12 results on '"Bergren, Matthew R."'
Search Results
2. Carrier multiplication in van der Waals layered transition metal dichalcogenides
- Author
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Kim, Ji-Hee, Bergren, Matthew R., Park, Jin Cheol, Adhikari, Subash, Lorke, Michael, Frauenheim, Thomas, Choe, Duk-Hyun, Kim, Beom, Choi, Hyunyong, Gregorkiewicz, Tom, and Lee, Young Hee
- Published
- 2019
- Full Text
- View/download PDF
3. Consensus statement: Standardized reporting of power-producing luminescent solar concentrator performance
- Author
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Yang, Chenchen, Atwater, Harry A., Baldo, Marc A., Baran, Derya, Barile, Christopher J., Barr, Miles C., Bates, Matthew, Bawendi, Moungi G., Bergren, Matthew R., Borhan, Babak, Brabec, Christoph J., Brovelli, Sergio, Bulović, Vladimir, Ceroni, Paola, Debije, Michael G., Delgado-Sanchez, Jose-Maria, Dong, Wen-Ji, Duxbury, Phillip M., Evans, Rachel C., Forrest, Stephen R., Gamelin, Daniel R., Giebink, Noel C., Gong, Xiao, Griffini, Gianmarco, Guo, Fei, Herrera, Christopher K., Ho-Baillie, Anita W.Y., Holmes, Russell J., Hong, Sung-Kyu, Kirchartz, Thomas, Levine, Benjamin G., Li, Hongbo, Li, Yilin, Liu, Dianyi, Loi, Maria A., Luscombe, Christine K., Makarov, Nikolay S., Mateen, Fahad, Mazzaro, Raffaello, McDaniel, Hunter, McGehee, Michael D., Meinardi, Francesco, Menéndez-Velázquez, Amador, Min, Jie, Mitzi, David B., Moemeni, Mehdi, Moon, Jun Hyuk, Nattestad, Andrew, Nazeeruddin, Mohammad K., Nogueira, Ana F., Paetzold, Ulrich W., Patrick, David L., Pucci, Andrea, Rand, Barry R., Reichmanis, Elsa, Richards, Bryce S., Roncali, Jean, Rosei, Federico, Schmidt, Timothy W., So, Franky, Tu, Chang-Ching, Vahdani, Aria, van Sark, Wilfried G.J.H.M., Verduzco, Rafael, Vomiero, Alberto, Wong, Wallace W.H., Wu, Kaifeng, Yip, Hin-Lap, Zhang, Xiaowei, Zhao, Haiguang, Lunt, Richard R., Integration of Photovoltaic Solar Energy, and Energy and Resources
- Subjects
Taverne - Abstract
Fair and meaningful device performance comparison among luminescent solar concentrator-photovoltaic (LSC-PV) reports cannot be realized without a general consensus on reporting standards in LSC-PV research. Therefore, it is imperative to adopt standardized characterization protocols for these emerging types of PV devices that are consistent with other PV devices. This commentary highlights several common limitations in LSC literature and summarizes the best practices moving forward to harmonize with standard PV reporting, considering the greater nuances present with LSC-PV. Based on these practices, a checklist of actionable items is provided to help standardize the characterization/reporting protocols and offer a set of baseline expectations for authors, reviewers, and editors. The general consensus combined with the checklist will ultimately guide LSC-PV research towards reliable and meaningful advances.
- Published
- 2022
4. Minimizing Scaling Losses in High-Performance Quantum Dot Luminescent Solar Concentrators for Large-Area Solar Windows.
- Author
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Makarov, Nikolay S., Korus, Daniel, Freppon, Daniel, Ramasamy, Karthik, Houck, Daniel W., Velarde, Andres, Parameswar, Ashray, Bergren, Matthew R., and McDaniel, Hunter
- Published
- 2022
- Full Text
- View/download PDF
5. Highly Efficient Carrier Multiplication in van der Waals layered Materials
- Author
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Kim, Ji-Hee, Bergren, Matthew R., Park, Jin Cheol, Adhikari, Subash, Lorke, Michael, Fraunheim, Thomas, Choe, Duk-Hyun, Kim, Beom, Choi, Hyunyong, Gregorkiewicz, Tom, and Lee, Young Hee
- Subjects
Condensed Matter - Mesoscale and Nanoscale Physics ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,FOS: Physical sciences ,Optics (physics.optics) ,Physics - Optics - Abstract
Carrier multiplication (CM), a photo-physical process to generate multiple electron-hole pairs by exploiting excess energy of free carriers, is explored for efficient photovoltaic conversion of photons from the blue solar band, predominantly wasted as heat in standard solar cells. Current state-of-the-art approaches with nanomaterials have demonstrated improved CM but are not satisfactory due to high energy loss and inherent difficulties with carrier extraction. Here, we report ultra-efficient CM in van der Waals (vdW) layered materials that commences at the energy conservation limit and proceeds with nearly 100% conversion efficiency. A small threshold energy, as low as twice the bandgap, was achieved, marking an onset of quantum yield with enhanced carrier generation. Strong Coulomb interactions between electrons confined within vdW layers allow rapid electron-electron scattering to prevail over electron-phonon scattering. Additionally, the presence of electron pockets spread over momentum space could also contribute to the high CM efficiency. Combining with high conductivity and optimal bandgap, these superior CM characteristics identify vdW materials for third-generation solar cell., 17 pages, 4 figures
- Published
- 2018
6. Optimizing the Aesthetics of High-Performance CuInS2/ZnS Quantum Dot Luminescent Solar Concentrator Windows.
- Author
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Velarde, Andrés R. M., Bartlett, Emily R., Makarov, Nikolay S., Castañeda, Chloe, Jackson, Aaron, Ramasamy, Karthik, Bergren, Matthew R., and McDaniel, Hunter
- Published
- 2020
- Full Text
- View/download PDF
7. Electron transfer in hydrogenated nanocrystalline silicon observed by time-resolved terahertz spectroscopy.
- Author
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Bergren, Matthew R., Simonds, Brian J., Baojie Yan, Guozhen Yue, Ahrenkiel, Richard, Furtak, Thomas E., Collins, Reuben T., Taylor, P. Craig, and Beard, Matthew C.
- Subjects
- *
CHARGE exchange , *SILICON , *TERAHERTZ spectroscopy , *ANALYTICAL mechanics , *PARTICLES (Nuclear physics) , *SOLAR energy , *PHOTOVOLTAIC cells - Abstract
We report on the ultrafast carrier dynamics in hydrogenated nanocrystalline silicon (nc-Si:H) using time-resolved terahertz spectroscopy. Photoexcitation at 407 nm primarily produces charge carriers in the a-Si phase, but they undergo a rapid electron transfer to the c-Si phase prior to complete thermalization into the band-tail states of a-Si. We studied the carrier dynamics on a range of nc-Si:H samples with varying crystalline volume fractions (Xc) and mapped out the carrier dynamics with sub-ps resolution. Our measurements are consistent with a model in which electrons are first trapped at interface states at the a-Si-c-Si boundary prior to being thermally emitted into the c-Si phase. Wavelength and temperature dependent measurements are consistent with our model. The phenomena observed here have implications toward solar cell structures that utilize an amorphous material as an absorber layer, previously thought to have a mobility value too low to attain effective charge transport in a device. [ABSTRACT FROM AUTHOR]
- Published
- 2013
- Full Text
- View/download PDF
8. Luminescent quantum dot films improve light use efficiency and crop quality in greenhouse horticulture.
- Author
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Hebert D, Boonekamp J, Parrish CH 2nd, Ramasamy K, Makarov NS, Castañeda C, Schuddebeurs L, McDaniel H, and Bergren MR
- Abstract
The spectral quality of sunlight reaching plants remains a path for optimization in greenhouse cultivation. Quantum dots represent a novel, emission-tunable luminescent material for optimizing the sunlight spectrum in greenhouses with minimal intensity loss, ultimately enabling improved light use efficiency of plant growth without requiring electricity. In this study, greenhouse films containing CuInS
2 /ZnS quantum dots were utilized to absorb and convert ultraviolet and blue photons from sunlight to a photoluminescent emission centered at 600 nm. To analyze the effects of the quantum dot film spectrum on plant production, a 25-week tomato trial was conducted in Dutch glass greenhouses. Plants under the quantum dot film experienced a 14% reduction in overall daily light integral, resulting from perpendicular photosynthetically active radiation transmission of 85.3%, mainly due to reflection losses. Despite this reduction in intensity, the modified sunlight spectrum and light diffusion provided by the quantum dot film gave rise to 5.7% improved saleable production yield, nearly identical total fruiting biomass production, 23% higher light use efficiency (g/mol), 10% faster vegetative growth rate, and 36% reduced tomato waste compared to the control, which had no additional films. Based on this result, materials incorporating quantum dots show promise in enabling passive, electricity-free spectrum modification for improving crop production in greenhouse cultivation, but extensive controlled crop studies are needed to further validate their effectiveness., Competing Interests: DH, CP, KR, NM, CC, HM, and MB were employed by the company UbiQD, Inc. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Hebert, Boonekamp, Parrish, Ramasamy, Makarov, Castañeda, Schuddebeurs, McDaniel and Bergren.)- Published
- 2022
- Full Text
- View/download PDF
9. Fiber-Coupled Luminescent Concentrators for Medical Diagnostics, Agriculture, and Telecommunications.
- Author
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Makarov NS, Ramasamy K, Jackson A, Velarde A, Castaneda C, Archuleta N, Hebert D, Bergren MR, and McDaniel H
- Subjects
- Agriculture trends, Clinical Laboratory Techniques trends, Humans, Lighting, Luminescence, Quantum Dots therapeutic use, Refractometry, Sunlight, Optical Fibers, Quantum Dots chemistry, Solar Energy, Telecommunications trends
- Abstract
While luminescent concentrators (LCs) are mainly designed to harvest sunlight and convert its energy into electricity, the same concept can be advantageous in alternative applications. Examples of such applications are demonstrated here by coupling the edge-guided light of high-performance LCs based on CuInSe
x S2 - x /ZnS quantum dots into optical fibers with emission covering visible-to-NIR spectral regions. In particular, a cost-efficient, miniature broadband light source for medical diagnostics, a spectral-conversion and light-guiding device for agriculture, and a large-area broadband tunable detector for telecommunications are demonstrated. Various design considerations and performance optimization approaches are discussed and summarized. Prototypes of the devices are manufactured and tested. Individual elements of the broadband light source show coupling efficiencies up to 1%, which is sufficient to saturate typical fiber-coupled spectrometers at a minimal integration time of 1 ms using 100 mW blue excitation. Agricultural devices are capable of delivering ∼10% of photosynthetically active radiation (per device) converted from absorbed sunlight to the lower canopy of plants, which boosted the tomato yield in a commercial greenhouse by 7% (fresh weight). Finally, large-scale prototype detectors can be used to discern time-modulated unfocused signals with an average power as low as 1 μW, which would be useful for free-space telecommunication systems. Fully optimized devices are expected to make significant impacts on speed and bandwidth of free-space telecommunication systems, medical diagnostics, and greenhouse crop yields.- Published
- 2019
- Full Text
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10. Size-Dependent Exciton Formation Dynamics in Colloidal Silicon Quantum Dots.
- Author
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Bergren MR, Palomaki PK, Neale NR, Furtak TE, and Beard MC
- Abstract
We report size-dependent exciton formation dynamics within colloidal silicon quantum dots (Si QDs) using time-resolved terahertz (THz) spectroscopy measurements. THz photoconductivity measurements are used to distinguish the initially created hot carriers from excitons that form at later times. At early pump/probe delays, the exciton formation dynamics are revealed by the temporal evolution of the THz transmission. We find an increase in the exciton formation time, from ∼500 to ∼900 fs, as the Si QD diameter is reduced from 7.3 to 3.4 nm and all sizes exhibit slower hot-carrier relaxation times compared to bulk Si. In addition, we determine the THz absorption cross section at early delay times is proportional to the carrier mobility while at later delays is proportional to the exciton polarizability, αX. We extract a size-dependent αX and find an ∼r(4) dependence, consistent with previous reports for quantum-confined excitons in CdSe, InAs, and PbSe QDs. The observed slowing in exciton formation time for smaller Si QDs is attributed to decreased electron-phonon coupling due to increased quantum confinement. These results experimentally verify the modification of hot-carrier relaxation rates by quantum confinement in Si QDs, which likely plays a significant role in the high carrier multiplication efficiency observed in these nanomaterials.
- Published
- 2016
- Full Text
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11. Ultrafast Electrical Measurements of Isolated Silicon Nanowires and Nanocrystals.
- Author
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Bergren MR, Kendrick CE, Neale NR, Redwing JM, Collins RT, Furtak TE, and Beard MC
- Abstract
We simultaneously determined the charge carrier mobility and picosecond to nanosecond carrier dynamics of isolated silicon nanowires (Si NWs) and nanocrystals (Si NCs) using time-resolved terahertz spectroscopy. We then compared these results to data measured on bulk c-Si as a function of excitation fluence. We find >1 ns carrier lifetimes in Si NWs that are dominated by surface recombination with surface recombination velocities (SRV) between ∼1100-1700 cm s(-1) depending on process conditions. The Si NCs have markedly different decay dynamics. Initially, free-carriers are produced, but relax within ∼1.5 ps to form bound excitons. Subsequently, the excitons decay with lifetimes >7 ns, similar to free carriers produced in bulk Si. The isolated Si NWs exhibit bulk-like mobilities that decrease with increasing excitation density, while the hot-carrier mobilities in the Si NCs are lower than bulk mobilities and could only be measured within the initial 1.5 ps decay. We discuss the implications of our measurements on the utilization of Si NWs and NCs in macroscopic optoelectronic applications.
- Published
- 2014
- Full Text
- View/download PDF
12. Control of PbSe quantum dot surface chemistry and photophysics using an alkylselenide ligand.
- Author
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Hughes BK, Ruddy DA, Blackburn JL, Smith DK, Bergren MR, Nozik AJ, Johnson JC, and Beard MC
- Subjects
- Crystallization methods, Lead radiation effects, Light, Materials Testing, Selenium Compounds radiation effects, Lead chemistry, Quantum Dots, Selenium chemistry, Selenium Compounds chemistry
- Abstract
We have synthesized alkylselenide reagents to replace the native oleate ligand on PbSe quantum dots (QDs) in order to investigate the effect of surface modification on their stoichiometry, photophysics, and air stability. The alkylselenide reagent removes all of the oleate on the QD surface and results in Se addition; however, complete Se enrichment does not occur, achieving a 53% decrease in the amount of excess Pb for 2 nm diameter QDs and a 23% decrease for 10 nm QDs. Our analysis suggests that the Se ligand preferentially binds to the {111} faces, which are more prevalent in smaller QDs. We find that attachment of the alkylselenide ligand to the QD surface enhances oxidative resistance, likely resulting from a more stable bond between surface Pb atoms and the alkylselenide ligand compared to Pb-oleate. However, binding of the alkylselenide ligand produces a separate nonradiative relaxation route that partially quenches PL, suggesting the formation of a dark hole-trap.
- Published
- 2012
- Full Text
- View/download PDF
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