Dr. Neal R. Armstrong Profile

Dr. Neal R. Armstrong

Professor at Univ of Arizona

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Author

Publications (19)

Proceedings Article | 5 August 2021 Presentation

Towards quantification of redox reactions at perovskite interfaces for enhanced stability in photovoltaics

Michel De Keersmaecker, Neal Armstrong, Erin Ratcliff

Proceedings Volume 11809, 1180911 (2021) https://doi.org/10.1117/12.2595072

KEYWORDS: Photovoltaics, Perovskite

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Proceedings Article | 19 September 2017 Presentation

Understanding the role of titanium dioxide (TiO2) surface chemistry on the nucleation and energetics of hybrid perovskite films (Conference Presentation)

R. Clayton Shallcross, Selina Olthof, Klaus Meerholz, Neal Armstrong

Proceedings Volume 10363, 103631I (2017) https://doi.org/10.1117/12.2274524

KEYWORDS: Interfaces, Chemistry, Photoemission spectroscopy, Thin films, Natural surfaces, Control systems, Titanium, Self-assembled monolayers, Thin film devices, Ions

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We demonstrate how amino-terminated silane monolayers alter the chemical and energetic composition of the TiO2 surface, which controls the interfacial nucleation, growth and energetics of device-relevant, hybrid perovskite (PVSK) thin films. The surface chemistry and energetics of compact TiO2 thin films are modified with a 3-aminopropyltriethoxysilane (APTES) monolayer that can either weakly coordinate Pb2+ ions (–NH2/free base form) or act as a surrogate organic cation (–NH3+/acid form) at the TiO2/PVSK interface, providing for significant differences in the nucleation free energy for the PVSK active layer as a function of NH3+/NH2 ratio. XPS spectra of amine-modified TiO2 surfaces (N 1s core level) demonstrate that we can achieve NH3+/NH2 ratios of between 3:1 and 1:3 depending upon subsequent acid and base treatment, respectively. Methylammonium lead triiodide (MAPbI3) films are incrementally co-evaporated on TiO2, TiO2/APTES-NH3+ and TiO2/APTES-NH2 interfaces, and the chemical composition, growth dynamics and energetics are systematically investigated using in situ X-ray photoelectron spectroscopy (XPS) and UV photoelectron spectroscopy (UPS). The XPS and UPS results reveal that initial nucleation and subsequent growth of the MAPbI3 PVSK film strongly depends on the chemical functionality of the TiO2 surface. The evaporated films display island-like growth on the bare TiO2 surface, which hinders nucleation of the PVSK phase until ca. 15 nm of precursor material is deposited. Conversely, film growth is more layer-by-layer on the amine-modified TiO2 interfaces, which promote nucleation of the PVSK phase within the first ca. 5 nm of deposition. In addition to vacuum evaporated thin films, we show how these TiO2 surface modifications control the morphology and crystallinity of solution-processed PVSK films based on formamidinium and methylammonium organic cations. These studies elucidate the role of TiO2 surface chemistry on the formation mechanism of hybrid PVSK active layers and the interfacial and bulk energetics, which have significant consequences related to the processing and operation of next-generation optoelectronic device platforms.

Proceedings Article | 5 October 2015 Presentation

Effect of substrate surface free energy on the optoelectronic and morphological properties of organolead halide perovskite solar cell materials (Presentation Recording)

R. Clayton Shallcross, James Stanfill, Neal Armstrong

Proceedings Volume 9549, 95491G (2015) https://doi.org/10.1117/12.2188843

KEYWORDS: Oxides, Solar energy, Natural surfaces, Optoelectronics, Solar cells, Thin films, Photoemission spectroscopy, Chemical vapor deposition, Atomic layer deposition, Perovskite

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Proceedings Article | 11 September 2008 Paper

Photovoltaic devices created from electrodeposited nano-textured poly(thiophene) films

Judith Jenkins, Erin Ratcliff, R. Clayton Shallcross, Jeffrey Head, Neal Armstrong

Proceedings Volume 7047, 70470J (2008) https://doi.org/10.1117/12.795482

KEYWORDS: Polymers, Polymer thin films, Nanoparticles, Electrodes, Photovoltaics, Doping, Resistance, Semiconductors, Remote sensing, Aluminum

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Proceedings Article | 25 August 2008 Paper

A planar integrated photometer/refractometer using an organic light emitting diode light source and an organic photovoltaic detector

Alex Veneman, Brian Zacher, Dan Huebner, Adam Simmonds, Neal Armstrong

Proceedings Volume 7054, 70541E (2008) https://doi.org/10.1117/12.796013

KEYWORDS: Organic light emitting diodes, Sensors, Refractive index, Light sources, OLED lighting, Chemical elements, Photons, Organic photovoltaics, Light, Absorption

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Proceedings Article | 21 August 2008 Paper

Critical interfaces in new solar cell materials: organic heterojunctions and heterojunctions involving semiconductor nanoparticles

Neal Armstrong, Dana Alloway, Amy Graham, Clayton Shallcross, Michael Brumbach, P. Alex Veneman, Diogenes Placencia, Weining Wang

Proceedings Volume 7034, 703402 (2008) https://doi.org/10.1117/12.795451

KEYWORDS: Heterojunctions, Interfaces, Solar cells, Neptunium, Nanoparticles, Excitons, Gold, Metals, Semiconductors, Polymers

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Proceedings Article | 3 November 2004 Paper

Modeling of organic photovoltaic cells with large fill factor and high efficiency

Seunghyup Yoo, Benoit Domercq, Seth Marder, Neal Armstrong, Bernard Kippelen

Proceedings Volume 5520, (2004) https://doi.org/10.1117/12.564896

KEYWORDS: Solar cells, Organic photovoltaics, Resistance, Circuit switching, Diodes, Instrument modeling, Electrodes, Photovoltaics, Copper, Aluminum

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Proceedings Article | 6 February 2004 Paper

Organic photovoltaic cells containing discotic liquid crystalline phthalocyanines

Seunghyup Yoo, Benoit Domercq, Carrie Donley, Chet Carter, Wei Xia, Britt Minch, David O'Brien, Neal Armstrong, Bernard Kippelen

Proceedings Volume 5215, (2004) https://doi.org/10.1117/12.506470

KEYWORDS: Solar cells, Organic photovoltaics, Annealing, Liquid crystals, Crystals, Molecules, Resistance, Liquids, Photovoltaics, Electrodes

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Proceedings Article | 17 December 1999 Paper

Determination of the electronic structure of organic Schottky contacts by photoemission spectroscopy

Ruediger Schlaf, Lisa Crisafulli, Hideyuki Murata, Charles Merritt, Zakya Kafafi, Paul Schroeder, M. Nelson, B. Parkinson, Paul Lee, Ken Nebesny, Neal Armstrong

Proceedings Volume 3797, (1999) https://doi.org/10.1117/12.372709

KEYWORDS: Interfaces, Gold, Metals, Photoemission spectroscopy, Organic semiconductors, Semiconductors, X-rays, Platinum, Thin films, Silver

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Proceedings Article | 18 May 1999 Paper

Hybrid bilayer organic light-emitting devices based on high Tg hole transport polymers

Ghassan Jabbour, Sean Shaheen, Michael Morrell, Jeffrey Anderson, Paul Lee, Sankaran Thayumanavan, Stephen Barlow, Seth Marder, Erika Bellmann, Robert Grubbs, Bernard Kippelen, Neal Armstrong, Nasser Peyghambarian

Proceedings Volume 3623, (1999) https://doi.org/10.1117/12.348406

KEYWORDS: Organic light emitting diodes, Polymers, External quantum efficiency, Telescopic pixel displays, Luminous efficiency, Aluminum, Quantum efficiency, Ionization, Electrodes, Interfaces

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Proceedings Article | 18 May 1999 Paper

Organic electroluminescent devices: aluminum alkali-halide composite cathode for enhanced device performance

Ghassan Jabbour, Bernard Kippelen, Neal Armstrong, Nasser Peyghambarian

Proceedings Volume 3623, (1999) https://doi.org/10.1117/12.348413

KEYWORDS: Composites, Organic light emitting diodes, Aluminum, Laser induced fluorescence, Magnesium, Metals, Lithium, External quantum efficiency, Luminous efficiency, Telescopic pixel displays

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Proceedings Article | 3 May 1999 Paper

New planar waveguide attenuated total reflectance techniques for organic thin film spectroscopy and chemical sensing

Darren Dunphy, Sergio Mendes, Lifeng Li, James Burke, John Lee, Neal Armstrong, S. Scott Saavedra

Proceedings Volume 3602, (1999) https://doi.org/10.1117/12.347515

KEYWORDS: Waveguides, Planar waveguides, Spectroscopy, Absorbance, Attenuated total reflectance, Thin films, Reflection, Proteins, Biological and chemical sensing, Reflectance spectroscopy

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Proceedings Article | 16 December 1998 Paper

Electrochemical models for the radical annihilation reactions in organic light-emitting diodes

Neal Armstrong, Jeffrey Anderson, Paul Lee, Erin McDonald, R. Wightman, Hank Hall, Tracy Hopkins, Anne Padias, Sankaran Thayumanavan, Stephen Barlow, Seth Marder

Proceedings Volume 3476, (1998) https://doi.org/10.1117/12.332611

KEYWORDS: Organic light emitting diodes, Telescopic pixel displays, Molecules, Polymers, Luminescence, OLED lighting, Heterojunctions, Electroluminescence, Absorbance, Oxidation

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Proceedings Article | 17 April 1998 Paper

Effects of insulating layers on the performance of organic electroluminescent devices

Ghassan Jabbour, Ruediger Schlaf, Neal Armstrong, Bernard Kippelen, Nasser Peyghambarian

Proceedings Volume 3281, (1998) https://doi.org/10.1117/12.305420

KEYWORDS: Laser induced fluorescence, Organic light emitting diodes, External quantum efficiency, Aluminum, Magnesium, Metals, Electron transport, Quantum efficiency, Doping, Electrodes

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Proceedings Article | 17 April 1998 Paper

Molecular self-assembly approaches to multilayer organic light-emitting-diode structures

Joshua Malinsky, Weijin Li, Homer Chou, Wuping Ma, Lifeng Geng, Tobin Marks, Ghassan Jabbour, Sean Shaheen, Bernard Kippelen, Nasser Peyghambarian, Pulak Dutta, Andrew Richter, Neal Armstrong, Paul Lee, Jeffrey Anderson

Proceedings Volume 3281, (1998) https://doi.org/10.1117/12.305415

KEYWORDS: Molecular self-assembly, Multilayers, Organic light emitting diodes, Electrodes, X-rays, Reflectivity, Bromine, Thin films, Light emitting diodes, Nonlinear optics

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Proceedings Article | 1 December 1997 Paper

Biexcitons in mixed-stack charge transfer solids, conjugated polymers, and molecular aggregates

Sumitendra Mazumdar, Michael Chandross, Y. Shimoi, Aparna Chakrabarti, Neal Armstrong, Nasser Peyghambarian

Proceedings Volume 3145, (1997) https://doi.org/10.1117/12.295541

KEYWORDS: Excitons, Solids, Polymers, Absorption, Molecular aggregates, Electrons, Thin films, Spectroscopy, Solid modeling, Systems modeling

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Proceedings Article | 9 December 1992 Paper

Organic/inorganic molecular beam epitaxy: photoelectrochemical and optical properties of epitaxially deposited single-component and multiple-component organic superlattices (Invited Paper)

Neal Armstrong, Lai Chau, Greg Collins, S. Chen, Ken Nebesny, Valorie Williams, Paul Lee, C. Arbour, James Danziger, E. Osburn, D. O'Brien, B. Parkinson

Proceedings Volume 1729, (1992) https://doi.org/10.1117/12.130578

KEYWORDS: Thin films, Metals, Multilayers, Excitons, Diffraction, Interfaces, Crystals, Molecules, Semiconductors, Absorbance

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Proceedings Article | 13 August 1992 Paper

Oxidation processes in magneto-optic and related materials

Paul Lee, Neal Armstrong, James Danziger, Craig England

Proceedings Volume 1663, (1992) https://doi.org/10.1117/12.137563

KEYWORDS: Oxides, Tantalum, Iron, Metals, Thin films, Corrosion, Oxygen, Terbium, Diffusion, Oxidation

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Proceedings Article | 1 December 1991 Paper

O/I-MBE: formation of highly ordered phthalocyanine/semiconductor junctions by molecular-beam epitaxy: photoelectrochemical characterization

Neal Armstrong, Ken Nebesny, Greg Collins, Paul Lee, Lai Chau, Claude Arbour, Bruce Parkinson

Proceedings Volume 1559, (1991) https://doi.org/10.1117/12.50653

KEYWORDS: Metals, Absorbance, Thin films, Crystals, Diffraction, Chemistry, Epitaxy, Physics, Reflectance spectroscopy, Excitons

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Showing 5 of 19 publications

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