32 results on '"Vladimir Bulovic"'
Search Results
2. Predicting Low Toxicity and Scalable Solvent Systems for High‐Speed Roll‐to‐Roll Perovskite Manufacturing
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David Beynon, Rahul Patidar, Richard Swartwout, Trystan Watson, Emma Belliveau, Vladimir Bulovic, Peter Greenwood, Benjia Dou, Dane W. deQuilettes, Moungi G. Bawendi, and Nicole Moody
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Materials science ,Inkwell ,business.industry ,Energy conversion efficiency ,Energy Engineering and Power Technology ,engineering.material ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,Roll-to-roll processing ,Solvent ,Coating ,Printed electronics ,engineering ,Electrical and Electronic Engineering ,Solubility ,Process engineering ,business ,Perovskite (structure) - Abstract
This manuscript introduces solvent toxicity in solar perovskite ink chemistries as a major technoeconomic limitation for the growth of the technology. More specifically, the capital and operational cost of handling such toxic chemicals to maintain a safe working environment can lead to significant added costs. As all record power conversion efficiency devices to date have been solution processed, this represents a major challenge for the perovskite optoelectronic field and of printed electronics as a whole. Knowing this limitation, we propose that solvent selections for ink chemistries should be more quantitative and focus on lowering toxicity. To this end, we show that a Hansen solubility model is effective in predicting ink systems using lower toxicity solvents. We also show that inks formed from this method are applicable for high-speed slot-die coating, limiting the need for long anneal times. These methods and results demonstrate a useful framework for quantitatively engineering solvent systems with reduced toxicity while simultaneously maintaining and surpassing performance. It therefore provides a pathway and major step forward towards the commercialization of solution coated perovskite technologies.
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- 2021
3. Monolayer Hexagonal Boron Nitride: An Efficient Electron Blocking Layer in Organic Photovoltaics
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Jing Kong, Mayuran Saravanapavanantham, Mohammad Mahdi Tavakoli, Vladimir Bulovic, Jihoon Park, and Jeremiah Mwaura
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Materials science ,Organic solar cell ,business.industry ,Energy conversion efficiency ,Hexagonal boron nitride ,Condensed Matter Physics ,Electron blocking layer ,Electronic, Optical and Magnetic Materials ,law.invention ,Biomaterials ,law ,Solar cell ,Monolayer ,Electrochemistry ,Optoelectronics ,business - Published
- 2021
4. Methylammonium Bismuth Iodide as a Lead‐Free, Stable Hybrid Organic–Inorganic Solar Absorber
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Riley E. Brandt, Jeremy R. Poindexter, Rachel C. Kurchin, Mark W. Wilson, Vladan Stevanović, Moungi G. Bawendi, Anna Osherov, Evelyn N. Wang, Samuel D. Stranks, Austin Akey, Robert L. Z. Hoye, Hyunho Kim, John D. Perkins, Tonio Buonassisi, and Vladimir Bulovic
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Photoluminescence ,business.industry ,Organic Chemistry ,Inorganic chemistry ,chemistry.chemical_element ,Halide ,02 engineering and technology ,General Chemistry ,Electronic structure ,Methylammonium lead halide ,Nanosecond ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Solar energy ,01 natural sciences ,Catalysis ,0104 chemical sciences ,Bismuth ,chemistry.chemical_compound ,chemistry ,0210 nano-technology ,Ternary operation ,business - Abstract
Methylammonium lead halide (MAPbX3 ) perovskites exhibit exceptional carrier transport properties. But their commercial deployment as solar absorbers is currently limited by their intrinsic instability in the presence of humidity and their lead content. Guided by our theoretical predictions, we explored the potential of methylammonium bismuth iodide (MBI) as a solar absorber through detailed materials characterization. We synthesized phase-pure MBI by solution and vapor processing. In contrast to MAPbX3, MBI is air stable, forming a surface layer that does not increase the recombination rate. We found that MBI luminesces at room temperature, with the vapor-processed films exhibiting superior photoluminescence (PL) decay times that are promising for photovoltaic applications. The thermodynamic, electronic, and structural features of MBI that are amenable to these properties are also present in other hybrid ternary bismuth halide compounds. Through MBI, we demonstrate a lead-free and stable alternative to MAPbX3 that has a similar electronic structure and nanosecond lifetimes.
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- 2016
5. 20.2: Ultra-Bright, Highly Efficient, Low Roll-Off Inverted Quantum-Dot Light Emitting Devices (QLEDs)
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Yajie Dong, Jonathan S. Steckel, Guo Liu, Seth Coe-Sullivan, Moungi G. Bawendi, Zoran B. Popović, Zhaoqun Zhou, Matthew Stevenson, Peter T. Kazlas, John T. Ho, Charles W. Hamilton, Vladimir Bulovic, and Jean-Michel Caruge
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Materials science ,business.industry ,chemistry.chemical_element ,Nanoparticle ,Zinc ,Luminance ,law.invention ,Optics ,chemistry ,Quantum dot ,law ,Caesium ,Optoelectronics ,business ,Current density ,Voltage ,Light-emitting diode - Abstract
We report an ultra-bright, highly efficient, low roll-off, inverted quantum dot-based red light emitting device (QLED) using solution-processed zinc oxide nanoparticles and cesium carbonate films as the electron injection and hole blocking layers, respectively. Record luminance of 165,000 Cd/m2 has been obtained at a current density of 1000 mA/cm2 with a low driving voltage of 5.8 V for deep red device with CIE coordinates of (0.69, 0.31).
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- 2015
6. Strongly Enhanced Photovoltaic Performance and Defect Physics of Air-Stable Bismuth Oxyiodide (BiOI)
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Judith L. MacManus-Driscoll, Kelvin H. L. Zhang, Vladimir Bulovic, Riley E. Brandt, Melany Sponseller, Moungi G. Bawendi, Lana C. Lee, Tahmida N. Huq, James Alexander Polizzotti, Vladan Stevanović, Tonio Buonassisi, Robert L. Z. Hoye, Ahmed Kursumovic, Lea Nienhaus, Rachel C. Kurchin, Joel Jean, Hoye, Robert [0000-0002-7675-0065], Apollo - University of Cambridge Repository, Massachusetts Institute of Technology. Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology. Department of Materials Science and Engineering, Massachusetts Institute of Technology. Department of Mechanical Engineering, Hoye, Robert L. Z., Kurchin, Rachel Chava, Sponseller, Melany Christine, Nienhaus, Lea, Brandt, Riley E, Jean, Joel, Polizzotti, James Alexander, Bawendi, Moungi G, Bulovic, Vladimir, Buonassisi, Anthony, and Magdalene College, University of Cambridge
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Materials science ,air-stability ,Library science ,Nanotechnology ,02 engineering and technology ,010402 general chemistry ,01 natural sciences ,09 Engineering ,General Materials Science ,Center (algebra and category theory) ,Nanoscience & Nanotechnology ,Physics ,02 Physical Sciences ,business.industry ,Mechanical Engineering ,Photovoltaic system ,ns2 compounds ,021001 nanoscience & nanotechnology ,0104 chemical sciences ,Renewable energy ,photovoltaics ,Work (electrical) ,Mechanics of Materials ,defect-tolerance ,03 Chemical Sciences ,0210 nano-technology ,business ,Research center ,Efficient energy use ,bismuth oxyiodide - Abstract
Bismuth-based compounds have recently gained increasing attention as potentially nontoxic and defect-tolerant solar absorbers. However, many of the new materials recently investigated show limited photovoltaic performance. Herein, one such compound is explored in detail through theory and experiment: bismuth oxyiodide (BiOI). BiOI thin films are grown by chemical vapor transport and found to maintain the same tetragonal phase in ambient air for at least 197 d. The computations suggest BiOI to be tolerant to antisite and vacancy defects. All-inorganic solar cells (ITO|NiO x |BiOI|ZnO|Al) with negligible hysteresis and up to 80% external quantum efficiency under select monochromatic excitation are demonstrated. The short-circuit current densities and power conversion efficiencies under AM 1.5G illumination are nearly double those of previously reported BiOI solar cells, as well as other bismuth halide and chalcohalide photovoltaics recently explored by many groups. Through a detailed loss analysis using optical characterization, photoemission spectroscopy, and device modeling, direction for future improvements in efficiency is provided. This work demonstrates that BiOI, previously considered to be a poor photocatalyst, is promising for photovoltaics., National Science Foundation (U.S.) (Grant CBET-1605495), United States. Department of Energy. Office of Basic Energy Sciences (Grant DE-SC0001088), National Science Foundation (U.S.) (Grant DMF-08019762)
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- 2017
7. Decreased Synthesis Costs and Waste Product Toxicity for Lead Sulfide Quantum Dot Ink Photovoltaics
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Anna Johnson, Ella Louise Wassweiler, Dasol Yoon, Moungi G. Bawendi, Vladimir Bulovic, Michel Nasilowski, and Nicole Moody
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Materials science ,Inkwell ,Renewable Energy, Sustainability and the Environment ,business.industry ,Nanotechnology ,Waste product ,chemistry.chemical_compound ,chemistry ,Quantum dot ,Photovoltaics ,Toxicity ,Lead sulfide ,business ,General Environmental Science - Published
- 2019
8. Micron‐Scale Patterning of High Quantum Yield Quantum Dot LEDs
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Francesca Stefania Freyria, Moungi G. Bawendi, Giovanni Azzellino, Michel Nasilowski, and Vladimir Bulovic
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Materials science ,business.industry ,Quantum yield ,Electroluminescence ,Industrial and Manufacturing Engineering ,law.invention ,Mechanics of Materials ,law ,Quantum dot ,Micron scale ,Optoelectronics ,General Materials Science ,business ,Inkjet printing ,Light-emitting diode - Published
- 2019
9. Controllable Perovskite Crystallization via Antisolvent Technique Using Chloride Additives for Highly Efficient Planar Perovskite Solar Cells
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Melany Sponseller, Vladimir Bulovic, Mohammad Mahdi Tavakoli, Jing Kong, Pankaj Yadav, Anna Osherov, and Daniel Prochowicz
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Materials science ,Planar ,Chemical engineering ,Renewable Energy, Sustainability and the Environment ,law ,medicine ,General Materials Science ,Crystallization ,Chloride ,medicine.drug ,law.invention ,Perovskite (structure) - Published
- 2019
10. ZnO Nanowire Arrays for Enhanced Photocurrent in PbS Quantum Dot Solar Cells
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Sehoon Chang, Silvija Gradečak, Moungi G. Bawendi, Patrick O. Brown, Vladimir Bulovic, Jayce J. Cheng, Joel Jean, and Paul H. Rekemeyer
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Materials science ,Nanowire ,Quantum dot solar cell ,Polymer solar cell ,chemistry.chemical_compound ,Electric Power Supplies ,Photovoltaics ,Materials Testing ,Quantum Dots ,Solar Energy ,General Materials Science ,Lead sulfide ,Selenium Compounds ,Photocurrent ,Nanotubes ,business.industry ,Mechanical Engineering ,Equipment Design ,Solar energy ,Equipment Failure Analysis ,Lead ,chemistry ,Mechanics of Materials ,Quantum dot ,Optoelectronics ,Zinc Oxide ,business - Abstract
Vertical arrays of ZnO nanowires can decouple light absorption from carrier collection in PbS quantum dot solar cells and increase power conversion efficiencies by 35%. The resulting ordered bulk heterojunction devices achieve short-circuit current densities in excess of 20 mA cm(-2) and efficiencies of up to 4.9%.
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- 2013
11. Cyclobutadiene-C60Adducts: N-Type Materials for Organic Photovoltaic Cells with High VOC
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Ggoch Ddeul Han, William R. Collins, Trisha L. Andrew, Timothy M. Swager, and Vladimir Bulovic
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Fullerene ,Materials science ,Cyclobutene ,Organic solar cell ,Condensed Matter Physics ,Photochemistry ,Polymer solar cell ,Electronic, Optical and Magnetic Materials ,Biomaterials ,chemistry.chemical_compound ,chemistry ,Electron affinity ,Electrochemistry ,Density functional theory ,Cyclobutadiene ,HOMO/LUMO - Abstract
New tetraalkylcyclobutadiene–C60 adducts are developed via Diels–Alder cycloaddition of C60 with in situ generated cyclobutadienes. The cofacial π-orbital interactions between the fullerene orbitals and the cyclobutene are shown to decrease the electron affinity and thereby increase the lowest unoccupied molecular orbital (LUMO) energy level of C60 significantly (ca. 100 and 300 meV for mono- and bisadducts, respectively). These variations in LUMO levels of fullerene can be used to generate higher open-circuit voltages (VOC) in bulk heterojunction polymer solar cells. The tetramethylcyclobutadiene–C60 monoadduct displays an open-circuit voltage (0.61 V) and a power conversion efficiency (2.49%) comparable to the widely used P3HT/PCBM (poly(3-hexylthiophene/([6,6]-phenyl-C61-butyric acid methyl ester) composite (0.58 V and 2.57%, respectively). The role of the cofacial π-orbital interactions between C60 and the attached cyclobutene group was probed chemically by epoxidation of the cyclobutene moiety and theoretically through density functional theory calculations. The electrochemical, photophysical, and thermal properties of the newly synthesized fullerene derivatives support the proposed effect of functionalization on electron affinities and photovoltaic performance.
- Published
- 2013
12. Triplet Exciton Dissociation in Singlet Exciton Fission Photovoltaics
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Patrick O. Brown, Nicholas J. Thompson, Eric Hontz, Priya Jadhav, Troy Van Voorhis, Benjamin H. Wunsch, Moungi G. Bawendi, Marc A. Baldo, Aseema Mohanty, Shane R. Yost, and Vladimir Bulovic
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Materials science ,Fullerene ,Fission ,Metal Nanoparticles ,Sulfides ,Imides ,Photochemistry ,Dissociation (chemistry) ,Condensed Matter::Materials Science ,chemistry.chemical_compound ,Solar Energy ,Physics::Atomic and Molecular Clusters ,General Materials Science ,Colloids ,Physics::Chemical Physics ,Selenium Compounds ,Spectroscopy ,Perylene ,Photocurrent ,Condensed Matter::Other ,Mechanical Engineering ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,Organic semiconductor ,Magnetic Fields ,Lead ,Semiconductors ,chemistry ,Mechanics of Materials ,Singlet fission ,Quantum Theory ,Fullerenes - Abstract
Triplet exciton dissociation in singlet exciton fission devices with three classes of acceptors are characterized: fullerenes, perylene diimides, and PbS and PbSe colloidal nanocrystals. Using photocurrent spectroscopy and a magnetic field probe it is found that colloidal PbSe nanocrystals are the most promising acceptors, capable of efficient triplet exciton dissociation and long wavelength absorption.
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- 2012
13. Top-illuminated Organic Photovoltaics on a Variety of Opaque Substrates with Vapor-printed Poly(3,4-ethylenedioxythiophene) Top Electrodes and MoO3Buffer Layer
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Miles C. Barr, Rachel M. Howden, Richard R. Lunt, Karen K. Gleason, and Vladimir Bulovic
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Photocurrent ,Materials science ,Organic solar cell ,Renewable Energy, Sustainability and the Environment ,business.industry ,Energy conversion efficiency ,Chemical vapor deposition ,Anode ,chemistry.chemical_compound ,chemistry ,PEDOT:PSS ,Optoelectronics ,General Materials Science ,business ,Layer (electronics) ,Poly(3,4-ethylenedioxythiophene) - Abstract
Organic photovoltaics devices typically utilize illumination through a transparent substrate, such as glass or an optically clear plastic. Utilization of opaque substrates, including low cost foils, papers, and textiles, requires architectures that instead allow illumination through the top of the device. Here, we demonstrate top-illuminated organic photovoltaics, employing a dry vapor-printed poly(3,4-ethylenedioxythiophene) (PEDOT) polymer anode deposited by oxidative chemical vapor deposition (oCVD) on top of a small-molecule organic heterojunction based on vacuum-evaporated tetraphenyldibenzoperiflanthene (DBP) and C60 heterojunctions. Application of a molybdenum trioxide (MoO3) buffer layer prior to oCVD deposition increases the device photocurrent nearly 10 times by preventing oxidation of the underlying photoactive DBP electron donor layer during the oCVD PEDOT deposition, and resulting in power conversion efficiencies of up to 2.8% for the top-illuminated, ITO-free devices, approximately 75% that of the conventional cell architecture with indium-tin oxide (ITO) transparent anode (3.7%). Finally, we demonstrate the broad applicability of this architecture by fabricating devices on a variety of opaque surfaces, including common paper products with over 2.0% power conversion efficiency, the highest to date on such fiber-based substrates.
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- 2012
14. Morphology of contact printed colloidal quantum dots in organic semiconductor films: Implications for QD‐LEDs
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Moungi G. Bawendi, Katherine E. Aidala, Matthew J. Panzer, Jonathan E. Halpert, Polina Anikeeva, and Vladimir Bulovic
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Materials science ,business.industry ,Nanotechnology ,Electroluminescence ,Condensed Matter Physics ,law.invention ,Organic semiconductor ,Nanocrystal ,Quantum dot ,law ,Monolayer ,Optoelectronics ,Quantum efficiency ,business ,Layer (electronics) ,Light-emitting diode - Abstract
Quantum dot light emitting devices (QD-LEDs) con-sist of a monolayer of QDs sandwiched between a hole transporting layer (HTL) and electron transporting layer (ETL) of organic materials. These hybrid devices emit with the narrow bandwidth characteristic of the QDs. The precise position of the QD layer, relative to the interface between the ETL and HTL, can affect the quantum efficiency of the device on the scale of 10 nm or less. Motivated by this observation, the exact nature of the morphology of contact printed and self-assembled QDs on typical organic materials is investigated. The QDs are substantially pressed into the organic material, to a somewhat greater extent when contact printed compared to self-assembled structures. Measured device characteristics from samples made with the two methods are consistent with these observations (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
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- 2010
15. Interfacial Recombination for Fast Operation of a Planar Organic/QD Infrared Photodetector
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Scott M. Geyer, Darcy D. Wanger, Alexi C. Arango, Timothy P. Osedach, Moungi Bawendi, Ni Zhao, Liang-Yi Chang, and Vladimir Bulovic
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Time Factors ,Materials science ,Fullerene ,Infrared Rays ,business.industry ,Infrared ,Mechanical Engineering ,Photodetector ,Electrons ,Sulfides ,Planar ,Lead ,Semiconductors ,Mechanics of Materials ,Quantum dot ,Quantum Dots ,Optoelectronics ,General Materials Science ,Fullerenes ,Hybrid material ,business ,Recombination - Published
- 2010
16. Interfacial Effects of Tin Oxide Atomic Layer Deposition in Metal Halide Perovskite Photovoltaics
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David S. Bergsman, Vladimir Bulovic, Kevin A. Bush, Hsin-Ping Wang, Melany Sponseller, Rohit Prasanna, Rongrong Cheacharoen, James A. Raiford, Michael D. McGehee, Maxmillian C. Minichetti, Axel F. Palmstrom, Stacey F. Bent, and Tomas Leijtens
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Materials science ,Renewable Energy, Sustainability and the Environment ,business.industry ,Halide ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Tin oxide ,01 natural sciences ,0104 chemical sciences ,Metal ,Atomic layer deposition ,Chemical engineering ,Photovoltaics ,visual_art ,visual_art.visual_art_medium ,General Materials Science ,0210 nano-technology ,business ,Perovskite (structure) - Published
- 2018
17. Contact-Printed Microelectromechanical Systems
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Apoorva Murarka, Martin A. Schmidt, Vladimir Bulovic, Corinne E. Packard, and Eric Lam
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Microelectromechanical systems ,Materials science ,Microscopy, Fluorescence ,Mechanics of Materials ,Mechanical Engineering ,Microcontact printing ,Printing ,General Materials Science ,Nanotechnology ,Micro-Electrical-Mechanical Systems ,Flexible electronics - Published
- 2010
18. Graphene-Perovskite Schottky Barrier Solar Cells
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Vladimir Bulovic, Yi Song, Jing Kong, and Anna Osherov
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Range (particle radiation) ,Materials science ,Renewable Energy, Sustainability and the Environment ,Graphene ,business.industry ,Exciton ,Schottky barrier ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Electron transport chain ,0104 chemical sciences ,law.invention ,Semiconductor ,law ,Optoelectronics ,0210 nano-technology ,business ,Short circuit ,General Environmental Science ,Perovskite (structure) - Abstract
Perovskite solar cells have attained incredible power conversion efficiencies but it is still unclear whether photogenerated carriers are free or excitonic in nature. Originally, it is believed that they are exciton-based devices, similar to organic or dye-sensitized solar cells. However, the emergence of efficient planar devices as well as measurements of exciton binding energy in the range of 10–100 meV suggest that they may be free carrier-based. In this work, the free carrier model is confirmed by building graphene/perovskite Schottky barrier solar cells, analogous to conventional metal/semiconductor Schottky barrier solar cells. To address the challenges of building such devices, solution-processing techniques are extensively investigated for depositing perovskite films directly onto graphene in order to obtain an intimate contact between the graphene and perovskite. Interestingly, these graphene/perovskite Schottky barrier devices have reasonably good efficiency—up to 10.6%—and short circuit current densities only slightly lower than control devices. Furthermore, devices with neither a hole transport layer nor an electron transport layers have power conversion efficiencies of up to 6%. These results provide convincing evidence supporting the free carrier model for methylammonium lead iodide perovskites and offer insights on potential alternative designs for perovskite solar cells.
- Published
- 2018
19. Inkjet-Printed Quantum Dot-Polymer Composites for Full-Color AC-Driven Displays
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Moungi G. Bawendi, Michael Scott Bradley, Jianglong Chen, Vladimir Bulovic, Jonathan E. Halpert, Vanessa Wood, and Matthew J. Panzer
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Materials science ,business.industry ,Mechanical Engineering ,High resolution ,Nanotechnology ,Phosphor ,Full color ,Electroluminescence ,Flexible electronics ,Mechanics of Materials ,Quantum dot ,Polymer composites ,Optoelectronics ,General Materials Science ,business ,Luminescence - Abstract
We demonstrate print-deposition of high resolution, patterned,multicolored thin films of luminescent colloidal quantum dot(QD)-polymer composites and use the printed patterns infabricating robust, bright, full-color AC-driven displays. Thebenefits of AC electroluminescent (EL) displays include simple,low-costfabricationandhighreliability;however,findingefficientand stable phosphors for full-colored displays remains a majorchallenge.
- Published
- 2009
20. High Definition Digital Fabrication of Active Organic Devices by Molecular Jet Printing
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Vladimir Bulovic, Marc A. Baldo, Martin A. Schmidt, V. Leblanc, Sung Hoon Kang, Jiangfong Chen, David M. Schut, and Paul J. Benning
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Fabrication ,Materials science ,business.industry ,Nanotechnology ,Condensed Matter Physics ,Stencil ,Electronic, Optical and Magnetic Materials ,Biomaterials ,Pentacene ,chemistry.chemical_compound ,Vacuum deposition ,chemistry ,Printed electronics ,Electrochemistry ,OLED ,Optoelectronics ,Field-effect transistor ,Thin film ,business - Abstract
We introduce a high resolution molecular jet (MoJet) printing technique for vacuum deposition of evaporated thin films and apply it to fabrication of 30 μm pixelated (800 ppi) molecular organic light emitting devices (OLEDs) based on aluminum tris(8-hydroxyquinoline) (Alq 3 ) and fabrication of narrow channel (15 μm) organic field effect transistors (OFETs) with pentacene channel and silver contacts. Patterned printing of both organic and metal films is demonstrated, with the operating properties of MoJet-printed OLEDs and OFETs shown to be comparable to the performance of devices fabricated by conventional evaporative deposition through a metal stencil. We show that the MoJet printing technique is reconfigurable for digital fabrication of arbitrary patterns with multiple material sets and high print accuracy (of better than 5 μm), and scalable to fabrication on large area substrates. Analogous to the concept of "drop-on-demand" in Inkjet printing technology, MoJet printing is a "flux-on-demand" process and we show it capable of fabricating multi-layer stacked film structures, as needed for engineered organic devices.
- Published
- 2007
21. Color-Saturated Green-Emitting QD-LEDs
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Preston T. Snee, Polina Anikeeva, Seth Coe-Sullivan, Lee Ann Kim, Jonathan S. Steckel, Vladimir Bulovic, Jonathan E. Halpert, Moungi G. Bawendi, and John P. Zimmer
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Photoluminescence ,Materials science ,business.industry ,Absorption cross section ,Nanotechnology ,General Chemistry ,General Medicine ,Electroluminescence ,Catalysis ,law.invention ,law ,Quantum dot ,Optoelectronics ,Emission spectrum ,Chromaticity ,business ,Light-emitting diode ,Visible spectrum - Abstract
Semiconductor nanocrystals (NCs) or quantum dots (QDs) show great promise for use in QD-LED (quantum dot lightemitting device) displays, owing to their unique optical properties and the continual development of new core and core–shell structures to meet specific color needs. This in combination with the recent development of more efficient and saturated QD-LEDs as well as new QD-LED fabrication techniques, suggests that QD-LEDs have the potential to become an alternative flat-panel display technology. The ideal red, green, and blue emission spectrum of an LED for a display application should have a narrow bandwidth and a wavelength such that its color coordinates on the Commission Internationale de l+Eclairage (CIE) chromaticity diagram lie outside the current National Television System Committee (NTSC) standard color triangle (see Figure 2). For a Gaussian emission spectrum with a full width at half maximum (FWHM) of 30 nm and a maximized perceived power, the optimal peak wavelength for display applications is l= 610– 620 nm for red, l= 525–530 nm for green, and l= 460– 470 nm for blue. For the red pixels, wavelengths longer than l= 620 nm become difficult for the human eye to perceive, while those shorter than l= 610 nm have coordinates that lie inside the standard NTSC color triangle. Optimization of wavelength for the blue pixels follows the same arguments as for the red pixel, but at the other extreme of the visible spectrum. For green pixels, l= 525–530 nm provides a color triangle with the largest area on the CIE chromaticity diagram (and therefore the largest number of colors accessible by a display). Wavelengths longer than l= 530 nm make some of the blue/green area of the triangle inaccessible. Wavelengths shorter than l= 525 nm compromise the yellow display emissions. To date, efficient red-emitting QD-LEDs with a peak emission wavelength optimized for display applications have been realized using (CdSe)ZnS core–shell NCs, while blue QD-LEDs with a peak wavelength of emission optimized for display applications have been realized with a (CdS)ZnS core–shell material. To date, although efficient green-emitting core–shell semiconductor NCs that emit at l= 525 nm have been synthesized, they have not been successfully incorporated into a QD-LED suitable for display applications. Previous work using (CdSe)ZnS core–shell NCs gave QD-LEDs that emit at wavelengths no shorter than l= 540–560 nm. 14] Using (CdSe)ZnS core–shell NCs to achieve l= 525 nm emission requires making small CdSe cores ( 2.5 nm in diameter). 16] Such small CdSe semiconductor NCs can be difficult to synthesize with narrow size distributions and high quantum efficiencies, and are also more difficult to process and overcoat with a higher-band-gap inorganic semiconductor, which is necessary for incorporation into solid-state structures. A core–shell composite, rather than an organically passivated NC, is desirable in a solid-state QD-LED device owing to the enhanced photoluminescence and electroluminescence (EL) quantum efficiencies of core– shell NCs and their greater tolerance to the processing conditions necessary for device fabrication. Larger NCs are also more desirable for use in QD-LEDs because the absorption cross section of NCs scales with size. Larger NCs with larger absorption cross sections lead to an increase in the efficiency of F?rster energy transfer from electroluminescing organic molecules to NCs in a working QD-LED, which in turn leads to more efficient devices. Herein, we report the synthesis of a CdxZn1 xSe alloy core on which we then grew a CdyZn1 yS shell to create a core– shell NC material with the ideal spectral characteristics for green emission in a QD-LED display and with a size large enough for fabricating a working QD-LED. Our CdxZn1 xSe core synthesis was based on work recently published, in which Cd and Se precursors were slowly introduced into a growth solution of ZnSe NCs. A three-step synthetic route was employed to prepare the (CdxZn1 xSe)CdyZn1 yS core–shell NCs. In the first step, ZnSe NCs were prepared by rapidly injecting 0.7 mmol of diethylzinc (Strem) and 1 mL of tri-noctylphosphine selenide (TOPSe; 1m) dispersed in 5 mL of tri-n-octylphosphine (TOP; 97% Strem) into a round-bottom flask containing 7 grams of degassed hexadecylamine (distilled from 90% Sigma–Aldrich) at 310 8C and by then growing the NCs at 270 8C for 90 min. The second step consisted of transferring 8 mL of the above ZnSe NC growth solution, at 160 8C, into a degassed solution of 16 grams of trin-octylphosphine oxide (TOPO; distilled from 90% Sigma– Aldrich) and 4 mmol of hexylphosphonic acid (HPA; Alfa Aesar), also at 160 8C. A solution of 1.1 mmol of dimethylcadmium (Strem) and 1.2 mL of TOPSe (1m) dispersed in 8 mL of TOP (97% Strem) was then introduced dropwise [*] Dr. J. S. Steckel, Dr. P. Snee, Dr. J. P. Zimmer, J. E. Halpert, Prof. M. G. Bawendi Massachusetts Institute of Technology Department of Chemistry Center for Materials Science and Engineering and The Institute for Soldier Nanotechnologies 77 Massachusetts Avenue, Room 6-221 Cambridge, MA 02139 (USA) Fax: (+1)617-253-7030 E-mail: mgb@mit.edu Dr. S. Coe-Sullivan, P. Anikeeva, L.-A. Kim, Prof. V. Bulovic Massachusetts Institute of Technology Laboratory of Organic Optics and Electronics Department of Electrical Engineering and Computer Science Cambridge, MA 02139 (USA) [] These authors contributed equally to this work.
- Published
- 2006
22. Highly Efficient Blue Electroluminescence from Poly(phenylene ethynylene) via Energy Transfer from a Hole-Transport Matrix
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Craig Breen, Vladimir Bulovic, Jonathan R. Tischler, and Timothy M. Swager
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Matrix (mathematics) ,Materials science ,Mechanics of Materials ,business.industry ,Mechanical Engineering ,Energy transfer ,Optoelectronics ,General Materials Science ,Electroluminescence ,business ,Poly(phenylene ethynylene) - Published
- 2005
23. Layer-by-Layer J-Aggregate Thin Films with a Peak Absorption Constant of 106 cm–1
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Jonathan R. Tischler, Michael Scott Bradley, and Vladimir Bulovic
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Carbon film ,Materials science ,Mechanics of Materials ,Mechanical Engineering ,Optoelectronic materials ,Layer by layer ,Analytical chemistry ,General Materials Science ,Thin film ,Absorption (electromagnetic radiation) ,Constant (mathematics) ,J-aggregate - Published
- 2005
24. Large-Area Ordered Quantum-Dot Monolayers via Phase Separation During Spin-Casting
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Seth Coe-Sullivan, Wing-Keung Woo, Jonathan S. Steckel, Vladimir Bulovic, and Moungi G. Bawendi
- Subjects
Materials science ,Nanotechnology ,Colloidal crystal ,Spin casting ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,Biomaterials ,Nanocrystal ,Quantum dot ,Phase (matter) ,Monolayer ,Electrochemistry ,Self-assembly ,Thin film - Abstract
We investigate a new method for forming large-area (> cm2) ordered monolayers of colloidal nanocrystal quantum dots (QDs). The QD thin films are formed in a single step by spin-casting a mixed solution of aromatic organic materials and aliphatically capped QDs. The two different materials phase separate during solvent drying, and for a predefined set of conditions the QDs can assemble into hexagonally close-packed crystalline domains. We demonstrate the robustness and flexibility of this phase-separation process, as well as how the properties of the resulting films can be controlled in a precise and repeatable manner. Solution concentration, solvent ratio, QD size distribution, and QD aspect ratio affect the morphology of the cast thin-film structure. Controlling all of these factors allows the creation of colloidal-crystal domains that are square micrometers in size, containing tens of thousands of individual nanocrystals per grain. Such fabrication of large-area, engineered layers of nanoscale materials brings the beneficial properties of inorganic QDs into the realm of nanotechnology. For example, this technique has already enabled significant improvements in the performance of QD light-emitting devices.
- Published
- 2005
25. 1.3μm to 1.55μm Tunable Electroluminescence from PbSe Quantum Dots Embedded within an Organic Device
- Author
-
Moungi G. Bawendi, Vladimir Bulovic, Seth Coe-Sullivan, and Jonathan S. Steckel
- Subjects
Photoluminescence ,Materials science ,Mechanics of Materials ,business.industry ,Quantum dot ,Quantum dot laser ,Mechanical Engineering ,Optoelectronics ,General Materials Science ,Electroluminescence ,business - Published
- 2003
26. Photoluminescent Arrays of Nanopatterned Monolayer MoS2
- Author
-
Grace G. D. Han, Caroline A. Ross, Farnaz Niroui, Xiaochen Wang, Wenshuo Xu, Jamie H. Warner, Si Zhou, Vladimir Bulovic, Kun-Hua Tu, and Jeffrey C. Grossman
- Subjects
Photoluminescence ,Materials science ,Nanotechnology ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Dark field microscopy ,0104 chemical sciences ,Electronic, Optical and Magnetic Materials ,Biomaterials ,chemistry.chemical_compound ,Nanomesh ,chemistry ,Monolayer ,Scanning transmission electron microscopy ,Electrochemistry ,Direct and indirect band gaps ,Nanorod ,Nanodot ,0210 nano-technology - Abstract
Monolayer 2D MoS 2 grown by chemical vapor deposition is nanopatterned into nanodots, nanorods, and hexagonal nanomesh using block copolymer (BCP) lithography. The detailed atomic structure and nanoscale geometry of the nanopatterned MoS 2 show features down to 4 nm with nonfaceted etching profiles defined by the BCP mask. Atomic resolution annular dark field scanning transmission electron microscopy reveals the nanopatterned MoS 2 has minimal large-scale crystalline defects and enables the edge density to be measured for each nanoscale pattern geometry. Photoluminescence spectroscopy of nanodots, nanorods, and nanomesh areas shows strain-dependent spectral shifts up to 15 nm, as well as reduction in the PL efficiency as the edge density increases. Raman spectroscopy shows mode stiffening, confirming the release of strain when it is nanopatterned by BCP lithography. These results show that small nanodots (≈19 nm) of MoS 2 2D monolayers still exhibit strong direct band gap photoluminescence (PL), but have PL quenching compared to pristine material from the edge states. This information provides important insights into the structure-PL property correlations of sub-20 nm MoS 2 structures that have potential in future applications of 2D electronics, optoelectronics, and photonics.
- Published
- 2017
27. Quantum Dot-Polymer Composites for Displays: Inkjet-Printed Quantum Dot-Polymer Composites for Full-Color AC-Driven Displays (Adv. Mater. 21/2009)
- Author
-
Jonathan E. Halpert, Jianglong Chen, Michael Scott Bradley, Vladimir Bulovic, Moungi G. Bawendi, Matthew J. Panzer, and Vanessa Wood
- Subjects
Materials science ,business.industry ,Mechanical Engineering ,Nanotechnology ,Full color ,Flexible electronics ,Mechanics of Materials ,Quantum dot ,Polymer composites ,Optoelectronics ,General Materials Science ,business ,Luminescence ,Inkjet printing - Published
- 2009
28. Cover Picture: High Definition Digital Fabrication of Active Organic Devices by Molecular Jet Printing (Adv. Funct. Mater. 15/2007)
- Author
-
Vladimir Bulovic, Marc A. Baldo, P. J. Benning, V. Leblanc, Martin A. Schmidt, Jianglong Chen, David M. Schut, and Sung Hoon Kang
- Subjects
Fabrication ,Materials science ,business.industry ,Nanotechnology ,Substrate (printing) ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,Biomaterials ,Pentacene ,chemistry.chemical_compound ,chemistry ,Vacuum deposition ,Printed electronics ,Electrochemistry ,OLED ,Optoelectronics ,Field-effect transistor ,Thin film ,business - Abstract
A new method for direct patterning of organic optoelectronic/electronic devices using a reconfigurable and scalable printing method is reported by Vladimir Bulovic and co-workers on p. 2722. The printing technique is applied to the fabrication of high-resolution printed organic light emitting devices (OLEDs) and organic field effect transistors (OFETs). Remarkably, the final print-deposited films are evaporated onto the substrate (rather than solvent printed), giving high-quality, solvent-free, molecularly flat structures that match the performance of comparable high-performance unpatterned films. We introduce a high resolution molecular jet (MoJet) printing technique for vacuum deposition of evaporated thin films and apply it to fabrication of 30 μm pixelated (800 ppi) molecular organic light emitting devices (OLEDs) based on aluminum tris(8-hydroxyquinoline) (Alq3) and fabrication of narrow channel (15 μm) organic field effect transistors (OFETs) with pentacene channel and silver contacts. Patterned printing of both organic and metal films is demonstrated, with the operating properties of MoJet-printed OLEDs and OFETs shown to be comparable to the performance of devices fabricated by conventional evaporative deposition through a metal stencil. We show that the MoJet printing technique is reconfigurable for digital fabrication of arbitrary patterns with multiple material sets and high print accuracy (of better than 5 μm), and scalable to fabrication on large area substrates. Analogous to the concept of “drop-on-demand” in Inkjet printing technology, MoJet printing is a “flux-on-demand” process and we show it capable of fabricating multi-layer stacked film structures, as needed for engineered organic devices.
- Published
- 2007
29. ZnO Nanowire Arrays for Enhanced Photocurrent in PbS Quantum Dot Solar Cells (Adv. Mater. 20/2013)
- Author
-
Sehoon Chang, Paul H. Rekemeyer, Moungi G. Bawendi, Jayce J. Cheng, Silvija Gradečak, Vladimir Bulovic, Patrick O. Brown, and Joel Jean
- Subjects
Photocurrent ,Materials science ,business.industry ,Mechanical Engineering ,Zno nanowires ,Nanowire ,chemistry.chemical_compound ,chemistry ,Mechanics of Materials ,Quantum dot ,Photovoltaics ,Optoelectronics ,General Materials Science ,Lead sulfide ,business - Published
- 2013
30. Paper Electronics: Direct Monolithic Integration of Organic Photovoltaic Circuits on Unmodified Paper (Adv. Mater. 31/2011)
- Author
-
Vladimir Bulovic, Jill A. Rowehl, Jingjing Xu, Sung Gap Im, Christopher M. Boyce, Miles C. Barr, Karen K. Gleason, Richard R. Lunt, and Annie Wang
- Subjects
Organic electronics ,Conductive polymer ,Materials science ,Organic solar cell ,Mechanics of Materials ,Mechanical Engineering ,Photovoltaic system ,General Materials Science ,Nanotechnology ,Electronics ,Hybrid solar cell ,Chemical vapor deposition ,Electronic circuit - Published
- 2011
31. 35.1: Invited Paper: Quantum Dot Light Emitting Devices for Pixelated Full Color Displays
- Author
-
Moungi G. Bawendi and Vladimir Bulovic
- Subjects
Materials science ,Fabrication ,Quantum dot laser ,Quantum dot ,business.industry ,Fabrication methods ,Quantum dot display ,Optoelectronics ,Nanotechnology ,Full color ,Thin film ,business ,Quantum - Abstract
Quantum dot light emitting devices (QD-LEDs) developed over the past four years demonstrate high external quantum efficiencies, saturated visible color emission, narrow-band infra-red emission, and can be fabricated with a scalable fabrication technique of high resolution. These recent advancements of QD-LED technology are due to progress in the chemistry of colloidal quantum dot synthesis and the development of new fabrication methods for generating thin films of QDs as outlined in this letter.
- Published
- 2006
32. Layer-by-Layer J-Aggregate Thin Films with a Peak Absorption Constant of 106 cm-1 (Adv. Mater. 2005, 15, 1881)
- Author
-
Jonathan R. Tischler, Vladimir Bulovic, and Michael Scott Bradley
- Subjects
Carbon film ,Materials science ,Mechanics of Materials ,Mechanical Engineering ,Optoelectronic materials ,Layer by layer ,Analytical chemistry ,General Materials Science ,Thin film ,Constant (mathematics) ,Absorption (electromagnetic radiation) ,J-aggregate - Published
- 2005
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