1
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Berweger S, Zhang F, Larson BW, Ferguson AJ, Palmstrom AF, Reid OG, Wallis TM, Zhu K, Berry JJ, Kabos P, Nanayakkara SU. Nanoscale Photoexcited Carrier Dynamics in Perovskites. J Phys Chem Lett 2022; 13:2388-2395. [PMID: 35257587 DOI: 10.1021/acs.jpclett.2c00233] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
The optoelectronic properties of lead halide perovskite thin films can be tuned through compositional variations and strain, but the associated nanocrystalline structure makes it difficult to untangle the link between composition, processing conditions, and ultimately material properties and degradation. Here, we study the effect of processing conditions and degradation on the local photoconductivity dynamics in [(CsPbI3)0.05(FAPbI3)0.85(MAPbBr3)0.15] and (FA0.7Cs0.3PbI3) perovskite thin films using temporally and spectrally resolved microwave near-field microscopy with a temporal resolution as high as 5 ns and a spatial resolution better than 50 nm. For the latter FACs formulation, we find a clear effect of the process annealing temperature on film morphology, stability, and spatial photoconductivity distribution. After exposure of samples to ambient conditions and illumination, we find spectral evidence of halide segregation-induced degradation below the instrument resolution limit for the mixed halide formulation, while we find a clear spatially inhomogeneous increase in the carrier lifetime for the FACs formulation annealed at 180 °C.
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Affiliation(s)
- Samuel Berweger
- Applied Physics Division, National Institute of Standards and Technology, Boulder, Colorado 80305, United States
| | - Fei Zhang
- National Renewable Energy Laboratory, Golden, Colorado 80401, United States
- School of Chemical Engineering and Technology, Tianjin University, Tianjin, 300072, China
| | - Bryon W Larson
- National Renewable Energy Laboratory, Golden, Colorado 80401, United States
| | - Andrew J Ferguson
- National Renewable Energy Laboratory, Golden, Colorado 80401, United States
| | - Axel F Palmstrom
- National Renewable Energy Laboratory, Golden, Colorado 80401, United States
| | - Obadiah G Reid
- National Renewable Energy Laboratory, Golden, Colorado 80401, United States
- Renewable and Sustainable Energy Institute, University of Colorado, Boulder, Colorado 80309, United States
| | - Thomas M Wallis
- Applied Physics Division, National Institute of Standards and Technology, Boulder, Colorado 80305, United States
| | - Kai Zhu
- National Renewable Energy Laboratory, Golden, Colorado 80401, United States
| | - Joseph J Berry
- National Renewable Energy Laboratory, Golden, Colorado 80401, United States
| | - Pavel Kabos
- Applied Physics Division, National Institute of Standards and Technology, Boulder, Colorado 80305, United States
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2
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Bauers SR, Tellekamp MB, Roberts DM, Hammett B, Lany S, Ferguson AJ, Zakutayev A, Nanayakkara SU. Metal chalcogenides for neuromorphic computing: emerging materials and mechanisms. Nanotechnology 2021; 32:372001. [PMID: 33882467 DOI: 10.1088/1361-6528/abfa51] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/04/2020] [Accepted: 04/21/2021] [Indexed: 06/12/2023]
Abstract
The approaching end of Moore's law scaling has significantly accelerated multiple fields of research including neuromorphic-, quantum-, and photonic computing, each of which possesses unique benefits unobtained through conventional binary computers. One of the most compelling arguments for neuromorphic computing systems is power consumption, noting that computations made in the human brain are approximately 106times more efficient than conventional CMOS logic. This review article focuses on the materials science and physical mechanisms found in metal chalcogenides that are currently being explored for use in neuromorphic applications. We begin by reviewing the key biological signal generation and transduction mechanisms within neuronal components of mammalian brains and subsequently compare with observed experimental measurements in chalcogenides. With robustness and energy efficiency in mind, we will focus on short-range mechanisms such as structural phase changes and correlated electron systems that can be driven by low-energy stimuli, such as temperature or electric field. We aim to highlight fundamental materials research and existing gaps that need to be overcome to enable further integration or advancement of metal chalcogenides for neuromorphic systems.
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Affiliation(s)
- Sage R Bauers
- Materials Science Center, National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, CO 80401, United States of America
| | - M Brooks Tellekamp
- Materials Science Center, National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, CO 80401, United States of America
| | - Dennice M Roberts
- Materials Science Center, National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, CO 80401, United States of America
| | - Breanne Hammett
- Materials Science Center, National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, CO 80401, United States of America
- Department of Chemistry, Colorado School of Mines, 1500 Illinois Avenue, Golden, CO 80401, United States of America
| | - Stephan Lany
- Materials Science Center, National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, CO 80401, United States of America
| | - Andrew J Ferguson
- Chemistry and Nanoscience Center, National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, CO 80401, United States of America
| | - Andriy Zakutayev
- Materials Science Center, National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, CO 80401, United States of America
| | - Sanjini U Nanayakkara
- Materials Science Center, National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, CO 80401, United States of America
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3
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Berweger S, Zhang H, Sahoo PK, Kupp BM, Blackburn JL, Miller EM, Wallis TM, Voronine DV, Kabos P, Nanayakkara SU. Spatially Resolved Persistent Photoconductivity in MoS 2-WS 2 Lateral Heterostructures. ACS Nano 2020; 14:14080-14090. [PMID: 33044054 DOI: 10.1021/acsnano.0c06745] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
The optical and electronic properties of 2D semiconductors are intrinsically linked via the strong interactions between optically excited bound species and free carriers. Here we use near-field scanning microwave microscopy (SMM) to image spatial variations in photoconductivity in MoS2-WS2 lateral multijunction heterostructures using photon energy-resolved narrowband illumination. We find that the onset of photoconductivity in individual domains corresponds to the optical absorption onset, confirming that the tightly bound excitons in transition metal dichalcogenides can nonetheless dissociate into free carriers. These photogenerated carriers are most likely n-type and are seen to persist for up to days. Informed by finite element modeling we reveal that they can increase the carrier density by up to 200 times. This persistent photoconductivity appears to be dominated by contributions from the multilayer MoS2 domains, and we attribute the flake-wide response in part to charge transfer across the heterointerface. Spatial correlation of our SMM imaging with photoluminescence (PL) mapping confirms the strong link between PL peak emission photon energy, PL intensity, and the local accumulated charge. This work reveals the spatially and temporally complex optoelectronic response of these systems and cautions that properties measured during or after illumination may not reflect the true dark state of these materials but rather a metastable charged state.
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Affiliation(s)
- Samuel Berweger
- Applied Physics Division, National Institute of Standards and Technology, Boulder, Colorado 80305, United States
| | - Hanyu Zhang
- Materials and Chemical Science and Technology Directorate, National Renewable Energy Laboratory, Golden, Colorado 80401, United States
| | - Prasana K Sahoo
- Department of Physics, University of South Florida, Tampa, Florida 33620, United States
- Materials Science Centre, Indian Institute of Technology Kharagpur, Kharagpur, 721302, India
| | - Benjamin M Kupp
- Applied Physics Division, National Institute of Standards and Technology, Boulder, Colorado 80305, United States
- The Pennsylvania State University, University Park, Pennsylvania 16802, United States
| | - Jeffrey L Blackburn
- Materials and Chemical Science and Technology Directorate, National Renewable Energy Laboratory, Golden, Colorado 80401, United States
| | - Elisa M Miller
- Materials and Chemical Science and Technology Directorate, National Renewable Energy Laboratory, Golden, Colorado 80401, United States
| | - Thomas M Wallis
- Applied Physics Division, National Institute of Standards and Technology, Boulder, Colorado 80305, United States
| | - Dmitri V Voronine
- Department of Physics, University of South Florida, Tampa, Florida 33620, United States
| | - Pavel Kabos
- Applied Physics Division, National Institute of Standards and Technology, Boulder, Colorado 80305, United States
| | - Sanjini U Nanayakkara
- Materials and Chemical Science and Technology Directorate, National Renewable Energy Laboratory, Golden, Colorado 80401, United States
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4
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Zhang H, Dunklin JR, Reid OG, Yun SJ, Nanayakkara SU, Lee YH, Blackburn JL, Miller EM. Disentangling oxygen and water vapor effects on optoelectronic properties of monolayer tungsten disulfide. Nanoscale 2020; 12:8344-8354. [PMID: 32236241 DOI: 10.1039/c9nr09326e] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
By understanding how the environmental composition impacts the optoelectronic properties of transition metal dichalcogenide monolayers, we demonstrate that simple photoluminescence (PL) measurements of tungsten disulfide (WS2) monolayers can differentiate relative humidity environments. In this paper, we examine the PL and photoconductivity of chemical vapor deposition grown WS2 monolayers under three carefully controlled environments: inert gas (N2), dry air (O2 in N2), and humid nitrogen (H2O vapor in N2). The WS2 PL is measured as a function of 532 nm laser power and exposure time and can be decomposed into the exciton, trion, and lower energy state(s) contributions. Under continuous illumination in either O2 or H2O vapor environment, we find dramatic (and reversible) increases in PL intensity relative to the PL in an inert environment. The PL bathochromically shifts in an O2 environment and is dominated by increased trion emission and diminished exciton emission. In contrast, the WS2 PL increase in a H2O environment results from an overall increase in emission from all spectral components where the exciton contribution dominates. The drastic increases in PL are anticorrelated with corresponding decreases in photoconductivity, as measured by time-resolved microwave conductivity. The results suggest that both O2 and H2O react photochemically with the WS2 monolayer surface, modifying the optoelectronic properties, but do so via distinct pathways. Thus, we use these optoelectronic differences to differentiate the amount of humidity in the air, which we show with 0%, 40%, and 80% relative humidity environments. This deeper understanding of how ambient conditions impact WS2 monolayers enables novel humidity sensors as well as a better understanding of the correlation between TMDC surface chemistry, light emission, and photoconductivity. Moreover, these WS2 measurements highlight the importance of considering the impact of the local environment on reported results.
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Affiliation(s)
- Hanyu Zhang
- Materials and Chemical Science and Technology Directorate, National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, Colorado 80401, USA.
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5
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Kale AS, Nemeth W, Guthrey H, Nanayakkara SU, LaSalvia V, Theingi S, Findley D, Page M, Al-Jassim M, Young DL, Stradins P, Agarwal S. Effect of Crystallographic Orientation and Nanoscale Surface Morphology on Poly-Si/SiO x Contacts for Silicon Solar Cells. ACS Appl Mater Interfaces 2019; 11:42021-42031. [PMID: 31610646 DOI: 10.1021/acsami.9b11889] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
High-efficiency crystalline silicon (Si) solar cells require textured surfaces for efficient light trapping. However, passivation of a textured surface to reduce carrier recombination is difficult. Here, we relate the electrical properties of cells fabricated on a KOH-etched, random pyramidal-textured Si surface to the nanostructure of the passivated contact and the textured surface morphology. The effects of both microscopic pyramidal morphology and nanoscale surface roughness on passivated contacts consisting of polycrystalline Si (poly-Si) deposited on top of an ultrathin, 1.5-2.2 nm, SiOx layer are investigated. Using atomic force microscopy, we show a pyramid face, which is predominantly a Si(111) plane to be significantly rougher than a polished Si(111) surface. This roughness results in a nonuniform SiOx layer as determined by transmission electron microscopy of a poly-Si/SiOx contact. Our device measurements also show an overall more resistive and hence a thicker SiOx layer over the pyramidal surface as compared to a polished Si(111) surface, which we relate to increased surface roughness. Using electron-beam-induced current measurements of poly-Si/SiOx contacts, we further show that the SiOx layer near the pyramid valleys is preferentially more conducting and hence likely thinner than over pyramid tips, edges, and faces. Hence, both the microscopic pyramidal morphology and nanoscale roughness lead to a nonuniform SiOx layer, thus leading to poor poly-Si/SiOx contact passivation. Finally, we report >21% efficient and ≥80% fill-factor front/back poly-Si/SiOx solar cells on both single-side and double-side textured wafers without the use of transparent conductive oxide layers, and show that the poorer contact passivation on a textured surface is limited to boron-doped poly-Si/SiOx contacts.
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Affiliation(s)
- Abhijit S Kale
- Department of Chemical and Biological Engineering , Colorado School of Mines , Golden , Colorado 80401 , United States
- National Renewable Energy Laboratory , Golden , Colorado 80401 , United States
| | - William Nemeth
- National Renewable Energy Laboratory , Golden , Colorado 80401 , United States
| | - Harvey Guthrey
- National Renewable Energy Laboratory , Golden , Colorado 80401 , United States
| | | | - Vincenzo LaSalvia
- National Renewable Energy Laboratory , Golden , Colorado 80401 , United States
| | - San Theingi
- National Renewable Energy Laboratory , Golden , Colorado 80401 , United States
| | - Dawn Findley
- National Renewable Energy Laboratory , Golden , Colorado 80401 , United States
| | - Matthew Page
- National Renewable Energy Laboratory , Golden , Colorado 80401 , United States
| | - Mowafak Al-Jassim
- National Renewable Energy Laboratory , Golden , Colorado 80401 , United States
| | - David L Young
- National Renewable Energy Laboratory , Golden , Colorado 80401 , United States
| | - Paul Stradins
- National Renewable Energy Laboratory , Golden , Colorado 80401 , United States
| | - Sumit Agarwal
- Department of Chemical and Biological Engineering , Colorado School of Mines , Golden , Colorado 80401 , United States
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6
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Garten LM, Moore DT, Nanayakkara SU, Dwaraknath S, Schulz P, Wands J, Rockett A, Newell B, Persson KA, Trolier-McKinstry S, Ginley DS. The existence and impact of persistent ferroelectric domains in MAPbI 3. Sci Adv 2019; 5:eaas9311. [PMID: 30746434 PMCID: PMC6357725 DOI: 10.1126/sciadv.aas9311] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/05/2018] [Accepted: 12/07/2018] [Indexed: 05/27/2023]
Abstract
Methylammonium lead iodide (MAPbI3) exhibits exceptional photovoltaic performance, but there remains substantial controversy over the existence and impact of ferroelectricity on the photovoltaic response. We confirm ferroelectricity in MAPbI3 single crystals and demonstrate mediation of the electronic response by ferroelectric domain engineering. The ferroelectric response sharply declines above 57°C, consistent with the tetragonal-to-cubic phase transition. Concurrent band excitation piezoresponse force microscopy-contact Kelvin probe force microscopy shows that the measured response is not dominated by spurious electrostatic interactions. Large signal poling (>16 V/cm) orients the permanent polarization into large domains, which show stabilization over weeks. X-ray photoemission spectroscopy results indicate a shift of 400 meV in the binding energy of the iodine core level peaks upon poling, which is reflected in the carrier concentration results from scanning microwave impedance microscopy. The ability to control the ferroelectric response provides routes to increase device stability and photovoltaic performance through domain engineering.
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Affiliation(s)
| | - David T. Moore
- National Renewable Energy Laboratory, Golden, CO 80401, USA
| | | | - Shyam Dwaraknath
- Lawrence Berkeley National Laboratory, 1 Cyclotron Rd, Berkeley, CA 94720, USA
| | - Philip Schulz
- National Renewable Energy Laboratory, Golden, CO 80401, USA
- CNRS, Institut Photovoltaïque d’Île de France, UMR 9006, 30 route départementale 128, Palaiseau 91120, France
| | - Jake Wands
- Colorado School of Mines, Golden, CO 80401, USA
| | | | - Brian Newell
- Colorado State University, Fort Collins, CO 80523, USA
| | - Kristin A. Persson
- Lawrence Berkeley National Laboratory, 1 Cyclotron Rd, Berkeley, CA 94720, USA
- The Pennsylvania State University, University Park, PA 16802, USA
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7
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Ferguson AJ, Reid OG, Nanayakkara SU, Ihly R, Blackburn JL. Efficiency of Charge-Transfer Doping in Organic Semiconductors Probed with Quantitative Microwave and Direct-Current Conductance. J Phys Chem Lett 2018; 9:6864-6870. [PMID: 30457866 DOI: 10.1021/acs.jpclett.8b03074] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Although molecular charge-transfer doping is widely used to manipulate carrier density in organic semiconductors, only a small fraction of charge carriers typically escape the Coulomb potential of dopant counterions to contribute to electrical conductivity. Here, we utilize microwave and direct-current (DC) measurements of electrical conductivity to demonstrate that a high percentage of charge carriers in redox-doped semiconducting single-walled carbon nanotube (s-SWCNT) networks is delocalized as a free carrier density in the π-electron system (estimated as >46% at high doping densities). The microwave and four-point probe conductivities of hole-doped s-SWCNT films quantitatively match over almost 4 orders of magnitude in conductance, indicating that both measurements are dominated by the same population of delocalized carriers. We address the relevance of this surprising one-to-one correspondence by discussing the degree to which local environmental parameters (e.g., tube-tube junctions, Coulombic stabilization, and local bonding environment) may impact the relative magnitudes of each transport measurement.
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Affiliation(s)
- Andrew J Ferguson
- National Renewable Energy Laboratory , Golden , Colorado 80401 , United States
| | - Obadiah G Reid
- National Renewable Energy Laboratory , Golden , Colorado 80401 , United States
- Renewable and Sustainable Energy Institute , University of Colorado Boulder , Boulder , Colorado 80303 , United States
| | | | - Rachelle Ihly
- National Renewable Energy Laboratory , Golden , Colorado 80401 , United States
| | - Jeffrey L Blackburn
- National Renewable Energy Laboratory , Golden , Colorado 80401 , United States
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8
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Benson EE, Zhang H, Schuman SA, Nanayakkara SU, Bronstein ND, Ferrere S, Blackburn JL, Miller EM. Balancing the Hydrogen Evolution Reaction, Surface Energetics, and Stability of Metallic MoS2 Nanosheets via Covalent Functionalization. J Am Chem Soc 2017; 140:441-450. [PMID: 29281274 DOI: 10.1021/jacs.7b11242] [Citation(s) in RCA: 113] [Impact Index Per Article: 16.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Affiliation(s)
- Eric E. Benson
- National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, Colorado 80401, United States
| | - Hanyu Zhang
- National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, Colorado 80401, United States
| | - Samuel A. Schuman
- National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, Colorado 80401, United States
| | - Sanjini U. Nanayakkara
- National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, Colorado 80401, United States
| | - Noah D. Bronstein
- National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, Colorado 80401, United States
| | - Suzanne Ferrere
- National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, Colorado 80401, United States
| | - Jeffrey L. Blackburn
- National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, Colorado 80401, United States
| | - Elisa M. Miller
- National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, Colorado 80401, United States
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9
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Crisp RW, Pach GF, Kurley JM, France RM, Reese MO, Nanayakkara SU, MacLeod BA, Talapin DV, Beard MC, Luther JM. Tandem Solar Cells from Solution-Processed CdTe and PbS Quantum Dots Using a ZnTe-ZnO Tunnel Junction. Nano Lett 2017; 17:1020-1027. [PMID: 28068765 DOI: 10.1021/acs.nanolett.6b04423] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/19/2023]
Abstract
We developed a monolithic CdTe-PbS tandem solar cell architecture in which both the CdTe and PbS absorber layers are solution-processed from nanocrystal inks. Due to their tunable nature, PbS quantum dots (QDs), with a controllable band gap between 0.4 and ∼1.6 eV, are a promising candidate for a bottom absorber layer in tandem photovoltaics. In the detailed balance limit, the ideal configuration of a CdTe (Eg = 1.5 eV)-PbS tandem structure assumes infinite thickness of the absorber layers and requires the PbS band gap to be 0.75 eV to theoretically achieve a power conversion efficiency (PCE) of 45%. However, modeling shows that by allowing the thickness of the CdTe layer to vary, a tandem with efficiency over 40% is achievable using bottom cell band gaps ranging from 0.68 and 1.16 eV. In a first step toward developing this technology, we explore CdTe-PbS tandem devices by developing a ZnTe-ZnO tunnel junction, which appropriately combines the two subcells in series. We examine the basic characteristics of the solar cells as a function of layer thickness and bottom-cell band gap and demonstrate open-circuit voltages in excess of 1.1 V with matched short circuit current density of 10 mA/cm2 in prototype devices.
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Affiliation(s)
- Ryan W Crisp
- National Renewable Energy Laboratory , Golden, Colorado 80401, United States
- Department of Physics, Colorado School of Mines , Golden, Colorado 80401, United States
| | - Gregory F Pach
- National Renewable Energy Laboratory , Golden, Colorado 80401, United States
- Department of Electrical, Computer, and Energy Engineering, University of Colorado , Boulder, Colorado 80309, United States
| | - J Matthew Kurley
- Department of Chemistry and James Franck Institute, University of Chicago , Chicago, Illinois 60637, United States
| | - Ryan M France
- National Renewable Energy Laboratory , Golden, Colorado 80401, United States
| | - Matthew O Reese
- National Renewable Energy Laboratory , Golden, Colorado 80401, United States
| | | | - Bradley A MacLeod
- National Renewable Energy Laboratory , Golden, Colorado 80401, United States
| | - Dmitri V Talapin
- Department of Chemistry and James Franck Institute, University of Chicago , Chicago, Illinois 60637, United States
- Center for Nanoscale Materials, Argonne National Laboratory , Argonne, Illinois 60439, United States
| | - Matthew C Beard
- National Renewable Energy Laboratory , Golden, Colorado 80401, United States
| | - Joseph M Luther
- National Renewable Energy Laboratory , Golden, Colorado 80401, United States
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10
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Abstract
A series of covalent organic framework (COF) structures is synthesized that possesses a tunable density of covalently bound nitroxyl radicals within the COF pores. The highest density of organic radicals produces an electron paramagnetic resonance (EPR) signal that suggests the majority of radicals strongly interact with other radicals, whereas for smaller loadings the EPR signals indicate the radicals are primarily isolated but with restricted motion. The dielectric loss as determined from microwave absorption of the framework structures compared with an amorphous control suggests that free motion of the radicals is inhibited when more than 25% of available sites are occupied. The ability to tune the mode of radical interactions and the subsequent effect on redox, electrical, and optical characteristics in a porous framework may lead to a class of structures with properties ideal for photoelectrochemistry or energy storage.
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Affiliation(s)
- Barbara K Hughes
- National Renewable Energy Laboratory , 15013 Denver West Pkwy, Golden, Colorado 80401, United States
| | - Wade A Braunecker
- National Renewable Energy Laboratory , 15013 Denver West Pkwy, Golden, Colorado 80401, United States
| | - David C Bobela
- National Renewable Energy Laboratory , 15013 Denver West Pkwy, Golden, Colorado 80401, United States
| | - Sanjini U Nanayakkara
- National Renewable Energy Laboratory , 15013 Denver West Pkwy, Golden, Colorado 80401, United States
| | - Obadiah G Reid
- National Renewable Energy Laboratory , 15013 Denver West Pkwy, Golden, Colorado 80401, United States
- Renewable and Sustainable Energy Institute, University of Colorado , Boulder, Colorado 80309, United States
| | - Justin C Johnson
- National Renewable Energy Laboratory , 15013 Denver West Pkwy, Golden, Colorado 80401, United States
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11
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Affiliation(s)
- Sanjini U. Nanayakkara
- National Renewable Energy Laboratory, 15013 Denver
West Parkway, Golden, Colorado 80401, United States
| | - Jao van de Lagemaat
- National Renewable Energy Laboratory, 15013 Denver
West Parkway, Golden, Colorado 80401, United States
| | - Joseph M. Luther
- National Renewable Energy Laboratory, 15013 Denver
West Parkway, Golden, Colorado 80401, United States
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12
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Cohen G, Halpern E, Nanayakkara SU, Luther JM, Held C, Bennewitz R, Boag A, Rosenwaks Y. Reconstruction of surface potential from Kelvin probe force microscopy images. Nanotechnology 2013; 24:295702. [PMID: 23807266 DOI: 10.1088/0957-4484/24/29/295702] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
We present an algorithm for reconstructing a sample surface potential from its Kelvin probe force microscopy (KPFM) image. The measured KPFM image is a weighted average of the surface potential underneath the tip apex due to the long-range electrostatic forces. We model the KPFM measurement by a linear shift-invariant system where the impulse response is the point spread function (PSF). By calculating the PSF of the KPFM probe (tip+cantilever) and using the measured noise statistics, we deconvolve the measured KPFM image to obtain the surface potential of the sample.The reconstruction algorithm is applied to measurements of CdS-PbS nanorods measured in amplitude modulation KPFM (AM-KPFM) and to graphene layers measured in frequency modulation KPFM (FM-KPFM). We show that in the AM-KPFM measurements the averaging effect is substantial, whereas in the FM-KPFM measurements the averaging effect is negligible.
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Affiliation(s)
- G Cohen
- School of Electrical Engineering, Tel-Aviv University, Tel-Aviv 69978, Israel
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13
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Maturova K, Nanayakkara SU, Luther JM, van de Lagemaat J. Fast current blinking in individual PbS and CdSe quantum dots. Nano Lett 2013; 13:2338-2345. [PMID: 23472703 DOI: 10.1021/nl3036096] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Fast current intermittency of the tunneling current through single semiconductor quantum dots was observed through time-resolved intermittent contact conductive atomic force microscopy in the dark and under illumination at room temperature. The current through a single dot switches on and off at time scales ranging from microseconds to seconds with power-law distributions for both the on and off times. On states are attributed to the resonant tunneling of charges from the electrically conductive AFM tip to the quantum dot, followed by transfer to the substrate, whereas off states are attributed to a Coulomb blockade effect in the quantum dots that shifts the energy levels out of resonance conditions due to the presence of the trapped charge, while at the same bias. The observation of current intermittency due to Coulomb blockade effects has important implications for the understanding of carrier transport through arrays of quantum dots.
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Affiliation(s)
- Klara Maturova
- Chemical and Materials Science Center, National Renewable Energy Laboratory, Golden, Colorado 80401, USA
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14
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Nanayakkara SU, Cohen G, Jiang CS, Romero MJ, Maturova K, Al-Jassim M, van de Lagemaat J, Rosenwaks Y, Luther JM. Built-in potential and charge distribution within single heterostructured nanorods measured by scanning Kelvin probe microscopy. Nano Lett 2013; 13:1278-1284. [PMID: 23379602 DOI: 10.1021/nl4000147] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
The electrostatic potential distribution across single, isolated, colloidal heterostructured nanorods (NRs) with component materials expected to form a p-n junction within each NR has been measured using scanning Kelvin probe microscopy (SKPM). We compare CdS to bicomponent CdS-CdSe, CdS-PbSe, and CdS-PbS NRs prepared via different synthetic approaches to corroborate the SKPM assignments. The CdS-PbS NRs show a sharp contrast in measured potential across the material interface. We find the measured built-in potential within an individual NR to be attenuated by long-range electrostatic forces between the sample substrate, cantilever, and the measuring tip. Surface potential images were deconvoluted to yield built-in potentials ranging from 375 to 510 meV in the heterostructured NRs. We deduce the overall built-in potential as well as the charge distribution across each segment of the heterostructured NRs by combining SKPM data with simulations of the system.
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Affiliation(s)
- Sanjini U Nanayakkara
- National Renewable Energy Laboratory, 1617 Cole Blvd., Golden, Colorado, United States
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15
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Han P, Kurland AR, Giordano AN, Nanayakkara SU, Blake MM, Pochas CM, Weiss PS. Heads and tails: simultaneous exposed and buried interface imaging of monolayers. ACS Nano 2009; 3:3115-3121. [PMID: 19772297 DOI: 10.1021/nn901030x] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
We have simultaneously imaged the chemically bound head groups and exposed tail groups in bicomponent alkanethiolate self-assembled monolayers on Au{111} with molecular resolution. This has enabled us to resolve the controversy of scanning tunneling microscopy image interpretation and to measure the molecular polar tilt and azimuthal angles. Our local measurements demonstrate that ordered domains with different superstructures also have varied buried sulfur head group structures.
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Affiliation(s)
- Patrick Han
- Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
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16
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Blake MM, Nanayakkara SU, Claridge SA, Fernández-Torres LC, Sykes ECH, Weiss PS. Identifying Reactive Intermediates in the Ullmann Coupling Reaction by Scanning Tunneling Microscopy and Spectroscopy. J Phys Chem A 2009; 113:13167-72. [DOI: 10.1021/jp903590c] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Meaghan M. Blake
- Departments of Chemistry and Physics, The Pennsylvania State University, University Park, Pennsylvania 16802-6300
| | - Sanjini U. Nanayakkara
- Departments of Chemistry and Physics, The Pennsylvania State University, University Park, Pennsylvania 16802-6300
| | - Shelley A. Claridge
- Departments of Chemistry and Physics, The Pennsylvania State University, University Park, Pennsylvania 16802-6300
| | - Luis C. Fernández-Torres
- Departments of Chemistry and Physics, The Pennsylvania State University, University Park, Pennsylvania 16802-6300
| | - E. Charles H. Sykes
- Departments of Chemistry and Physics, The Pennsylvania State University, University Park, Pennsylvania 16802-6300
| | - Paul S. Weiss
- Departments of Chemistry and Physics, The Pennsylvania State University, University Park, Pennsylvania 16802-6300
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Nanayakkara SU, Sykes ECH, Fernández-Torres LC, Blake MM, Weiss PS. Long-range electronic interactions at a high temperature: bromine adatom islands on Cu(111). Phys Rev Lett 2007; 98:206108. [PMID: 17677717 DOI: 10.1103/physrevlett.98.206108] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/04/2006] [Indexed: 05/16/2023]
Abstract
Long-range electronic interactions between Br adatom islands, which are formed at approximately 600 K, on Cu(111) are mediated by substrate surface-state electrons at that elevated temperature. Using scanning tunneling microscopy at 4 K, we have quantified nearest neighbor island separations and found favored spacings to be half-multiples of the Fermi wavelength of Cu(111). The strong interaction potential and decay length of the interisland interactions are discussed in terms of the interaction of Br with the substrate surface state.
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Affiliation(s)
- Sanjini U Nanayakkara
- Department of Chemistry, The Pennsylvania State University, 104 Davey Laboratory, University Park, Pennsylvania 16802-6300, USA
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Smith RK, Nanayakkara SU, Woehrle GH, Pearl TP, Blake MM, Hutchison JE, Weiss PS. Spectral Diffusion in the Tunneling Spectra of Ligand-Stabilized Undecagold Clusters. J Am Chem Soc 2006; 128:9266-7. [PMID: 16848426 DOI: 10.1021/ja061040r] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We report diffusion in the tunneling spectra of isolated, ligand-stabilized undecagold (Au11) clusters immobilized by attachment to alpha,omega-alkanedithiolate tethers inserted into alkanethiolate self-assembled monolayers. We use scanning tunneling microscopy and spectroscopy at cryogenic (UHV, 4 K) conditions to measure these clusters' conductance with complete control of their chemical and physical environment; additionally, thermal broadening of their electronic states as well as their mobility is minimized. At low temperature, the Au11 clusters demonstrate Coulomb blockade behavior, with zero-conductance gaps resulting from quantum size effects. Surprisingly, chemically identical and even single particles produced different families of tunneling spectra, comparable to previous results for heterogeneous distributions of particles. We hypothesize that, while these particles are chemically attached to the surface of the SAM for measurement, these assemblies may still be sufficiently dynamic to affect their transport properties significantly.
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Affiliation(s)
- Rachel K Smith
- Departments of Chemistry and Physics, 104 Davey Laboratory, The Pennsylvania State University, University Park, Pennsylvania 16802-6300, USA
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Abstract
Chemisorption of hydrogen on Pd{111} is a relatively simple, yet important surface chemical process. By using low-temperature scanning tunneling microscopy, tip-induced motion of adsorbed atomic hydrogen at 4 K has been observed at low coverage. The motion has been ascribed to excitation of vibrational modes that decay into translational modes; vibrational spectroscopy via inelastic electron tunneling corroborates this assignment, and the barrier to hydrogen atom motion has been determined. At higher coverages, tip-induced motion of vacancies in the hydrogen overlayer is observed, and the associated barrier has also been determined.
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Affiliation(s)
- Luis C Fernandez-Torres
- Departments of Chemistry and Physics, 104 Davey Laboratory, The Pennsylvania State University, University Park, Pennsylvania 16802-6300
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Sykes ECH, Fernández-Torres LC, Nanayakkara SU, Mantooth BA, Nevin RM, Weiss PS. Observation and manipulation of subsurface hydride in Pd[111] and its effect on surface chemical, physical, and electronic properties. Proc Natl Acad Sci U S A 2005; 102:17907-11. [PMID: 16322103 PMCID: PMC1312391 DOI: 10.1073/pnas.0506657102] [Citation(s) in RCA: 87] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2005] [Indexed: 11/18/2022] Open
Abstract
We report the observation and manipulation of hydrogen atoms beneath the surface of a Pd[111] crystal by using low-temperature scanning tunneling microscopy. These subsurface hydride sites have been postulated to have critical roles in hydrogen storage, metal embrittlement, fuel cells, and catalytic reactions, but they have been neither observed directly nor selectively populated previously. We demonstrate that the subsurface region of Pd can be populated with hydrogen atoms from the bulk by applying voltage pulses from a scanning tunneling microscope tip. This phenomenon is explained with an inelastic excitation mechanism, whereby hydrogen atoms in the bulk are excited by tunneling electrons and are promoted to more stable sites in the subsurface region. We show that this selectively placed subsurface hydride affects the electronic, geometric, and chemical properties of the surface. Specifically, we observed the effects of hydride formation on surface deformation and charge and on adsorbed hydrogen on the surface. Hydrogen segregation and overlayer vacancy ordering on the Pd[111] have been characterized and explained in terms of the surface changes attributable to selective hydrogen occupation of subsurface hydride sites in Pd[111].
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Affiliation(s)
- E Charles H Sykes
- Department of Chemistry, Pennsylvania State University, University Park, 16802-6300, USA
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