Alejandro L. Briseno

University of Massachusetts Amherst, Amherst Center, Massachusetts, United States

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Publications (103)816.91 Total impact

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    ABSTRACT: We report the use of Ta:TiO2|BiVO4 as a photoanode for use in solar water splitting cells. This host−guest system makes use of the favorable band alignment between the two semiconductors. The nanowire architecture allows for simultaneously high light absorption and carrier collection for efficient solar water oxidation.
    No preview · Article · Feb 2016
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    ABSTRACT: Charge transport in polymer- and oligomer-based semiconductor materials depends strongly on the structural ordering of the constituent molecules. Variations in molecular conformations influence the electronic structures of polymers and oligomers, and thus impact their charge-transport properties. In this study, we used Scanning Tunneling Microscopy and Spectroscopy (STM/STS) to investigate the electronic structures of different alkyl-substituted oligothiophenes displaying varied torsional conformations on the Au(111) surface. STM imaging showed that on Au(111) oligothiophenes self-assemble into chain-like structures, binding to each other via interdigitated alkyl ligands. The molecules adopted distinct planar conformations with alkyl ligands forming cis- or trans- mutual orientations. For each molecule, by using STS mapping, we identify a progression of particle-in-a-box-like states corresponding to the LUMO, LUMO+1 and LUMO+2 orbitals. Analysis of STS data revealed very similar unoccupied molecular orbital energies for different possible molecular conformations. By using density functional theory calculations, we show that the lack of variation in molecular orbital energies among the different oligothiophene conformers implies that the effect of the Au-oligothiophene interaction on molecular orbital energies is nearly identical for all studied torsional conformations. Our results suggest that cis-trans torsional disorder may not be a significant source of electronic disorder and charge carrier trapping in organic semiconductor devices based on oligothiophenes.
    No preview · Article · Jan 2016 · Physical Chemistry Chemical Physics
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    ABSTRACT: Charge transport in electronic applications involving molecular semiconductor materials strongly depends on the electronic properties of molecular-scale layers interfacing with external electrodes. In particular, local variations in molecular environments can have a significant impact on the interfacial electronic properties. In this study, we use scanning tunneling microscopy and spectroscopy to investigate the self-assembly regimes and resulting electronic structures of alkyl-substituted quaterthiophenes adsorbed on the Au(111) surface. We find that at dilute molecular concentrations, dimerized cis conformers were formed, while at higher concentrations corresponding to small fractions of a submonolayer, the molecular conformation converted to trans, with the molecules self-assembled into ordered islands. At approximately half-monolayer concentrations, the structure of the self-assembled islands transformed again showing a different type of the trans conformation and qualitatively different registry with the Au(111) lattice structure. Molecular distributions are observed to vary significantly due to variations in local molecular environments, as well as due to variations in the Au(111) surface reactivity. While the observed conformational diversity suggests the existence of local variations in the molecular electronic structure, significant electronic differences are found even with molecules of identical apparent adsorption configurations. Our results show that a significant degree of electronic disorder may be expected even in a relatively simple system composed of conformationally flexible molecules adsorbed on a metal surface, even in structurally well-defined self-assembled molecular layers.
    No preview · Article · Nov 2015 · The Journal of Physical Chemistry C
  • Changhuai Ye · Lei Zhang · Guopeng Fu · Alamgir Karim · Thein Kyu · Alejandro L Briseno · Bryan D Vogt
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    ABSTRACT: We demonstrate a simple route to directionally grown crystals of oligothiophenes, based on 2,5-bis(3-alkylthiophen-2-yl)thieno[3,2-b]thiophene with degree of polymerization 2 (BTTT-2) and 4 (BTTT-4) via zone annealing (ZA) of pre-seeded films. ZA of spun cast films of BTTT-2 does not yield highly aligned crystals. However if the film is oven annealed briefly prior to ZA, highly aligned crystals that are millimeters in length can be grown, whose length depends on the velocity of the ZA front. The pre-crystallized region provides existing nuclei that promote crystal growth and limit nucleation of new crystals in the melted region. Aligned crystals of BTTT-2 can be obtained even when the moving velocity for ZA is an order of magnitude greater than the crystal growth rate. The relative nucleation rate to crystallization rate for BTTT-4 is greater than that for BTTT-2, which decreases the length over which the BTTT-4 can be aligned to ~500 µm for the conditions examined. The temperature gradient and moving velocity of ZA enable control of the length of the aligned crystalline structure at the macroscale.
    No preview · Article · Sep 2015 · ACS Applied Materials & Interfaces
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    Full-text · Dataset · Sep 2015
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    ABSTRACT: Replacing or minimizing the use of halogenated organic solvents in the processing and manufacturing of conjugated polymer-based organic electronics has emerged as an important issue due to concerns regarding toxicity, environmental impact, and high cost. To date, however, the processing of well-ordered conjugated polymer nanostructures has been difficult to achieve using environmentally benign solvents. In this work, we report the development of water and alcohol processable nanowires (NWs) with well-defined crystalline nanostructure based on the solution assembly of azide functionalized poly(3-hexylthiophene) (P3HT-azide) and subsequent photo-cross-linking and functionalization of these NWs. The solution-assembled P3HT-azide NWs were successfully cross-linked by exposure to UV light, yielding good thermal and chemical stability. Residual azide units on the photo-cross-linked NWs were then functionalized with alkyne terminated polyethylene glycol (PEG-alkyne) using copper catalyzed azide-alkyne cycloaddition chemistry. PEG functionalization of the cross-linked P3HT-azide NWs allowed for stable dispersion in alcohols and water, while maintaining well-ordered NW structures with electronic properties suitable for the fabrication of organic field effect transistors (OFETs).
    No preview · Article · Aug 2015 · Nano Letters
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    ABSTRACT: Alkyl-substituted quaterthiophenes on Au(111) form dimers linked by their alkyl substituents and, instead of adopting the trans-conformation found in bulk oligothiophene crystals, assume cis-conformations. Surprisingly, the impact of the conformation is not decisive in determining the LUMO energy. Scanning Tunneling Microscopy and Spectroscopy of the adsorption geometries and electronic structures of alkyl-substituted quaterthiophenes show that the orbital energies vary substantially due to the local variations in the Au(111) surface reactivity. These results demonstrate that interfacial oligothiophene conformations and electronic structures may differ substantially from those expected based on the band structures of bulk oligothiophene crystals.
    No preview · Article · Jul 2015 · ACS Applied Materials & Interfaces
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    Marcos A Reyes-Martinez · Alfred J Crosby · Alejandro L Briseno
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    ABSTRACT: With the impending surge of flexible organic electronic technologies, it has become essential to understand how mechanical deformation affects the electrical performance of organic thin-film devices. Organic single crystals are ideal for the systematic study of strain effects on electrical properties without being concerned about grain boundaries and other defects. Here we investigate how the deformation affects the field-effect mobility of single crystals of the benchmark semiconductor rubrene. The wrinkling instability is used to apply local strains of different magnitudes along the conducting channel in field-effect transistors. We discover that the mobility changes as dictated by the net strain at the dielectric/semiconductor interface. We propose a model based on the plate bending theory to quantify the net strain in wrinkled transistors and predict the change in mobility. These contributions represent a significant step forward in structure-function relationships in organic semiconductors, critical for the development of the next generation of flexible electronic devices.
    Preview · Article · May 2015 · Nature Communications
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    ABSTRACT: We demonstrate that graphene surfaces provide highly selective nucleation of poly(3-hexyl thiophene) (P3HT) nanofibers (NFs) from supersaturated solutions. Solvent conditions are identified that give rise to a wide hysteresis between crystallization and melting centered around room temperature, yielding metastable solutions that are stable against homogeneous nucleation for long periods of time but that allow for heterogeneous nucleation by graphene. Selective growth of P3HT crystals is found for multilayer graphene (MLG) supported on either Si or ITO substrates, with nucleation kinetics that are more rapid for MLG on Si but slower in both cases than for highly oriented pyrolytic graphite (HOPG). Although the NFs grow vertically from the substrate with face-on orientation of P3HT chains, we observe edge-on orientation in dried films, presumably due to capillary forces that cause collapse of the NFs onto the substrate during solvent evaporation.
    No preview · Article · Apr 2015 · ACS Macro Letters
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    ABSTRACT: Air-stable material for vacuum or liquid-processed n-type organic field-effect transistors is easily synthesized by cyano-substitutions on para and ortho positions versus nitrogen of soluble triphenodioxazines. This regioisomer promotes favorable molecular packing while increasing the electron affinity. Without encapsulation and after 30 days, the performances of devices remain high under air measurement conditions.
    Full-text · Article · Apr 2015
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    ABSTRACT: A novel naphthalene diimide (NDI)-based small molecule (BiNDI) is designed and synthesized by linking two NDI monomers via a vinyl donor moiety. The electronic structure of BiNDI is carefully investigated by ultraviolet photoelectron spectroscopy (UPS). Density functional theory (DFT) sheds further light on the molecular configuration and energy level distribution. Thin film transistors (TFT) based on BiNDI show a highest electron mobility of 0.365 cm2 V−1 s−1 in ambient atmosphere. Organic photovoltaics (OPVs) by using BiNDI as the acceptor show a highest power conversion efficency (PCE) of 2.41%, which is the best result for NDI-based small molecular acceptors. Transmission electron microscopy (TEM), atomic force microscopy (AFM), grazing incidence wide-angle X-ray diffraction (GIXD), and X-ray photo­electron spectroscopy (XPS) characterization to understand the morphology and structure order of the bulk heterojunction film are performed. It is found that small amount of 1,8-diiodooctane (DIO) (i.e., 0.5%) in the blended film facilitates the crystallization of BiNDI into fibrillar crystals, which is beneficial for the improvement of device performance.
    Full-text · Article · Apr 2015 · Advanced Energy Materials
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    ABSTRACT: Improved organic field effect transistor (OFET) performance through a polymer-oligomer semiconductor blend approach is demonstrated. Incorporation of 2,5-bis(3-dodecylthiophen-2-yl)thieno[3,2-b]thiophene (BTTT) into poly(3-hexylthiophene) (P3HT) thin-films lead to approximately a 5-fold increase in charge carrier mobility, a 10-fold increase in current on-off ratio, and concomitantly, decrease threshold voltage to as low as 1.7 V in comparison to single component thin-films. The blend approach required no pre- and/or post treatments, and processing was conducted under ambient conditions. The correlation of crystallinity, surface morphology and photophysical properties of the blend thin-films was systematically investigated via X-ray diffraction, atomic force microscopy and optical absorption measurements respectively, as a function of blend composition. The dependence of thin-film morphology on the blend composition is illustrated for the P3HT:BTTT system. The blend approach provides an alternative avenue to combine the advantageous properties of conjugated polymers and oligomers for optimized semiconductor performance.
    No preview · Article · Mar 2015 · ACS Applied Materials & Interfaces
  • Marcos A. Reyes-Martinez · Nicholas S. Colella · Alejandro L. Briseno
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    ABSTRACT: This chapter reviews the electronic and structural properties that give organic single crystals their remarkable characteristics when compared to organic polycrystalline films. It looks into novel materials design/synthesis, suitable for different types of crystallization (growth from vapor phase and growth from solution) and various applications. Then it examines published work where organic single crystals have been successfully applied into flexible electronics and other advances that promise to make a significant impact on the field of organic single-crystal-based flexible electronics. Finally, the chapter discusses some of the obstacles that need to be overcome in order to realize practical applications of organic single crystals in fundamental flexible studies and consumer electronics technology.
    No preview · Chapter · Jan 2015
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    ABSTRACT: We demonstrate the use of poly(sulfobetaine methacrylate) (PSBMA), and its pyrene-containing copolymer, as solution-processable work function reducers for inverted organic electronic devices. A notable feature of PSBMA is its orthogonal solubility relative to solvents typically employed in the processing of organic semiconductors. A strong permanent dipole moment on the sulfobetaine moiety was calculated by density functional theory. PSBMA interlayers reduced the work function of metals, graphene, and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) by over 1 eV, and an ultrathin interlayer of PSBMA reduced the electron injection barrier between indium tin oxide (ITO) and C70 by 0.67 eV. As a result, the performance of organic photovoltaic devices with PSBMA interlayers is significantly improved, and enhanced electron injection is demonstrated in electron-only devices with ITO, PEDOT:PSS, and graphene electrodes. This work makes available a new class of dipole-rich, counterion-free, pH insensitive polymer interlayers with demonstrated effectiveness in inverted devices.
    No preview · Article · Dec 2014 · Journal of the American Chemical Society
  • Ilhan Yavuz · Lei Zhang · Alejandro L. Briseno · K. N. Houk
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    ABSTRACT: Semiconductor poly(3,3"-didodecyl-quaterthiophene) (PQT-12) polymer for which the hole mobility exceeds 0.1 cm(2)/(V s) exhibits promising charge-transport characteristics as an organic thin-film transistor. A family of its oligomeric analogs, DDQT-n (3,3"-didedocylquaterthiophene-n) has been synthesized (with n = 1-6) and extensively characterized [Zhang, L.; et al. J. Am. Chem. Soc. 2013, 135, 844-854]. Through atomistic molecular dynamics and charge-transport simulations, we have studied the morphologies and electronic properties of crystalline didodecylquaterthiophenes (DDQT-1, DDQT-2, and DDQT-3). The morphologies are characterized by molecular ordering and paracrystallinity, while charge-transport is characterized by electronic-coupling, reorganization energy, energetic disorder, and hole mobility, calculated with VOTCA package. We observed increasing transport efficiency with increasing molecule size, as the morphologies evolve from oligomeric to polymeric packing arrangements. The trend is related to decreasing hole reorganization energy, energetic disorder, and increasing efficacy of transport topology. We also elucidate a direct link between molecular ordering and charge-carrier mobility of different DDQT-n oligomers.
    No preview · Article · Dec 2014 · The Journal of Physical Chemistry C
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    ABSTRACT: Absorption and photoluminescence properties of terrylene derivative 7,8,15,16-tetraazaterrylene (TAT) in its solution and crystal phases have revealed rather unusual spectral characteristics that defy classification in terms of simple H- or J-aggregate-coupled systems. TAT readily forms crystalline aggregates by either self-assembly in solution or physical vapor deposition, based on π stacks aligned roughly along the crystallographic a axis. Using a Holstein-style Hamiltonian including both Frenkel and charge-transfer (CT) excitons, the crystal absorption and steady-state photoluminescence (PL) spectra/line shapes are shown to be determined by a competition between long-range Coulombic coupling, which induces H-aggregate behavior, and short-range charge-transfer-mediated coupling, which induces J-like behavior. Such “HJ” aggregates display J-aggregate signatures in the low-energy region of the absorption spectrum and H-aggregate signatures at higher energies, which are in excellent agreement with our experiments. The H/J competition also results in a sharp reduction in the exciton bandwidth and the appearance of an exciton band minima at k ≈ ±π/2, where k is the dimensionless wave vector along the stacking axis. The presence of a band minimum for nonzero values of k bestows hybrid HJ behavior in the PL spectrum. We present a new design paradigm for organic electronic materials on the basis of the constructive or destructive interference of short- and long-range coupling, postulating the existence of HH, JJ, JH, and HJ aggregates with unique transport and radiative properties.
    Full-text · Article · Dec 2014 · The Journal of Physical Chemistry C
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    ABSTRACT: Polycyclic aromatic hydrocarbons (PAHs), consisting of laterally fused benzene rings, are among the most widely studied small-molecule organic semiconductors, with potential applications in organic field-effect transistors (OFETs) and organic photovoltaics (OPVs). Linear acenes, including tetracene, pentacene, and their derivatives, have received particular attention due to the synthetic flexibility in tuning their chemical structure and properties and to their high device performance. Unfortunately, longer acenes, which could exhibit even better performance, are susceptible to oxidation, photodegradation, and, in solar cells which contain fullerenes, Diels–Alder reactions. This Account highlights recent advances in the molecular design of two-dimensional (2-D) PAHs that combine device performance with environmental stability.
    No preview · Article · Dec 2014 · Accounts of Chemical Research

Publication Stats

4k Citations
816.91 Total Impact Points

Institutions

  • 2010-2015
    • University of Massachusetts Amherst
      • Department of Polymer Science and Engineering
      Amherst Center, Massachusetts, United States
  • 2007-2013
    • University of Washington Seattle
      • Department of Chemistry
      Seattle, Washington, United States
  • 2009-2010
    • University of California, Berkeley
      • • College of Chemistry
      • • Department of Chemistry
      Berkeley, California, United States
  • 2006-2007
    • Stanford University
      • Department of Chemical Engineering
      Palo Alto, California, United States
  • 2004-2007
    • University of California, Los Angeles
      • • Department of Chemistry and Biochemistry
      • • Department of Materials Science and Engineering
      Los Angeles, California, United States
  • 2001-2004
    • California State University, Los Angeles
      • Department of Chemistry and Biochemistry
      Los Angeles, CA, United States