxial shell thickness, allowing for bandgap modulation through band alignment and strain engineering. Specifically, we have demonstrated the synthesis of germanium nanocrystals with epitaxially grown silicon shells using a single-stage flow-through nonthermal plasma. The core/shell structure of these nanocrystals with minimal intermixing at the interface has been confirmed by electron microscopy. We find that the resulting core/shell system compressively strains the germanium core, due to the smaller lattice constant of silicon and minimal defect formation at the interface. Through this compressive strain we have demonstrated an ability to manipulate the band structure of the germanium core by controlling core and shell dimensions. In this case, the epitaxial silicon shell provides an additional degree of control over the core properties, while providing added stability against environmental degradation. This work has been motivated by the success of solution-phase core/shell growth, which has proven to be indispensable in the colloidal nanocrystal community as a means to improve optoelectronic properties of II-VI crystallites. Despite the technological importance of group IV semiconductors, core/shell quantum dot structures involving Si and Ge nanocrystals have yet to be deeply explored. In contrast to colloidal methods, this plasma process does not require the addition of insulating ligands and may allow for deliberate doping of nanocrystal core and/or shell, while minimizing chemical waste. K.I. Hunter acknowledges support by the National Science Foundation Graduate Research Fellowship Program under Grant No. 00039202. This work was supported primarily by the U.S. National Science Foundation through the University of Minnesota MRSEC under Award Number DMR-1420013. Parts of this work were carried out in the Characterization Facility, University of Minnesota, which receives partial support from NSF through the MRSEC program.
3:45 PM - ED6.2.04
Colloidal III-V Nanocrystals—New Syntheses and Defect Annealing Strategies
Vishwas Srivastava 1 , Eric Janke 1 , Dmitri Talapin 1
1 , University of Chicago, Chicago, Illinois, United States
Show AbstractIII-V semiconductors form a major class of materials for optoelectronic and photovoltaic devices. Colloidal synthesis of III-V nanocrystals has made significant progress in recent years, especially for InP NCs. However other III-V materials remain largely under-explored. One of the major reasons that limits the development of efficient synthetic protocols, specifically for arsenide based semiconductor nanocrystals like InAs and GaAs, is the unavailability of suitable precursors. We report on the development of new synthetic strategies for colloidal InAs and GaAs nanocrystals. We show a facile and size tunable synthetic route to produce InAs nanocrystals from commercially available precursors. The as-synthesized InAs nanocrystals show size dependent excitonic features in their absorption spectrum and band-edge photoluminesce. For the case of GaAs nanocrystals, their anomalous optical properties are explored in detail and understood through detailed structural characterization. This work sheds light on the role of structural defects in determining the optical properties of covalent semiconductors like GaAs. We also show a novel approach to alleviate these structural defects and show the effect of quantum confinemnent in GaAs crystals.
ED6.3: Quantum Photovoltaics
Session Chairs
Philipp Stadler
Dmitri Talapin
Tuesday PM, April 18, 2017
PCC North, 100 Level, Room 132 C
4:30 PM - *ED6.3.01
PbS QD Solar Cells—The Open Circuit Voltage Problem
Maria Antonietta Loi 1
1 , University of Groningen, Groningen Netherlands
Show AbstractLead sulfide quantum dots (PbS QDs) have been the topic of intense study for over a decade due to their excellent optoelectronic properties and their large versatility in applications such as infrared sensors, infrared photon sources, and solar cells.
PbS QD solar cells in particular have seen a rapid rise in solar cell performance, from less than 1% in 2005 to about 11% in 2016. This progress has been made possible by several factors including: improvements in the synthesis of the QDs, improvements in the post deposition passivation, and optimised device structures. To further improve solar cell efficiencies, the prevailing limitations must be understood and addressed. Between them, the open circuit voltage (VOC) in particular falls well short of it theoretical maximum and must be improved if PbS QD solar cells are to become a viable technology.
In this presentation I will report about the temperature dependent behavior of highly efficient solar cells comprising a layer of TBAI- and a layer of EDT-capped PbS. A large increase in device performance at lower temperatures, with efficiency going from about 9 % to above 10%, mainly due to an increased VOC with only slightly decreasing short circuit current (JSC) is observed.
The VOC is found to be governed solely by the reverse saturation current, which can be explained using the Shockley PN-junction model. Based on this model, increasing the doping levels in the PN-junction structure is a promising method for increasing the VOC in future QDs based solar cells. Specifically, the doping concentration of the p-type layer should be at least 1 order of magnitude higher than the n-type layer for a favorable depletion width distribution.
5:00 PM - ED6.3.02
Highly-Efficient, Air-Stable, Blade-Coated Colloidal Quantum Dot Photovoltaics Fabricated under High Humidity Conditions
Ahmad Kirmani 1 , Arif Sheikh 1 , Muhammad Niazi 1 , Mengxia Liu 2 , Edward (Ted) Sargent 2 , Aram Amassian 1
1 , King Abdullah University of Science and Technology (KAUST), Thuwal Saudi Arabia, 2 , University of Toronto, Toronto, Ontario, Canada
Show AbstractDespite the spectacular rise of colloidal quantum dot (CQD) photovoltaics over the past few years, successful roll-to-roll compatible fabrication of CQD solar cells (SCs) under realistic, high humidity conditions has remained a challenge. Here, we deploy the latest,[1] high-performing hybrid organic-inorganic CQD inks to fabricate SCs in a facile, single-step employing blade coating under realistic conditions of relative humidity >50%, at industrially viable coating speeds of >5.0 m min-1. Exposing these as-prepared ca. 5% power conversion efficiency (PCE) SCs to dry air leads to oxygen doping of the CQD hole transporting layer (HTL). This effectively tunes band alignment at the hole collecting junction, improves charge collection and leads to 9.3% PCE solar cells with excellent dry air-stability over several months. This simple oxygen doping recipe also allows us to demonstrate high performing (6.5%) flexible CQD SCs showcasing outstanding bending durability. These findings, for the first time, successfully demonstrate the humidity-resilience of high-performance CQD PV fabrication and are a major milestone towards reliable, roll-to-roll manufacturable CQD optoelectronics under realistic environmental conditions.
[1]. Liu, M., et al, Nat. Mater., 2016, in press
5:15 PM - ED6.3.03
Lead Sulfide Quantum Dot Ink Solar Cells via Spray Deposition
Hyekyoung Choi 1 , Sohee Jeong 1
1 , Korea Institute of Machinery and Materials, Daejeon Korea (the Republic of)
Show AbstractLead chalcogenide (PbE, X=S, Se, Te) quantum dots (QDs) are promising materials for next-generation photovoltaics because of their tunable bandgaps from visible to near-infrared (NIR) wavelength range. For QD-based photovoltaics, the ligand exchange of long chain organic ligands with short ligands should be needed for the conductive films. Typically, spin coating and dip coating with layer-by-layer processing have been used in recent years for photovoltaics but these methods have suffered from a large amount of loss of the QD solution and formation of cracks and voids. Here, we report the first use of spray coating to deposit conductive films with conductive PbS QD inks. The PbS QD inks synthesized with a solution-state ligand exchange reaction, stabilized with methyl ammonium lead iodide (MAPbI3), which are colloidal stable in ambient air condition over 4 weeks due to the formation of electrical double layer. The PbS QD ink photovoltaics via spray deposition enable the economic and controllable deposition techniques, leading to a solar cell power conversion efficiency of 3.7%.
5:30 PM - ED6.3.04
Investigation of ZnO/PbS Nanocrystal Interfaces for Photonic Device Applications
Diogenes Placencia 1 , Ian Sellers 2 , Janice Boercker 1 , Paul Lee 3 , Joseph Tischler 1
1 , Naval Research Laboratory, Washington, District of Columbia, United States, 2 Physics and Astronomy, University of Oklahoma, Norman, Oklahoma, United States, 3 Chemistry & Biochemistry Department, University of Arizona, Tucson, Arizona, United States
Show AbstractResearch into lead sulfide (PbS) nanocrystal devices has garnered much attention recently due to their notable performance as photovoltaic devices and short wave infrared photodetectors, among other applications.1,2 Common within such devices is the use of metal oxide thin-films (e.g., ZnO, ITO, NiO, etc.) that act as charge-selective contacts. Therefore, characterization of the interfacial properties between metal oxides and PbS nanocrystals is crucial to the overall development of these technologies. In this contribution, we present our investigations into the properties that dominate operational efficiency of the ZnO/PbS heterojunction. Through a series of varying oxide pre-treatments (e.g., plasma cleaning and small-molecule surface modifications), we investigate how the state of the surface affects band-edge offsets (via Ultraviolet Photoemission Spectroscopy), changes in the surface chemistry at the interface (through X-ray Photoemission Spectroscopy), and overall structural changes (utilizing Scanning Probe Microscopy). Additionally, we provide insight into how these pre-treatments affect overall device performance in the standard inverted device geometry.
[1] E. H. Sargent, Chem. Rev. 115, 12732(2015).
[2] R. J. Curry, Nat. Photonics 10, 81(2016).
5:45 PM - ED6.3.05
Development of Balanced Charge Transfer in Efficient Eco-Friendly Quantum Dot Sensitized Solar Cells
Muhammad Sajjad 1 , Jinhyung Park 2 , Dmitry Aldakov 2 , Ashu Bansal 1 , Arvydas Ruseckas 1 , Peter Reiss 2 , Ifor Samuel 1
1 , University of St Andrews, St Andrews United Kingdom, 2 , CEA, INAC-SPRAM, Grenoble France
Show AbstractQuantum dots (QDs) are very attractive materials and have been used for biological labelling, light-emitting diodes and photovoltaic devices due to their high absorption coefficients, size dependence and easy tunability of their optical and electronic properties due to quantum confinement. Furthermore, semiconductor QDs offer the possibility of multiple exciton generation,1 which could allow them to overcome the Shockley−Queisser limit in solar cells.2 Power conversion efficiency of more than 8% was achieved with QD based solar cells3 and are widely considered as a viable alternative to silicon and inorganic thin film based cells.4 However, typically colloidal quantum dots used for solar cells contain toxic heavy metals (Cd or Pb), which limits their industrial applications. So it is very important to explore alternative non-toxic materials, such as CuInS2 derivatives. In our study we used “eco-friendly” quantum dots (CuInS2 and CuInSxSe2-x) along with either n-type (TiO2 or ZnO) or p-type electrodes (NiO or CuScN nanowires) for solar cell fabrication.
One of main barriers which limits the efficiency of QD sensitized solar cells is efficient charge transfer at interface. In the classical QD sensitized solar cells the light is absorbed by the QDs, which then inject electrons into an n-type material (TiO2 or ZnO), while the hole is regenerated by the liquid electrolyte.5 The main limiting step in such cells is hole transfer, which occurs slower and less efficiently than electron transfer. One way to overcome this is to invert the configuration of the cell to benefit from photoinduced hole injection from the QDs into a p-type material (NiO or CuScN nanowires). We found that hole injection rate (108 s-1) improves significantly in inverted configuration and becomes comparable to electron injection rate in conventional n-type QD based solar cells. Furthermore this hole transfer rate becomes an order of magnitude higher for the case of CuInSxSe2-x compared to CuInS2 when we used them with NiO. After optimization of electron and hole transfer separately, we measured combined charge transfer in the presence of both n- and p-type material and found that charge recombination is main factor which limits the power conversion efficiency of devices. To overcome charge recombination, we introduced Al2O3 nanoparticle layer which improves charge transfer rates by 50%. Inverted solar cells fabricated with various QDs demonstrate excellent power conversion efficiencies which is 4 times higher than the best values for previous inverted QD sensitized cells.6
1 A. J. Nozik, et al., Chem. Rev., 2010, 110, 6873–90.
2 J. B. Sambur, et al.,, Science, 2010, 330, 63–6.
3 K. Zhao, et al., J. Am. Chem. Soc., 2015, 137, 5602–5609.
4 P. V Kamat, J. Phys. Chem. Lett., 2013, 4, 908–918.
5 D. Aldakov , et al., J. Mater. Chem. A 2015, 3, 19050
6 J. Park, et al., J. Mater. Chem. A, 2016, 4, 827-837
ED6.4: Poster Session I: Quantum Materials for Optoelectronic Devices
Session Chairs
Mykhailo Sytnyk
Susanna Thon
Wednesday AM, April 19, 2017
Sheraton, Third Level, Phoenix Ballroom
9:00 PM - ED6.4.01
Enhancing the Color Rendering Index for White LED Lighting Using Quantum Dot Resins
Min-Sang Lee 1 , Kwang-Yeal Lee 2 , Hyo-Jung Kim 2 , Da-Hye Lim 3 , Yeon-Su Kang 3 , Jong-Soo Lee 3
1 , Nanoqnt Co.,Ltd., Daegu Korea (the Republic of), 2 , Ecolumy, Daegu Korea (the Republic of), 3 Energy Systems Engineering, DGIST, Daegu Korea (the Republic of)
Show AbstractLED lighting market is expected to grow over a compound annual growth rate(CAGR) of 25%, recessed modular will emerge the largest LED luminaire market by replacing incumbents such as fluorescent. This trend is accelerating the adoption of emerging technologies, such as alternating current LEDs and high-color rendering index LEDs in recessed modular, high-bay and roadway luminaires, Semiconductor quantum dots (QDs) with high quantum yield can be used to turn the quality of white LED lighting, which can be evaluated by color temperature and color rendering index. In this work, we present the controlled colloidal synthesis of core-shell quantum dots, and uniformly dispersing quantum dots in a transparent resin. Quantum dot resins with tunable multi-emission color were applied on white LED lighting and it showed color rendering index (CRI) of 94 or more as compared to a 5000~5500 K blackbody reference.
9:00 PM - ED6.4.02
Solution-Processed Quantum Dot Light Emitting Diode Prepared with EHD-Jet Printing
Kyung-Hyung Lee 1 , Namhun Baek 1 , Woon-Seop Choi 1
1 , Hoseo University, Asan Korea (the Republic of)
Show AbstractIn recent years, colloidal quantum-dots based light-emitting diodes (QD-LEDs) have been considered as the attractive display device because of remarkable electrical/optical characteristics of colloidal quantum dots. QD-LEDs are of particular interest due to their wide-range color tunability, high brightness and good color purity by narrow emission bandwidth. Challenges remain, however, in achieving the necessary multilayer device structures using printing. In this study, quantum dots and silver electrode as a cathode were printed by electrohydrodynamic jet printer and were applied to all solution-processed QD-LED (quantum dot light-emitting diodes). The J-V-L characteristic of the QD-LED with silver cathode (work function, 4.26-4.74) was compared with the QD-LED with an evaporated aluminum cathode (work function, 4.06-4.26). The QDs as the emitting layer was also printed by EHD-Jet, and ZnO NPs and TiO2, as the carrier transporting layers were synthesized using solution mediated process. The optimized QD-LED device showed a luminance of 5,710 cd/m2, current efficiency of 1.75 cd/A, and EQE of 1.51 %.
9:00 PM - ED6.4.03
The Mechanism of Energy Transfer and Parameters Affecting the Upconversion in a Hybrid Molecule-Nanocrystal System
Melika Mahboub 1 , Hadi Maghsoudi 1 , Andrew Pham 2 , Narek Megerdich 3 , Zhiyuan Huang 2 , MingLee Tang 1 2
1 Materials Science and Engineering, University of California, Riverside, Riverside, California, United States, 2 Chemical Science, University of California, Riverside, Riverside, California, United States, 3 Chemical Engineering, University of California, Riverside, Riverside, California, United States
Show AbstractOur recently introduced hybrid-upconversion system that utilizes both colloidal synthesized NCs and organic molecules has gained a lot of attention due to NCs band gap tunability, low excitation power and great photostability.1 Here we study the mechanism of energy transfer as well as the parameters affecting the upconversion QY such as NC size, NC core and shell composition, shell thickness, and ligand exchange conditions. We analyze the mechanism of energy transfer from NCs to rubrene with both steady-state and time-resolved experiments. To investigate the mechanism of energy transfer, we varying the inorganic shell thickness (CdS) as well as the aliphatic chain length (replacing the original ligand with carboxylic acid molecules that have 6 different alkane chain lengths (CnH2n+1 COOH, n= 3, 7, 9, 11, 13, 15)). We discovered that Dexter energy transfer from NCs to rubrene prevails. The damping coefficient, β, of an inorganic shell for the first time were calculated to be 3.4± 0. 1 Å−1. We believe an understanding of the mechanism and parameters affecting upconversion QY will facilitate the design and engineering of an efficient NIR upconversion system.
Reference:
1. Huang, Z.; Li, X.; Mahboub, M.; Hanson, K. M.; Nichols, V. M.; Le, H.; Tang, M. L.; Bardeen, C. J., Hybrid Molecule–Nanocrystal Photon Upconversion Across the Visible and Near-Infrared. Nano Letters 2015, 15 (8), 5552-5557.
9:00 PM - ED6.4.04
Temperature-Dependent Photoluminescence of Cesium Lead Halide Perovskite Quantum Dots
Jiwon Bang 1 , See Mak Lee 1 , Cheol Joo Moon 2 , Myong Yong Choi 2
1 , Korea Institute of Ceramic Engineering and Technology, Jinju Korea (the Republic of), 2 Department of Chemistry (BK21+) and Research Institute of Natural Science, Gyeongsang National University, Jinju Korea (the Republic of)
Show AbstractColloidal synthesis routes to all-inorganic cesium lead halide perovskite quantum dots (QDs) exhibited outstanding optical properties such as bright photoluminescence (PL) and narrow PL bandwidth. The all-inorganic perovskite QDs attract great interest to become a new class of fluorophores in display. However, the exciton behavior of the perovskite QDs are still investigated and not fully understood. The temperature dependence of PL properties can provide insight into the exciton relaxation processes and exciton-phonon coupling. We studied temperature dependent PL properties, e.g., PL intensity change, spectral shift of PL and PL broadening, of the CsPbBr3, CsPb(Br/I)3, and CsPbI3 QD samples. As the Temperature was increased from 20 to 290 K, the PL intensity decreased and the PL emission peak blue-shifted due to the thermally decomposition of excitons and lattice deformations. The CsPbBr3 QD PL bandwidth was monotonic increased as temperature increased, while the PL bandwidth of CsPb(Br/I)3 alloyed QD sample showed quite insensitive to temperature. We have also observed two exciton peaks in the CsPbBr3 QD sample when the temperature is lower than 250K. This phenomenon might be originated from the generation of the new optical allowed transition state inside the energy band gap at low temperature. Our experimental results can provide useful insight into the exciton properties of cesium lead halide perovskite QDs, which promote their future applications in optoelectronic materials and devices.
9:00 PM - ED6.4.05
Synthesis of Manganese-Doped Zinc Oxide Quantum Dots
Ozlem Yildirim 2 , Caner Durucan 1
2 , Selçuk University, Konya Turkey, 1 , METU, ANKARA Turkey
Show AbstractSynthesis of manganese-doped zinc oxide (ZnO:Mn) diluted magnetic semiconductor quantum dots is reported. The synthesis was carried out by room temperature precipitation method using zinc acetate and manganese acetate as precursors and ethylene glycol as solvent. Analytical characterization was performed by x-ray diffraction (XRD) and transmission electron microscopy (TEM). The lattice parameters of ZnO:Mn quantum dots-as estimated from the XRD analyses-slightly increased compared to those of undoped ZnO. This suggests substitutional incorporation of Mn into ZnO lattice. TEM examinations revealed single crystalline ZnO:Mn quantum dots with an average particle size smaller than 3 nm.
9:00 PM - ED6.4.06
Fabrication of Blue, Green and Red Nanorod Light-Emitting Diodes as Planar-Surface Light Sources
Yun Jae Eo 1 , Gang Yeol Yoo 2 , Chan Sik Kim 1 , Hye Lim Kang 1 , Heejoon Kang 1 , Minji Koh 1 , Heeyeon Yoo 1 , Woong Kim 2 , Young Rag Do 1
1 , Kookmin University, Seoul Korea (the Republic of), 2 , Korea University, Seoul Korea (the Republic of)
Show AbstractIn this study, we fabricated nanorod arrays on an epi-wafer with a GaN- or GaAs-based light-emitting diode (LED) structure using polystyrene (PS) nanosphere lithography. Additionally, we manufactured ink which is contained in individually separated nanorod LEDs in the nanorod array and produced nanorod LED devices on pre-patterned electrodes using the nanorod LED dispersed ink by an electric field-assisted assembly method known as dielectrophoresis. These large-area (0.7 cm x 0.6 cm) surface LED devices can emit blue (B), green (G), or red (R) light depending on the epi-wafer used. The assembled B, G, or R LED devices underwent a post-treatment process of thermal annealing to improve the interconnections between the nanorod LEDs and the electrodes. As a result, the optical performance capabilities of the LED devices, specifically the luminance levels, were greatly increased. Hence, the devices produced as a result of this study have the potential to be used in planar-surface emitting applications such as displays and lightings.
9:00 PM - ED6.4.07
Optical Polarization in c-Plane Al-Rich AlN/AlxGa1-xN Quantum Wells
Talal Al Tahtamouni 1 , Jingyu Lin 2 , Hongxing Jiang 2
1 , Qatar University, Doha Qatar, 2 , Texas Tech University, Lubbock, Texas, United States
Show AbstractIn this work, we report on the systematic investigation of the optical polarization anisotropy in AlN/Al0.65Ga0.35N single quantum wells (QWs) grown on c-plane sapphire substrates using low temperature deep ultraviolet photoluminescence (PL) emission spectroscopy. We demonstrate that the polarization of the light in these QWs can be switched from transverse magnetic (TM) to transverse electric (TE) by decreasing well width (Lw), which means that the TE polarization of the emission can be achieved at wavelengths as short as 220 nm. It is found that the predominant polarization switched from E ∥ c to E ⊥ c at Lw ~ 2 nm. The emissions from QWs thicker than 2 nm show E ∥ c polarization, whereas that of QWs thinner than 2 nm show E ⊥ c polarization. This indicated that the topmost valence band changed from split-off-hole band to heavy-hole band with decreasing well width. The degree of polarization decreases with increasing well width. Furthermore, the emission intensity with polarization of E ⊥ c decreases with increasing well width, meanwhile, the emission intensity with polarization of E ∥ c increases with increasing well width. As will be discussed, these findings will serve as a guideline for designing optimal deep UV light emitter structures.
9:00 PM - ED6.4.08
Surface Chemistry and Doping of Colloidal Perovskite Nanocrystals
Weon-kyu Koh 1 , Sungjun Park 1 , Hyojin Kim 2 , Eunji Shim 2
1 , Samsung Advanced Institute of Technology, Suwon Korea (the Republic of), 2 , Yonsei University, Seoul Korea (the Republic of)
Show AbstractColloidal perovskite nanocrystals (NCs) show promising and unique optoelectronic properties, which is quite different from conventional colloidal semiconductor NCs. There are lots of advantages for their photonic applications, but the practical applications are still far from reality due to their notable degradation under ambient condition. There are a few approaches to improve instability of bulk perovskites as well as their device performance, although the instability of perovskite NCs is still hard to solve due to more complicated nature of their surface and ligand chemistry. We demonstrate improved stability of colloidal perovskite NCs by designing their surface ligands, confirmed by steady-state spectroscopy and ultrafast spectroscopy, mass spectrometry, and other analytic measurements. On top of that, we show density functional theory (DFT) calculations for the surface chemistry and doping properties of colloidal perovskite NCs, which connects experimental observations to the theoretical understanding of this new type of nanoscale materials.
- Reference: ChemistrySelect 1 (13), 3479-3482
9:00 PM - ED6.4.09
Synthesis and Characterization of Quantum Confined Semiconductor Nanomaterials for Advanced Spin-/Opto-Electronics
Jiwoong Yang 1 2 , Moon Kee Choi 1 2 , Taeghwan Hyeon 1 2
1 Center for Nanoparticle Research, Institute for Basic Science, Seoul Korea (the Republic of), 2 School of Chemical and Biological Engineering, Seoul National University, Seoul Korea (the Republic of)
Show AbstractSemiconductor nanomaterials under quantum confinement exhibit unique magnetic, optical, and electronic properties which cannot be achieved by their bulk counterparts. This leads to a great level of attraction for the research for advanced spin-/opto-electronics using quantum dots (QDs). Here, our recent achievements on synthesis and characterization of semiconductor quantum nanostructures for spin-/opto-electronics will be presented. First, magnetically doped magic-sized CdSe clusters, which can be cartegorized as the ultra-small diluted magnetic semiconductors, will be discussed.[1-4] Owing to extremly strong quantum confinement, the doped clusters exhibit multiple excitonic states with different magneto-optical activities. Furthermore, these clusters show solotronic behaviors because of the high effective doping concentration even with a single dopant and antiferromagnetic couplings in bidoped species. Second, our recent studies on advanced optoelectonic devices (including solar cells[5,6] and light-emitting diodes[7,8]) using quantum dots will be described. Efficient heavy-metal-free quantum dot solar cells could be obtained by band alignment and surface engineering of Cu-In-Se QDs. In addition, wearable quantum dot arrays were demonstrated using high-resolution QD printing techniques.
References
[1] Jisoo Lee*, Jiwoong Yang* et al. Nature Reviews Materials 2016, 1, 16034. (*co-first author)
[2] Jiwoong Yang et al. Journal of the American Chemical Society 2015, 137, 12776.
[3] Franziska Muckel*, Jiwoong Yang*, et al. ACS Nano 2016, 10, 7135. (*co-first author)
[4] Jiwoong Yang et al. Chemistry of Materials 2013, 25, 1190.
[5] Jae-Yup Kim*, Jiwoong Yang* et al. ACS Nano 2015, 9, 11286. (*co-first author)
[6] Jiwoong Yang et al. Physical Chemistry Chemical Physics 2013, 15, 20517.
[7] Moon Kee Choi*, Jiwoong Yang* et al. Nature Communications 2015, 6, 7149. (*co-first author)
[8] Jiwoong Yang et al. Advanced Materials 2016, 28, 1176.
9:00 PM - ED6.4.10
Raman Spectroscopy of Multi-Stacked Tandem Quantum Nanostructures
Krit Kongulai 1 , Chonlatit Songchumsai 1 , Supachok Thainoi 1 , Aniwat Tandaechanurat 2 , Suwit Kiravittaya 3 , Noppadon Nuntawong 4 , Suwat Sopitopan 5 , Songphol Kanjanachuchai 1 , Somchai Ratanathammaphan 1 , Somsak Panyakeow 1
1 , Chulalongkorn University, Bangkok Thailand, 2 , International School of Engineering, Faculty of Engineering, Chulalongkorn University, Pathumwan, Bangkok, Thailand, 3 Department of Electrical and Computer Engineering, Faculty of Engineering, Naresuan University, Phitsanulok, Phitsanulok, Thailand, 4 , National Electronic and Computer Center (NECTEC), National Science and Technology Development Agency, Patumthani, Patumthani, Thailand, 5 , Thailand Microelectronic Center (TMEC), National Science and Technology Development Agency, Chachoengsao, Chachoengsao, Thailand
Show AbstractTandem-cell structures have been expected to improve efficiency of solar photovoltaic cells owing to their vertically stacking cells with different solar-energy harvesting bandgaps. By embedding quantum dot nanostructures in a bulk semiconductor, a variety of quantum dot bandgaps can be tuned to harvest solar energy that are typically not absorbed by the bulk material, in particular that in the infrared region, resulting in the creation of additional electric current. Furthermore, GaSb quantum dots in a GaAs matrix and InSb quantum dots in a GaAs matrix are of great interest for photovoltaic applications due to their unique type-II quantum structure characteristics, including having long carrier life times and low bandgap energies. In this work, multi-stacked tandem quantum nanostructure samples with InAs, GaSb and InSb quantum dots in a GaAs matrix, which is a combination of type-I and type-II quantum dots, grown on GaAs substrate are prepared by molecular beam epitaxy. All nanostructures are in situ fabricated by strain relaxation mechanism. Raman spectroscopy is used to study the strain characteristics of these tandem structure samples. Raman shift of LO and TO GaAs peaks as well as the peaks related to the embedded nanostructure materials are observed. We then probe the Raman spectra usingdifferent excitation laser wavelengths, i.e. 473, 532, 633, and 785 nm. As the excitation laser with longer wavelength penetrates deeper into the sample, we qualitatively depict the evolution of strain along the sample growth direction.
9:00 PM - ED6.4.11
Growth Control of Twin InSb/GaAs Nano-Stripes by Molecular Beam Epitaxy
Jirayu Supasil 1 , Phisut Narabadeesuphakorn 1 , Supachok Thainoi 1 , Aniwat Tandaechanurat 2 , Suwit Kiravittaya 3 , Noppadon Nuntawong 4 , Suwat Sopitopan 5 , Songphol Kanjanachuchai 1 , Somchai Ratanathammaphan 1 , Somsak Panyakeow 1
1 , Chulalongkorn University, Bangkok Thailand, 2 , International School of Engineering (ISE), Faculty of Engineering, Chulalongkorn University, Pathumwan, Bangkok, Thailand, 3 , Department of Electrical and Computer Engineering, Faculty of Engineering, Naresuan University, Phitsanulok, Phitsanulok, Thailand, 4 , National Electronic and Computer Center (NECTEC), National Science and Technology Development Agency, Patumthani, Patumthani, Thailand, 5 , Thailand Microelectronic Center (TMEC), National Science and Technology Development Agency, Chachoengsao, Chachoengsao, Thailand
Show AbstractInSb has been considered promising for spintronic applications owing to its pronounced spin effects as a result of large intrinsic electronic g-factor [1,2]. In addition, embedding InSb quantum nanostructures in a GaAs matrix could create type-II band alignment, where radiation lifetimes are longer than those of the typical type-I systems. Such characteristics are promising for memory devices and IR photonic applications. The growth of InSb/GaAs quantum nanostructures by strain driven mechanism using molecular beam epitaxy with low growth temperature, slow growth rate, Sb soaking process prior to In deposition, and small amount of In deposition typically creates a mixture of twin and single nano-stripe structures with truncated pyramid shape [3]. In this work, we further investigate the growth mechanism of such twin InSb/GaAs nano-stripes by controlling the growth conditions, consisting of nanostructure growth duration and growth temperature. When the growth temperature is kept to less than 300°C and In deposition is set to only a few monolayers, we found that 25-40% of formed nanostructures are twin InSb/GaAs nano-stripes [3]. However, when the In deposition is stopped immediately after the spotty RHEED patterns are observed, the ratio of twin nano-stripes to single ones is increased to 80-90%. We therefore describe the growth mechanism of twin nano-stripes as the early state of single nano-stripe formation, where the twin nano-stripes are initially formed during the first monolayer of InSb formation as a result of large lattice mismatch of 14.6%. When In deposition is increased to a few monolayers, the gap between twin nano-stripes is filled up and consequently forms the single nano-stripes instead. With this particular twin nano-stripe growth mechanism, the preservation of high ratio of twin nano-stripe formation can be expected by further reducing the growth temperature, i.e. less than 260°C. These twin nano-stripes may find applications in the fields of spintronics and novel interference nano-devices.
References
[1] C. R. Pidgeon et. al., Phys. Rev. 154, 737 (1967).
[2] Y. V. Terent'ev et. al., Phys. Rev. B 87, 045315 (2013).
[3] S. Kiravittaya et. al., ICPS 2016, Mo-P.029 (2016).
9:00 PM - ED6.4.12
Quasi-1D Effects in Conducting and Conjugated Polymers
Philipp Stadler 1 , Dominik Farka 1 2 , Halime Coskun 1 , Christoph Cobet 2 , Kurt Hingerl 2 , Serdar Sariciftci 1
1 Institute of Physical Chemistry, Johannes Kepler University Linz, Linz Austria, 2 Center for Surface- and Nanoanalytics, Johannes Kepler University Linz, Linz Austria
Show AbstractThe 1-dimension delocalization in conjugated polymers drives various interesting optoelectronic effects on the free-carrier dynamics. In particular it is the anisotropy that causes a strong electron-phonon coupling of free carriers along the polymer chains. The accompanied vibronic energy dissipation emerges as a shift of the free-carrier absorption. This leads to an unique material class offering high conductivity and high transparency spanning the UV-visible and mid-infrared spectral region.
Our studies take an in-depth view to the delocalization character of various conjugated and conductive polymers, in particular on their corrensponding free carrier transport dynamics. We use spectroscopic ellipsometry in combination with magneto-transport to point at the origin of the anisotropic delocalization and the advantages and potential of this materials class in optoelectronic applications as powerful, next-generation transparent conductors.1,2
(1) Stadler, P.; Farka, D.; Coskun, H.; Glowacki, E. D.; Yumusak, C.; Uiberlacker, L. M.; Hild, S.; Leonat, L. N.; Scharber, M. C.; Klapetek, P.; Menon, R.; Sariciftci, N. S. Local Order Drives the Metallic State in PEDOT:PSS. J. Mater. Chem. C 2016, 4 (29), 6982–6987.
(2) Cobet, C.; Gasiorowski, J.; Menon, R.; Hingerl, K.; Schlager, S.; White, M. S.; Neugebauer, H.; Sariciftci, N. S.; Stadler, P. Influence of Molecular Designs on Polaronic and Vibrational Transitions in a Conjugated Push-Pull Copolymer. Sci. Rep. 2016, 6, 35096.
9:00 PM - ED6.4.13
Molecular Beam Epitaxy Growth of CuInSe2 Quantum Dots
Kamal Abderrafi 1 2 , Rodrigo Ribeiro-Andrade 1 , Nicoleta Nicoara 1 2 , Maria Guimaraes Cerqueira 1 , Henrique Limborco 3 , Pedro Salome 1 , Juan Gonzalez 3 , Jorge Garcia 2 , Fernando Briones 2 , Sascha Sadewasser 1
1 , International Iberian Nanotechnology Laboratory, Braga Portugal, 2 , IMM-Instituto de Microelectrónica de Madrid (CNM-CSIC), Madrid Spain, 3 , Universidade Federal de Minas Gerais, Belo Horizonte Brazil
Show AbstractPrevious attempts to implement III-V quantum dots (QDs) by MBE in photovoltaic (PV) devices have been reasonably successful and adequate to study the involved physics [1]; Considering that the absorption coefficient of Cu(In,Ga)Se2 is about one order of magnitude larger than that of III-V semiconductors, the fabrication of chalcopyrite-type QDs and the exploration of their potential for PV applications is highly desirable and promising. The conversion efficiency potential of these approaches is significantly higher than that of current single pn-junction technologies and reaches up to 67% [2].
In this contribution we explore the possibility of growing chalcopyrite CuInSe2 (CISe) quantum dots and characterize their structural properties. CISe quantum dots were grown on GaAs(111) substrates using a molecular beam epitaxy system where the elemental constituents Cu, In, and Se are evaporated from elemental sources at low evaporation rates of 0.4 Å/s. The overall composition of CISe is slightly off stoichiometry ([Cu]/[In] = 0.7-0.75 ) in order to avoid the formation of Cu-Se binary alloys. The formation of CISe QDs is controlled in-situ by reflection high energy electron diffraction (RHEED). Characterization by atomic force microscopy shows that the QDs have a pyramidal shape with a size range from 5 to 8nm in height. Analysis by high-resolution transmission electron microscopy (HR-TEM) shows the successful growth of CISe tetrahedral chalcopyrite QDs and proves the epitaxial relation between substrate and QDs. Raman spectroscopy confirms single phase CuInSe2. Reciprocal space mapping under grazing incidence geometry reveals the local tetragonal distortion of CuInSe2 islands grown on GaAs(111). This method is in principle capable of determining the complete three-dimensional strain and chemical status of any island-substrate system.
References
A.Luquel, A. Martí, C.R. Stanley et al., Nature Photonics. 16, 146 (2012).
A.J. Nozik, Nano Lett. 10, 2735 (2010).
9:00 PM - ED6.4.14
High Performance IR Photo-Detectors Based on PbS Nanocrystals with Epitaxialy Coherent 0D Perovskite Clusters Ligand Shell
Mykhailo Sytnyk 1 , Sergii Yakunin 2 , Rainer Lechner 3 , Dominik Kriegner 2 , Heiko Groiss 2 , Wolfgang Heiss 1 2
1 Department of Materials Science and Engineering, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen Germany, 2 Institute of Semiconductor and Solid State Physics, Johannes Kepler University Linz, Linz Austria, 3 Institute of Physics, Montanuniversitaet Leoben, Leoben Austria
Show AbstractLead sulfide colloidal nanocrystals are attractive candidates for next generation infrared photodetectors and solar cells. To obtain sufficient charge transport in PbS nanocrystal films enabling device applications, the nanocrystals (NCs) organic ligand shells have to be exchanged.1 Since epitaxial growth techniques enable nearly defect free heterostructures with coherent interfaces, here we introduce so called “0D perovskites” ligands where six iodides bind to each metal cation resulting in an octahedral complex cluster, which are perfectly matched to the coordination geometry of the Pb-to-S bonds in the cubic rock-salt lattice of the nanocrystals core material. The direct evidence of the epitaxial ligand shell is provided by wide angle x-ray scattering, which confirmed the coherence of the PbS/ligand core/shell interface. Indirectly, among the tested ligands, there is a clear correlation between the ligand to PbS crystal lattice mismatch and the performance of solution processed photo-conductive films made of PbS NCs/epitaxial ligands. For instance, the light on/off current ratio scales with the decrease of lattice mismatch, whereas the dark current significantly decreased for the same devices. Such solution deposited films of PbS NCs/epitaxial ligands enable efficient photoresponse of up to 1.5A/W and ultra-fast response times in the order of 300ps, evidencing high carrier mobility and corresponding to cut-off frequencies beyond 3GHz.
(1) Tang, J. et al. Nature materials, Colloidal-quantum-dot photovoltaics using atomic-ligand passivation, 2011, 10, 765.
9:00 PM - ED6.4.15
Understanding the Photoluminescence Mechanism of Carbon Dots
Zhoufeng Jiang 1 2 , Antara Antu 1 , Shashini Premathilka 1 2 , Liangfeng Sun 1 2
1 Physics and Astronomy, Bowling Green State University, Bowling Green, Ohio, United States, 2 Center of Photochemical Sciences, Bowling Green State University, Bowling Green, Ohio, United States
Show AbstractThe light-emitting mechanism of the carbon dots was investigated by using laser spectroscopy. The photoluminescence spectra show two distinguished emissions: one peaked at 450 nm which is independent of excitation wavelength; the other with a shifting peak depending on the excitation wavelength, not follows Kasha’s rule. The absolute photoluminescence quantum yield of the carbon dots also depends on the excitation wavelength with a maximum at around 400 nm, showing a molecular signature. Further photoluminescence lifetime measurements show that the lifetime of the excited state is at nanosecond level even at the temperature as low as 32 K. This indicate the light-emitting from the carbon dots is unlikely due to the radiative relaxation of triplet states as reported in the literature for polyamides.
9:00 PM - ED6.4.16
Solution-Processed Photovoltaic Devices Utilizing Semiconductor Excitonic Nanoshells (SENS)
Natalia Razgoniaeva 1 , Mikhail Zamkov 1
1 , Bowling Green State University, Bowling Green, Ohio, United States
Show AbstractExcitonic solar cells represent a promising technology for low-cost production of renewable energy. Fabricated from “soft” materials, such as organic molecules or colloidal quantum dots, these devices offer unique advantages that are not found in first or second generation phtotovoltaics. Of a particular benefit are the tunable band gap of excitonic absorbers and the solution-phase deposition of the device active layer. The appeal of this technology, however, is compromised by the poor electrical conductivity of solution-cast films. Limited by the small size of excitonic colloids, the electrical transport in nanostructured solids occurs via tunneling or “hopping” of photoinduced charges, which strongly impedes the electrical flow to electrodes. To mitigate this issue, we have explored a novel class of solution-processed solar cells which enable a high electrical conductivity in the excitonic absorber layer. The core of the innovation lies in the unique geometry of colloidal nanocrystals which channels the motion of electrons and holes into the shell domain of a composite nanostructure. As a result, the quantum behavior of electrical charges can be achieved even in large-diameter semiconductor nanoparticles. A larger “grain” size promotes a faster and more extended diffusion of charge carriers, which should ultimately lead to an improved charge extraction from the photovoltaic film.
9:00 PM - ED6.4.17
Effects of Structural and Electronic Disorder on Optical Properties of Colloidal InP Nanocrystals
Eric Janke 1 , Dmitri Talapin 1
1 , University of Chicago, Chicago, Illinois, United States
Show AbstractColloidal quantum dots have recently attracted interest as tunable emitters with narrow emission linewidths that produce saturated colors. To date, II-VI semiconductor core shell systems incorporating cadmium have achieved the best combination of performance parameters such as stability, luminescence quantum yield and sharp linewidth. Nanocrystals of InP are a promising candidate as a nontoxic alternative to cadmium based emitters that retain the desired range of size tunable emission energy. Current methods of surface passivation by HF photoetching or by shelling with a II-VI semiconductor result in quantum yields of up to 80%. However, photoluminescence linewidths are persistently double or more compared to what is achievable with cadmium based nanocrystals.
We provide evidence for a role of crystalline disorder in broadening the emission lines of InP nanocrystals that are passivated and made luminescent by current methods. Both HF photoetching and common ZnS shelling protocols result in a material that has a broad and redshifted emission. Data from energy selective linear spectroscopies, eg. photoluminescence excitation, suggest that broad emitting colloids of InP are not well described as a heterogeneous collection of individually narrow emitters. Rather the behavior is a better match for a trap assisted emission process. Pump probe experiments find that electrons are largely untrapped on photoluminescence relevant timescales pointing to emission from recombination of holes in shallow traps recombining with free electrons. The hole traps likely arise from disorder related states slightly above the valence band. Resonance Raman measurements find evidence of disorder in luminescent InP in the form of activation of non Brillouin zone center phonon scattering due to loss of translational symmetry. The result is emission from states with localized holes that more strongly couple to optical phonons.
9:00 PM - ED6.4.18
Chalcogenidometallates for New Solution-Processed II-VI Materials
Margaret Hudson 1 , Dmitri Talapin 1 2
1 , The University of Chicago, Chicago, Illinois, United States, 2 Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractChalcogenidometallates, anionic metal chalcogenide species, serve as remarkable precursors for solution-processed semiconducting materials. We have synthesized sodium selenocadmate (Na2Cd2Se3) and explored its interaction with other species to form new II-VI materials. The single crystal x-ray structure reveals that sodium selenocadmate forms a polymeric one-dimensional chain of (Cd2Se3)n2n- charge-balanced by Na+ and stabilized by coordinating hydrazine. Exchanging the sodium cation with tetraethylammonium or didodecyldimethylammonium expands the versatility of selenocadmate by improving its solubility in a variety of polar and nonpolar solvents, while EXAFS measurements indicate that the anion structure remains unchanged. Ordered organic-inorganic hybrid CdSe mesostructures form upon combination of selenocadmate with a micelle-forming cationic surfactant. This chalcogenidometallate chemistry can be extended to other II-VI materials including CdTe, HgSe, HgTe, and mixed phases.
9:00 PM - ED6.4.19
Morphology Control of Indium Phosphide Colloidal Quantum Dots Using Reducing Agents
Dongwoon Shin 1 2 , Hyekyoung Choi 1 2 , Sohee Jeong 1 2
1 Department of Nanomechatronics, Korea University of Science and Technology (UST), Daejeon Korea (the Republic of), 2 Nano-Mechanical Systems Research Division, Korea Institute of Machinery and Materials (KIMM), Daejeon Korea (the Republic of)
Show AbstractColloidal quantum dots (CQDs) exhibit a wide range of optical and electrical properties that depend on both size and shape. The III-V CQDs such as InP, InAs, and InSb have more covalent character than that of II–VI and IV-VI CQDs. Covalent character usually needs high reaction temperatures and long reaction times.1 For these reason, to separate nucleation and growth steps is difficult and synthesis of uniform CQDs cannot be easily achieved. Furthermore, shape control of CQDs is even more challenging in the III-V CQDs. There have been few reports on shape control of InP CQDs.2, 3 Here, we suggest a new synthetic route for shape control InP CQDs using reducing agents. Precise control of morphology can be obtained by varying concentration of reducing agents, reaction temperature and growth time.
(1) Tamanng et al, Chem. Mater. 2016, 28, 2491-2506
(2) Kim et al, Angew. Chem. Int. Ed. 2016, 55, 3714–3718
(3) Srivastava, Chem. Mater., 2016, 28 (18), 6797–6802
Symposium Organizers
Philipp Stadler, Johannes Kepler University Linz
Edward (Ted) Sargent, University of Toronto
Mykhailo Sytnyk, Friedrich-Alexander-Universität Erlangen-Nürnberg
Susanna Thon, Johns Hopkins University
Symposium Support
Lake Shore Cryotronics, Inc.
LOT, Quantum Design
ED6.5: Quantum Materials Light Emission
Session Chairs
Maria Antonietta Loi
Susanna Thon
Wednesday AM, April 19, 2017
PCC North, 100 Level, Room 132 C
9:00 AM - *ED6.5.01
Recent Advances in Colloidal Quantum Dot Lasing—Towards Solution-Processible Laser Diodes
Victor Klimov 1
1 , Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Show AbstractSince the invention of expitaxially-grown semiconductor laser diodes, these devices have become ubiquitous in our daily life and can be found in applications ranging from barcode readers in grocery stores to broadband optical communication and ophthalmic surgery. Chemically synthesized quantum dots (QDs) can potentially enable a new class of highly flexible laser diodes processible from solutions without complications associated with vacuum-based epitaxial techniques. Colloidal QDs feature near-unity emission quantum yields and widely tunable emission wavelengths controlled by their size and/or composition. Further, a wide separation between electronic levels and low degeneracies of band-edge states reduce the lasing threshold and enhance temperature stability compared to semiconductor quantum wells used in traditional laser diodes. Despite a considerable progress over the past years [1-2], colloidal-QD lasing is still at the laboratory stage and an important challenge - realization of lasing with electrical injection - is still unresolved. A major complication, which hinders the progress in this field, is fast nonradiative Auger recombination of gain-active multi-carrier species [3-5]. Here we present the first successful demonstration of population inversion in colloidal QDs achieved using direct current (dc) electrical pumping, which is a necessary step on the path to QD laser diodes. The key element of this work is a new generation of compositionally graded type-I QDs (cg-QDs) that demonstrate a considerable suppression of Auger decay to the extent that it can be outpaced by electrical injection [2,6]. To obtain large QD occupancies required for population inversion, we apply a special "current-focusing" device architecture, which allows for producing high current densities (up to ~12 A cm-2) without damaging either the QDs or the injection layers [6]. The quantitative analysis of electro-luminescence (EL) spectra indicates that at high driving currents, the population inversion is achieved not only for the band-edge 1S state, but also the higher-energy 1P state, suggesting the feasibility of single- and even two-color lasing under dc electrical injection.
[1] J. M. Pietryga, et al., Spectroscopic and device aspects of nanocrystal quantum dots, Chem. Rev. ASAP (2016)
[2] Y.-S. Park, et al., Effect of Auger Recombination on Lasing in Heterostructured Quantum Dots with Engineered Core/Shell Interfaces, Nano Lett. 15, 7319 (2015)
[3] Klimov, et al., Optical gain and stimulated emission in nanocrystal quantum dots. Science 290, 314 (2000).
[4] V. Klimov, et al., Quantization of multi-particle Auger rates in semiconductor quantum dots, Science 287, 1011 (2000).
[5] V. I. Klimov, et al., Single-exciton optical gain in semiconductor nanocrystals, Nature 447, 441 (2007).
[6] W. K. Bae, et al., Controlling the influence of Auger recombination on the performance of quantum-dot light-emitting diodes, Nature Comm. 4, 2661 (2013)
9:30 AM - ED6.5.02
Highly Stable Alloying Core/Multishell CdSe@ZnS/ZnS Quantum Dots
Yan Fu 1 , Hyungseok Moon 1 , Woosuk Lee 1 , Heeyeop Chae 1
1 , Sungkyunkwan University, Suwon Korea (the Republic of)
Show AbstractColloidal semiconductor nanocrystals known as quantum dots (QDs), exhibit excellent optical and optoelectronic properties for widespread applications in light emitting diodes (LEDs), solar cells, biomarkers and so on. However, efficiency and stability of quantum dots needs to be improved. In order to enhance photoluminescence quantum yield (PL QY) of QDs, it is required to reduce non-radiative recombination caused by surface defects, Förster resonance energy transfer (FRET) and Auger recombination (AR).
In this work we report the increase of quantum yield by appropriate QD structure design. We synthesize a series of the alloying core/multishell (AC/MS) structure of CdSe@ZnS/ZnS QDs by a single step synthetic method. By controling different shell thickness, the AC/MS QDs exhibits the unprecedented increase on PL QY from less than 5% CdSe QDs up to ~100%. The thick shell effectively suppress non-radiative AR and FRET, and the the PL lifetime measured by a time correlated single photon counting (TCSPC) system increases from 10.7ns up to 16.3ns in solutions and from 3.6ns up to 5.1ns in films. We also investigate the stability of AC/MS QDs by varying the shell thickness. Considering the combination of UV/ozone treatment in photochemical stability, thick shelled QDs reserve 50% original PL which is enhanced nearly 20-fold performance over AC QDs. More importantly, AC/MS QD films with thick shell QDs show less than 6% reduced PL in thermal stability test (over 400h in harsh environment). These results indicate that optimized thick shell could provide a physical barrier between the optically active core and the evironment by passivating surface nonradiative recombination sites. We also fabricate a inverted quantum dot light emitting diode, which shows maximum luminance (L), current efficiency(CE) and external quantum efficiency (EQE) values of 62,706 cd/m2, 56.6 cd/A and 14.8 %. These values are 3-fold increase in brightness and over 7-fold increase in device efficiency compare with regular AC QDs-device. Therefore, we can conclude that optimizing multishell plays multiple roles of saturating the surface trap states, suppressing the dot-to-dot energy transfer and reduce the non-radiative recombination to enhance the device performance.
9:45 AM - ED6.5.03
Observation of Broadband Optical Gain Mediated by a Hot Electron-Hole Plasma in Quasi-2D CdSe Nanoplatelets
Renu Tomar 1 2 , Zeger Hens 1 2 , Pieter Geiregat 1 2
1 Department of Inorganic and Physical Chemistry, University of Gent, Gent Belgium, 2 , Center for Nano and Biophotonics, Gent Belgium
Show AbstractSolution processable nanomaterials for photonic applications, in particular light emission and lasing, have received much attention in the past decade(s). A demonstration of ultralow continuous wave optical gain and lasing using CdSe platelets, quasi-2D materials in a colloidal dispersion, was the most recent milestone in this field. Until now, the optical gain in these quasi-2D systems was though to originate from the biexciton-to-exciton transition, much as is the case for 0D colloidal QDs. The net gain should therefore occur at biexciton carrier densties and moreover only develop in a narrow region below the lowest energy exciton feature. Here, we show that at low carrier densities exciton-mediated gain mechanisms prevail, yet at higher densities the 2D system is able to deliver broadband optical gain. This gain is caused by the formation of a high temperature, unbound electron-hole gas, a first demonstration for a solution processable material. These results shed a new light on the role of excitons in solution processable inorganic gain media and pave the way for the development of more efficient gain media.
10:00 AM - ED6.5.04
Improved Performance of Quantum Dot Light-Emitting Diodes by Ligand Exchange of Quantum Dots
Heeyoung Jung 1 , Ikjun Cho 2 4 , Byeong Guk Jeong 3 4 , Doh Lee 3 , Jinhan Cho 2 , Wan Ki Bae 4 , Changhee Lee 1
1 , Seoul National University, Seoul Korea (the Republic of), 2 , Korea University, Seoul Korea (the Republic of), 4 , Korea Institute of Science and Technology, Seoul Korea (the Republic of), 3 , Korea Advanced Institute of Science and Technology, Daejeon Korea (the Republic of)
Show AbstractNanocrystal quantum dots (QDs) are promising candidates for lighting and display applications caused by narrow spectral bandwidth, emission wavelength tunability from ultraviolet to infrared by changing construction of core material and by controlling the core size of QDs. Furthermore, cost-efficient solution processes such as the ink-jet printing are acceptable due to the solution processibility of QDs. However, the efficiency of quantum dot light-emitting diodes is restricted by the imbalanced injection of electron and hole to QDs arising from the mobility and energy barrier difference of electron transport layer (ETL) and hole transport layer (HTL). In this study, we use amine functionalized dendrimer ligands as the electron injection controlling interfacial layer. Dendrimer ligands replace the surfactant-ligand of the QDs. By increasing chain length of the dendrimer ligands, we could control the electron injection properties of ETL to QDs. Based on these results, we can fabricate red quantum dot light-emitting diodes with high efficiency over 11% external quantum efficiency.
10:15 AM - ED6.5.05
Thick-Shell Heterostructured Nanocrystals with Near-Unity Photoluminescence Quantum Yield and Suppressed Blinking
Byeong Guk Jeong 1 , Young-Shin Park 2 3 , Jun Hyuk Chang 4 , Ikjun Cho 5 , Kookheon Char 4 , Jinhan Cho 5 , Victor Klimov 2 , Doh Lee 1 , Wan Ki Bae 6
1 , Korea Advanced Institute of Science and Technology, Daejeon Korea (the Republic of), 2 , Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 3 , University of New Mexico, Albuquerque, New Mexico, United States, 4 , Seoul National University, Seoul Korea (the Republic of), 5 , Korea University, Seoul Korea (the Republic of), 6 , Korea Institute of Science and Technology, Seoul Korea (the Republic of)
Show AbstractCore/shell heterostructure has been utilized to manipulate the optical properties of nanocrystals such as high photoluminescence quantum yield (PL QY) and photochemical stability. Particularly, thick-shell permits to achieve the nanocrystals with suppression of blinking and diminished energy transfer between neighboring NCs. However, the use of thick-shell heterostructured NCs in applications has been limited due to the low photoluminescence quantum yield (PL QY ≤ 60%) at room temperature. The PL QY loss in core/thick-shell NCs is attributed to the formation of defects sites due to the increased strain between two different lattices in core/shell NCs. Applying the alloyed layer at the core/shell interface helps alleviate the structural stress and improve the optical properties of NCs. Despite these efforts, the PL QYs of core/thick-shell NCs have never been exceeded 60%.
Here, we demonstrate novel heterostructured NCs with CdS/CdSe/CdS seed/spherical quantum well/shell (SQW) geometry that show near-unity PL QY at room temperature and suppression of blinking, which have never been proposed with conventional core/shell heterostructures. The comparative studies based on spectroscopic analysis and XRD patterns with the conventional CdSe/CdS core/shell NCs reveals that the misfit defects are responsible for the PL QY loss in core/thick-shell NCs and the reduced lattice mismatch between CdSe emissive layer and CdS layers, which is originated from the coherently strained heterostructure, suppresses the formation of misfit defects and consequently allows for the near-unity PL QY and significantly suppressed blinking in SQW NCs with a thick CdS shell (≥ 5 nm) simultaneously. Systematic studies with various geometries of SQW NCs offer the valid effect of SQW heterostructure on the optical propertices of NCs. The superior optical properties of SQW NCs are preserved in the cases of concentrated dispersions and films during high temperature annealing process. To the best of our knowledge, this study is the first systematic approach of the coherently strained heterostructure in NCs. SQW NCs will promote the use of thick-shell heterostructured NCs for applications in solid-state lightings and luminescent solar concentrators.
10:30 AM - ED6.5.06
Preparation of Thermally Stable Silica-Coated Quantum Dots and Its Improved Performance in Quantum Dot Enhancement Film
Wen-Hsin Tsai 1
1 , National Tsing Hua University, Hsinchu Taiwan
Show AbstractIn this study, we present a synthetic process of silica-coated CdSe-ZnS Quantum Dots (QDs). We make a detailed investigation in the relationship between the different morphologies of CdSe-ZnS QDs/SiO2 nanocomposites and its performance in quantum dot enhancement film. First, we present several CdSe-ZnS QDs synthetic process and therefore we can get different physical and chemical properties of CdSe-ZnS QDs/SiO2 nanocomposites. Next, we applicate these silica-coated CdSe-ZnS QDs in the quantum dot enhancement film and analyze its influence to optical properties and thermal stability. These research provide a systemic and efficient way to study silica-coated CdSe-ZnS QDs.
ED6.6: Quantum Photonics I
Session Chairs
Victor Klimov
Philipp Stadler
Wednesday PM, April 19, 2017
PCC North, 100 Level, Room 132 C
11:30 AM - *ED6.6.01
Controlling Optical Properties of Semiconductor Quantum Dots with Nanophotonics for Photovoltaics and Ultrathin Film Devices
Vivian Ferry 1
1 , University of Minnesota, Minneapolis, Minnesota, United States
Show AbstractOur research group studies interactions between quantum confined materials and nanophotonic structures for implementation in optoelectronic and photonic devices. This talk will discuss several recent projects that combine plasmonic and dielectric nanophotonic materials with quantum confined semiconductors.
The first part of the talk will discuss our recent research in applying photonics to luminescent solar concentrators. Luminescent solar concentrators downshift and concentrate incident sunlight onto edge-mounted solar cells, and the tunability and high quantum yield of semiconductor nanocrystals make them natural candidates as the luminescent material. We show that the narrow-band emission from core-shell quantum dots in combination with photonic mirrors improves concentration factors, and that the use of metamaterial mirrors changes the design requirements on the luminescent material. By applying metamaterial mirrors that redirect the angle of light propagation through the concentrator, optical losses to the escape cone can be reduced and device operation is less sensitive to quantum yield and Stokes shift. For example, our designs show that the same performance can be achieved by a nanocrystal with 76% quantum yield when combined with photonic mirrors as a 99% quantum yield nanocrystal in a standard device.
The second part of this talk will discuss our research into other photonic systems that combine semiconductor quantum dots and optical control. One consistent difficulty with designing devices that integrate nanophotonics and semiconductor quantum dots is the unknown complex refractive index of a solution processed film: factors such as the nanocrystal size, ligand, and packing fraction all influence the effective refractive index of the material. We have systematically studied the optical properties of quantum-confined nanocrystal films using spectroscopic ellipsometry to reveal underlying trends in the complex refractive index. Using this knowledge to assist with computational models then allowed us to design and study interactions between semiconductor quantum dots and both dielectric and metallic metamaterials, and to understand the influence of electromagnetic environment on the optical properties of films.
12:00 PM - ED6.6.02
Silicon Quantum Dots for Optoelectronic Devices
Xiaodong Pi 1 , Ting Yu 1 , Shuangyi Zhao 1 , Wei Gu 1 , Xiangkai Liu 1 , Deren Yang 1
1 , State Key Laboratory of Silicon Materials, Zhejiang University, Hangzhou China
Show AbstractAmong all kinds of semiconductor quantum dots (QDs), silicon (Si) QDs hold an advantageous position given the abundance and nontoxicity of Si and their compatibility with conventional Si technologies.[1] We have incorporated Si QDs into the classical bulk-heterojunction organic solar cells based on poly (3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM).[2] It is found that the solar cell efficiency may increase by ~ 40% when ~ 5% of PCBM in the original P3HT:PCBM blend is replaced with Si QDs. The efficiency enhancement is enabled by the improved short-wavelength absorption, optimized film structure and cascade energy-level alignment. By coating graphene that is on the top of bulk Si with Si QDs we have fabricated Si-QD/graphene/bulk-Si Schottky-junction photodetectors.[3] The porous Si-QD films with anti-reflection effect increases the light absorption of the photodetectors. Charge transfer between Si QDs and graphene raises the Schottky–barrier height. Therefore, the Si-QD/graphene/bulk-Si photodetectors show excellent responsivity and detectivity in the wide spectral range of 300 - 1000 nm. We have found that Si-QD light-emitting diodes (LEDs) can work much more efficiently after the use of MoO3 interlayers between ITO and PEDOT:PSS to enhance the hole transport of the devices.[4] MoO3 increases the work function of ITO, leading to better hole injection. The resulting mitigated charge unbalance causes both the external quantum efficiency (EQE) and stability of Si-QD LEDs to significantly increase (up to about 170% for EQE and about 240% for device half lifetime).
[1] X. K. Liu, Y. H. Zhang, T. Yu, X. S. Qiao, R. Gresback, X. D. Pi and D. Yang, "Optimum quantum yield of the light emission from 2 - 10 nm hydrosilylated silicon quantum dots", Particle and Particle Systems Characterization 33, 44-52 (2016).
[2] S. Y. Zhao, X. D. Pi, C. Mercier, Z. C. Yuan, B. Q. Sun and D. Yang, "Silicon-nanocrystal-incorporated ternary hybrid solar cells", Nano Energy 26, 305-312 (2016).
[3] T. Yu, F. Wang, Y. Xu, L. L. Ma, X. D. Pi and D. Yang, "Graphene coupled with silicon quantum dots for high-performance bulk-silicon-based Schottky-junction photodetectors", Advanced Materials 28, 4912-4919 (2016).
[4] Wei Gu, Xiangkai Liu, Xiaodong Pi, Xingliang Dai, Shuangyi Zhao, Li Yao, Dongsheng Li, Yizheng Jin, Deren Yang and Guogang Qin, “Silicon-quantum-dot light-emitting diodes with interlayer-enhanced hole transport”, submitted (2016).
12:15 PM - ED6.6.03
Synthesis of CdSe/ZnS Core/Shell Nanoplatelets for Photonic Applications
Anatolii Polovitsyn 1 2 , Zhiya Dang 1 , Beatriz Garcia 1 , Guillaume Bertrand 3 , Rosaria Brescia 1 , Iwan Moreels 1
1 , IIT, Genova Italy, 2 Chemistry and industrial chemistry, University of Genova, Genova, Liguria, Italy, 3 Polymer Chemistry, CEA, Paris France
Show AbstractIn contrast with more conventional colloidal quantum dots (QDs) that are confined in all three dimensions, 2D nanoplatelets (NPLs)[1] combine the benefits of strong confinement in one direction, with expanded lateral sizes that lead only to weak in-plane confinement of charge carriers. Their thickness can be controlled with monolayer precision, yielding narrow, homogeneously broadened band-edge absorption and emission peaks[2].
We present procedures to coat cubic CdSe NPLs with a ZnS shell, whose thickness varies from a monolayer up to shells with 9-10 atomic layers. High resolution TEM analysis shows a relative dilatation of 12% between the CdSe core and ZnS shell, compatible with the lattice mismatch between bulk CdSe and ZnS. The resulting strain leads to significantly curved CdSe NPLs. The core/shell NPLs display quantum efficiencies of about 30-50 %. Interestingly, upon increasing the ZnS shell thickness we observed a continuous shift of the band-edge absorption and emission, in contrast with the stepwise red shift of the fluorescence peak position as one increases the number of monolayers within the CdSe NPLs. The core/shell NPLs preserve the fast exciton recombination of the core-only nanoplatelets, as opposed to CdSe/CdS NPLs [3, 4] that show an increase in fluorescence lifetime after growing a CdS shell[5].
The tailored synthesis of CdSe/ZnS core/shell NPLs proposed here enables materials with precisely controlled opto-electronic properties across the visible spectral range. Furthermore, the high-band gap shell enhances the optical stability, and we were able to transfer the NPLs to different media without substantial loss of fluorescence. This opens the way to practical photonic applications of 2D-confined colloidal nanocrystal on a solution-processed platform.
12:30 PM - ED6.6.04
Quantum Dot Integrated Nanofibers for White LEDs
Evren Mutlugun 1 , Yemliha Altintas 1 , Nuri Burak Kiremitler 2 , Sinan Genc 1 , Mustafa Onses 2
1 , Abdullah Gul University, Kayseri Turkey, 2 , Erciyes University, Kayseri Turkey
Show Abstract0-D materials, also known as quantum dots (QDs) have attained considerable interest in the last decades due to their exotic optical properties, i.e. narrow emission bandwidth, tunable emission spectra, large absorption window and high photoluminescence quantum yield. Although their synthesized form has superiour potential for future optoelectronic applicatons, their solid state forms still under investigation for light harvesting applications. The confinement of the colloidal QDs into a physically defined zone i.e., a polymeric matrix, remains challenge with the difficulty to control their interparticle distance. In that respect, in this work we propose and demonstrate novel platforms of nano emitter integrated nanofibers to control and monitor their interparticle distance. CdSe/ZnS quantum dots with photoluminescence quantum yield near unity have been synthesized and employed as light harvesting platforms within the electrospun nanofibers. As being the first work reported of this kind, we have focused on the control of the quantum dot spatial distribution in nanofibers by modifying the concentration of the emitters within the nanofiber and observe their emission kinetics.The concentration of the green and red QDs inside the nanofiber has been varied and Förster type nonradiative energy transfer has been empolyed systematically to control the output light content. A systematic control of the concentration of the donor (green emitting) and acceptor (red emitting) QDs have been monitored by using time resolved photoluminescence spectroscopy. Emission kinetics have been analysed from the donor emission and acceptor emission window. Introducing acceptors to the nanofiber, prepared by only donor emitters, we have shown up to 40.2% decrease in the lifetime of the donor emitter, which leads to 28.1% increase in the acceptor lifetime due to the energy feeding. The systematic tuning of the donor and acceptor concentration ratio have been studied in the low and high concentration regimes. The results have further been supported by steady state measurements and spectral modification of the output light have been with a decrease in the green emission, and enhancement of the red emission due to nonradiative energy transfer. As a potential application of these QD-nanofibers, we have used them as white LED platfroms when hybridized with blue LED. Using the QDs with peak emission wavelength of 632 nm and 538 nm with full width half maximum of 35nm and 38nm respectively, our simulations of the peak intensities have shown that with such narrow emitters, potentially highest achievable CRI with CCT<4000 K would be 62.1 and we have fabricated a white LED with color rendering index value of 59.5 and correlated color temperature of 3632 K. The study and understanding of excitonic interaction among nano emitters confined in 1D structures is an important step towards using them for optoelectronic applications.
This work is supported by TUBITAK project no 114E107.
12:45 PM - ED6.6.05
Luminescent Solar Concentrators with High Power- and Cost-Efficiency Based on Ultra-Earth-Abundant Indirect Band Gap Silicon Quantum Dots
Sergio Brovelli 1 , Francesco Meinardi 1 , Uwe Kortshagen 2 , Samantha Ehrenberg 2
1 , University of Milano Bicocca, Milano Italy, 2 , University of Minnesota, Minneapolis, Minnesota, United States
Show AbstractBuilding integrated photovoltaics (BIPV) is gaining consensus as a renewable energy technology for producing electricity at the point of use. Luminescent solar concentrators (LSCs) could extend the architectural integration to the urban environment by realizing electrode-less semitransparent PV windows. Crucial for the achievement of large-area LSCs is the suppression of reabsorption losses, which requires emitters with negligible overlap between their absorption and emission spectra. Here, we demonstrate an as-yet unexplored concept for achieving reabsorption-free LSCs, that is, the use of indirect band-gap semiconductor nanostructures, such as highly-emissive silicon quantum dots (Si-QDs). Silicon is non-toxic, low-cost and ultra-earth-abundant, which avoids limitations to industrial scaling of QDs comprising of low-abundance elements. Suppressed reabsorption and scattering losses lead to nearly ideal large-area LSCs with optical efficiency, η=2.85%, matching state-of-the-art semitransparent LSCs. Application of back-reflectors boosts the performance up to η~4%, which is the highest value reported for large-area LSCs. Monte-Carlo simulations indicate that optimized Si-QDs LSCs have a clear path to η>5% for 1m2 devices. We finally realize flexible LSCs with performances comparable to flat concentrators, which opens the way to new design freedom of BIPV elements.
ED6.7: Quantum Photonics II
Session Chairs
Vivian Ferry
Mykhailo Sytnyk
Wednesday PM, April 19, 2017
PCC North, 100 Level, Room 132 C
2:30 PM - *ED6.7.01
Mechanical Control of Excitonic States in Epitaxial Quantum Dots
Armando Rastelli 1
1 , Johannes Kepler University, Linz Austria
Show AbstractSeveral systems are under investigation for their potential use in the fields of quantum information and communication. Epitaxial semiconductor quantum dots (QDs), also dubbed “artificial atoms”, are one of such systems, as they can be used both as sources and hosts of “quantum bits” and can be easily integrated into compact devices and photonic structures. However, unlike natural atoms, no two QDs are identical - a major obstacle towards their actual application.
In this talk I will show how elastic strain produced by novel piezoelectric actuators can be used to overcome problems arising from unavoidable fluctuations during QD growth and to reshape the QD electronic structure and excitonic emission after fabrication. I will first discuss the effects of strain on bulk GaAs and initially unstrained GaAs QDs in AlGaAs matrix [1-3]. After this, I will illustrate (on the InGaAs/GaAs material system) how any arbitrarily chosen QD can be employed as a wavelength-tunable source of entangled photon pairs [4,5]. This is achieved by integrating the QDs onto micromachined piezoelectric actuators capable of controlling the components of the in-plane strain tensor in the QD and surrounding matrix [3-4]. A discussion on future perspectives will conclude the talk.
[1] Y. Huo et al. Nature Physics 10, 46–51 (2014)
[2] H. Huang et al., arXiv:1602.02122
[3] J. Martín-Sánchez et al., Advanced Optical Materials 4, 682 (2016)
[4] R. Trotta et al., Physical Review Letters 114, 150502 (2015)
[5] R. Trotta et al., Nature Communications 7, 10375 (2016)
3:00 PM - ED6.7.02
Optical Gain Measurements of Optically-Pumped AlN/GaN Quantum Well Structures for Deep-UV Emission
Galen Harden 1 , SM Islam 2 , Kevin Lee 2 , Vladimir Protasenko 2 , Huili Xing 2 , Debdeep Jena 2 , Anthony Hoffman 1
1 , University of Notre Dame, Notre Dame, Indiana, United States, 2 , Cornell University, Ithaca, New York, United States
Show AbstractThin GaN quantum wells are a promising path towards electrically-injected lasing in the deep-UV. For these quantum confined structures, the large bandgap of GaN and the ground state energy of the quantum well enable optical emission below 270 nm. Recent research has focused on the growth of AlN/GaN heterostructures on bulk AlN substrates to minimize defects during the crystal growth. Here, we characterize the optical gain of optically-pumped AlN/GaN quantum well structures that are grown via molecular beam epitaxy on bulk AlN.
Several samples with active regions comprising two-monolayer GaN quantum wells separated by 2.5 nm AlN barriers were grown via molecular beam epitaxy. The samples differed in the number of repeats of the GaN/AlN quantum wells and the surrounding cladding regions. The calculated modal confinement factor ranged from 2 – 14%: the highest confinement factor was achieved using a thin ternary cap layer with >80% transmission and 10 quantum wells. Cavities approximately 3 mm long were cleaved for testing.
An ArF excimer laser emitting at 193 nm was used for optical excitation. The excimer laser beam was focused into a 100 μm wide stripe on the top surface of the laser cavity, and a micrometer-controlled slit was used to adjust the length of the pump beam on the sample. The gain was determined by measuring the light emitted from the facet versus the length of the optical pumping stripe. Pumping densities from 25 kW/cm2 to 10 MW/cm2 were used. All of the samples exhibit short gain saturation lengths (~150 μm), indicating a short carrier lifetime. A peak gain of approximately 5 cm-1 was measured for the sample with the highest confinement factor.
3:15 PM - ED6.7.03
Single Photon Emission by InP/ZnSe Quantum Dots
Zeger Hens 1 , Vigneshwaran Chandrasekaran 1 , Mickael Tessier 1 , Dorian Dupont 1 , Edouard Brainis 1
1 , Ghent University, Gent Belgium
Show AbstractColloidal quantum dots have been identified since long as possible room temperature single photon emitters. Whereas photon antibunching has been amply demonstrated for Cd-based quantum dots, the intermittant photoluminescence or blinking that was found characteristic of individual quantum dots compromises their use as single-photon-on-demand sources. Strategies to suppress blinking through interfacial alloying have been developed, yet they suppress blinking by slowing down the non-radiative Auger recombination of trion or biexciton states. This strongly deteriorates the single-photon emission characteristics (photon antibunching), especially under high intensity pulsed optical pumping.
Here, we analyse single photon emission by individual InP/ZnSe core/shell quantum dots. We use InP/ZnSe QDs with an ensemble photoluminescence centered at around 630 nm with a full width at half maximum of 45-50 nm that are synthesized using recently developed synthesis protocols based on aminophosphines. We first show that under increased optical pumping, the QD emission mimicks the saturation behavior of a two level system. Next, studying about 100 individual QDs, we find that their room temperature emission is typically 18-20 nm wide with a central wavelength that varies from 580 to 670 nm. This confirms that the rather broad ensemble emission - as compared to CdSe-based QDs - is not a property intrinsic to InP-based quantum dots, yet reflects the sample heterogeneity.
Importantly, we find that many InP/ZnSe QDs show little blinking, with on/off statistics comparable to CdSe-based QDs classified in the literature as non blinking. Moreover, this comes with an exquisite antibunching behavior, with g2(0) that can be as low as 0.05 and 0.02 under continuous and pulsed excitation, respectively. Opposite from typical CdSe/CdS QDs, the antibunching characteristics persist upon increasing the pump intensities up to levels above the saturation intensity, where the emission lifetime estimated from intensity dependent antibunching (19.8 ns) matches the average lifetime from time-resolved photoluminescence on single InP/ZnSe QDs.
In summary, we show that individual InP/ZnSe QDs combine a narrow, hardly-blinking emission with a pronounced photon antibunching, even under enhanced pump intensity. This suggests that irrespective of the reduced blinking, biexciton emission is effectively suppressed in these QDs making them promising photon-on-demand emitters..
ED6.8: Quantum Materials—Surface and Trapping
Session Chairs
Armando Rastelli
Susanna Thon
Wednesday PM, April 19, 2017
PCC North, 100 Level, Room 132 C
4:30 PM - *ED6.8.01
Surface Engineering and Electron-Phonon Interactions in Colloidal Quantum Dots
Vanessa Wood 1
1 , ETH Zurich, Zurich Switzerland
Show Abstract
Over the past thirty years, it has been observed that surface engineering of colloidal nanocrystals (NC) is key to their performance parameters. In this talk, I will discuss the impact of surface engineering on electron-phonon interactions in NCs and how these interactions play a role in device performance. In the case of lead chalcogenide NCs, for example, replacing thiols with halide anion surface termination has been shown to increase power conversion efficiency in NC-based solar cells. Our experimental and computational work shows that the surface of both the thiol- and halide-terminated PbS NCs exhibit low and high-energy phonon modes with large thermal displacements not present in bulk PbS; however, halide anion surface termination reduces the overlap of the electronic wavefunctions with these vibrational modes. These findings suggest that electron-phonon interactions will be reduced. This work explains why electron-phonon interactions are crucial to charge carrier dynamics in NCs and how surface engineering can be applied to systematically control their electronic and phononic properties.
5:00 PM - ED6.8.02
Hot Carrier Trapping in Core/Shell Quantum Dots
Marcello Righetto 1 , Renato Bozio 1
1 , Università degli Studi di Padova, Padua Italy
Show AbstractThe outstanding optical properties of Semiconductor Quantum Dots (QDs) attracted much interest for over two decades. The development of synthetic methods for the production of core-shell QDs opened the way to attaining almost ideal emitting properties. Their implementation in opto-electronic devices, such as LEDs and lasers, requires a full understanding of the fine details of their photo-physics. The widespread application of QDs greatly profits from their broad absorption band. However, the variable nature of excitations within these bands results in undesired excitation energy dependence of steady state emission properties. Differences in hot and cold carrier trapping process were investigated by means of steady state and time-resolved optical spectroscopy. The excitation energy dependence of photoluminescence quantum yields (PLQY) was analyzed in different CdSe/CdxZn1-xS (x = 0, 0.5, 1) quantum dots to identify best performing heterostructures, in terms of shell thickness and composition. Considerations on carrier trapping dynamics were combined with those on its energetics, starting from a previously established kinetic model. The subtle balance between trapping and de-trapping processes and the generation of long-living photo-charged QDs were found to lay at heart of steady-state PL properties. Our rationalization of the hot-carriers behavior was based on microscopic Marcus-Jortner charge transfer model. The combination of experimental results and PLQY modeling unveiled the role of hot-carrier trapping. Furthermore, by re-definition of PLQY, considering QDs as three-level systems, trion Auger recombinations were explicitly considered. The dynamical signature of these processes was obtained by Broadband Transient Absorption (TA) spectroscopy.
This work provides a deeper insight into trapping process in quantum dots, relating its energetics and dynamics. The accurate understanding of the processes determining photoluminescence efficiency will represent a fundamental step toward the application of QDs.
5:15 PM - ED6.8.03
Stable and Low-Threshold Gain of CdSe/CdS@CdS Core/Crown@Shell Colloidal Nanoplatelets
Yusuf Kelestemur 1 , Burak Guzelturk 1 , Onur Erdem 1 , Murat Olutas 1 2 , Kivanc Gungor 1 , Hilmi Demir 1 3
1 , Bilkent University, Ankara Turkey, 2 , Abant Izzet Baysal University, Bolu Turkey, 3 , Nanyang Technological University, Singapore Singapore
Show Abstract
Free-standing colloidal nanoplatelets (NPLs) with magic-sized vertical thickness have recently been emerging as a highly promising class of semiconductor nanocrystals.[1] Owing to their tight quantum confinement only in the vertical direction, they exhibit unique thickness-dependent optical properties. Thanks to colloidal synthesis of NPLs having atomically-flat surfaces, they exhibit extremely narrow emission bandwidths (<9 nm) with suppressed inhomogeneous broadening. Also, they feature ultrafast fluorescence lifetime due to their giant oscillator strength. In addition, they possess high linear and nonlinear absorption cross-section, which makes them highly attractive for lasing applications.[2] However, similar to other classes of semiconductor nanocrystals, core-only NPLs have suffered from serious stability issues and low photoluminescence quantum yield (PL-QY). To date, to improve the stability and PL-QY of NPLs, core/crown (laterally grown shell) and core@shell (vertically grown shell) NPLs have been synthesized. While core/crown NPLs have suffered from serious stability issues due to the lack of proper passivation on their larger surfaces, core@shell NPLs have suffered from the formation of trap sites during the shell growth, which limits their performance. Therefore, newly designed architectures of NPLs are highly welcomed.
Here, to address this need, we synthesized and demonstrated CdSe/CdS@CdS core/crown@shell NPLs resembling a platelet-in-box structure.[3] We found that the core/crown@shell NPLs always exhibit higher PL-QY (up to ~40%) when compared to core@shell NPLs regardless of their core size, crown size and shell thickness. This enhancement in the PL-QY of core/crown@shell NPLs can be attributed to critical passivation of the periphery of CdSe core with CdS crown layer. The passivation of trap sites was also verified with the disappearance of the fast nonradiative decay component from the time-resolved fluorescence measurements. Also, the core/crown@shell NPLs exhibit relatively symmetric emission behavior with suppressed lifetime broadening at cryogenic temperatures when compared to core@shell NPLs, further suggesting the suppression of trap sites. Finally, we have studied optical gain performances of NPLs. Thanks to the enhanced excitonic properties of the core/crown@shell NPLs, they exhibit the lowest gain threshold (~20 µJ/cm2) among the different heterostructures of NPLs. Also, with the synthesis of core/crown@shell NPLs having a novel 3D architecture, we achieved much greater stability up to 2.5 × 107 pump laser shots, which that corresponds to many hours of continuous excitation depending on the repetition rate.
[1] E. Lhuillier, et al., Acc. Chem. Res., 48, 1, 22–30, (2015).
[2] B. Guzelturk, Y. Kelestemur, et al., ACS Nano, 8, 7, 6599–6605, (2014).
[3] Y. Kelestemur, et al., Adv. Funct. Mater., 26, 21, 3570–3579, (2016).
5:30 PM - ED6.8.04
Electronic States in Mercury Chalcogenide Colloidal Quantum Dots
Menglu Chen 1 , Philippe Guyot-Sionnest 1
1 , University of Chicago, Chicago, Illinois, United States
Show AbstractIn the past few years, colloidal quantum dots based on the zinc-blend mercury chalcogenides, Hg(S, Se, Te), have become leaders in efforts to transform mid-IR technologies with solutions based materials. Understanding the electronic states, the doping, and the relative band positions of the three materials and the colloidal dots is essential for current and future investigations.
We use spectroscopy and electrochemistry to monitor the electronic states, the mobility of electrons in films, the origin of the spontaneous doping in several of the systems, and the effects of the surface.
We will describe how a single cyclic voltammetry curve on one particular sample of quantum dots already reveals much novel information, such as predicting if the system is spontaneously doped, the Fermi level, the electron injection energies, the degree of reversibility, the presence of surface states, and the mobility of electrons hopping from different states.
We will then present our complete set of electrochemical and spectroscopic data collected on the three different chalcogenides, with a systematic range of sizes and surface chemistry, and these unveil an unprecedented view on the materials and of their properties as quantum dots.
5:45 PM - ED6.8.05
Investigation of Energy Transfer Mechanism between Nickel Oxide Thin Film and CdSe/ZnS Alloyed Nanocrystals
Ramesh Vasan 2 , Feng Gao 1 , Omar Manasreh 2 , Colin Heyes 1
2 Department of Electrical Engineering, University of Arkansas, Fayetteville, Arkansas, United States, 1 Department of Chemistry and BioChemistry, University of Arkansas, Fayetteville, Arkansas, United States
Show AbstractEnergy transfer between nickel oxide thin film and CdSe/ZnS alloyed core/shell nanocrystals is investigated to determine the charge transport in all-inorganic quantum dot LED. The crystal structure and composition of the nickel oxide thin film are evaluated by using X-ray diffraction and X-ray photoelectron spectroscopies. The atomic ratio of Ni:O in the film is 1:1.7 indicating a Ni deficient film with defect states within the band gap. The optical properties of a bilayer thin film of nickel oxide-CdSe/ZnS nanocrystals are studied by measuring the absorbance and photoluminescence spectra as time resolved photoluminescence decay. The absorbance spectrum of the CdSe/ZnS nanocrystals shows a strong overlap with the defect-related emission spectrum of the nickel oxide thin film. The CdSe/ZnS nanocrystals exhibit longer life times on the nickel oxide thin film than on bare glass. Moreover, the emission intensity of the CdSe/ZnS nanocrystals spin coated on the nickel oxide thin film higher when compared to the emission intensity of the same nanocrystals spin coated on bare glass. All these results point to a strong interaction in the form of resonant energy transfer from the nickel oxide defect states to the CdSe/ZnS nanocrystals.
Symposium Organizers
Philipp Stadler, Johannes Kepler University Linz
Edward (Ted) Sargent, University of Toronto
Mykhailo Sytnyk, Friedrich-Alexander-Universität Erlangen-Nürnberg
Susanna Thon, Johns Hopkins University
Symposium Support
Lake Shore Cryotronics, Inc.
LOT, Quantum Design
ED6.9: Quantum Materials—Synthesis and Theory
Session Chairs
Philipp Stadler
Vanessa Wood
Thursday AM, April 20, 2017
PCC North, 100 Level, Room 132 C
9:15 AM - *ED6.9.01
Effects of Nanogeometry on Carrier Multiplication in Lead Chalcogenide Materials for Photovoltaics
Laurens Siebbeles 1
1 , TU Delft, Delft Netherlands
Show AbstractAbsorption of sufficiently energetic photons in a bulk semiconductor leads to hot electrons and holes that usually cool to the band edge by thermal relaxation. In semiconductor nanomaterials this cooling can be intercepted by excitation of additional electrons across the band gap. In this way, one photon generates multiple electron-hole pairs via a process known as Carrier Multiplication (CM), which is of interest for the development of highly efficient solar cells and photodetectors.
We studied charge carrier photogeneration, CM, charge mobility and decay in: a) films of 0D PbSe nanocrystals coupled by organic ligands, b) 1D PbSe nanorods, c) 2D superlattices of directly coupled PbSe nanocrystals in a square or honeycomb pattern, and c) PbS nanosheets. The studies were performed using ultrafast pump-probe spectroscopy with optical or terahertz conductivity detection.
The nanogeometry of the material was found to have enormous effects on CM and the charge mobility. In 2D superlattices of nanocrystals coupled by atomic bonds CM occurs in a step-like fashion with threshold near the minimum energy of twice the band gap. In these superlattices the CM efficiency and charge mobility are much higher than for films of QDs that are coupled by organic ligands. When the thickness of PbS nanosheets is reduced, the CM efficiency becomes higher.
The effects of dimensionality and nanogeometry on the efficiency of CM and impact on power conversion in photovoltaic devices will be discussed.
9:45 AM - ED6.9.02
High Density Formation of and Light Emission from Si Quantum Dots with Ge Core
Seiichi Miyazaki 1 , Kentaro Yamada 1 , Mitsuhisa Ikeda 1 , Katsunori Makihara 1
1 Graduate School of Engineering, Nagoya University, Nagoya Japan
Show AbstractLight emission from Si-based nanostructures including Si- and Ge- quantum dots (QDs) has stimulated considerable interest in the field of silicon-based photonics because of its potential to combine photonic processing with electronic processing on a single chip. Much effort to improve light emission efficiency and its stability has been devoted with deliberate approaches which include not only the confinement of injected carriers but also the use of strained structures and impurity doping. So far, we have reported the formation of Si-QDs with Ge core on ultrathin SiO2 by controlling the thermal decomposition of pure SiH4 and 5% GeH4 diluted with He alternately and confirmed type II energy band alignment between Si-clad and Ge core. In fact, unique charge storage characteristics of an individual Si-QD with a Ge core, that is, electrons are stored in the Si clad and holes in the Ge core, have been confirmed from the surface potential measurements before and after electron injection and emission by means of AFM/Kelvin probe microscopy.
In this presentation, we report our recent achievements on high-density formation and characterization of Si-QDs with Ge core on SiO2. In particular, we focus on how photoluminescence (PL) properties from Si-QDs are changed with embedding of Ge core and P-doping to Ge core. From comparative study of PL properties of core less Si-QDs as well as Ge core size dependence of PL properties, it is confirmed that radiative recombination between quantized states in Ge core is a major origin of PL. And we aslo demonstrate that, in a double stack structure of Si-QDs with Ge formed on 2nm-SiO2/c-Si, electroluminescence due to radiative recombination through higher order quantized states in Ge core is promoted efficiently by forward bias application over 2V.
10:00 AM - ED6.9.03
A Mechanism Describing the Formation of Highly Anisotropic, Quasi-2D Nanoplatelets from Isotropic Materials
Florian Ott 1 , Andreas Riedinger 1 , Sergio Mazzotti 1 , Aniket Mule 1 , Philippe Knuesel 1 , Stephan Kress 1 , Steven Erwin 2 , David Norris 1
1 , ETH Zurich, Zurich Switzerland, 2 Center for Computational Materials Science, Naval Research Laboratory, Washington, District of Columbia, United States
Show AbstractColloidal nanoplatelets are atomically flat, quasi-two-dimensional sheets of semiconductor exhibiting efficient, spectrally pure fluorescence. Their formation is not fully understood and especially surprising when the underlying crystal structure has cubic symmetry, for example in zincblende CdSe. In this case the crystal structure of the material appears to contradict its highly anisotropic shape. Here, we demonstrate that an intrinsic instability in the kinetics of crystal growth on small facets leads to highly anisotropic platelet crystallites even for materials with cubic crystal structure. This instability arises because the nucleation of a stable island–the rate-limiting step in crystal growth–has a strongly reduced energy barrier on narrow facets, as we confirm using density functional theory calculations for CdSe. Kinetic Monte Carlo simulations show, moreover, that the stochastic nature of crystal growth leads to nanoplatelets even from initial crystal seeds that are perfectly cubic in shape. Our model predicts enhanced growth rates only for a small range of narrow facet widths. Even within this range the growth rates rapidly decrease with facet size, in agreement with experimental results. Finally, we map our microscopic mechanism to standard concepts of volume, surface, and edge energy, allowing easy application of the growth instability criterion to many other crystalline materials.
10:15 AM - ED6.9.04
Synthesis and Characterization of PbS Quantum Dots with Size-Tunable Near-Infrared Emission
Yi-Ching Yang 1
1 Department of Materials Science & Engineering, National Tsing Hua University, Hsinchu Taiwan
Show AbstractColloidal PbS quantum dots (QDs) have been studied extensively for their size-tunable near-infrared emission. We synthesized PbS QDs based on the diffusion-controlled heterogeneous reaction using a higher concentration of lead chloride as precursors in oleylamine that can inhibit Ostwald ripening. By varying the reaction parameters, we obtained PbS QDs with emission wavelength between 1015 to 1575 nm. Furthermore, in order to evaluate the above synthetic method, we also synthesized PbS QDs based on a homogeneous reaction using lead oleate and bis(trimethylsilyl)-sulfide as precursors in octadecene, which led to different particle morphology. Finally, we have suggested a possible model to describe the nucleation and growth of PbS QDs with oleylamine capping in the current growth system.
10:30 AM - ED6.9.05
Colloidal Synthesis of HgTe/CdTe Core/Shell Quantum Dots with Enhanced Thermal Stability
Guohua Shen 1 , Philippe Guyot-Sionnest 1
1 , The University of Chicago, Chicago, Illinois, United States
Show AbstractHgTe colloidal quantum dot (QD) absorb and emit light in the mid-IR and far-IR, and they are studied for optoelectronic devices that work in those regions. While HgTe QDs are synthesized with good size tunability and monodispersity, they have a poor surface stability which leads to two problems. First, HgTe QDs easily aggregate and crash from solution, while as films, confinement is lost under mild heating at 100 °C. Second, in order to stabilize the colloid, one has to use strongly-binding ligands (like thiols), which makes further surface modification almost impossible.
CdTe is lattice matched with a type I band alignment and should be an ideal shell. However, unlike HgS/CdS1, prior attempts at HgTe/CdTe failed. Here, we report the first synthesis of HgTe/CdTe core/shell QDs. Shell growth is verified by infrared absorption, photoluminescence, XRD, XPS, TEM. The core/shell structure solves the two earlier problems. First, the colloidal stability is excellent with no aggregation in solution while films resist annealing temperature as high as 150°C; Second, ligand exchange on the core/shell allows to find the best surface environment for a specific application. The newly found robustness and versatility afforded by the HgTe/CdTe core/shell opens up many avenues to improve HgTe QD devices.
1. Shen, G.; Guyot-Sionnest, P., HgS and HgS/CdS Colloidal Quantum Dots with Infrared Intraband Transitions and Emergence of a Surface Plasmon. The Journal of Physical Chemistry C 2016.
10:45 AM - ED6.9.06
Ligand-Induced Shape Transformation of PbSe Nanocrystals
Joep Peters 1
1 , University of Utrecht, Utrecht Netherlands
Show AbstractWe present a study of the relation between the surface chemistry and nanocrystal shape of PbSe nanocrystals capped with a variable density of oleate ligands. The oleate ligand density and binding configuration is monitored by FTIR absorbance spectroscopy allowing us to quantify the number of surface-attached ligands per NC and the nature of the surface-Pb-oleate configuration. The three-dimensional shape of the PbSe nanocrystals is obtained from HAADF-STEM combined with an atom counting method. We show that the enhanced oleate capping results in a stabilization and extension of the {111} facets, and a crystal shape transformation from a truncated nanocube to a truncated octahedron.
ED6.10: Quantum Colloids—Tuning Size and Shape
Session Chairs
Laurens Siebbeles
Mykhailo Sytnyk
Thursday PM, April 20, 2017
PCC North, 100 Level, Room 132 C
11:30 AM - *ED6.10.01
Exploiting the Nanocrystal Library to Construct Electronic and Optoelectronic Devices
Cherie Kagan 1
1 , University of Pennsylvania, Philadelphia, Pennsylvania, United States
Show AbstractSynthetic methods produce libraries of colloidal semiconducting, metallic, and insulating nanocrystals tailorable in their size, shape, and composition. In this talk, we exploit the diversity in colloidal nanocrystals and design the materials, interfaces, and processes used to construct electronic and optoelectronic devices. For example, we use metallic silver, semiconducting cadmium selenide, and insulating aluminum oxide nanocrystals to realize high conductivity electrodes, high mobility channel layers, and high dielectric constant gate insulator layers and form the components of field-effect transistors.1 Integration of these nanocrystal layers to realize excellent device function requires the development orthogonal solution-based processes, surface chemical modification, and the incorporation of metallic indium nanocrystals into the source and drain electrodes to passivate and dope the cadmium selenide nanocrystal channel layer. Solution-processable, all-nanocrystal field-effect transistors are fabricated on flexible plastics with electron mobilities of 21.7 cm2/Vs. In another example, we introduce a cadmium selenide nanocrystal buffer layer at the interface between lead sulfide and zinc oxide nanocrystal layers to create an advanced architecture for nanocrystal solar cells.2 We optimize the band alignment and carrier concentration across and in the nanocrystal layers by tailoring the size and surface chemistry of the nanocrystals. Measurements show that the additional cadmium selenide nanocrystal buffer layer suppresses interface recombination and contributes additional photocarriers, increasing the open circuit voltage and short circuit current and thereby leading to a 25% increase in solar cell power conversion efficiency.
(1) Choi, J.-H.; Wang, H.; Oh, S. J.; Paik, T.; Sung, P.; Sung, J.; Ye, X.; Zhao, T.; Diroll, B. T.; Murray, C. B.; et al. Exploiting the Colloidal Nanocrystal Library to Construct Electronic Devices. Science (80-. ). 2016, 352, 205–208.
(2) Zhao, T.; Goodwin, E. D.; Guo, J.; Wang, H.; Diroll, B. T.; Murray, C. B.; Kagan, C. R. Advanced Architecture for Colloidal PbS Quantum Dot Solar Cells Exploiting a CdSe Quantum Dot Buffer Layer. ACS Nano 2016, acsnano.6b03175.
12:00 PM - ED6.10.02
Aqueous HgTe Quantum Dot Based Phototransistors Enabling Room Temperature High Sensitivity Photodetection Beyond 2000 nm Spectral Range
Mengyu Chen 1 , Haipeng Lu 1 , Nema Abdelazim 2 , Stephen Kershaw 2 , Andrey Rogach 2 , Ni Zhao 1
1 , Chinese University of Hong Kong, Shatin Hong Kong, 2 , City University of Hong Kong, Hong Kong Hong Kong
Show AbstractNear-to-mid infrared photodetection has great application potential in military or civil night vision, environmental gas monitoring and chemical spectroscopy. However, current mid-infrared (MIR) photodetectors are fabricated from costly and size-limited epitaxial growth technologies, and they rely on bulky low-temperature operation systems to achieve high specific detectivity. These limitations greatly hinder the market development of compact detection systems that can be deployed for large-area, portable or multi-site sensing applications. Here, we report an aqueous HgTe quantum dot (QD) based phototransistor with > 2000 nm spectral response. The QDs are synthesized via an automated aprotic solvent gas-injection route and exhibit a record high quantum yield of 18 % in the MIR range. Through parametric analysis and device optimization, we improved the room temperature detectivity of the phototransistor to more than 2×1010 cm Hz1/2 W-1, comparable to the state-of-the-art commercialized photodetectors operated at or below 150K. The photosensing ability of the phototransistor can be further tripled at 250-270 K, a temperature range that can be easily achieved with a small thermoelectric device. We demonstrated the practical application of such phototransistor by implementing the device in a carbon monoxide gas sensing system, where the device exhibit a reliable response to gas fluctuation. This work systematically investigate the influence of material and device engineering on the noise, bandwidth and responsivity of MIR QD photodetectors, and it paves the way of integrating such devices with commercial silicon-based read-out circuits to realize low cost and compact spectroscopy and imaging systems.
12:15 PM - ED6.10.03
Effects of Phenyldithiocarbamate Decomposition during Nanocrystal Ligand Exchange
Andrea Munro 2 , Levi Lystrom 1 , Svetlana Kilina 1
2 Department of Chemistry, Pacific Lutheran University, Tacoma, Washington, United States, 1 Department of Chemistry and Biochemistry, North Dakota State University, Fargo, North Dakota, United States
Show AbstractRationally designing ligands for quantum dots (QDs) has attracted the attention of the scientist community because with the correct ligand QD’s optoelectronic properties are tunable. These designed ligands cannot be used to synthesis QDs because they are thermally unstable. Thus, ligand exchange of native ligands (carboxylic acid, amine, and phosphine derivatives) for the designed ligands is needed. One class of designer ligands are dithiocarbamate (DTC) but DTC undergoes decomposition when dissolved in solvents. This decomposition of DTCs during ligand exchange is typically ignored and the overall effect is reported. Our experimental results show that DTC decompose rates are faster when dissolved in polar and acidic solvents. This is problematic because ligand exchange uses methanol to precipitate the QDs that allows exchange. Density functional theory (DFT) calculations were performed to understand the effect of solvent polarity on binding energies of the native ligands, DTC and the products of decomposition. The results of the DFT study show that deprotonated DTC, oleic acids and aniline (one of the products of decomposition) bind to the QDs with oleic acid integration being the strongest. To understand ligand exchange we investigated a possible mechanism. In this mechanism Cd(oleate)2 is formed and replaced by a DTC. This mechanism does not describe how DTC binds because DTC binds to Cd2+ sites where Cd(oleate)2 binds to Se2-. From our DFT calculations if DTC- forms s complex with Cd2+, then this complex can bind to surface Se2- resulting in ligand exchange.
12:30 PM - ED6.10.04
Experimental Observation of Two-Dimensional Ostwald Ripening in Semiconductor Nanoplatelets
Philippe Knuesel 1 , Andreas Riedinger 1 , Aurelio Rossinelli 1 , Florian Ott 1 , Aniket Mule 1 , David Norris 1
1 , ETH Zurich, Zurich Switzerland
Show AbstractThe synthesis of colloidal semiconductor nanoplatelets presents an intriguing violation of commonly accepted crystallographic principles, because it involves two-dimensional crystal growth in a cubic material. For zinc blende CdE (E = S, Se, Te) nanoplatelets, symmetry breaking occurs because of an intrinsic kinetic instability that leads to enhanced growth on narrow facets if the growth is not diffusion-limited. Here, we synthesize small (“baby”) nanoplatelets and experimentally show that under non-diffusion-limited conditions, thicker nanoplatelet populations will grow laterally at the expense of thinner ones that dissolve. We use this theoretically predicted form of Ostwald ripening to investigate the growth mechanism of colloidal nanoplatelets. By mixing different materials, we are able to synthesize core-crown nanoplatelets, hence demonstrating material transfer between the individual nanoplatelets. Furthermore, we directly grow nanoplatelets in a thin film of metal carboxylates, thus showing how Ostwald ripening can be applied as a facile and potentially versatile concept for nanoplatelet thin film synthesis.
12:45 PM - ED6.10.05
InAs Colloidal Quantum Dots Synthesis via Aminopnictogen Precursor Chemistry
Valeriia Grigel 1 , Dorian Dupont 1 , Kim Nolf 1 , Zeger Hens 1 , Mickael Tessier 1
1 , University of Gent, Gent Belgium
Show AbstractInAs colloidal quantum dots (QDs) cover the short-wave IR with possible applications in infrared hotodetectors, photovoltaic or in-vivo imaging. However, InAs QDs have attracted considerably less attention than more classical II-VI materials due to their complex syntheses that require hazardous precursors.
Recently, aminophosphine has been introduced as a cheap, easy-to-use and efficient phosphorus precursor to synthesize high quality InP quantum dots.1 In the syntheses aminophosphine provides the phosphorus to be incorporated in the InP QDs and also acts as a reducing agent.2 Here, we present a colloidal hot injection method to form monodisperse InAs QDs starting from tris(dimethylamino)arsine, a commercially available, cheap and safe-to-handle arsenic compound. We implement an approach inspired by the dual role played by aminophosphine in the synthesis of InP QDs. Although analogous disproportionation does not occur for aminoarsine, we find that InAs QDs can be formed by using aminophosphine as the reducing agent of the reaction.3 This results in state-of-the-art InAs quantum dots with respect to the size dispersion and band gap range. Moreover, we present shell coating procedures that lead to InAs/ZnS(e) core/shell QDs that emit in the infrared region. This innovative synthesis approach can greatly facilitate the research on InAs quantum dots and may lead to synthesis protocols for a wide range of III-V quantum dots.
(1) Tessier, M. D.; Dupont, D.; De Nolf, K.; De Roo, J.; Hens, Z. Chem. Mater. 2015, 27, 4893–4898.
(2) Tessier, M. D.; De Nolf, K.; Dupont, D.; Sinnaeve, D.; De Roo, J.; Hens, Z. J. Am. Chem. Soc. 2016, 138, 5923–5929.
(3) Grigel, V.; Dupont, D.; De Nolf, K.; Hens, Z.; Tessier, M. D. J. Am. Chem. Soc. 2016, jacs.6b07533.
ED6.11: Quantum Solids and Superstructures
Session Chairs
Cherie Kagan
Susanna Thon
Thursday PM, April 20, 2017
PCC North, 100 Level, Room 132 C
2:30 PM - *ED6.11.01
Enhanced Energy Transfer and Doping in Semiconductor-Metal Nanocrystal Superlattices
Matteo Cargnello 1 , Benjamin Diroll 2 , Christopher Murray 3
1 , Stanford University, Stanford, California, United States, 2 , Argonne National Laboratory, Lemont, Illinois, United States, 3 Chemistry and Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States
Show AbstractMultifunctional materials are of great interest for their potential in a variety of fields such as sensing, catalysis, solar cell technology, electronic devices. Binary nanocrystal superlattices (BNSLs) combine nanocrystals (NCs) with distinct physical properties by self-assembly of monodisperse components. The periodic ordering in BNSLs specifies stoichiometry and interparticle spacing with precision that are not achievable in glassy films or random mixtures and allows engineering of the interactions between the building blocks. Given the wide spectrum of crystalline and quasi-crystalline structures that have been obtained, the opportunities for exploration of these interactions in BNSLs are numerous. In this contribution, we show two types of interactions leading to different properties in BNSLs.
In a first example, the self-assembly of quasi-quaternary AB13- and AB2-type NSLs using exclusively core-shell particles as building blocks is demonstrated. The NSLs are made of Au/Fe3O4 nanostructures and CdSe/ZnS, CdSe/ZnS/CdS or PbSe/CdSe quantum dots (QDs). We investigated energy-transfer processes in the assemblies by measuring the photoluminescence (PL) of QDs in the final quasi-quaternary NSLs. We demonstrate that energy transfer is enhanced in the assemblies compared to random mixtures due to the maximized number of interactions between the components as a result of the ordering and the higher density of ordered phases.
In a second example, we introduce the concept of nanocrystal (NC) doping in superlattices. We show that, by matching the size of monodisperse gold nanocrystals (Au NCs) with that of semiconducting nanocrystals of cadmium selenide (CdSe) or lead selenide (PbSe) quantum dots (QDs), it is possible to purposely dope the semiconductor superlattices and induce novel properties in these self-assembled materials. We demonstrate that, comparably to the case of atomic doping, the Au NCs take random positions in the superlattice and their concentration can be tuned over a wide range. We show that the electronic and optical properties of the superlattices are affected by the presence of the Au dopants, which increase the conductivity and the photoconductivity of bare CdSe films by several orders of magnitude. We anticipate that this approach can originate a wide variety of NC-doped structures with applications in several fields including electronic materials, solar cells, sensors and catalysis.
3:00 PM - ED6.11.02
Charge Carrier Hopping Dynamics in Homogeneously Broadened PbS Quantum Dot Solids
Rachel Gilmore 1 , Elizabeth Lee 1 , Mark Weidman 1 , Adam Willard 1 , William Tisdale 1
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractEnergetic disorder in quantum dot solids adversely impacts charge carrier transport in quantum dot solar cells and electronic devices. Here, we use ultrafast transient absorption spectroscopy to show that homogeneously broadened PbS quantum dot arrays (σhom2:σinh2 > 19:1, σinh/kBT < 0.4) can be realized if quantum dot batches are sufficiently monodisperse (δ ≤ 3.3%). The homogeneous linewidth is found to be an inverse function of quantum dot size, monotonically increasing from ~25 meV for the largest quantum dots (5.8 nm diameter/0.92 eV energy) to ~55 meV for the smallest (4.1 nm/1.3 eV energy). Furthermore, we show that intrinsic charge carrier hopping rates are faster for smaller quantum dots. This finding is opposite the mobility trend commonly observed in device measurements, but is consistent with theoretical predictions. Fitting our data to a kinetic Monte Carlo model, we extract charge carrier hopping times ranging from 80 ps for the smallest quantum dots to over 1 ns for the largest, with the same ethanethiol ligand treatment. Additionally, we make the surprising observation that, in slightly polydisperse (δ ≤ 4%) quantum dot solids, structural disorder has a greater impact than energetic disorder in inhibiting charge carrier transport. These findings emphasize how small improvements in batch size dispersity can have a dramatic impact on intrinsic charge carrier hopping behavior and will stimulate further improvements in quantum dot device performance.
3:15 PM - ED6.11.03
Ultrasensitive Color Detection from Monolayered Quantum Dots Buried in Amorphous-Oxide Transistors
Kyung-Sang Cho 1 , Chan-Wook Baik 1 , Heejeong Jeong 1
1 Device Lab, Samsung Advanced Institute of Technology, Suwon, Kyunggi, Korea (the Republic of)
Show AbstractColloidal quantum dots (QDs), often referred to as semiconductor nanocrystals, are easily processible for integration onto various substrates using a low-cost, solution-coating method. They have unique optical properties, such as bandgap energies tunable by adjusting their sizes, narrow emission bandwidths, broad absorption spectrum, and high photoluminescence quantum efficiencies. These outstanding advantages have incited considerable research efforts towards the development of QD photodetectors, which now target the performance of conventional state-of-the-art photodetectors. Among various types of photodetection devices (e.g., photodiode, photoconductor and phototransistor), phototransistors provide a wider degree of photocurrent control, which is achievable by adjusting the gate voltages (VG) as well as the source-drain voltages and incident light intensities. Recently, QD-hybrid phototransistors have been introduced for use in combination with high-mobility materials, e.g., amorphous-oxide semiconductors (AOSs)1 and graphene2 to overcome the intrinsic low-mobility problem of QD films.
Here, we report ultrasensitive color detection by monolayered colloidal quantum dots (QDs) buried in amorphous-oxide phototransistors. The proposed active channel in phototransistors is a hybrid configuration of oxide-QD-oxide (OQO) layers, where the gate-tunable electrical property of the silicon-doped, indium-zinc-oxide (SIZO) layers is incorporated with the QD color-selective optical property. A record-high detectivity (8.1×1013 Jones) is obtained, along with three major findings: fast charge separation in QD monolayers; efficient charge transport through high-mobility SIZO layers (20 cm2 V-1 s-1); and gate-tunable drain-current modulation. Particularly, the fast charge separation rate of 3.3 ns-1 measured with time-resolved photoluminescence is attributed to the intermediate QDs in the OQO configuration. These results facilitate the realization of red-green-blue (RGB), color-selective detection exhibiting a photoconductive gain of 107, obtained using a room-temperature deposition of SIZO layers and a QD-solution process. This work offers promising opportunities in emerging applications for color detection with sensitivity, transparency, and flexibility.
References
[1] Liu, X. et al. Photo-modulated thin film transistor based on dynamic charge transfer within quantum-dots-InGaZnO. Appl. Phys. Lett. 104, 113051 (2014).
[2] Konstantatos, G. et al. Hybrid graphene–quantum dot phototransistors with ultrahigh gain. Nature Nanotech. 7, 363–368 (2012).
3:30 PM - ED6.11.04
Strongly Scale-Dependent Charge Transport Mechanisms for an Interconnected Random Network of Silicon Quantum Dots and Nanowires
Serim Ilday 1
1 , Bilkent University, Ankara Turkey
Show AbstractShape and size of nanomaterials significantly alters their optical, electrical, magnetic and structural properties. However, an entirely new paradigm emerges when they are organized hierarchically and interconnected in a way that forms three dimensional, multiscale topologies. Here, we show strongly scale-dependent charge transport mechanisms for such a complex, hierarchical topology, namely an interconnected network of silicon quantum dots and nanowires. The entire structure is electrically percolated, however having different microscale and nanoscale topologies has implications for charge transport and photoemission with subtly different characteristics for charges that are locally generated (up to ∼10 nm) through the photoelectric effect, and for those that are injected externally through the electrodes (over tens to hundreds of nanometers). Charge transport analyses not only provide additional and independent confirmation of the multiscale topology, but also reveal how the remarkably different characteristics of charge conduction at DC and ultrahigh frequencies arise as a result of different topologies in the atomic and microscopic scales. Our claims and findings are supported by thorough structural and morphological analyses.
ED6.12: Hybrid and Organic Quantum Materials
Session Chairs
Matteo Cargnello
Philipp Stadler
Thursday PM, April 20, 2017
PCC North, 100 Level, Room 132 C
4:45 PM - ED6.12.02
Influence of Charge Traps in Bombyx Mori (Silkworm) Silk Derived Carbon Nanodots on Gas Interaction
Anwesha Mukherjee 1 , Siva Reddy 1 , Buddha Deka Boruah 1 , Abha Misra 1
1 , Indian Institute of Science, Bangalore, Bangalore India
Show AbstractAmong the carbon based nano materials, recently photoluminescent carbon nano dots (CNDs) with sizes less than 10 nm have been the topic of research interests for their remarkable photoluminescence, high water solubility, low cytotoxicity, excellent bio-compatibility, unlike their semiconductor counterparts and organic dyes. These intriguing properties render them to be useful potential candidates for various promising applications like bioimaging, drug delivery, optoelectronic and energy devices and sensors [1].
In our work, we have considered Bombyx mori (silkworm) silk which is a highly appreciated biomaterial as the natural source for CNDs by microwave assisted pyrolysis of aqueous silk fibroin solution following a low cost, efficient, environment friendly, facile technique for large scale synthesis of carbon dots. A systematic study on the effect of variation of microwave heating time and power on the size of the carbon dots has been performed. Importantly, as-synthesized carbon dots exhibit both excitation wavelength independent and dependent photoluminescence characteristics that are related to the presence of surface states created by several functional groups attached to the carbon dots.
Apart from exploiting the usual optical properties, it is also important to harness the electrical properties of the CNDs in order to further expand their functionalities. In our work, we have explored the electrical properties of CNDs by fabricating a two terminal CND device by dropcasting CND solution on interdigitated electrodes forming a thin film of CND. A nonlinear I-V response is obtained in the form of hysteresis upon sweeping external applied voltage to the device in both forward and backward directions. The various functional groups on CNDs attract ambient water molecules which in turn act as charge traps and give rise to hysteresis and are responsible for transient current response of the device to step voltage [2]. This important physical phenomena of charge trapping in CNDs also has a major influence on surface interactions. To the best of our knowledge in our finding, for the first time this hysteresis response has been further exploited to study the interaction of the CNDs with nitrogen dioxide gas. A significant variation in the hysteresis response was observed upon interaction with the nitrogen dioxide gas. The hysteresis area is observed to be dependent on the time of gas interaction with the CNDs therefore revealing the interaction mechanism of the CNDs with the gas.
The results reveal an exciting finding on water adsorbates induced charge traps in CNDs, which in turn induce nonlinear electrical hysteresis and play a major role to cultivate an understanding on the mechanism of charge transport in CNDs on surface interactions provided by external stimuli like gas.
References
[1] Baker S N and Baker G A 2010 Angew. Chemie - Int. Ed. 49 6726
[2] Kalita H, Harikrishnan V, Shinde D B, Pillai V K and Aslam M 2013 Appl. Phys. Lett. 102 143104
5:00 PM - ED6.12.03
Ultrafast Energy Transfer from Lead Chalcogenide Nanocrystals to Functionalized Acenes
MingLee Tang 1 , Xin Li 1 , Zhiyuan Huang 1 , Melika Mahboub 1
1 , University of California, Riverside, Riverside, California, United States
Show AbstractEfficient energy transfer between inorganic semiconductor nanocrystal and organic molecules is a widely sought after. Here we report efficient energy transfer from PbS nanocrystal to surface bound tetracene and pentacene molecules anchored with a carboxylic acid group. Steady state photoluminescence quenching experiments indicate that the triplet energy transfer (TET) occurs when the bandgap of PbS NC is larger than the triplet state energy of pentacene (0.86 eV). The larger band gap of smaller PbS leads to the increasing driving force, thus promoting the rate of TET. Ultra-fast transient absorption shows that energy transfer to acene molecules occurs rapidly, within 0.5 ps, as measured by the fast ground state bleaching of PbS and formation of acene molecules excited states at the same timescale.
5:15 PM - ED6.12.04
Ultrafast Transient Absorption Spectroscopy as a Tool for Probing Efficient Charge Carrier Transfer and Dynamics in Resonantly Coupled Organic-Inorganic Nanostructures
Jannika Lauth 1 , Sachin Kinge 2 , Arjan J. Houtepen 1 , Marcus Scheele 3 , Laurens Siebbeles 1
1 , Delft University of Technology, Delft Netherlands, 2 , Toyota Motor Europe, Zaventem Belgium, 3 , University Tübingen, Tuebingen Germany
Show AbstractEfficient coupling of semiconductor nanocrystals (NCs) with organic semiconductor molecules yields a new class of hybrid materials – Coupled Organic-Inorganic Nanostructures (COIN) – that have high potential for optoelectronics.1 COIN composed of PbS NCs functionalized with metal phthalocyanines (Pc) for example assumedly have a combination of both components: the excellent photodetecting properties of the PbS NCs and the selective response of phatholcyanines to vapors/as molecular noses.
For the first time we show that the first excited hole state of PbS NCs indeed can be coupled resonantly to the HOMO of Zn-Pc by applying ultrafast transient absorption spectroscopy.2 Under photoexcitation, PbS-Zn-Pc COIN show significantly faster decay kinetics as compared to uncoupled PbS NCs and a broad redshift of the first excitonic transition. The HOMO-LUMO transition of the Zn-Pc (at 700 nm) is bleached by exciting the PbS nanocrystals only (at 970 nm). Our findings represent the first spectroscopic and electronic structure proof for resonant coupling in COIN and will advance their applicability.
1. Scheele, M.; Brutting, W.; Schreiber, F. Coupled organic-inorganic nanostructures (COIN). PCCP 2015, 17, 97-111.
2. Lauth, J.; Kinge, S.; Siebbeles, L. D. A. Ultrafast Transient Absorption and Terahertz Specroscopy as Tools to Probe Photoexcited States and Dynamics in Colloidal 2D Nanostructures, submitted.
5:30 PM - ED6.12.05
Sample-Transmitted Excitation Photoluminescence (STEP) Technique for Quantifying the Energy Flow on Nanoscale
Mikhail Zamkov 1
1 , Bowling Green State University, Bowling Green, Ohio, United States
Show AbstractUnderstanding the energy flow on nanoscale is an important step towards designing artificial molecular systems with configurable optoelectronic and photochemical properties. Experimental methods for probing the intermolecular energy transfer, however, are quite challenging and often require an individual spectroscopic treatment of specific donor-acceptor combinations. The main issue concerns the spectral crosstalk in the excitation region which is prevalent in most inorganic nanostructures or complex biological systems. Here, we demonstrate a general spectroscopic strategy for measuring the energy transfer efficiency between nanostructured or molecular dyes featuring a significant donor-acceptor spectral overlap. The reported approach relies on filtering the broadband excitation light with solutions of either donor or acceptor molecules designed to selectively turn off the excitation of the respective donor or acceptor species in the sample. The resulting changes in the acceptor emission are then used to determine the quantum efficiency and the rate of the energy transfer (ET) process between arbitrary fluorephores (molecules, nanoparticles, polymers) with unprecedented accuracy. The method also allows differentiating between charge transfer and energy transfer contributions. The feasibility of the reported method is demonstrated using two control donor-acceptor systems: a low-overlap DNA-bridged Cy3-Cy5 dye pair, and high-overlap CdSe560-CdSe610 inorganic film.
ED6.13: Poster Session II: Quantum Materials for Optoelectronic Devices
Session Chairs
Mykhailo Sytnyk
Susanna Thon
Friday AM, April 21, 2017
Sheraton, Third Level, Phoenix Ballroom
9:00 PM - ED6.13.01
Photoluminescent UV Curable Polymer-Quantum Dot Composite as Luminescent Down-Shifting Layer for Photovoltaics
Guy Draaisma 1 , Damien Reardon 1 , Romain Cauchois 1 , Albertus Schenning 2 , Stefan Meskers 2 , Cees Bastiaansen 2 3
1 , DSM Ahead R&D, Eindhoven Netherlands, 2 Department of Chemical Engineering and Chemistry, Eindhoven University of Technology, Eindhoven Netherlands, 3 School of Engineering and Materials Science, Queen Mary University of London, London United Kingdom
Show AbstractThe efficiency of solar cells with a poor UV response can be improved by altering the incident light spectrum with luminescence down-shifting. Stable luminescent additives with a large Stokes shift, high photoluminescence quantum yield and a high absorption coefficient are required for this purpose. Quantum dots are attractive candidates which meet most of the basic requirements for luminescence down-shifting additives. Herein, commercially available heavy metal free core shell CuInS2/ZnS quantum dots are theoretically and experimentally evaluated as luminescence down-shifting additives. The small apolar dodecanethiol ligands of the quantum dots are exchanged with thiol functional oligo-caprolactone ligands, via a ligand exchange process, to improve the quantum dots compatibility with the UV curable resin matrix. Aggregation of the quantum dots is prevented to a large extent in the polymer–quantum dots composite films and the material exhibits luminescence properties which are virtually identical to the luminescence of the quantum dots dispersed in chloroform. Raman spectroscopy and NMR spectroscopy are used to elucidate the ligand exchange and ligand binding processes. It is shown that well-dispersed CuInS2/ZnS quantum dots are required with a near unity quantum yield to increase the efficiency of solar cells significantly especially if high performance inorganic solar cells are employed.
9:00 PM - ED6.13.02
Stacking InAs Quantum Dots Over ErAs Semimetal Nanoparticles on GaAs(001) Using Molecular Beam Epitaxy
Krishnamurthy Mahalingam 1 , Kurt Eyink 1 , Yuanchang Zhang 1 , Joseph Peoples 1 , Lawrence Grazulis 1 , Madelyn Hill 1
1 Nano-Electronic Materials Branch, Air Force Research Laboratory, Wright-Patterson Air Force Base, Ohio, United States
Show AbstractWe have been studying the epitaxial growth of ErAs metal nanoparticles (MNP) in conjunction with InAs quantum dot (QD) for the purpose of producing all epitaxial MNP-QD hybrids which can elicit an enhanced optical response. Many critical parameters exist in the formation of these hybrid structures. Some are related to the MNP or QD shapes, but two are related to the geometry of the MNP-QD hybrid. One is the separation between the MNP and the QD and the other is the orientation of the MNP relative to the QD. In this work, we study the growth of InAs QDs separated from an ErAs MNP layer by a GaAs spacer layer. We have varied the thickness of the GaAs spacer layer after the ErAs MNP growth from 4-20nm and then assess the vertical alignment and separation. We found that the QDs can be aligned to underlying MNPs by careful control of the InAs growth conditions. This alignment process is completely different from the vertical stacking which occurs in QDs stacking and is more easily thought of as directed assembly of a QD in a self-assembled pore structure. Specifically, we show that due to the high surface free energies involved at the ErAs/GaAs interface, nano-sized pores self-assemble over the ErAs MNP. The resulting pore structure is then used in a directed assembly growth of InAs QDs to produce the vertical stacking. We found significant stacking in these growths, however considerable variability existed in the separation of the MNP to the QD. By studying the growth of GaAs over the ErAs nanoparticles by transmission electron microscopy and atomic force microscopy, we have devised a method to look at the variability in the pore structure and found significant variation in pore depth. We suggest this is due to the underlying MNP size, indicating that improvement in the MNP uniformity is essential for producing more uniform MNP-QD couples by this approach.
9:00 PM - ED6.13.03
Light Emitting Mechanisms Dependent on Silicon Nitride Stoichiometry in Si-rich-SiNX Films Grown by PECVD
Tetyana Torchynska 1 , Georgiy Polupan 1 , Larysa Khomenkova 2 , Jose Luis Casas Espinola 1
1 , Instituto Politecnico Nacional, Mexico City, FDM, Mexico, 2 Photoelectronics, V. Lashkaryov Institute of Semiconductor Physics at NASU, Kiev Ukraine
Show AbstractBandgap engineering of Si-based materials through the control of the distribution of Si nanocrystals (Si-NCs) offered future applications of Si-based nanostructured materials in optoelectronics as low-cost, miniaturized, and CMOS-compatible, light-emitting, solar cell and photovoltaic devices. Present work deals with the Si-rich silicon nitride films grown by PECVD technique on silicon substrates. The film stoichiometry was controlled via variation of NH3/SiH4 ratio from R=0.45 up to 1.0. Thermal treatment was performed at 1100°C for 30 min in nitrogen flow to form Si-NCs. To control structural and light emitting properties of the films Raman scattering, X-ray diffraction (XRD),Transmission electron microscopy (TEM), Atomic force microscope (AFM) and photoluminescence (PL) methods were used.The evolutions of PL spectra with the temperature of measurements from 20 to 300 K, as well as with the change of the excitation light quanta and excitation power densities, were studied aiming the determination of the types of optical transitions.
The PL spectra were found to be complex and the shape and magnitude of PL spectra depends on silicon nitride stoichiometry. The increase of gas ratio from R=0.45 to R=1.0 results in the shift of PL peak position from 1.5 eV up to 2.9-3.0 eV. Analysis of the temperature dependence of PL spectra revealed the presence of several PL components with the maxima at: 2.9-3.0 eV, 2.5-2.7 eV, 2.0-2.2 eV, 1.8-1.9 eV and 1.5-1.9eV. The former three PL components were detected in PL spectra of the silicon nitride films obtained at gas ratio within the range R=0.71-1.0. The peak position of the former three PL components unchanged with decreasing the temperature of measurements. This allows describing all these components to the deep defects in silicon nitride host.
The PL band with the peaks at 1.9 eV dominates in PL spectra of silicon nitride films obtained at gas ratio within the range R=0.63-0.59. With ratio R decreasing from 0.59 down to 0.45 the PL band 1.9eV shits and at R equal 0.45-0.50eV this PL band has the peak at 1.5 eV. The high-energy shift of this PL band with sample cooling, the correlation of the temperature dependence of PL peak with the temperature shrinking of Si band gap permits to assign the 1.5-1.9eV PL band to the exciton recombination in Si nanocrystals embedded in silicon nitride films. The presence of these latter was confirmed by Raman scattering spectra and TEM images.
In addition in PL spectra of silicon nitride films obtained at gas ratio within the range R=0.45-0.56 the new PL band 1.8-1.9eV appears.As follows from Raman scattering spectra the amorphous Si phase appears in Si-rich silicon nitride films for mentioned R ratio.This permits to assign the PL band 1.8-1.9eV to the optical transitions related to the Si amorphous phase nanoparticles.The nature of light emitting defects in silicon nitride, the mechanism of photoluminescence and the way for the optimization of optical properties are discussed.
9:00 PM - ED6.13.04
Distinctive Extrinsic Atom Effects on the Structural, Optical, and Electronic Properties of Bi2S3-xSex Solid Solutions
Ajara Rahman 1 , Luisa Whittaker-Brooks 1
1 , University of Utah, Salt Lake City, Utah, United States
Show AbstractNanoscale materials with at least one dimension smaller than 100 nm exhibit remarkable properties that are often not observed for their bulk counterparts. The dramatic modifications to physical and chemical properties at nanoscale dimensions originates from quantum confinement effects, fairly subtle structural changes such as surface reconstruction and lattice expansion/contraction, or the increased contributions from atoms residing on the surface. Over the past decade, several research directions have been focused on the elucidation of finite size effects in semiconductors; indeed, metal chalcogenides nanostructures such as CdS, CdSe, PbS, and PbSe represent well-developed examples where remarkable applications in the areas of photovoltaics and thermoelectrics become accessible upon scaling these materials to nanoscale dimensions. Particularly, to-date, much effort has been devoted to the synthesis and assembly of large bandgap electron and hole transporting materials (i.e., TiO2, ZnO), however these materials still possess limited absorption in the Vis-NIR region. Conversely, little attention has been paid to the synthesis and assembly of low bandgap inorganic materials as a prospective approach to harvest more sunlight in solar cell devices. Amongst several low bandgap inorganic materials (i.e., PbSe, PbS, Bi2S3, and PbS), Bi2S3 has been recognized as a key player in the fabrication of devices for solar energy conversion, thermoelectric technologies, and optoelectronics in the IR region due to its low toxicity, low bandgap (1.3–1.7 eV, which facilitates broad coverage of the solar spectrum), and strong absorption coefficient (105 cm-1). Despite these superb properties, Bi2S3 suffers from low electrical and high thermal conductivities. To mitigate these challenges, our talk will describe the synthesis and optoelectronic properties of Bi2S3 nanowires as potential low bandgap electron transporting materials for solar cells and waste-heat recovery. Also, as part of our talk, we will present several of the synthetic strategies we have developed to fabricate undoped and doped metal chalcogenides with excellent optical and electrical properties with the ultimate goal of building efficient solar-thermal hybrid generators.
9:00 PM - ED6.13.05
Circular Dichroism of Organolead Halide Perovskite Induced by Chiral Organic Cations
Jihoon Ahn 1 , Wooseok Yang 1 , Eunsong Lee 1 , Jeiwan Tan 1 , Hyeok-Chan Kwon 1 , Jooho Moon 1
1 Department of Materials Science and Engineering, Yonsei University, Seoul Korea (the Republic of)
Show AbstractCircularly polarized light (CPL) is defined as the light that has a rotating electric field vector within clockwise or anti-clockwise manner, carrying photons with spin angular momentum in an aligned direction. When a material differently absorbs the two oppositely rotating light, such a phenomenon is referred to as circular dichroism (CD). Although CD can be ubiquitously found in natural organic compounds spanning from the small amino acids to the peptides and DNA lacking in the mirror symmetry (chirality), condensed inorganic materials based CD has been rarely reported to date.
Very recently, chirality transfer from surface organic ligands to inorganic optical materials such as quantum dots and plasmonic metal nanomaterials was discovered, modifying the non-chiral inorganic materials to exhibit the CD at their excitonic or plasmonic band edge, respectively. Because the CD is closely related to the electron spin states of the materials, potential utilization of such materials in spintronic devices is also expected. However, in such a nanomaterial-chiral ligand system, the interaction between chiral ligand and nanomaterials is restricted only at the surface. Therefore, their property is inevitably affected by surface-to-volume ratio of material that is critical to the band tuning of quantum dots and metal nanoparticles. Furthermore, the barrier of organic ligands hampers charge carrier transfer between particles, resulting in hurdles for electronic device application.
Herein, we introduce organolead iodide perovskite materials that enable the CD. By adopting R or S configured chiral organic cations (i.e., R or S-C6H5CH(CH3)NH3+ denoted as R-MBA or S-MBA, respectively), 2-dimensional perovskite in the form of (R-MBA)2PbI4 or (S-MBA)2PbI4 can be obtainable. It was discovered that the perovskite materials are capable of demonstrating either positive or negative CD at the band edge (~510 nm) depending to the R or S configurations of cations, while racemic organic cation mixture does not induce the CD of the perovskite. The organolead iodide perovskite can be considered as an ideal platform for the chirality transfer as compared to the aforementioned materials because organic molecules are incorporated in the crystalline structure so that the surface-to-volume ratio becomes ineffective. Also, as recently demonstrated in the photovoltaic devices, facile electronic device fabrication with scalable solution processes is feasible for perovskite materials. To demonstrate the potential of our material in the device application, chiral perovskite based CPL detector was fabricated. The photocurrent could be modulated due to light helicity dependent absorptions, enabling the determination of the rotating direction of CPL. Beyond this simple proof-of-concept device, advanced optic and spintronic devices are further expected based on our newly developed chiral perovskite materials.
9:00 PM - ED6.13.06
Synthesis of Highly Luminescent Blue Emitting Cd1-xZnxS/ZnS Quantum Dots and Their Application in Light-Emitting Diodes
Pin Ru Chen 1
1 Materials Science and Engineering, National Tsing Hua University, Hsinchu Taiwan
Show AbstractSynthesis and application of highly luminescent blue emitting Cd1-xZnxS/ZnS core/shell quantum dots (QDs) is reported in this study. As-synthesized QDs exhibited superior properties with the quantum yield as high as 82 % and the emission spectral bandwidth as narrow as 14 nm while the photoluminescence (PL) spectra could be flexibly controlled between 400 to 470 nm in the blue region. In addition, TEM and ICP-MS analysis revealed that Cd content was lower than 15 %, which makes these QDs less toxic to environment. Moreover, effects of concentrations of monomers, coordinating solvents and reaction time on the QD emission properties have been investigated which demonstrates this synthesis protocol has potential for mass production. Finally, the as-prepared QDs were applied to electroluminescence devices, which is highly promising for next generation lighting and displays.
9:00 PM - ED6.13.07
On-Chip Integrated Quantum-Dot Silicon-Nitride Microdisk Lasers
Weiqiang Xie 1 , Yunpeng Zhu 1 , Dries Van Thourhout 1 , Thilo Stoeferle 2 , Gabriele Raino 2 , Rainer Mahrt 2 , Pieter Geiregat 1 , Suzanne Bisschop 1 , Tangi Aubert 1 , Edouard Brainis 1 , Zeger Hens 1
1 , Ghent University, Gent Belgium, 2 , IBM-Zurich, Zurich Switzerland
Show AbstractSilicon nitride (SiN) has emerged as an outstanding platform for compact, low-loss and broad wavelength photonic integrated circuits (PICs). However, like silicon-on-insulator, SiN is limited to passive PICs. Colloidal quantum dots (QDs) make for an excellent gain material amenable to versatile, solution-based processing. Yet, harnessing these unique properties in integrated photonic circuits requires a CMOS compatible process flow that maximized overlap between the QDs and the optical modes while leaving the QD properties intact.
Here, we present a new design and processing route that is based on SiN/QD/SiN stacks formed through successive depositions of a SiN bottom layer, a film of QDs and a SiN top layer. By adjusting the deposition conditions of the top layer and subsequent etching recipes, the QD properties can be preserved and photonic structures can be formed through lithography and etching.
Focusing first on strip waveguides with embedded CdSe/CdS QDs emitting at 630 nm, we show that waveguide losses measured at 900 nm can be limited to ≈2.5 dB/cm. Upon femtosecond optical pumping, such waveguides show amplified spontaneous emission at wavelengths close to the QD photoluminescence peak. Pumping waveguides with different lengths, modal gains are estimated at 100-120 cm-1, a number in agreement with the QD material gain as measured using transient absorption spectroscopy.
In a second step, we produced SiN/QD/SiN microdisks vertically coupled to an underlying SiN bus waveguide. Under low intensity optical pumping, the light coupled to the bus waveguide shows the nearly background free line spectrum of the TE and TM whispering gallery modes (WGM) of the disks imprinted on the QD photoluminescence. Upon increasing pump power, we observe a sharp increase of emission intensity in a single WGM mode at a threshold of only 27 μJ/cm2 femtosecond pumping for 7 μm disks. The concomittent narrowing of the emission line, the reduction of the emission lifetime to a few ps only and the enhanced temporal coherence of the emitted light further attest the transition to a lasing regime. Moreover, similar observations are made under nanosecond pumping.
In summary, we demonstrate an extremely compact low-threshold waveguide-coupled QD laser based on the CMOS compatible SiN-platform. We thus show that photonic integrated circuits can tap the acclaimed potential of QDs as broad, tunable and stable optical gain materials. Given the extensive processing possibilities of SiN, this approach opens up new paths for optical communication, lab-on-a-chip, gas sensing and, potentially, on-chip cavity quantum electrodynamics and quantum optics.
9:00 PM - ED6.13.08
Interconnected Network of Quantum Dots for the Enhancement of Color Conversion Efficiency
Heeyeop Chae 1 , Changmin Lee 1
1 , Sungkyunkwan University, Suwon Korea (the Republic of)
Show AbstractColloidal quantum dots (QDs) have attracted much attention as color conversion and light emitting materials not only for light emitting devices but also for color conversion in liquid crystal display panels, Recently, QD-embedded color conversion films are adopted in liquid crystal display panels for the enhancement of color gamut.
In this work, QDs are covalently interconnected to one another and the inter-QD distance is controlled. And the enhancement of color conversion efficiency was demonstrated. The color conversion film was fabricated by reaction oligomers with ligands on the surface of quantum dots (QDs). Alcohol groups were introduced to the end of ligands on the surface of QDs and isocyanate groups were employed as components for the matrix, because it is widely known the reaction between an alcohol group and an isocyanate group. The reaction was easily completed and produced a urethane bonding. The react-enabled components with the ligands were consisted with long alkyl chains and they enabled the QDs to be kept over certain distances each other. The substituted ligand were characterized by FT-IR and 1H-NMR. The enhanced optical property was investigated and compared with QD embedded PMMA film by their absolute photo-luminescence. The urethane film showed 126% higher luminescent efficiency than the PMMA film.
9:00 PM - ED6.13.09
FRET in Colloidal Nanoplatelet Stacks as a Markov Chain
Onur Erdem 1 , Burak Guzelturk 1 , Murat Olutas 1 2 , Yusuf Kelestemur 1 , Hilmi Demir 1 3
1 , Bilkent University, Ankara Turkey, 2 , Abant Izzet Baysal University, Bolu Turkey, 3 , Nanyang Technological University, Singapore Singapore
Show AbstractColloidal semiconductor nanoplatelets (NPLs) make a new class of colloidal nanocrystals with atomically flat surfaces and magic-sized vertical thicknesses of typically 1-2 nm. NPLs display narrow emission spectrum (~10 nm) and fast excitonic lifetime of a few ns [1]. NPLs are also known to form self-assembled one-dimensional structures on solid films, which are commonly regarded as NPL stacks. In stacked formation, NPLs come very close together and form one-dimensional superstructures that can be as long as 1 µm [2]. It has been shown that stacked NPLs have lower quantum yield and faster exciton recombination compared to their nonstacked counterparts due to the ultrafast Förster resonance energy transfer (FRET) between closely packed NPLs in a stack [3].
Here we systematically studied the emission kinetics of stacked and nonstacked NPLs as a function of temperature and experimentally investigated the strong FRET process along the long stacks of these NPLs and modeled the resulting FRET-assisted trapping mechanism using Monte Carlo approach. We found out that the temperature-dependent evolution of PL intensity and fluorescence lifetime greatly differs between the nonstacked and stacked NPLs. The fluorescence decay lifetime of the stacked NPLs is much smaller than that of the nonstacked ones at all temperatures studied. Moreover, the PL intensity of nonstacked NPLs continuously increases by more than 40% when the temperature is decreased from the room temperature to 150 K, whereas the increase in PL is only 8% for the stacked NPLs in the same temperature range [4].
To account for these differences between the stacked and nonstacked NPLs, we considered FRET-induced charge trapping observed in the stacked NPLs. We modeled the fast exciton transfer within a NPL stack as a Markov chain to estimate the quantum yield and fluorescence lifetime of stacked NPLs. Our findings through Monte Carlo simulations indicate that there is a competition between the radiative recombination and the FRET-assisted exciton trapping in the stacked NPLs, which can explain the significant difference in the excitonic kinetics of the stacked and nonstacked NPLs [4]. Our results show that it is essential to take stacking into consideration when understanding the emission kinetics of NPL assemblies.
[1] S. Ithurria et al., “Colloidal nanoplatelets with two-dimensional electronic structure,” Nat. Mater., vol. 10, no. 12, pp. 936–941, 2011.
[2] B. Abécassis et al., “Self-Assembly of CdSe Nanoplatelets into Giant Micrometer-Scale Needles Emitting Polarized Light,” Nano Lett., vol. 14, pp. 710–715, 2013.
[3] B. Guzelturk, O. Erdem et al., “Stacking in Colloidal Nanoplatelets: Tuning Excitonic Properties,” ACS Nano, vol. 8, no. 12, pp. 12524–12533, 2014.
[4] O. Erdem et al., “Temperature-Dependent Emission Kinetics of Colloidal Semiconductor Nanoplatelets Strongly Modified by Stacking,” J. Phys. Chem. Lett., vol. 7, no. 3, pp. 548–554, 2016.
9:00 PM - ED6.13.10
Single- and Multi-Exciton Dynamics in Cesium-Lead-Halide Perovskite Quantum Dots—Implications for Light-Harvesting and Light-Emitting Applications
Istvan Robel 1 , Nikolay Makarov 1 , Shaojun Guo 1 , Oleksandr Isaienko 1 , Wenyong Liu 1 , Victor Klimov 1
1 , Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Show AbstractAll-inorganic Cs–Pb-halide perovskite nanocrystals, or quantum dots, fabricated via a moderate-temperature colloidal synthesis have shown promise for a range of applications from color-converting phosphors and light-emitting diodes to lasers, and even room-temperature single-photon sources. Here we apply various time-resolved spectroscopic techniques to conduct a comprehensive study of spectral and dynamical characteristics of single- and multiexciton states in CsPbX3 nanocrystals with X being either Br, I, or their mixture. Specifically, we measure exciton radiative lifetimes, absorption cross-sections, and derive the degeneracies of the band-edge electron and hole states. We also characterize the rates of intraband cooling and nonradiative Auger recombination and evaluate the strength of exciton–exciton coupling. The overall conclusion of this work is that spectroscopic properties of Cs–Pb-halide quantum dots are largely similar to those of quantum dots of more traditional semiconductors such as CdSe and PbSe. At the same time, we observe some distinctions including, for example, an appreciable effect of the halide identity on radiative lifetimes, considerably shorter biexciton Auger lifetimes, and apparent deviation of their size dependence from the “universal volume scaling” previously observed for many traditional nanocrystal systems. The high efficiency of Auger decay in perovskite quantum dots requires control in their prospective applications in light-emitting devices and lasers. This points toward the need for the development of approaches for effective suppression of Auger recombination in these nanomaterials, using perhaps insights gained from previous wavefunction engineering approaches employed for II–VI nanocrystals.
9:00 PM - ED6.13.11
Study of Quantum Dot Light Conversion Film
Ying-Ju Chen 1 , Hsueh-Shih Chen 1
1 Department of Materials Science & Engineering, National Tsing Hua University, Hsinchu Taiwan
Show AbstractDue to the high photoluminescence (PL) efficiency, broad absorption band and narrow width of the emission band, quantum dots (QDs) are increasingly used in displays to achieve wide color gamut and high optical efficiency. In liquid crystal display (LCD) backlight applications, QD-based film serves as a color enhancement film for LCD which improves the color gamut and energy efficiency. In this study, we fabricated uniform QD-based film with high light conversion efficiency (LCE) and investigated PL of QD in the film. Dispersing QD in an acrylate monomer reduced the QD aggregation which not only improve the haze problem but also increased the PL efficiency and photo-stability of QD films. Effect of the QD concentration, ratio of green to red QDs and scattering medium in QD thin films will be discussed in this study.
9:00 PM - ED6.13.12
Saturated Energy Transfer among InP/ZnS Quantum Dot Solids
Yemliha Altintas 1 , Evren Mutlugun 1
1 , Abdullah Gul University, Kayseri Turkey
Show AbstractColloidal quantum dots have been used as potential candidates of Nonradiative Energy Transfer (NRET) agents in recent years due to their tunable emission characteristics and high quantum yield. They have been employed as Förster Resonance Energy Transfer donors and acceptors based on the application and investigation there of. One of the important aspect of the observation of the energy transfer is the minimal overlap among the donor and acceptor emission, which would otherwise does noes not reveal the emission kinetics both at the donor and the acceptor emission window. Although II-VI group CdSe and core shell type CdSe/ZnS quantum dots provide narrow emission bandwidth along with high quantum yield, making them superior candidates for NRET based applications, III-V group InP based quantum dots suffer from their lower quantum yield and wider full width half maximum (FWHM). In this work, as an effort to investigate the energy transfer among different sized Cd-free quantum dots in a polymer matrix, we have synthesized very high quality InP/ZnS quantum dot donors of green emitters (peak emission at 525 nm) with quantum yield 86% along with 53 nm FWHM, which is amongst the best optical property of this material system, and coupled them to nearby red acceptors emitting at 624 nm with FWHM of 56 nm. Systematically changing the donor to acceptor quantum dot ratio in the polymer film, we have studied the FRET from donor to acceptor quantum dots. Whereas the green emitting QD film has a lifetime of 20.463 ns, introducing acceptor QDs to in close proximity to donor QDs, the lifetime of the donor changes to 12.359 ns in the case of (0.5:1 acceptor to donor ratio), to 9.227 ns in the case of (1:1), and to 9.306 ns in the case of (2:1). The saturation of the energy transfer has been observed with increasing the number of acceptors in the close proximity of donors. In a similar argument we have shown the elongated lifetime of the acceptor due to the energy feeding in the low and high concentration regimes. In the low concentration case, the bare acceptor lifetime is found as 12.788 ns and increases to 21.040 ns as donor QDs are introduced. However, in the high concentration of the acceptor case, the bare lifetime only increases from 16.685 ns to 21.555 ns, which would provide insight about the saturation of the energy transfer for the QD-QD FRET pairs. The investigation of the environmentally friendly high quantum yield emitters along with narrow emission bandwidth III-V nanoparticles and the investigation of the limits of the excitonic interaction among them will provide new insight for the potential use of these emitters for various optoelectronic applications. This work is supported by TUBITAK Project No: 114E107.
9:00 PM - ED6.13.13
Hybrid System of Quasi-0D and Quasi-2D Semiconductor Nanocrystals for Ultra-Efficient Energy Transfer
Murat Olutas 1 2 , Burak Guzelturk 1 , Yusuf Kelestemur 1 , Kivanc Gungor 1 , Hilmi Demir 1 3
1 Department of Electrical and Electronics Engineering, Department of Physics, UNAM Institute of Materials Science and Nanotechnology, Bilkent University, Ankara Turkey, 2 Department of Physics, Abant Izzet Baysal University, Bolu Turkey, 3 3LUMINOUS! Center of Excellence for Semiconductor Lighting and Displays, School of Electrical and Electronics Engineering, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore Singapore
Show AbstractNonradiative energy transfer (NRET), also known as Förster resonance energy transfer (FRET), has been an empowering means to efficiently use and master excitons at the nanoscale in low dimensional semiconductors including colloidal nanocrystals and organic semiconductors and to exploit them in their optoelectronic applications. This near-field phenomenon crucially depends on shape, dimensionality, nanoscale morphology and intrinsic photophysical properties of the donor and acceptor species. To date, although NRET has been widely studied in a variety of quantum-confined materials in different dimensionality [1,2], donor-acceptor assembly systems of the colloidal nanocrystals having mixed-dimensionality using zero-dimensional (0D-) and two-dimensional (2D-) colloidal semiconductor nanocrystals have not been elucidated.
Here we have demonstrated for the first time study of nonradiative energy transfer from colloidal quasi-0D nanocrystals (i.e., colloidal quantum dots, CQDs) to a new class of atomically flat quasi-2D nanocrystals [3], which are also dubbed as colloidal quantum wells (CQWs) or nanoplatelets (NPLs), in their hybrid solid films [4]. In this work, systematic investigation of NRET using steady-state and time-resolved fluorescence spectroscopy as a function of the temperature allowed us to explore and understand its efficiency limits. Our findings show that the resulting NRET, which enables exciton feeding from the CQDs to CQWs, can be as efficient as 90% at room temperature. Importantly, the energy transfer efficiency reaches an extra ordinary level of 94% at cryogenic temperatures. The underlying reason behind achieving NRET with an almost near-unity efficiency level is found to be the exceptional strong absorption (ultra-large absorption cross-section) [5] in the CQWs allowing for efficient NRET to extend to unconventional long distances at the nanoscale, which would otherwise not be possible by using any other colloidal nanocrystals as acceptor except for the CQWs. We also show that highly linear NRET efficiency behavior as a function of the temperature is observed, which makes the proposed hybrid system highly appealing for a new approach of non-contact sensitive temperature probing at nanoscale.
[1] X. Liu , J. Qiu , Chem. Soc. Rev., 44, 8714-8746 (2015) .
[2] B. Guzelturk, M. Olutas, et al, Nanoscale, 7, 2545-2551 (2015).
[3] E. Lhuillier, S. Pedettiet, et al., Acc. Chem. Res., 48, 1, 22-30, (2015).
[4] M. Olutas, B. Guzelturk, Y. Kelestemur, et al., Adv. Funct. Mater., 26, 2891-2899, (2016).
[5] A. Yeltik , S. Delikanli , M. Olutas, et al., J. Phys. Chem. C, 119 , 26768-26775, (2015).
9:00 PM - ED6.13.14
Structural and Optical Properties of Molecular Beam Epitaxy Grown InAsBi
Arvind Shalindar 1 2 , Preston Webster 1 3 , Barry Wilkens 4 , Terry Alford 2 3 , Shane Johnson 1 3
1 Center for Photonics Innovation, Arizona State University, Tempe, Arizona, United States, 2 Engineering of Matter, Transport and Energy, Arizona State University, Tempe, Arizona, United States, 3 Electrical, Computer and Energy Engineering, Arizona State University, Tempe, Arizona, United States, 4 LeRoy Eyring Center for Solid State Science, Arizona State University, Tempe, Arizona, United States
Show AbstractSeveral nearly lattice-matched, droplet-free, 1 μm thick, narrow bandgap InAsBi layers grown by molecular beam epitaxy on GaSb substrates are examined using Rutherford backscattering spectrometry (RBS) and X-ray diffraction (XRD) [1]. The samples are grown at temperatures ranging from 270 to 280 °C with As/In flux ratios from 0.96 to 1.05 and Bi/In flux ratios from 0.060 to 0.065 [2]. Transmission electron microscopy measurements of these samples indicate excellent crystallinity, no ordering, no visible defects over large lateral distances, and lateral fluctuations in the Bi mole fraction on a 10 nm length scale [3]. Ion channeling measurements indicate that all the Bi atoms are substitutional. Random RBS measurements indicate that the average Bi content of the InAsBi sample set ranges from 5.03% to 6.45%, and XRD measurements show sidebands near the main (004) diffraction peak, confirming that the Bi mole fraction is not perfectly uniform in the lateral direction. The average out-of-plane tetragonal distortion is determined by simulating the main and sideband diffraction peaks, from which the average InAsBi lattice constant is determined. By comparing the InAsBi lattice constant inferred from the XRD measurements with the Bi mole fraction measured using RBS, the lattice constant of zinc blende InBi is determined to be 6.6107 Å.
The absorption coefficient of the InAsBi sample containing 6.45% Bi is measured using spectroscopic ellipsometry [4]. The room temperature bandgap of the nearly lattice-matched InAs0.9355Bi0.0645 layer is 60.6 meV, which is significantly smaller than the 354 meV bandgap of InAs. The bandgap and band edge alignment of InAs1-xBix is characterized as a function of mole fraction using the band anticrossing model.
[1] A. J. Shalindar, P. T. Webster, B. J. Wilkens, T. L. Alford, S. R. Johnson, J. Appl. Phys. 120, 145704 (2016).
[2] P. T. Webster, N. A. Riordan, C. Gogineni, S. Liu, J. Lu, X.-H. Zhao, D. J. Smith, Y.-H. Zhang, S. R. Johnson, J. Vac. Sci. Technol. B 32, 02C120 (2014).
[3] J. Lu, P. T. Webster, S. Liu, Y.-H. Zhang, S. R. Johnson, D. J. Smith, J. Cryst. Growth 425, 250 (2015).
[4] P. T. Webster, A. J. Shalindar, N. A. Riordan, C. Gogineni, H. Liang, A. R. Sharma, S. R. Johnson, J. Appl. Phys. 119, 225701 (2016).
9:00 PM - ED6.13.15
Solution Processed MoO2 and ZnO Heterojunction Electrical and Optical Characteristics
Hemant Kumar 1 , Yogesh Kumar 1 , Gopal Rawat 1 , Chandan Kumar 1 , Bratindranath Mukherjee 2 , Bhola Nath Pal 3 , Satyabrata Jit 1
1 Electronics Engineering, IIT (BHU), Varanasi, Uttar Pardesh, India, 2 Metallurgy, IIT(BHU), Varanasi, Uttar Pardesh, India, 3 School of Material Science and Technology, IIT(BHU), Varanasi, Uttar Pardesh, India
Show AbstractIn this work solution processed heterojunction between MoO2 and ZnO QDs is analyzed for the electrical and optical properties. The ZnO QDs are used for the fabrication of heterojunction with MoO2, are synthesized using hot-injection method. The synthesis of ZnO QDs is optimized by the variable constraints of temperature and time, with the size of ZnO QDs achieved to be ~2.33nm with a standard deviation of < 5%. Solution processed technique is used for the epitaxial growth of MoO2 over the ZnO QDs. The solution processed synthesis of MoO2 allows the device to be annealed at 270oC which improves the quality of the MoO2 film and uniformity of the heterojunction between ZnO QD and MoO2. The solution-processed films of ZnO QDs and MoO2 have been analyzed for reflectance, transmittance, absorption and photoluminescence properties to analyze the optical behavior and band to band transition of the materials. Further, the heterojunction of MoO2 and ZnO QDs is analyzed for built-in potential, carrier density, the width of the depletion region, and responsivity at the applied bias of zero volts. The obtained values are 0.046 V, ~6.153x1015 cm-3, ~36 nm, and 0.12AW-1 respectively. We have also demonstrated for the first time diffusion of MoO2 into the layer of ZnO QDs for thermally evaporated and solution processed MoO2. MoO2 deposited via solution route and the heterojunction of solution processed MoO2, and ZnO QDs shows better stability with the increasing temperature.
9:00 PM - ED6.13.16
Commercial Prospects for Using Quantum Dots in Solid-State Lighting
Hunter McDaniel 1 , Matt Bergren 1 , Karthik Ramasamy 1 , Aaron Jackson 1 , Nikolay Makarov 1
1 , UbiQD, LLC, Los Alamos, New Mexico, United States
Show AbstractSolid-state lighting (SSL) using LEDs is the most efficient and longest-lasting method to generate light from electricity. Typically, white light is created by downconverting a portion of the emission from a high-efficiency near-ultraviolet or blue LED using phosphors. Present day phosphors have relatively broad emission peaks, with linewidths (full width at half the maximum, FWHM) exceeding 100 nm. For the red phosphor, this results in a significant portion of the emission being wasted since it extends beyond the response of the human eye. Peak emission wavelength is largely fixed by material choice, which limits design flexibility in optimizing trade-offs between color-quality and performance.
Quantum dots (QDs) offer solutions to these problems in their narrow and extraordinarily tunable emission. Unfortunately, existing QD technologies also create new problems with their toxicity (cadmium or lead based), high costs, and sometimes poor stability. Despite these issues, companies are investigating QDs as on-chip materials for white light-emitting diodes. The QD industry recognizes the “cadmium problem” and some companies are now investigating InP QDs as an alternative. However, despite the reduced toxicity of InP, the material is a known carcinogen and is expensive to manufacture.
UbiQD solves the problems with existing QD technologies by producing toxic-heavy-metal-free CuInS2 QDs at a much lower cost than alternatives. The broadness of the PL (FWHM) is currently worse for CuInS2 than CdSe or InP but UbiQD views this as development goal and not an intrinsic limitation of the material. On other performance metrics CuInS2 QDs are favorable; for example, we have achieved QY > 95%, with significantly less self-absorption, and better thermal stability (up to ~200 C) than CdSe. This talk will broadly discuss why QDs are interesting for SSL and then focus on UbiQD’s efforts to study performance of CuInS2 QDs in commercial silicones.
9:00 PM - ED6.13.18
Mg Doping Effects on Optical and Electrical Properties of Solution-Processed ZnO Quantum Dots Based Thin Film Devices
Yogesh Kumar 1 , Hemant Kumar 1 , Gopal Rawat 1 , Chandan Kumar 1 , Bratindranath Mukherjee 1 , Bhola Nath Pal 1 , Satyabrata Jit 1
1 , IIT (BHU), VARANASI India
Show AbstractThe effects of Mg doping on the optical and electrical properties of solution-processed ZnO quantum dots (QDs) thin film has been analyzed. The particle size ~2.33nm was confirmed from the Transmission Electron Microscopy (TEM), which is less than the Bohr's radius of ZnO (~2.87nm). The thin films of ZnO QDs with a different doping concentration of Mg (2% and 4%) are deposited over the cleaned glass substrate using solution processing. The effect of doping is evident on the bandgap of the material as the doped QD shows a blue shift in the transmission spectrum. Further, we have analyzed fabricated device of Mg-doped ZnO QD and calculated the carrier concentration, Hall mobility, and sheet resistance of the film. The values found to be 1.01x1015 cm-3, 4.49 cm2V-1S-1, and 5.18x108 Ω Squre-1 respectively for Mg(2%)-doped ZnO QDs and 6.39x1015 cm-3, 6.60 cm2V-1S-1, and 6.39x107 Ω Squre-1 respectively for Mg(4%)-doped ZnO QDs. The device with doping of 4% Mg shows the better electrical properties comparative to ZnO QDs with Mg doping of 2% and 0%. The transmittance curve of ZnO QDs shows the sharp cut-off for the visible region with an increase in doping percentage and Mg(4%)-doped ZnO shows ~90% transmittance across the visible region. These characteristics of Mg-doped ZnO can be further utilized for photo-detection application of short wavelengths or filter the short wavelengths for visible detectors.
9:00 PM - ED6.13.19
Fabrication of Color-by-Blue White-Light-Emitting Diodes Using Cesium Lead Halide Perovskite Quantum Dots
Hee Chang Yoon 1 , Keyong Nam Lee 1 , Soyoung Lee 1 , Sohee Kim 1 , Young Rag Do 1
1 , Kookimin University, Seoul Korea (the Republic of)
Show AbstractWe synthesized cesium lead halide (CsPbX3, X = Cl, Br, I, and their mixture) perovskite quantum dots (PeQD) and fabricated CsPbX3 PeQD-based monochromatic down-converted light-emitting diodes (DC-LEDs) and a combination of these components into a multi-package white DC-LED. CsPbX3 PeQDs with narrow full-width-at-half-maximum (FWHM) values, useful visible-emissive properties, and excellent quantum yields (QYs) were synthesized by means of a colloidal hot injection method. In this study, by controlling the halide ratio, we were able to realize the emission six colors from the CsPbX3 PeQDs (cyan (C), green (G), yellowish green (Y), amber (A), orange (O), and red (R)) in a measured emission wavelength range of 488 – 645 nm with a QY range of 0.5 – 0.8 and a narrow FWHM of 19 nm – 35 nm. To realize CsPbX3-based DC-LEDs, we utilized a UV-curable binder (as an encapsulant), an InGaN blue (B) LED (as an excitation source), and a long-wavelength pass-dichroic filter (LPDF, as a blue-mirror-yellow window). The fabricated color-by-blue six-color (CGAYOR) monochromatic CsPbX3-based DC-LEDs and B LED can be combined to realize a white DC-LED with three- (BGR), four- (BGAR), five- (BCGAR) and six-color (BCGYOR) combined multi-packages. In the six-color combined multi-package white DC-LED, we report excellent vision and color performance factors with feasible luminous efficacy levels (LEs) in the range of 38.8 – 61.4 lm/W and high color rendering indexes (CRIs) ranging from 94 to 96.
Symposium Organizers
Philipp Stadler, Johannes Kepler University Linz
Edward (Ted) Sargent, University of Toronto
Mykhailo Sytnyk, Friedrich-Alexander-Universität Erlangen-Nürnberg
Susanna Thon, Johns Hopkins University
Symposium Support
Lake Shore Cryotronics, Inc.
LOT, Quantum Design
ED6.14: Perovskite Quantum Materials
Session Chairs
Wolfgang Heiss
Mykhailo Sytnyk
Friday AM, April 21, 2017
PCC North, 100 Level, Room 132 C
9:45 AM - *ED6.14.01
Solar Cells of Perovskite Quantum Dots—Stable Cubic CsPbI3 Films for High-Efficiency Photovoltaics
Abhishek Swarnkar 1 2 , Ashley Marshall 1 4 , Erin Sanehira 1 3 , Boris Chernomordik 1 , David Moore 1 , Jeffrey Christians 1 , Tamoghna Chakrabarti 5 , Joseph Luther 1
1 , National Renewable Energy Laboratory, Lakewood, Colorado, United States, 2 , IISER, Pune India, 4 , University of Colorado, Boulder, Colorado, United States, 3 , University of Washington, Seattle, Washington, United States, 5 , Colorado School of Mines, Golden, Colorado, United States
Show AbstractWe show nanoscale phase stabilization of CsPbI3 quantum dots (QDs) to low temperatures that can be used as the active component of efficient optoelectronic devices. CsPbI3 is an all-inorganic analog to the hybrid organic cation halide perovskites, but the cubic phase of bulk CsPbI3 (a-CsPbI3)—the variant with desirable band gap—is only stable at high temperatures. We describe the formation of a-CsPbI3 QD films that are phase-stable for months in ambient air. The films exhibit long-range electronic transport and were used to fabricate colloidal perovskite
QD photovoltaic cells with an open-circuit voltage of 1.23 volts and efficiency of 10.77%. These devices also function as light-emitting diodes with low turn-on voltage and tunable emission.
10:15 AM - ED6.14.02
Improvement of Stability of Methylammoium Lead Halide Nanocrystals via Star-Like Triblock Copolymer Template-Assisted Strategy
Yanjie He 1 , Zhiqun Lin 1
1 , Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractMethylammoium lead halide perovskites quantum dots (CH3NH3PbX, X=Cl, Br, I) possess excellent excitonic and optical properties owing to high photoluminescence quantum yield and narrow emission band, giving rise to tremendous applications in high-efficiency solar cells and light-emitting diodes. Unfortunately, organic-inorganic hybrid perovskites quantum dots (PQDs) with large surface area and high activity suffer from poor stability and extreme moisture sensitivity. To overcome the instability issue, in this study, we developed a versatile and unconventional synthetic strategy for the preparation of methylammoium lead halide PQDs with silica coating for the purpose of improving the stability of PQDs. By employing 21-arm star-like poly(4-vinylpyridine)-b-poly(tert-butyl acrylate)-b-polyethylene oxide (P4VP-b-PtBA-b-PEO), nearly monodisperse lead halide nanocrystals tethered with PtBA-b-PEO are generated due to the strong coordination ability of pyridine groups in P4VP blocks, followed by hydrolysis of PtBA blocks to PAA blocks. Lead halide nanocrystals are converted to PQDs by reacting with corresponding ammonium halide. Silica coating is achieved by hydrolysis of tetramethyl orthosilicate on the surface of resulting PQDs, generating PQDs with markedly improved stability. Our copolymer template-assisted approach provides a viable method to prepare stable PQDs which is in contrast with conventional ligand-assisted reprecipitation method.
10:30 AM - ED6.14.03
Perovskite Nanocrystals as a Color Converter for Visible Light Communication
Ibrahim Dursun 1 , Chao Shen 2 , Manas Parida 1 , Jun Pan 1 , Smritakshi Sarmah 1 , Davide Priante 2 , Noktan AlYami 1 , Jiakai Liu 1 , Makhsud Saidaminov 1 , MohdSharizal Alias 2 , Ahmed Abdelhady 1 , Tien Khee Ng 2 , Omar Mohammed 1 , Boon Ooi 2 , Osman Bakr 1
1 , KAUST Solar Center, Thuwal Saudi Arabia, 2 Photonics Laboratory, KAUST, Thuwal Saudi Arabia
Show AbstractData and wireless communication support much of the social and economic structures critical for daily lives. As the increasing demand for data and wireless communication, current radio frequency (RF) and microwave wireless technologies cannot sustain with this surging demand due to their congested spectra and limited bandwidth. Visible light communication (VLC) is an emerging technology that uses light-emitting diodes (LEDs) or laser diodes for simultaneous illumination and data communication. This technology is envisioned to be a major part of the solution to the current bottlenecks in data and wireless communication. Nevertheless, the conventional lighting phosphors that are typically integrated with LEDs have limited modulation bandwidth and therefore cannot afford the bandwidth required to realize the potential of VLC. Here, we present a promising light converter for VLC by designing solution-processed CsPbBr3 perovskite nanocrystals (NCs) with a conventional red phosphor. The fabricated CsPbBr3 NC phosphor-based white light converter exhibits an unprecedented modulation bandwidth of 491 MHz, which is ∼40 times greater than that of conventional phosphors, and the capability to transmit a high data rate of up to 2 Gbit/s. Moreover, this perovskite-enhanced white light source combines ultrafast response characteristics with a high color rendering index of 89 and a correlated color temperature of 3236 K, thereby enabling dual VLC and solid-state lighting functionalities.
10:45 AM - ED6.14.04
Control of Morphology, Photoluminescence, and Stability of Colloidal Methylammonium Lead Bromide Nanocrystals by Oleylamine Capping Molecules
Cheng-Hsin Lu 1 , Jiaang Hu 1 , Wan Shih 2 , Wei-Heng Shih 1
1 Materials Science and Engineering, Drexel University, Philadelphia, Pennsylvania, United States, 2 School of Biomedical Engineering, Science, and Health Systems, Drexel University, Philadelphia, Pennsylvania, United States
Show AbstractMethylammonium lead bromide (CH3NH3PbBr3) thin films and nanocrystals are useful for solar cells and LED applications. In order to improve stability in ambient environments, CH3NH3PbBr3 nanocrystals have been synthesized using oleylamine as the capping molecule. It was found that by increasing the oleylamine to CH3NH3PbBr3 perovskite ratio (OPR), the photoluminescence wavelengths of CH3NH3PbBr3 nanocrystals could be varied from 505 nm (green) to 450 nm (blue). The change in emission wavelength is associated with a morphological change from nanoplatelets of ~10 nm in width with OPR<1 to nanoparticles of ~3 nm in diameter with OPR>1. It is suggested that the morphological change of nanocrystals is a result of geometric constraints of packing oleylamine with PbBr3 octahedra. The nanocrystals with OPR=0.75 could retain the photoluminescent property for more than 6 months under the ambient conditions and sustain a high temperature of 150°C for 30 minutes.
References
Cheng-Hsin Lu, Jiaang Hu, Wan Y. Shih, Wei-Heng Shih, “Control of morphology, photoluminescence, and stability of colloidal methylammonium lead bromide nanocrystals by oleylamine capping molecules,” J. Colloid & Interface Science, 484, 17–23 (2016)
ED6.15: Quantum Devices and Plasmonics
Session Chairs
Joseph Luther
Philipp Stadler
Friday PM, April 21, 2017
PCC North, 100 Level, Room 132 C
11:30 AM - *ED6.15.01
From Ultrathin Perovskite Solar Cells to Photonic Sources with Solid-State Nanopore Confinement
Martin Kaltenbrunner 1
1 , Johannes Kepler University, Linz Austria
Show AbstractFlexibility, compliance and weight will turn out to be key metrics for future electronic appliances and their power supplies. Emerging applications like solar powered aviation or wearable electronics require photovoltaic technologies that are highly efficient, light-weight, low-cost, and stable during operation. Organolead halide perovskites constitute a highly promising class of materials, but suffer limited stability under ambient conditions without heavy and costly encapsulation. In this talk we introduce methods, materials and design strategies for ultrathin (3 µm), highly flexible perovskite solar cells with a record power-per-weight as high as 23 W/g. To facilitate air stable operation, we introduce a chromium oxide-chromium interlayer that effectively protects the metal top contacts from reactions with the perovskite. We show prolonged stable operation in ambient air of ultrathin non-encapsulated planar perovskite solar cells with gold, copper and aluminium electrodes. These ultra-lightweight solar cells are successfully used to power aviation models. Potential future applications include unmanned aerial vehicles - from airplanes to quad-copters and weather balloons - for environmental and industrial monitoring, rescue and emergency response, and tactical security applications. In a hybrid architecture laminated atop pre-strained elastomers, such solar cells are highly stretchable and conformable. Tuning the band gap of perovskite semiconductors via quantum size effects is currently advancing optoelectronics. Here we introduce a general strategy of controlling shape and size of perovskite nanocrystallites (less than 10 nm) in domains that exhibit strong quantum size effects. Without manipulation of halide stoichiometry, we achieve fine-tuning of band gap across a wide colour gamut from near infrared to ultraviolet through solid-state confinement in nanoporous alumina (npAAO) or silicon (npSi) scaffolds. Confinement in npSi facilitates a ~50 nm hypsochromic shift from green to blue photoluminescence for caesium-bromide perovskite nanocrystals. By infiltrating electrically addressable npAAO templates, we fabricate perovskite nanorod light-emitting diodes achieving blue shifted narrow-band emission. Our device demonstrations corroborate band gap engineering through solid-state confinement as a powerful tool to precisely control the optoelectronic properties of perovskite nanocrystal emitters in next generation solution-derived photonic sources.
12:00 PM - ED6.15.02
Near Field Coupling of Localized Surface Plasmon Resonance in Metal Oxide Nanocrystals
Delia Milliron 1 , Ankit Agrawal 1
1 , The University of Texas at Austin, Austin, Texas, United States
Show AbstractSemiconductors can be rendered plasmonic by doping to create high concentrations of free carriers. Degenerately doped wide band gap metal oxides are commonly used as transparent conductive thin films in optoelectronic devices, and these same materials exhibit localized surface plasmon resonance (LSPR) when synthesized as discrete colloidal nanocrystals. Based on the dynamic responsive behavior of the infrared LSPR absorption of these new materials, we are developing a new class of smart windows that can dynamically control heat loads and daylighting in buildings. Advancing further applications of plasmonic oxide nanocrystals, relies on better understanding LSPR in prototypical materials like ITO and developing innovative approaches to control doping, shape, and size, including novel compositions. Many applications of interest will hinge, in part, on the ability to concentrate infrared light into nanoscale volumes and to enhance electronic and vibrational state transitions via associated field enhancement effects. We are engineering the selection of dopants and crystalline properties of our nanocrystals to tune their LSPR modes, with a conceptual underpinning of density functional theory and electromagnetic simulations. By measuring LSPR spectra of individual nanocrystals using tip-enhanced synchrotron FTIR spectroscopy we characterize the intrinsic dielectric properties of these new materials. As such we can predict strong near field of infrared light is possible using plasmonic metal oxide nanocrystals. Finally, the first results demonstrating strong coupling in the near field will be presented.
12:15 PM - ED6.15.03
Ultrasmall Mode Volumes in Plasmonic Cavities of Nanoparticle-on-a-Mirror Structures
Shengxi Huang 1 , Tian Ming 1 , Qifeng Ruan 2 , Jianfang Wang 2 , Mildred Dresselhaus 1 , Jing Kong 1
1 Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Department of Physics, The Chinese University of Hong Kong, Hong Kong China
Show AbstractThe mode volume and Purcell factor are two important parameters to assess the performance of optical nanocavities. Achieving small mode volumes and high Purcell factors for nanocavity structures while simplifying their fabrication has been a major task to realize high-performance and large-scale photonic devices and systems. In this work, we systematically analyze different optical resonators based on nanoparticle-on-mirror (NPoM) structures, which are easy to fabricate and flexible to use. Direct comparison of these optical resonators is made through finite-difference time-domain simulations. We demonstrate the achievement of ultra-small mode volumes below 10-7 (λ/n)3 based on the NPoM structure by rationally selecting the structural parameters. Such NPoM structures provide a decent Purcell factor on the order of 107, which can effectively enhance spontaneous emission and facilitate a number of photonic applications. The simulation results are confirmed by our dark field scattering measurements. Moreover, careful experimental explorations using second-harmonic generation reveal that the surface and bulk properties of the optical cavity are sensitive to the gap distance between the nanoparticle and the metal film and affect the nonlinear optical tensors. This work is scientifically important, and offers practical guidelines for the design of optical resonators for state-of-the-art optical and photonic devices.
12:30 PM - ED6.15.04
High-Efficiency Germanium Quantum Dot Photodetectors—Noise Performance and Operating Temperature Effects
Stylianos Siontas 1 , Alexander Zaslavsky 1 , Domenico Pacifici 1
1 , Brown University, Providence, Rhode Island, United States
Show AbstractWe present results on the noise performance of high efficiency germanium quantum dot (Ge QD) photodetectors. The devices were fabricated by co-sputtering Ge and SiO2 targets to create a 200 nm-thick oxide film containing Ge QDs on n-Si substrates held at 400oC. A 500oC annealing step was then performed in a N2 environment for 30 min to improve the quality of the oxide matrix while generating larger size QDs with better crystallinity. Subsequently, an optically transparent, highly conductive 100 nm-thick ITO layer was grown as the top gate electrode. Finally, photolithography was performed to define several devices with 0.5 and 1.5 mm2 active areas, obtained by etching away the ITO and Ge QD/SiO2 layers using a dilute HCl solution. The photolithographically defined detectors showed suppressed dark current, compared to cleaved samples of same area, attributed to reduced leakage current at the periphery. Furthermore, they exhibited a strong spectral photoresponse extending into the near infrared, with photocurrent values (Iph) three orders of magnitude higher than the dark current, leading to responsivities up to 2 A/W over the 400–1100 nm wavelength range and internal quantum efficiency (IQE) up to 400% at reverse bias of –10 V. In addition, the noise analysis of the best performing 0.5 mm2 device was carried out in order to estimate the signal to noise ratio (SNR) and specific detectivity (D*). In evaluating the SNR = Iph/σn, the contributions to the total noise current (σn) taken into consideration were the Poisson (shot) noise σs2 = 2e(Iph+Id)B*IQE and Johnson-Nyquist noise σj2 = 4kTB/R, where B is the experimentally measured 3 dB bandwidth, and R is the detector's load resistance. Measuring the dependence of Iph, B and IQE on incident power yielded SNR up to 105. As for D* = (A*B)1/2/NEP, where A is the detector active area and NEP the noise equivalent power, we calculated the NEP by linearly extrapolating the thermally-dominated range of the measured SNR to SNR = 1 yielding D* = 6*1012 cmHz1/2W-1. Finally, the characterization procedure followed above was repeated as a function of temperature, by mounting the photodetector into a variable temperature cryostat with optical access and lowering the temperature in steps of 50oK down to 200oK so as to study a possible enhancement in their performance. The observed effect of lower operating temperature was significant reduction in dark current – approximately an order of magnitude per 50oK of decrease, whereas the photocurrent values remained roughly unchanged. This resulted in reduced thermal noise and in turn higher SNR and D* values compared to room temperature operation, without negatively impacting the responsivity. The aforementioned figures of merit suggest that Ge QDs in an oxide matrix are a promising alternative material for high-performance photodetectors working in the visible to near-infrared spectral range, with particular improvement when operated in the low temperature regime.
12:45 PM - ED6.15.05
Antimonide-Based Membranes—Synthesis, Integration, and Strain-Engineering
Seyedeh Marziyeh Zamiri 1 , Farhana Anwar 1 , Brianna Klein 1 , Amin Rasoulof 1 , Ted Schuler-Sandy 1 , Christoph Deneke 2 , Sukarno Ferreira 3 , Francesca Cavallo 1 , Sanjay Krishna 1
1 , University of New Mexico, Albuquerque, New Mexico, United States, 2 , Laboratório Nacional de Nanotecnologia , Campinas Brazil, 3 , Departamento de Física, Universidade Federal de Viçosa, Viçosa Brazil
Show AbstractDespite the numerous demonstrations of III-V semiconductor membranes, Sb-based heterostructures have not been isolated from their epitaxial growth substrate. Here, we will discuss a few examples to illustrate the technological value of Sb-based membranes in the field of infra-red imaging and microelectronics. We will demonstrate a versatile release and transfer technique, which enables integration of any Sb-based heterostructure with a variety of hosts, including Si, polydimethylsiloxane and metal coated substrates. Our approach is based on capping the surface as well as the sidewalls of the membrane during release. Electron microscopy shows structural integrity of transferred membranes with thickness of 100 nm to 2.5 μm and lateral sizes from 24×24 μm2 to 1×1 cm2. Atomic force and electron microscopy reveal the excellent quality of the membrane interface with the new host. The crystalline structure of the membrane is not altered by the fabrication process, and a minimal elastic relaxation occurs during the release step, as demonstrated by X-ray diffraction and mechanical modeling. A method to engineer strain in Sb-compounds by bending is theoretically illustrated. Continuum elasticity theory shows that up to ~3.5% compressive strain can be induced in an InSb quantum well through external bending. Photoluminescence spectroscopy and characterization of an infrared photodetector based on InAs/InAsSb bonded to Si demonstrate the functionality of transferred membranes in the infrared range.
ED6.16: Quantum Optical Devices
Session Chairs
Friday PM, April 21, 2017
PCC North, 100 Level, Room 132 C
2:30 PM - *ED6.16.01
Optical Fiber Antennae with Quantum Dots for Gas Sensing
Feng Gao 1 , Yang Wang 1 , Ming Tang 1 , Huan Liu 1
1 , Huazhong University of Science and Technology, Wuhan China
Show AbstractSensitive and selective detection of toxic or hazardous gases has become increasingly important for environmental monitoring, personal safety protection, and industrial manufacturing. Optical fiber sensors possess a number of desirable advantages over their electrical counterparts for gas sensing, such as the immunity to electromagnetic interference as well as the ability for muti-parameters measurement and long-distance networking. Motivated by the sensing function of antennae in arthropods, we constrcut optical fiber antennas for gas sensing, in which the colloidla quantum dots conformally coated on the fiber surface behave like olfactory receptors. The gas molecules adsorbed on the quantum dots change the local carrier concentration in quantum dot solids, which leads to a change in their refractive index. This interatction of gas molecules with quantum dots could be transfromed into optical signals through the optical fiber antennae. Owing to the large surface area, highly tunable physical and chemical properties of colloidal quantum dots, combined with the versatile fiber microstructure, the optical fiber antennae with quantum dots offer a new degree of freedom to precise, real-time and large-scale gas monitoring.
3:00 PM - ED6.16.02
Quantum Dot Light Emitting Diode Fabricate by Transfer Printing
Kuo-Yang Lai 1
1 Department of Materials Science Engineering, National Tsing Hua University, Hsinchu Taiwan
Show AbstractIn this study, we use transfer printing process to fabricate quantum dots light-emitting diodes (QLED). Different from inkjet printing, transfer printing is a much simpler and cheaper process to make a patterned device. First, we modified the Si substrate with octadecyltrichlorosilane (ODTS) and spin-coated the QDs on the substrate. Then, we used polydimethylsiloxane (PDMS) as a transfer stamp to print QD film onto devices. The printing process is controlled by a homemade transfer printer. The printed films showed that the QD layer were closely packed and had the excellent surface topography. It has demonstrated that the transfer printing method is a promising method for fabricating micro-LEDs and large-scale flexible displays.
3:15 PM - ED6.16.03
An All-Solution-Based High-Gain Hybrid CMOS-Like Quantum Dot/Carbon Nanotube Inverter
Artem Shulga 1 , Vladimir Derenskyi 1 , Jorge Mario Salazar Rios 1 , Dmitry Dirin 2 3 , Maksym Kovalenko 2 3 , Maria Antonietta Loi 1
1 , University of Groningen, Groningen Netherlands, 2 Department of Chemistry and Applied Biosciences, ETH Zurich, Zurich Switzerland, 3 , Empa-Swiss Federal Laboratories for Materials Science and Technology, Dübendorf Switzerland
Show AbstractQuantum confined materials are highly promising candidates for low-cost, flexible electronic devices and circuits due to the low-temperature, solution-based processability. Such materials as colloidal quantum dots (QDs) and single walled carbon nanotubes (SWCNTs) have been reported as components of basic logic devices, e.g. inverters. However, in order to fabricate high performance, CMOS-like inverters, semiconducting properties of such materials in FETs are constrained by several conditions such as unipolar charge transport, matched threshold voltages for p-type and n-type FETs, and low voltage operation. These are generally large challenges for solution-based electronics.
Here we report a hybrid CMOS-like inverter, based on all-solution-based FETs gated with a high-k (k=35) P(VDF-TrFE-CFE)/PMMA polymer dielectric. We show that by depositing a thin dielectric PMMA layer on top of the relaxor ferroelectric P(VDF-TrFE-CFE) we can reduce the hysteresis and fabricate a complementary pair of FETs based on QD films and polymer-selected SWCNT random networks on a single substrate. The n-type FETs (using I- capped PbS QDs as an active layer) show an on-off ratio of 105, a subthreshold swing of 114 mV per decade, a threshold voltage of 0.2 V, a hysteresis of 20 mV, and contact-resistance-corrected electron mobility of 0.22 cm2V-1s-1. The unipolar charge transfer was achieved by using low-work-function metal electrodes that block hole and favor electron injection. The high on-off ratio and subthreshold swing are the consequences of the low degree of QD sintering of the thin films, which is also shown by the modest redshift of the absorption spectra in film respect to solution. The complementary p-type transistor (using a random network of SWCNTs as an active layer) features an on-off ratio of 105, a subthreshold swing of 63 mV per decade, a threshold voltage of -0.2 V, a hysteresis of 20mV, and a linear mobility of 0.04 cm2V-1s-1. The p-type FET shows an excellent off state for low source drain voltages (up to 1 V) but at increasing voltage the electron injection process limits the off state because of the ambipolar nature of SWCNTs. The relatively low hole mobility is a consequence of the underestimation of the channel parameters and of the high contact resistance due to low density of the SWCNT used for the random network. The CMOS-like inverters operate in the sub-1V range (with a power supply voltage of 0.9 V), and show high static gain (76 V/V), large noise margins (80%), and small hysteresis (10 mV), which are the best reported values for an all-solution-processable inverter to date.
3:30 PM - ED6.16.04
Infrared Photodiodes Based on Lead-Sulfide Quantum Dots
David Cheyns 1 , Jorick Maes 2 , Kuo-Hao Chen 1 , Epimitheas Georgitzikis 1 , Oscar Enzing 1 , Mehedi Mamun 1 , Afshin Hadipour 1 , Zeger Hens 2 , Pawel Malinowski 1
1 , imec, Leuven Belgium, 2 , University of Ghent, Gent Belgium
Show AbstractThe interest in lead sulfide (PbS) based colloidal quantum dots(QDs) for opto-electronic devices has led to a rapid increase in device performance for photovoltaics (PV) with near-infrared absorption. These PV devices incorporate small PbS QDs to push the absorption range towards wavelengths of 1000-1200 nm. The quantum effect in larger QDs will decrease the bandgap towards the one of bulk PbS. The photon-to-carrier conversion in these larger quantum dots is less studied in practical devices. Here, we present thin-film photodetectors with detection up to wavelengths of 1500 nm by utilizing relative large (> 5 nm) PbS colloidal QDs.
In our structure, the QD layers are sandwiched between two transparent, thickness tunable transport layers in order to create a simple photodiode. On one side, doped TiOx is used as electron transport layer, while on the other side a doped organic semiconductor is used as hole transport layer. All semiconducting layers are deposited from solution, and the temperature budget is kept at the minimum (max substrate temperature of 100°C).
The two major performance parameters that determine the detectivity of a photodetector are the external quantum efficiency and the dark current. Due to the low capture cross-section for infrared light (extinction coefficient below 0.1), an optical design is crucial. Depending on the maximum usable QD layer thickness, we optimize the transport layers to maximize the intrinsic cavity effect of the device structure. We show that for 150 nm thick QD layers a maximum EQE of 25% can be expected from optical modeling, a value that we almost reach experimentally (20%).
The major effect on the dark current are the ligand type and the quality of the ligand termination of the QDs: optimized recipes obtain values below uA/cm2.
Finally, we will show the progress of incorporating these layers on top of silicon CMOS compatible structures for imagers. The structure is adapted from a bottom illumination device to a top illumination device using thin metal layers. A good light incoupling can be obtained by utilizing an organic-metal-metal oxide top contact stack. First results of EQE values of 5% and similar dark current compared to the bottom illuminated devices are presented.
ED6.17: Quantum Materials for Catalysis
Session Chairs
Friday PM, April 21, 2017
PCC North, 100 Level, Room 132 C
4:15 PM - *ED6.17.01
Structured Solid-State Materials in Energy Conversion—Multi-Component and Anisotropic Nanostructures
Thomas Kempa 1
1 , Johns Hopkins University, Baltimore, Maryland, United States
Show AbstractStructured solid-state materials and devices fashioned from them enable researchers to investigate and define advances in energy transport and conversion, charge storage, optoelectronics, meta-materials, and biological sensing. A series of solution- and gas-phase synthetic breakthroughs over previous decades have given rise to increasingly complex nanostructured materials. However, the synthesis of low-dimensional and nanostructured materials with more sophisticated and precisely tunable structures/compositions is needed to advance our understanding of materials nucleation and growth and of the technological impacts that are possible. For example, multi-component and anisotropic nanostructures are sought after for the unique optical, catalytic, and mechanical functionalities they can support due to their broken symmetry. In this talk, we will discuss how a multi-component nanoscale architecture can serve as a reliable test bed for the study of catalytic mechanisms, and how it could lead to more active and selective catalysts for hydrodesulfurization and CO2 reduction reactions. In addition, we will discuss our synthesis of significantly asymmetric nanostructures, which possess unique optical transitions.
4:45 PM - ED6.17.02
Utilizing Auger-Induced Electron Emission in Quantum Dots toward High-Efficiency, Tunable, Robust Photocathodes
Istvan Robel 1 , Nikolay Makarov 1 , Jaehoon Lim 1 , Qianglu Lin 1 , John Lewellen 1 , Nathan Moody 1 , Jeffrey Pietryga 1
1 , Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Show AbstractThe use of colloidal quantum dots (QDs) as bright, tunable phosphors in real applications has relied upon the engineering of their surfaces to suppress the loss of excited carriers to surface trap states or to the surrounding medium. Here, we explore the use of QDs in an application that directly exploits their propensity toward photoionization, namely as efficient and robust photocathodes for use in next-generation electron guns. In order to establish the relevance of QDs as photocathodes, we evaluate the quantum efficiency of electron photoemission in QD films of a variety of compositions in a typical dc electron gun configuration under vacuum. By quantifying photocurrent as a function of excitation photon energy, excitation intensity, and pulse duration, we establish the dominant mechanism, Auger-induced photoionization, responsible for electron emission in the multi-photon excitation regime. We also demonstrate the effect of QD wavefunction engineering on electron photoemission efficiency, which suggests numerous pathways for further enhancements. Finally, we show that QD photocathodes offer superior efficiencies relative to standard copper cathodes under identical conditions and are robust against degradation under ambient conditions.
5:00 PM - ED6.17.03
Synthesis and Properties of Si-Based Alloyed Quantum Dots
Atta ul Haq 1 , Sadegh Askari 1 2 , Conor Rocks 1 , Chengsheng Ni 3 , Mark T. Lusk 4 , Vladimir Svrcek 5 , Paul D. Maguire 1 , John Irvine 3 , Davide Mariotti 1
1 Nanotechnology and Integrated Bioengineering Centre (NIBEC), Ulster University, Newtownabbey United Kingdom, 2 Department of Physics, Chemistry and Biology (IFM), Linköping University, Linköping Sweden, 3 School of Chemistry, University of St Andrews, St Andrews United Kingdom, 4 Department of Physics, Colorado School of Mines, Golden, Colorado, United States, 5 Research Center of Photovoltaics, National Institute of Advanced Industrial Science (AIST), Tsukuba Japan
Show AbstractSilicon-based alloyed quantum dots (all-QDs) with tailored energy band structures are highly desirable for a range of energy and environmental applications that include solar cells, photo-catalysis and bio-imaging. However, silicon-based all-QDs face great synthetic challenges with traditional bottom-up approaches. Here we will present a synthesis method based on an atmospheric-pressure plasma to produce QDs made of Si alloyed with carbon (SiC) and with tin (SiSn). We will discuss the synthesis of ultra-small QDs and their size control within strong quantum confinement regimes (1.4-5.3 nm). Transmission electron microscopy was used to investigate the structural features of all-QDs. The optical properties were studied by carrying out ultraviolet/visible absorption and photoluminescence measurements. A Kelvin probe and Mott-Schottky measurements were used to determine the Fermi level position while the band-edges were analyzed using ultraviolet and x-ray photoelectron spectroscopy. We were therefore able to produce the full energy band structure of all-QDs and verify both quantum confinement and composition tuning effects. We will finally discuss the usefulness and opportunities offered by these materials for catalysis and photovoltaic applications.