The Experts below are selected from a list of 318 Experts worldwide ranked by ideXlab platform
David L. Carroll - One of the best experts on this subject based on the ideXlab platform.
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Bulk Heterojunction organic photovoltaic based on polythiophene–polyelectrolyte carbon nanotube composites
Solar Energy Materials and Solar Cells, 2007Co-Authors: M. Reyes-reyes, Román López-sandoval, David L. CarrollAbstract:Abstract It is shown that carbon nanotubes can be used to enhance carrier mobility for efficient removal of the charges in thin film polymer-conjugated/fullerene photovoltaic devices. The fabricated photovoltaic devices consist of poly(3-octylthiophene) (P3OT) polymer blended with undoped multiwalled carbon nanotubes (MWNTs) and carbon nanotubes doped with nitrogen (CNx-MWNTs). Nanophase Formation and dispersion problems associated with the use of carbon nanotubes in polymer devices were addressed through the generation of functional groups and electrostatic attaching of the polyelectrolyte poly(dimethyldiallylamine) chloride (PDDA) in both MWNTs and CNx-MWNT systems. The resultant nanophase was highly dispersed allowing for excellent bulk Heterojunction Formation. Our results indicate that CNx-MWNTs enhance the efficiency of P3OT solar cells in comparison with MWNTs.
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thermal diffusion processes in bulk Heterojunction Formation for poly 3 hexylthiophene c60 single Heterojunction photovoltaics
Applied Physics Letters, 2006Co-Authors: David L. CarrollAbstract:We have fabricated bulk Heterojunction (BHJ) photovoltaic (PV) devices by thermal annealing of poly-3-hexylthiophene (P3HT)/C60 single Heterojunction (HJ) PV devices at near the melting point of P3HT. The BHJ PV devices exhibited an increased efficiency of 12 times compared with single HJs. We found that the annealing of HJ devices produces an interpenetrated network of interfaces between the P3HT and C60 layers. This plays a major role in carrier separation and mobility enhancement. Also the Formation of crystalline C60 domains, concurrent with polymer crystallinity, contributes to an increase in the overall external conversion efficiency. Surprisingly, the Heterojunction morphology, as inferred through device performance, strongly depends on the thermal gradient across the film.
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Thermal diffusion processes in bulk Heterojunction Formation for poly-3-hexylthiophene/C60 single Heterojunction photovoltaics
Applied Physics Letters, 2006Co-Authors: David L. CarrollAbstract:We have fabricated bulk Heterojunction (BHJ) photovoltaic (PV) devices by thermal annealing of poly-3-hexylthiophene (P3HT)/C60 single Heterojunction (HJ) PV devices at near the melting point of P3HT. The BHJ PV devices exhibited an increased efficiency of 12 times compared with single HJs. We found that the annealing of HJ devices produces an interpenetrated network of interfaces between the P3HT and C60 layers. This plays a major role in carrier separation and mobility enhancement. Also the Formation of crystalline C60 domains, concurrent with polymer crystallinity, contributes to an increase in the overall external conversion efficiency. Surprisingly, the Heterojunction morphology, as inferred through device performance, strongly depends on the thermal gradient across the film.
Art J. Nelson - One of the best experts on this subject based on the ideXlab platform.
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X-ray photoemission analysis of chemically modified TlBr surfaces for improved radiation detectors
Journal of Applied Physics, 2013Co-Authors: Art J. Nelson, Lars F. Voss, Patrick R. Beck, R. T. Graff, Adam M. Conway, Rebecca J. Nikolic, S.a. Payne, L. CirignanoAbstract:Device-grade TlBr was subjected to various chemical treatments used in room temperature radiation detector fabrication to determine the resulting surface composition and electronic structure. As-polished TlBr was treated separately with HCl, SOCl2, Br:MeOH, and HF solutions. High-resolution photoemission measurements on the valence band electronic structure and Tl 4f, Br 3d, Cl 2p, and S 2p core lines were used to evaluate surface chemistry and shallow Heterojunction Formation. Surface chemistry and valence band electronic structure were correlated with the goal of optimizing the long-term stability and radiation response.
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X-ray photoemission analysis of chemically treated I–III–VI semiconductor surfaces
Journal of Vacuum Science and Technology, 1997Co-Authors: Art J. Nelson, C. R. Schwerdtfeger, G. C. Herdt, D. King, Miguel A. Contreras, K. Ramanathan, W. L. O’brienAbstract:Device-grade thin-film CuInSe2 was subjected to various chemical treatments commonly used in photovoltaic device fabrication to determine the resulting microscopic surface composi- tion/morphology and the effect on II–VI CuInSe2 Heterojunction Formation. HCl (38%), Br–MeOH (
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novel method for growing cds on cdte surfaces for passivation of surface states and Heterojunction Formation
Journal of Vacuum Science and Technology, 1997Co-Authors: Art J. Nelson, Dean LeviAbstract:Large-grain polycrystalline CdTe was subjected to in situ H2S plasma processing for <30 min at 100 and 200 °C. High-resolution x-ray photoemission measurements on the Cd 4d, Te 4d, and S 2p core levels, and the valence band were used to determine the resultant chemical environment of S and the electronic structure at the CdTe surface following plasma processing. Auger electron spectroscopy compositional depth profiling was also used to determine the distribution of S in the near surface region. Furthermore, time-resolved photoluminescence was used to measure carrier lifetimes and, thus, determine the degree of passivation of CdTe surface states. These results provide evidence for a CdS/CdS1−xTex/CdTe Heterojunction device structure, as a result of the H2S plasma processing, and a reduction in the surface recombination velocity through passivation of surface states. This is a novel method of fabricating CdS/CdTe Heterojunction devices.
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Novel method for growing CdS on CdTe surfaces for passivation of surface states and Heterojunction Formation
Journal of Vacuum Science and Technology, 1997Co-Authors: Art J. Nelson, Dean LeviAbstract:Large-grain polycrystalline CdTe was subjected to in situ H2S plasma processing for
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XPS Analysis of Chemically Treated I-III-VI Semiconductor Surfaces and the Relation to II-VI/I-III-VI Heterojunction Formation
MRS Proceedings, 1996Co-Authors: Art J. Nelson, C. R. Schwerdtfeger, G. C. Herdt, D. King, Miguel A. Contreras, K. Ramanathan, W. L. O’brienAbstract:AbstractDevice-grade thin-film CuInSe2 was subjected to various chemical treatments commonly used in photovoltaic device fabrication to determine the resulting microscopic surface composition/morphology and the effect on II-VI/CuInSe2 Heterojunction Formation. HCI (38%), Br-MeOH (<1% Br), (NH4)2S, and NH4OH/thiourea solutions were used separately to modify the surface chemistry of the CuInSe2 polycrystalline films. Scanning electron microscopy was used to evaluate the resultant surface morphology. Angle-resolved high-resolution photoemission measurements on the valence band electronic structure and Cu 2p, In 3d, Ga 2p and Se 3d core lines were used to evaluate the chemistry of the chemically treated surfaces. CdS overlayers were then deposited in steps on these chemically treated surfaces. Photoemission measurements were acquired after each growth to determine the resultant Heterojunction valence-band discontinuity between the CdS and the chemically modified CuInSe2 surface.
Carlo A. Pignedoli - One of the best experts on this subject based on the ideXlab platform.
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intraribbon Heterojunction Formation in ultranarrow graphene nanoribbons
ACS Nano, 2012Co-Authors: Stephan Blankenburg, Rached Jaafar, Daniele Passerone, Roman Fasel, Xinliang Feng, Pascal Ruffieux, Klaus Müllen, Carlo A. PignedoliAbstract:Graphene nanoribbons—semiconducting quasi-one-dimensional graphene structures—have great potential for the realization of novel electronic devices. Recently, graphene nanoribbon Heterojunctions—interfaces between nanoribbons with unequal band gaps—have been realized with lithographic etching techniques and via chemical routes to exploit quantum transport phenomena. However, standard fabrication techniques are not suitable for ribbons narrower than ∼5 nm and do not allow to control the width and edge structure of a specific device with atomic precision. Here, we report the realization of graphene nanoribbon Heterojunctions with lateral dimensions below 2 nm via controllable dehydrogenation of polyanthrylene oligomers self-assembled on a Au(111) surface from molecular precursors. Atomistic simulations reveal the microscopic mechanisms responsible for intraribbon Heterojunction Formation. We demonstrate the capability to selectively modify the Heterojunctions by activating the dehydrogenation reaction on sin...
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Intraribbon Heterojunction Formation in ultranarrow graphene nanoribbons
ACS Nano, 2012Co-Authors: Stephan Blankenburg, Rached Jaafar, Daniele Passerone, Roman Fasel, Xinliang Feng, Pascal Ruffieux, Jinming Cai, Klaus Müllen, Carlo A. PignedoliAbstract:Graphene nanoribbons-semiconducting quasi-one-dimensional graphene structures-have great potential for the realization of novel electronic devices. Recently, graphene nanoribbon Heterojunctions-interfaces between nanoribbons with unequal band gaps-have been realized with lithographic etching techniques and via chemical routes to exploit quantum transport phenomena. However, standard fabrication techniques are not suitable for ribbons narrower than ~5 nm and do not allow to control the width and edge structure of a specific device with atomic precision. Here, we report the realization of graphene nanoribbon Heterojunctions with lateral dimensions below 2 nm via controllable dehydrogenation of polyanthrylene oligomers self-assembled on a Au(111) surface from molecular precursors. Atomistic simulations reveal the microscopic mechanisms responsible for intraribbon Heterojunction Formation. We demonstrate the capability to selectively modify the Heterojunctions by activating the dehydrogenation reaction on single units of the nanoribbons by electron injection from the tip of a scanning tunneling microscope.
H Hochst - One of the best experts on this subject based on the ideXlab platform.
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Soft x‐ray photoemission investigation on the effect of In doping in CdS/CuInSe2 Heterojunction Formation
Journal of Applied Physics, 1992Co-Authors: Art J. Nelson, David W. Niles, Dennis Rioux, R. Patel, H HochstAbstract:Synchrotron radiation soft x‐ray photoemission spectroscopy was used to investigate the development of the electronic structure at the CdS(In)/CuInSe2 Heterojunction interface. In‐doped CdS overlayers were deposited in steps on single‐crystal n‐type CuInSe2 at 250 °C. Results indicate that the CdS(In) grows in registry with the substrate, initially in a two‐dimensional growth mode followed by three‐dimensional island growth as is corroborated by reflection high‐energy electron diffraction analysis. Photoemission measurements were acquired after each growth in order to observe changes in the valence‐band electronic structure. The results were used to correlate the interface chemistry with the electronic structure at these interfaces and to directly determine the CdS(In)/CuInSe2 Heterojunction valence‐band discontinuity and the consequent Heterojunction band diagram as a function of In dopant concentration. We measured a valence‐band offset ΔEv=0.3 eV, independent of In doping.
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The effect of In doping in CdS/CuInSe2 Heterojunction Formation: A photoemission investigation
AIP Conference Proceedings, 1992Co-Authors: Art J. Nelson, David W. Niles, Dennis Rioux, R. Patel, H HochstAbstract:Synchrotron radiation soft x‐ray photoemission spectroscopy was used to investigate the development of the electronic structure at the CdS(In)/CuInSe2 Heterojunction interface. In‐doped CdS overlayers were deposited in steps on single‐crystal n‐type CuInSe2 at 250 °C. Results indicate that the CdS(In) grows in registry with the substrate, initially in a two dimensional growth mode followed by three dimensional island growth as is corroborated by RHEED analysis. Photoemission measurements were acquired after each growth in order to observe changes in the valence band electronic structure as well as changes in the In4d, Se3d, Cd4d, and S2p core lines. The results were used to correlate the interface chemistry with the electronic structure at these interfaces and to directly determine the CdS(In)/CuInSe2 Heterojunction valence band discontinuity and the consequent Heterojunction band diagram as a function of In dopant concentration. We measured a valence band offset ΔEv=0.3 eV, independent of In doping.
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synchrotron radiation photoemission study of cds cuinse2 Heterojunction Formation
Physical Review B, 1990Co-Authors: Art J. Nelson, Steve Gebhard, Angus Rockett, E Colavita, Mike Engelhardt, H HochstAbstract:Synchrotron-radiation soft-x-ray photoemission spectroscopy was used to investigate the development of the electronic structure at the CdS/CuInSe{sub 2} Heterojunction interface. CdS overlayers were deposited in steps on single-crystal {ital p}- and {ital n}-type CuInSe{sub 2} at 250 {degree}C. Results indicate that the CdS grows in registry with the substrate, initially in a two-dimensional growth mode followed by three-dimensional island growth as is corroborated by reflection high-energy electron-diffraction analysis. Photoemission measurements were acquired after each growth in order to observe changes in the valence-band electronic structure as well as changes in the In 4{ital d}, Se 3{ital d}, Cd 4{ital d}, and S 2{ital p} core lines. The results were used to correlate the interface chemistry with the electronic structure at these interfaces and to directly determine the CdS/CuInSe{sub 2} Heterojunction valence-band discontinuity and the consequent Heterojunction band diagram. These results show that the Katnani-Margaritondo method is unreliable in determining offsets for Heterojunctions where significant Fermi-level pinning may occur and where the local structure and chemistry of the interface depends strongly on the specific Heterojunction.
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Synchrotron-radiation photoemission study of CdS/CuInSe2 Heterojunction Formation
Physical Review B, 1990Co-Authors: Art J. Nelson, Steve Gebhard, Angus Rockett, E Colavita, Mike Engelhardt, H HochstAbstract:Synchrotron-radiation soft-x-ray photoemission spectroscopy was used to investigate the development of the electronic structure at the CdS/CuInSe{sub 2} Heterojunction interface. CdS overlayers were deposited in steps on single-crystal {ital p}- and {ital n}-type CuInSe{sub 2} at 250 {degree}C. Results indicate that the CdS grows in registry with the substrate, initially in a two-dimensional growth mode followed by three-dimensional island growth as is corroborated by reflection high-energy electron-diffraction analysis. Photoemission measurements were acquired after each growth in order to observe changes in the valence-band electronic structure as well as changes in the In 4{ital d}, Se 3{ital d}, Cd 4{ital d}, and S 2{ital p} core lines. The results were used to correlate the interface chemistry with the electronic structure at these interfaces and to directly determine the CdS/CuInSe{sub 2} Heterojunction valence-band discontinuity and the consequent Heterojunction band diagram. These results show that the Katnani-Margaritondo method is unreliable in determining offsets for Heterojunctions where significant Fermi-level pinning may occur and where the local structure and chemistry of the interface depends strongly on the specific Heterojunction.
Stephan Blankenburg - One of the best experts on this subject based on the ideXlab platform.
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intraribbon Heterojunction Formation in ultranarrow graphene nanoribbons
ACS Nano, 2012Co-Authors: Stephan Blankenburg, Rached Jaafar, Daniele Passerone, Roman Fasel, Xinliang Feng, Pascal Ruffieux, Klaus Müllen, Carlo A. PignedoliAbstract:Graphene nanoribbons—semiconducting quasi-one-dimensional graphene structures—have great potential for the realization of novel electronic devices. Recently, graphene nanoribbon Heterojunctions—interfaces between nanoribbons with unequal band gaps—have been realized with lithographic etching techniques and via chemical routes to exploit quantum transport phenomena. However, standard fabrication techniques are not suitable for ribbons narrower than ∼5 nm and do not allow to control the width and edge structure of a specific device with atomic precision. Here, we report the realization of graphene nanoribbon Heterojunctions with lateral dimensions below 2 nm via controllable dehydrogenation of polyanthrylene oligomers self-assembled on a Au(111) surface from molecular precursors. Atomistic simulations reveal the microscopic mechanisms responsible for intraribbon Heterojunction Formation. We demonstrate the capability to selectively modify the Heterojunctions by activating the dehydrogenation reaction on sin...
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Intraribbon Heterojunction Formation in ultranarrow graphene nanoribbons
ACS Nano, 2012Co-Authors: Stephan Blankenburg, Rached Jaafar, Daniele Passerone, Roman Fasel, Xinliang Feng, Pascal Ruffieux, Jinming Cai, Klaus Müllen, Carlo A. PignedoliAbstract:Graphene nanoribbons-semiconducting quasi-one-dimensional graphene structures-have great potential for the realization of novel electronic devices. Recently, graphene nanoribbon Heterojunctions-interfaces between nanoribbons with unequal band gaps-have been realized with lithographic etching techniques and via chemical routes to exploit quantum transport phenomena. However, standard fabrication techniques are not suitable for ribbons narrower than ~5 nm and do not allow to control the width and edge structure of a specific device with atomic precision. Here, we report the realization of graphene nanoribbon Heterojunctions with lateral dimensions below 2 nm via controllable dehydrogenation of polyanthrylene oligomers self-assembled on a Au(111) surface from molecular precursors. Atomistic simulations reveal the microscopic mechanisms responsible for intraribbon Heterojunction Formation. We demonstrate the capability to selectively modify the Heterojunctions by activating the dehydrogenation reaction on single units of the nanoribbons by electron injection from the tip of a scanning tunneling microscope.