Gopal K Mor

Pennsylvania State University, University Park, MD, United States

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Publications (62)271.83 Total impact

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    Dataset: jp052736u
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    ABSTRACT: Control of interfacial electron transfer between electron transporting oxide semiconductors and molecular adsorbates in organic-inorganic hybrid solar cells is a research area of intense interest, with the poor optical harvesting in the red and near-IR (NIR) portion of the solar spectrum a significant limitation to device performance. We fabricate hybrid solar cells, using two new hemicyanine photosensitizers having different π-conjugation lengths that absorb sunlight from visible to NIR range, as well as unsymmetrical squaraine dye. These organic dyes are used not only as a photosensitizer, but also as electronic mediator for n-type TiO<sub>2</sub> nanotube arrays, vertically oriented from the fluorine-doped tin oxide coated glass substrate, which are subsequently infiltrated with p-type regio-regular poly(3-hexyl thiophene 2,5 diyl), enabling broad-spectrum response. In general, the organic-dye-inorganic photovoltaic structure appears a promising method for harvesting a broad portion of the solar spectrum energy from a relatively simple photovoltaic device.
    IEEE Journal of Selected Topics in Quantum Electronics 01/2011; · 4.08 Impact Factor
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    ABSTRACT: Tantalum nitride (Ta3N5) has a band gap of approximately 2.07 eV, suitable for collecting more than 45% of the incident solar spectrum energy. We describe a simple method for scale fabrication of highly oriented Ta3N5 nanotube array films, by anodization of tantalum foil to achieve vertically oriented tantalum oxide nanotube arrays followed by a 700 degrees C ammonia anneal for sample crystallization and nitridation. The thin walled amorphous nanotube array structure enables transformation from tantalum oxide to Ta3N5 to occur at relatively low temperatures, while high-temperature annealing related structural aggregation that commonly occurs in particle films is avoided. In 1 M KOH solution, under AM 1.5 illumination with 0.5 V dc bias typical sample (nanotube length approximately 240 nm, wall thickness approximately 7 nm) visible light incident photon conversion efficiencies (IPCE) as high as 5.3% were obtained. The enhanced visible light activity in combination with the ordered one-dimensional nanoarchitecture makes Ta3N5 nanotube arrays films a promising candidate for visible light water photoelectrolysis.
    Nano Letters 10/2010; · 13.03 Impact Factor
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    Journal of Photochemistry and Photobiology A Chemistry 09/2010; 215(s 2–3):229. · 2.42 Impact Factor
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    ABSTRACT: The full text of the corrigendum is available in the pdf provided.
    Nanotechnology 09/2010; 21(49). · 3.84 Impact Factor
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    ABSTRACT: The functionalized unsymmetrical benzothiazole squaraine organic sensitizers 5-carboxy-2-({3-[(3-hexylbenzothiazol-2(3H)-ylidene)methyl]-2-hydroxy-4-oxo-2-cyclobuten-1-ylidene}methyl)-1-hexyl-3,3-dimethyl-3H-indolium (hereafter named as SK-11) and 5-carboxy-2-({3-[(3-hexyl-5-methoxybenzothiazol-2(3H)-ylidene)methyl]-2-hydroxy-4-oxo-2-cyclobuten-1-ylidene}methyl)-1-hexyl-3,3-dimethyl-3H-indolium (coded as SK-12) are designed and developed to observe an intense and wider absorption band in the red/NIR wavelength region. DFT/TDDFT calculations have been performed on the two unsymmetrical squaraine sensitizers to gain insight into their electronic and optical properties. The utility of these dyes in solid state dye sensitized solar cells (SS-DSSCs) is demonstrated.
    Langmuir 08/2010; 26(16):13486-92. · 4.38 Impact Factor
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    ABSTRACT: Solid-state dye-sensitized solar cells (SS-DSCs) offer the potential to make low cost solar power a reality, however their photoconversion efficiency must first be increased. The dyes used are commonly narrow band with high absorption coefficients, while conventional photovoltaic operation requires proper band edge alignment significantly limiting the dyes and charge transporting materials that can be used in combination. We demonstrate a significant enhancement in the light harvesting and photocurrent generation of SS-DSCs due to Förster resonance energy transfer (FRET). TiO(2) nanotube array films are sensitized with red/near IR absorbing SQ-1 acceptor dye, subsequently intercalated with Spiro-OMeTAD blended with a visible light absorbing DCM-pyran donor dye. The calculated Förster radius is 6.1 nm. The donor molecules contribute a FRET-based maximum IPCE of 25% with a corresponding excitation transfer efficiency of approximately 67.5%.
    Nano Letters 07/2010; 10(7):2387-94. · 13.03 Impact Factor
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    ABSTRACT: Highly ordered vertically oriented TiO(2) nanotube arrays fabricated by electrochemical anodization offer a large surface area architecture with precisely controllable nanoscale features. These nanotubes have shown remarkable properties in a variety of applications including, for example, their use as hydrogen sensors, in the photoelectrochemical generation of hydrogen, dye-sensitized and solid-state heterojunction solar cells, photocatalytic reduction of carbon dioxide into hydrocarbons, and as a novel drug delivery platform. Herein we consider the development of the various nanotube array synthesis techniques, different applications of the TiO(2) nanotube arrays, unresolved issues, and possible future research directions.
    Physical Chemistry Chemical Physics 03/2010; 12(12):2780-800. · 4.20 Impact Factor
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    ABSTRACT: It appears that the efficiency of dye-sensitized solar cells (DSSCs) has reached a ceiling due to the limited absorption spectrum of currently available dyes. To achieve new record efficiencies, light absorption must be extended into the near-infrared region of the spectrum without sacrificing performance in the visible region. No single dye has this ability, but there is greater strength in numbers. Forster resonance energy transfer (FRET) may be used to link two or more materials to provide strong absorption across a broad portion of the solar spectrum. This process has been shown to be effective and efficient, and a recent breakthrough in FRET-enhanced DSSCs is presented in this issue. This Perspective explores the background of this topic and considers directions for future development.
    ACS Nano 03/2010; 4(3):1253-8. · 12.03 Impact Factor
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    ABSTRACT: We examine the visible light water-photoelectrolysis and photoelectrochemical properties of highly ordered titania nanotube arrays as a function of nanotube crystallinity, length (up to 6.4 μm), and pore size. Most noteworthy of our results, under visible light AM 1.5 illumination (100 mW/cm2) the titania nanotube array photoanodes (1 cm2 area), pore size 110 nm, wall thickness 20 nm, and length 6 μm, generate hydrogen by water photoelectrolysis at a rate of 175 μL/h, with a photoconversion efficiency of 0.6%. The energy–time normalized hydrogen evolution rate is 1.75 mL/h W. The oxygen bubbles evolving from the nanotube array photoanode do not remain on the sample, hence the output remains stable with time irrespective of the duration of hydrogen production.
    Journal of Photochemistry and Photobiology A Chemistry 01/2010; · 2.42 Impact Factor
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    ABSTRACT: The development of high-efficiency solid-state excitonic photovoltaic solar cells compatible with solution processing techniques is a research area of intense interest, with the poor optical harvesting in the red and near-IR (NIR) portion of the solar spectrum a significant limitation to device performance. Herein we present a solid-state solar cell design, consisting of TiO(2) nanotube arrays vertically oriented from the FTO-coated glass substrate, sensitized with unsymmetrical squaraine dye (SQ-1) that absorbs in the red and NIR portion of solar spectrum, and which are uniformly infiltrated with p-type regioregular poly(3-hexylthiophene-2,5-diyl) (P3HT) that absorbs higher energy photons. Our solid-state solar cells exhibit broad, near-UV to NIR, spectral response with external quantum yields of up to 65%. Under UV filtered AM 1.5G of 90 mW/cm(2) intensity we achieve typical device photoconversion efficiencies of 3.2%, with champion device efficiencies of 3.8%.
    Nano Letters 09/2009; 9(12):4250-7. · 13.03 Impact Factor
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    ABSTRACT: A significant enhancement in the photoconversion efficiency of anodically grown, thermally annealed titania nanotube array photoanodes was observed when subjected to an ethanol vapor treatment that resulted in improved crystallization. Ethanol vapor treatment of 6 mm long vertically aligned titania nanotube array films initially annealed at 580 C for 6 h in an oxygen environment, under autogeneous pressure at 140 C (z50 psi), resulted in an increase of up to $30% in the photoconversion efficiency. A significant improvement in the crystallinity as revealed by glancing angle X-ray diffraction (GAXRD) and Raman spectroscopy studies as well as incident photon to current conversion efficiency (IPCE) is observed in the vapor treated samples.
    Journal of Materials Chemistry 01/2009; · 6.63 Impact Factor
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    ABSTRACT: In this article, we present recent advances that we have achieved toward improving the properties of anodically formed semiconducting TiO 2 nanotubes as well as nanowire arrays as electrodes for oxidative photoelectro-chemistry. The morphology, crystallinity, composition, and illumination geometry of nanotube or nanowire arrays are critical factors in their performance as photoelectrodes. We discuss the key aspects relating to each factor and the advances achieved in improving each. With respect to the more fully investigated nanotube arrays, the ability to control the morphological parameters such as pore size, tube length, and wall thickness of the nanotube architecture has enabled high performance in applications such as water photoelectrolysis, photocatalysis, dye-sensitized solar cells, and heterojunction TiO 2 -polymer hybrid solar cells. We begin by reviewing the photoelectrochemical performance of state-of-the-art nanotube arrays fabricated on planar substrates. We then present more recent results related to the growth of TiO 2 nanotube arrays on nonplanar substrates designed in such a way that reflected light normally lost to free space is instead directed to a different point on the device, in turn improving overall photoconversion efficiency. Insofar as the crystallinity of the nanotubes is concerned, the use of a high-temperature oxygen or air-ambient anneal to crystallize the nanotube arrays is disadvantageous, since it results in a thick barrier layer where recombination losses occur and also because it precludes compatibility with polymeric substrates. In this regard, we discovered a two-step fabrication process for synthesis of crystallized nanotube arrays at low-temperatures. The photoelectro-chemical applications of TiO 2 are limited by its large electronic band gap. We briefly review the cationic and anionic doping approaches popularly used to modify the TiO 2 band gap. We consider the use of ternary oxide systems containing titania as both a structural support and corrosion-inhibitor, in particular fabrication and performance of n-type Ti-Fe-O nanotubes and p-type copper-rich Cu-Ti-O nanotubes, with a note on our recent synthesis of iron oxide nanotube arrays by anodic oxidation of iron. Fabrication and photoelec-trochemical properties of CdS-TiO 2 and CdTe-TiO 2 nanotube array heterojunction photoelectrodes are discussed. The article concludes by examining low temperature synthesis, and resulting properties, of single crystal vertically oriented TiO 2 nanowire arrays on transparent conductive glass substrates; preliminary investigation of these nanowire array photoelectrodes for water photolysis reveals them to have low series resistance and provide excellent separation of photogenerated charges.
    The Journal of Physical Chemistry C 01/2009; · 4.84 Impact Factor
  • Craig A. Grimes, Gopal K. Mor
    TiO2 Nanotube Arrays: Synthesis, Properties, and Applications, ISBN 978-1-4419-0067-8. Springer-Verlag US, 2009. 01/2009;
  • Langmuir 12/2008; · 4.38 Impact Factor
  • The Journal of Physical Chemistry B 11/2008; · 3.61 Impact Factor
  • Nano Letters 09/2008; · 13.03 Impact Factor
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    ABSTRACT: The paper describes the electronic charging and conducting properties of vertically oriented TiO 2 nanotube arrays formed by anodization of Ti foil samples. The resulting films, composed of vertically oriented nanotubes approximately 10 mum long, wall thickness 22 nm, and pore diameter 56 nm, are analyzed using impedance spectroscopy and cyclic voltammetry. Depending on the electrochemical conditions two rather different electronic behaviors are observed. Nanotube array samples in basic medium show behavior analogous to that of nanoparticulate TiO 2 films used in dye-sensitized solar cells: a chemical capacitance and electronic conductivity that increase exponentially with bias potential indicating a displacement of the Fermi level. Nanotube array samples in acidic medium, or samples in a basic medium submitted to a strong negative bias, exhibit a large increase in capacitance and conductivity indicating Fermi level pinning. The contrasting behaviors are ascribed to proton intercalation of the TiO 2. Our results suggest a route for controlling the electronic properties of the ordered metal-oxide nanostructures for their use in applications including supercapacitors, dye-sensitized solar cells, and gas sensing.
    Journal of the American Chemical Society 09/2008; 130(34):11312-6. · 10.68 Impact Factor
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    ABSTRACT: Copper and titanium remain relatively plentiful in the earth's crust; hence, their use for large-scale solar energy conversion technologies is of significant interest. We describe fabrication of vertically oriented p-type Cu-Ti-O nanotube array films by anodization of copper rich (60% to 74%) Ti metal films cosputtered onto fluorine doped tin oxide (FTO) coated glass. Cu-Ti-O nanotube array films 1 mum thick exhibit external quantum efficiencies up to 11%, with a spectral photoresponse indicating that the complete visible spectrum, 380 to 885 nm, contributes significantly to the photocurrent generation. Water-splitting photoelectrochemical pn-junction diodes are fabricated using p-type Cu-Ti-O nanotube array films in combination with n-type TiO 2 nanotube array films. With the glass substrates oriented back-to-back, light is incident upon the UV absorbing n-TiO 2 side, with the visible light passing to the p-Cu-Ti-O side. In a manner analogous to photosynthesis, photocatalytic reactions are powered only by the incident light to generate fuel with oxygen evolved from the n-TiO 2 side of the diode and hydrogen from the p-Cu-Ti-O side. To date, we find under global AM 1.5 illumination that such photocorrosion-stable diodes generate a photocurrent of approximately 0.25 mA/cm (2), at a photoconversion efficiency of 0.30%.
    Nano Letters 08/2008; 8(7):1906-11. · 13.03 Impact Factor
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    ABSTRACT: Donor antenna dyes provide an exciting route to improving the efficiency of dye sensitized solar cells owing to their high molar extinction coefficients and the effective spatial separation of charges in the charge-separated state, which decelerates the recombination of photogenerated charges. Vertically oriented TiO(2) nanotube arrays provide an optimal material architecture for photoelectrochemical devices because of their large internal surface area, lower recombination losses, and vectorial charge transport along the nanotube axis. In this study, the results obtained by sensitizing TiO(2) nanotube arrays with the donor antenna dye Ru-TPA-NCS are presented. Solar cells fabricated using an antenna dye-sensitized array of 14.4 microm long TiO(2) nanotubes on Ti foil subjected to AM 1.5 one sun illumination in the backside geometry exhibited an overall conversion efficiency of 6.1%. An efficiency of 4.1% was obtained in the frontside illumination geometry using a 1 microm long array of transparent TiO(2) nanotubes subjected to a TiCl(4) treatment and then sensitized with the Ru-TPA-NCS dye. Open circuit voltage decay measurements give insight into the recombination behavior in antenna-dye sensitized nanotube photoelectrodes, demonstrating outstanding properties likely due to a reduction in the influence of the surface traps and reduced electron transfer from TiO(2) to ions in solution.
    Nano Letters 07/2008; 8(6):1654-9. · 13.03 Impact Factor

Publication Stats

3k Citations
271.83 Total Impact Points

Institutions

  • 2003–2011
    • Pennsylvania State University
      • • Department of Electrical Engineering
      • • Department of Materials Science and Engineering
      University Park, MD, United States
  • 2010
    • Texas Tech University
      • Department of Electrical and Computer Engineering
      Lubbock, TX, United States
  • 2008
    • Universitat Jaume I
      • Departament de Física
      Castelló de la Plana, Valencia, Spain
  • 2006
    • University of Patras
      Rhion, West Greece, Greece
  • 2004–2005
    • Boston University
      • Department of Biomedical Engineering
      Boston, MA, United States