Alejandro L Briseno

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

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Publications (90)729.03 Total impact

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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.
    ACS Applied Materials & Interfaces 07/2015; DOI:10.1021/acsami.5b03516 · 6.72 Impact Factor
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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.
    Nature Communications 05/2015; 6:6948. DOI:10.1038/ncomms7948 · 10.74 Impact Factor
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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.
    ACS Macro Letters 04/2015; 4(5):483-487. DOI:10.1021/acsmacrolett.5b00038 · 5.24 Impact Factor
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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.
    04/2015; DOI:10.1002/aelm.201500072
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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.
    Advanced Energy Materials 04/2015; DOI:10.1002/aenm.201500195 · 16.15 Impact Factor
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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.
    ACS Applied Materials & Interfaces 03/2015; 7(12). DOI:10.1021/am509090j · 6.72 Impact Factor
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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.
    Large Area and Flexible Electronics, 01/2015: pages 133-162; , ISBN: 9783527336395
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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.
    Journal of the American Chemical Society 12/2014; 137(1). DOI:10.1021/ja512148d · 11.44 Impact Factor
  • 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.
    The Journal of Physical Chemistry C 12/2014; 119(1):158-165. DOI:10.1021/jp510567d · 4.84 Impact Factor
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    ABSTRACT: Conspectus 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. New synthetic techniques have been developed to create stable PAHs that extend conjugation in two dimensions. The stability of these novel compounds is consistent with Clar's sextet rule as the 2-D PAHs have greater numbers of sextets in their ground-state configuration than their linear analogues. The ionization potentials (IPs) of nonlinear acenes decrease more slowly with annellation in comparison to their linear counterparts. As a result, 2-D bistetracene derivatives that are composed of eight fused benzene rings are measured to be about 200 times more stable in chlorinated organic solvents than pentacene derivatives with only five fused rings. Single crystals of the bistetracene derivatives have hole mobilities, measured in OFET configuration, up to 6.1 cm(2) V(-1) s(-1), with remarkable Ion/Ioff ratios of 10(7). The density functional theory (DFT) calculations can provide insight into the electronic structures at both molecular and material levels and to evaluate the main charge-transport parameters. The 2-D acenes with large aspect ratios and appropriate substituents have the potential to provide favorable interstack electronic interactions, and correspondingly high carrier mobilities. In stark contrast to the 1-D acenes that form mono- and bis-adducts with fullerenes, 2-D PAHs show less reactivity with fullerenes. The geometry of 2-D PAHs plays a crucial role in determining both the barrier and the adduct stability. The reactivity and stability of the 2-D PAHs with regard to Diels-Alder reactions at different reactive sites were explained via DFT calculations of the reaction kinetics and of thermodynamics of reactions and simple Hückel molecular orbital considerations. Also, because of their increased stability in the presence of fullerenes, these compounds have been successfully used in OPVs. The small-molecule semiconductors highlighted in this Account exhibit good charge-transport properties, comparable to those of traditional linear acenes, while being much more environmentally stable. These features have made these 2-D PAHs excellent molecules for fundamental research and device applications.
    Accounts of Chemical Research 12/2014; 48(3). DOI:10.1021/ar500278w · 24.35 Impact Factor
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    Yue Zhang, Adam J. Wise, Michael D. Barnes, Alejandro L. Briseno
    Materials Today 11/2014; 11(9). DOI:10.1016/j.mattod.2014.10.004 · 10.85 Impact Factor
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    ABSTRACT: Due to the unique crystallinity of poly(2,5-bis(3-alkylthiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT), it is an excellent model polymer to study the structure-property relationship in organic devices, especially those relying on junctions of electron and hole transporting materials. Here, we report the synthesis and characterization of a series of monodisperse PBTTT oligothiophenes (n = 1-5) and systematically examine the evolution of crystalline behavior, morphology, and interaction with PC71BM as the molecular conjugation length increases. We discovered that fullerene intercalation occurs when there is enough free volume between the side-chains to accommodate the fullerene molecule. The intercalation of PC71BM is observed beyond BTTT-2 and longer oligomers, likely similar to that of PBTTT. Interestingly, both experiments and molecular simulations show that the PC71BM intercalation also appears to "catalyze" a more efficient packing of the BTTT-2 dimers. Crystal structure analysis revealed that the straight BTTT-2 side chains form 1D channels that could perfectly host PC71BM but, in the pure material, accommodate the interdigitated side chains from adjacent layers. In the blend with PC71BM, these channels are maintained and enable the co-crystallization and intercalation of PC71BM. This is the first time the actual sub-lattice cell of PC71BM has been determined from the X-ray data and we feel that this work sets a fine example of the utility of a material's oligomers to behave as model systems for their polymer counterparts and other conjugated polymers. Among the organic photovoltaic devices (OPVs) made from the BTTT oligomers and PC71BM blends, the ones using the BTTT-2 dimer exhibit the highest performance.
    Journal of the American Chemical Society 11/2014; 136(52). DOI:10.1021/ja510976n · 11.44 Impact Factor
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    ABSTRACT: Accurate atomic displacement parameters (ADPs) are a good indication of high-quality diffraction data. Results from the newly commissioned time-of-flight Laue diffractometer TOPAZ at the SNS are presented. Excellent agreement is found between ADPs derived independently from the neutron and X-ray data emphasizing the high quality of the data from the time-of-flight Laue diffractometer.
    11/2014; 70(6). DOI:10.1107/S2053273314015599
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    ABSTRACT: In polymer-based photovoltaic (PV) devices optimizing and controlling the active layer morphology is important to enhance the device efficiency. Using poly(3-hexylthiophene) (P3HT) with well-defined molecular weights, synthesized by the Grignard Metathesis method (GRIM), we show that the morphology of the PV active layer and the absorption and crystal structure of the P3HT are dependent on the molecular weight. Differential scanning calorimetry (DSC) showed that the crystallinity of P3HT reached a maximum for intermediate molecular weights. Grazing incidence wide-angle x-ray diffraction (GIXD) showed that the spacing of the (100) planes of P3HT increased with increasing molecular weight, while the crystal size decreased. Nonlinear crystal lattice expansions were found for both the (100) and (020) lattice planes, with an unusual π-π stacking enhancement observed between 50 to 100 °C. The melting point depression for P3HT, when mixed with [6,6]-phenyl C61- butyric acid methyl ester (PCBM), and, hence, the Flory-Huggins interaction parameter, depended on molecular weight. PCBM was found to perturb the ordering of P3HT chains. In PV devices, P3HT with a molecular weight of ~20k showed the best device performance. The morphologies of these blends were studied by grazing incidence small angle x-ray scattering (GISAXS) and resonant soft x-ray scattering (RSoXS). In GISAXS, we observed that the low molecular weight P3HT more readily crystallizes, promoting a phase-separated morphology.
    ACS Applied Materials & Interfaces 10/2014; 6(22). DOI:10.1021/am505283k · 6.72 Impact Factor
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    ABSTRACT: Poly(3-hexyl thiophene) (P3HT)-block-poly(3-(3-aminopropyl)oxymethyl thiophene) (P3AmT) diblock copolymers were synthesized and assembled into nanowires by solvent-induced crystallization. Bis(4-[1,6-hexyldiisocyanate]benzylpyrrolidine)-C60 was synthesized and used to covalently cross-link the structures, affording robust p-type/n-type nanowires. These cross-linked nanowires proved stable to solvents and temperatures that would disrupt conventional P3HT-nanowires, as characterized by transmission electron microscopy (TEM) and ultraviolet-visible (UV-Vis) spectroscopy. Photoluminescence spectroscopy showed quenching of the PL signal of the fullerene-crosslinked material, suggesting electronic communication between the polymer and fullerene in these novel donor/acceptor assemblies. Grazing incidence X-ray diffraction (GIXD) showed a similar crystal structure for nanowires before and after cross-linking, while field effect transistor transfer measurements of the cross-linked nanowires showed hole and electron mobilities of 3.5 × 10−5 cm2 V−1 s−1 and 4.6 × 10−5 cm2 V−1 s−1, respectively.
    10/2014; 2(45). DOI:10.1039/C4TC01898B
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    ABSTRACT: The most efficient architecture for achieving high donor/acceptor interfacial area in organic photovoltaic (OPV) devices would employ arrays of vertically interdigitated p- and n- type semiconductor nanopillars (NPs). Such morphology could have an advantage in bulk heterojunction systems; however, precise control of the dimension morphology in a crystalline, interpenetrating architecture has not yet been realized. Here we present a simple, yet facile, crystallization technique for the growth of vertically oriented NPs utilizing a modified thermal evaporation technique that hinges on fast deposition rate, short substrate-source distance and ballistic mass transport. A broad range of organic semiconductor materials is beneficial from the technique to generate NP geometries. Moreover, this technique can also be generalized to various substrates, namely, graphene, PEDOT, ZnO, CuI, MoO3, and MoS2. The advantage of the NP architecture over the conventional thin film counterpart is demonstrated with an increase of power conversion efficiency of 32% in solar cell devices. This technique will advance the knowledge of organic semiconductor crystallization, and create opportunities for the fabrication and processing of NPs for applications that include solar cells, charge storage devices, sensors and vertical transistors.
    Nano Letters 09/2014; 14(10). DOI:10.1021/nl501933q · 13.59 Impact Factor
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    ABSTRACT: We report the morphological characterization of triisopropylsilylethynyl-dibenzochrysene (TIPS-DBC:PCBM) blends, a bulk heterojunction (BHJ) solar cell system based on a highly crystalline small molecule donor. We found that processing the blends from a volatile solvent such as chloroform is beneficial in controlling the crystal size and phase separation of the donor-acceptor phases. When a less-volatile solvent such as chlorobenzene is used, large crystalline domains formed, exceeding the length scale suitable for BHJ solar cells. When the BHJ films are thermally annealed, enhanced domain purity is observed for the chloroform processed thin films, which led to an increased short circuit current in the devices.
    09/2014; 2(44). DOI:10.1039/C4TC01451K
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    ABSTRACT: High molecular weight PBTTT-C12 is blended with the pure trimer, BTTT-3, to enhance intergrain connectivity and charge transport. Analysis of the morphology and crystallinity of the blends shows that the polymer and oligomer are well-integrated, leading to high hole mobilities, greater than 0.1 cm2 V-1 s-1, in films that contain as much as 83% oligomer.
    Physical Chemistry Chemical Physics 09/2014; DOI:10.1039/C4CP02944E · 4.20 Impact Factor
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    ABSTRACT: The primary role of substituted side chains in organic semiconductors is to increase their solubility in common organic solvents. In the recent past, many literature reports have suggested that the side chains play a critical role in molecular packing and strongly impact the charge transport properties of conjugated polymers. In this work, we have investigated the influence of side-chains on the charge transport behavior of a novel class of diketopyrrolopyrrole () based alternating copolymers. To investigate the role of side-chains, we prepared four diketopyrrolopyrrole-diketopyrrolopyrrole () conjugated polymers with varied side-chains and carried out a systematic study of thin film microstructure and charge transport properties in polymer thin-film transistors (PTFTs). Combining results obtained from grazing incidence X-ray diffraction (GIXD) and charge transport properties in PTFTs, we conclude side-chains have a strong influence on molecular packing, thin film microstructure, and the charge carrier mobility of copolymers. However, the influence of side-chains on optical properties was moderate. The preferential "edge-on" packing and dominant n-channel behavior with exceptionally high field-effect electron mobility values of >1 cm(2) V(-1) s(-1) were observed by incorporating hydrophilic (triethylene glycol) and hydrophobic side-chains of alternate DPP units. In contrast, moderate electron and hole mobilities were observed by incorporation of branched hydrophobic side-chains. This work clearly demonstrates that the subtle balance between hydrophobicity and hydrophilicity induced by side-chains is a powerful strategy to alter the molecular packing and improve the ambipolar charge transport properties in based conjugated polymers. Theoretical analysis supports the conclusion that the side-chains influence polymer properties through morphology changes, as there is no effect on the electronic properties in the gas phase. The exceptional electron mobility is at least partially a result of the strong intramolecular conjugation of the donor and acceptor as evidenced by the unusually wide conduction band of the polymer.
    Physical Chemistry Chemical Physics 07/2014; 16(32). DOI:10.1039/c4cp02322f · 4.20 Impact Factor
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    ABSTRACT: The Diels-Alder (DA) reactions of pentacene (PT), 6,13-bis(2-trimethylsilylethynyl)pentacene (TMS-PT), bistetracene (BT), and 8,17-bis(2-trimethylsilylethynyl)bistetracene (TMS-BT) with the [6,6] double bond of [60]fullerene have been investigated by density functional theory (DFT) calculations. Reaction barriers and free energies have been obtained to assess the effects of frameworks and substituent groups on the Diels-Alder reactivity and product stability. Calculations indicate that TMS-BT is about 5 orders of magnitude less reactive than TMS-PT in the reactions with [60]fullerene. This accounts for the observed much higher stability of TIPS-BT than TIPS-PT when mixed with PCBM. Surprisingly, calculations predict that the bulky silylethynyl substituents of TMS-PT and TMS-BT have only a small influence on reaction barriers. However, the silylethynyl substituents significantly destabilize the corresponding products due to steric repulsions in the adducts. This is confirmed by experimental results here. Architectures of the polycyclic aromatic hydrocarbons (PAHs) play a crucial role in determining both the Diels-Alder barrier and the adduct stability. The reactivities of different sites in various PAHs are related to the loss of aromaticity, which can be predicted using the simple Hückel molecular orbital (HMO) localization energy calculations.
    Journal of the American Chemical Society 07/2014; 136(30). DOI:10.1021/ja505240e · 11.44 Impact Factor

Publication Stats

3k Citations
729.03 Total Impact Points


  • 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
      • • Department of Materials Science and Engineering
      • • Department of Chemistry
      Berkeley, California, United States
  • 2006–2007
    • University of California, Los Angeles
      • Department of Chemistry and Biochemistry
      Los Angeles, California, United States
  • 2005–2007
    • Stanford University
      • Department of Chemical Engineering
      Palo Alto, California, United States
  • 2001–2004
    • California State University, Los Angeles
      • Department of Chemistry and Biochemistry
      Los Angeles, CA, United States