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  • 1.
    Lin, Lili
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Theoretical Modeling of Intra- and Inter-molecular Charge Transport2012Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis focuses on theoretical study of charge transportproperties in molecular systems. The understanding of the transportprocess and mechanism in molecular systems is essential forthe design of new functional molecular materials and molecularelectronic devices. The molecular junctions and organic molecularcrystals have been used as the model systems to highlight the usefulnessof theoretical modelling. A molecular junction is a system that consists ofone or several molecules sandwiched between two electrodes.The charge transport in molecular junctions is a very complex processthat is affected by the interaction between molecules and electrodes,the surroundings, as well as electron-electron (e-e) andelectron-phonon (e-p) couplings. When the molecule-electrode couplingis strong, the transport process can be very quick. If the e-p couplingis weak, the inelastic tunneling has only negligible contributions to thetotal current and the elastic electron tunneling plays the dominant role.Furthermore, the hopping process becomes dominant in the case of strong e-pcoupling, for which the geometric relaxation of the molecule needsto be considered. In this thesis, we have examined these three kinds oftransport processes separately.

    The first studied system is a molecular junction consisting of aromaticallycoupled bimolecules. Its elastic electron tunneling property is simulatedusing Green's functional theory at density functional theory level.The dependence of the conductance of bimolecular junctions on the vertical distances,horizontal distances and the tilt angles has been systematically studied. Theinelastic electron tunneling spectra (IETS) of molecular junctions have beencalculated for several systems that were experimentally measured with conflictingresults and controversial assignments. Our calculations provide the reliableassignments for the experimental spectra and revealed unprecedented detailsabout the molecular conformations within the junctions under different conditions.It demonstrates that a combined theoretical and experimental IETS study is capableof accurately determining the structure of a single molecule inside the junction.The hopping process is a dominant charge transfer process in organic molecularcrystals. We have studied the charge transport ability of four kinds of n-typeorganic semiconductor materials to find out the related structure-to-propertyrelationship. It is done by adopting the quantum charge transfer rate equationcombined with the random walk approach.

  • 2.
    Lin, Lili
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Geng, Hua
    Shuai, Zhigang
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Charge Transport inPerylene Diimides Based n-type Organic SemiconductorsArticle in journal (Other academic)
  • 3.
    Lin, Lili
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Geng, Hua
    Shuai, Zhigang
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Theoretical insights into the charge transport in perylene diimides based n-type organic semiconductors2012In: Organic electronics, ISSN 1566-1199, E-ISSN 1878-5530, Vol. 13, no 11, p. 2763-2772Article in journal (Refereed)
    Abstract [en]

    We employed a tunneling enabled hopping model to investigate the charge transport properties for four n-type organic semiconductors perylene diimides compounds. The molecular parameters are calculated by density functional theory and the transport is modeled by kinetic Monte Carlo simulation. It is found that the substitutions at the bay positions of the perylene core have large influences on the charge transport properties through modifications in molecular conformation, the charge reorganization energy as well as the stacking networks in the crystals. The temperature dependence of the mobility shows typical "band-like", in agreement with the recent experiment, but we ascribe it to be the characteristic of nuclear tunneling effect for a localized charge, not by a delocalized band. The largest charge mobility is calculated to be 16.96 cm(2)/V s for the cyano substitution, in good comparison with the experimental value of 6 cm(2)/V s.

  • 4.
    Lin, Lili
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Jiang, Jun
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Elastic and inelastic electron transport in metal-molecule(s)-metal junctions2013In: Physica. E, Low-Dimensional systems and nanostructures, ISSN 1386-9477, E-ISSN 1873-1759, Vol. 47, p. 167-187Article, review/survey (Refereed)
    Abstract [en]

    An overview of studies on-elastic and inelastic electron transport properties of molecular junction devices is presented. The development of the experimental fabrication and characterization of molecular junctions as well as the corresponding theoretical modeling is briefly summarized. The functions of molecular devices are generally governed by the intrinsic structure-property relationships, and strongly affected by various environment factors including temperature, solvent and intermolecular interactions. Those detailed structural and environmental information could be probed by a powerful tool of inelastic electron tunneling spectroscopy, for which the theoretical modeling becomes particularly important. With many successful examples, it is demonstrated that the combination of theoretical simulations and experimental measurements can help not only to understand the electron-phonon interaction, but more importantly also to accurately determine the real configurations of molecules inside the junctions.

  • 5.
    Lin, Lili
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. Shandong Normal Univ, Coll Phys & Elect, China.
    Li, Xin
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Tian, Guangjun
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Geng, Hua
    Shuai, Zhigang
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. Univ Sci & Technol China, Hefei Natl Lab Phys Sci Microscale, China.
    First-principles investigations on the anisotropic charge transport in 4,4 '-bis((E)-2-(naphthalen-2-yl)vinyl)-1,1 '-biphenyl single crystal2014In: Theoretical Chemistry accounts, ISSN 1432-881X, E-ISSN 1432-2234, Vol. 133, no 9, p. 1551-Article in journal (Refereed)
    Abstract [en]

    We applied the master equation method to investigate the anisotropic transport property of the 4,4'-bis((E)-2-(naphthalen-2-yl)vinyl)-1,1'-biphenyl molecular crystal based on first-principles calculation. It is found that the hole mobility has the largest value along the [100] direction, while electrons have the best transport property along the [010] direction. The anisotropic transport property was found to have close relationship with the charge transfer integral which is determined by the molecular stacking network in the crystals as well as the intermolecular frontier orbital overlap. In addition, the effect of the charge carrier density and the electronic field on the charge transport was also studied, and little effect was found except that the density is larger than 0.01 and the electronic field is increased to 1.0 x 106 V/cm. The kinetic Monte Carlo simulation method has also been used to study the anisotropic charge transport property, and consistent results were obtained as with the master equation method.

  • 6.
    Lin, Li-Li
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Song, Xiu-Neng
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Leng, Jian-Cai
    Li, Zong-Liang
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Wang, Chuan-Kui
    Determination of the Configuration of a Single Molecule Junction by Inelastic Electron Tunneling Spectroscopy2010In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 114, no 11, p. 5199-5202Article in journal (Refereed)
    Abstract [en]

    First-principles calculations for inelastic electron tunneling spectroscopy (IETS) of a single 1,3-propanedithiol molecule covalently bound to gold electrodes are presented. Inelastic electron tunneling spectra of the single molecule junction with different contact geometries and molecular orientations at the interface are simulated. It is demonstrated that the delicate variation in the configuration of the single molecule junction caused by separating the two electrodes call result in significant changes in the inelastic electron tunneling spectral profile of the junction. The two Most probable configurations of the molecular junction formed in the experiment (Nano Lett. 2008, 8, 1673) are theoretically identified, and the experimental IET spectra are correctly assigned.

  • 7.
    Lin, Li-Li
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Song, Xiu-Neng
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Wang, Chuan-Kui
    Formation and electronic transport properties of bimolecular junctions based on aromatic coupling2010In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 22, no 32, p. 325102-Article in journal (Refereed)
    Abstract [en]

    A systematic first-principles study on conductance-voltage characteristics of bi-(quasi) oligo(phenylene ethynylene)-monothiol molecular junctions reported by Wu et al (2008 Nat. Nanotechnol. 3 569) is presented. The so-called ortho-and para-conformations of the bimolecular junction are considered. Our calculation indicates that the bimolecular junction prefers to take the ortho-conformation because of its lower energy. The simulation supports the experimental findings that aromatic coupling between two molecules is strong enough to induce the formation of molecular junctions. By comparing with experimental results, structure parameters for a probable bimolecular junction are determined. The underlying mechanism for formation of the bimolecular junction and its electron transport is discussed.

  • 8.
    Lin, Li-Li
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Wang, Chuan-Kui
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Inelastic Electron Tunneling Spectroscopy of Gold-Benzenedithiol-Gold Junctions: Accurate Determination of Molecular Conformation2011In: ACS NANO, ISSN 1936-0851, Vol. 5, no 3, p. 2257-2263Article in journal (Refereed)
    Abstract [en]

    The gold benzenedithiol gold junction is the classic prototype of molecular electronics. However, even with the similar experimental setup, it has been difficult to reproduce the measured results because of the lack of basic information about the molecular confirmation inside the junction. We have performed systematic first principles study on the inelastic electron tunneling spectroscopy of this classic junction. By comparing the calculated spectra with four different experimental results, the most possible conformations of the molecule under different experimental conditions have been successfully determined. The relationship between the contact configuration, and the resulted spectra is revealed. It demonstrates, again that one should always combine the theoretical and experimental inelastic electron tunneling spectra to determine the molecular conformation in a junction. Our simulations have also suggested that in terms of the reproducibility and stability, the electromigrated nanogap technique is much better than the mechanically controllable break junction technique.

  • 9.
    Lin, Li-Li
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Zou, Bin
    Wang, Chuan-Kui
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Assignments of Inelastic Electron Tunneling Spectra of Semifluorinated Alkanethiol Molecular Junctions2011In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 115, no 41, p. 20301-20306Article in journal (Refereed)
    Abstract [en]

    The peculiar experimental inelastic electron tunneling spectra of a series of hexadecanethiol molecular junctions have finally been reproduced by first-principles simulations. It is found that the debated spectral profile around 0.38 eV indeed originated from the C-H stretching vibration associated with at least two terminal methylene groups close to the sulfur atom. The intensity of this spectral peak becomes dominant, as observed in the experiments when the molecule is titled -40 degrees relative to the normal of the electrode surface, which is due to the opening of a new tunneling pathway bypassing the end sulfur atom. The dependence of this strong vibrational feature on the titled angle of the molecule is predicted with the help of the concept of effective coupling energy. The degree of the fluorination on the inelastic electron tunneling spectrum of hexadecanethiol molecules has also been discussed in detail.

  • 10. Segerie, Audrey
    et al.
    Liegeois, Vincent
    Champagne, Benoit
    Lin, Li-Li
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Theoretical Insight into the Inelastic Electron Tunneling Spectra of an Anil Derivative2013In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 117, no 48, p. 12783-12795Article in journal (Refereed)
    Abstract [en]

    First-principles simulations have been employed to simulate the inelastic electron tunneling (JET) spectra of the enol and keto forms of an anil molecular switch and to analyze them with respect to the character of the vibrational normal modes. When the molecules are sandwiched between Au plates, the dominant JET signatures appear at very similar voltages for both forms, but their intensities are clearly different, which makes JET an efficient technique to probe the molecular state of the switch. The JET-active modes are also similar for both anil forms and consist of in-plane molecular motions, CC and ring stretching, and C-H bending motions. Moreover, the JET activity of the vibrational modes specific to the enol and keto forms, i.e., those involving bending motions of the C-O-H and C-N-H groups, respectively, demonstrates that JET spectroscopy is an efficient technique to distinguish unambiguously between the two states of the keto/enol switch.

  • 11. Segerie, Audrey
    et al.
    Lin, Li-Li
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Liegeois, Vincent
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Champagne, Benoit
    Effects of the basis set and of the exchange-correlation functional on the Inelastic Electron Tunneling signatures of 1,4-benzenedithiol2014In: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy, ISSN 1386-1425, E-ISSN 1873-3557, Vol. 119, p. 34-41Article in journal (Refereed)
    Abstract [en]

    The effects of the atomic basis set and of the exchange-correlation (XC). functional on the Inelastic Electron Tunneling (LET) spectra have been investigated by considering the prototypical 1,4-benzenedithiol molecule. These studies have been completed by tackling the reliability of the same methods for predicting the IR absorption spectrum of the same molecule. The main conclusions are (i) the B3LYP XC functional is suitable to predict the relative vibrational frequencies, (ii) provided a scaling factor is used, the root mean square error on the vibrational frequencies goes down to 18 cm(-1), (iii) triple-zeta basis sets and in particular the cc-pVTZ basis set is a good compromise between accuracy and computational needs, (iv) basis set effects on the IET intensities are larger than those of the XC functional, and (v) the cc-pVTZ, cc-pVQZ, and aug-cc-pVDZ basis sets provide consistent IET intensities.

  • 12.
    Xu, Bo
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry. KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Tian, Haining
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry. KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD. Uppsala University, Sweden.
    Lin, Lili
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. Shandong Normal University, China.
    Qian, Deping
    Chen, Hong
    Zhang, Jinbao
    Vlachopoulos, Nick
    Boschloo, Gerrit
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Zhang, Fengling
    Hagfeldt, Anders
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry. KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD. KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Integrated Design of Organic Hole Transport Materials for Efficient Solid-State Dye-Sensitized Solar Cells2015In: Advanced Energy Materials, ISSN 1614-6832, Vol. 5, no 3, article id 1401185Article in journal (Refereed)
    Abstract [en]

    A series of triphenylamine-based small molecule organic hole transport materials (HTMs) with low crystallinity and high hole mobility are systematically investigated in solid-state dye-sensitized solar cells (ssDSCs). By using the organic dye LEG4 as a photosensitizer, devices with X3 and X35 as the HTMs exhibit desirable power conversion efficiencies (PCEs) of 5.8% and 5.5%, respectively. These values are slightly higher than the PCE of 5.4% obtained by using the state-of-the-art HTM Spiro-OMeTAD. Meanwhile, transient photovoltage decay measurement is used to gain insight into the complex influences of the HTMs on the performance of devices. The results demonstrate that smaller HTMs induce faster electron recombination in the devices and suggest that the size of a HTM plays a crucial role in device performance, which is reported for the first time.

1 - 12 of 12
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