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3.3 adhesion of a single p3ht molecule on the zinc oxide surface 33Figure 3.2.: Trench grooves (T.G.) and row of dimers (R.D.) in a portionof ZnO.scale model after atomic relaxation based on MPMD is reportedin Figure 3.2 The atomic scale structure of the (10¯10)surface exhibit trench grooves alternated with rows of ZnOdimers (channels), both oriented along the [010] crystallographicdirection. Hereafter in this chapter, the x axis isalways chosen parallel to this [010] crystallographic directionFigure 3.2. As already discussed in chapter 1, in orderto describe the ZnO crystalline surface, we adopt theBuckingham-type potential. This potential describes properlyseveral properties of bulk and nanocrystals such aselastic constants, equilibrium lattice energy, cell parameters,elastic and dielectric constants [72].3.3 adhesion of a single p3ht molecule on thezinc oxide surfaceThe first step in the analysis of the ZnO/P3HT interfaceis the study of the adhesion of a single polymer moleculeon the surface. For this purpose a P3HT molecule composedby 16 monomers is put at different distances fromthe surface with the thiophene rings parallel to it (face-onalignment) and the backbone parallel to the ZnO dimers.The basin of interaction between the ZnO and the P3HTis reported in Figure 3.3, where the unrelaxed energy (calculatedwithout allowing atomic relaxation of the polymerdue to the surface) is reported as a function of the relativedistance between molecule and surface. The minimumof the interaction is found at 3.7 Å and corresponds to
34 polymer/semiconductor interfacean energy 0.35 eV/thiophene. The interaction vanishedat distances larger than 8 Å. By starting from the minimumenergy distance and by further relaxing the systemwe identify the lowest energy configuration of the polymeron the surface with a binding energy as large as 0.73eV/thiophene. The driving force for this binding energy isdue to the attraction beween the negative carbon atoms ofthe thiophene rings of the polymer and the positive zincatoms of the surface. The P3HT polymer on the ZnO surfacepreservs the quasi-planar configuration of the isolatedmolecule.Figure 3.3.: Interaction and adhesion of a P3HT molecule on a ZnOsurface.3.4 p3ht/zno interfaceIn order to generate models of the P3HT/ZnO interfacewe consider a planar ZnO surface ideally perfect andwe put on it the organic polymer. There are three possibleways to apply boundary conditions to the interface: (i)periodic boundary conditions for both ZnO and polymer;(ii) no periodic conditions at all, i.e. finite size cluster; (iii)mixed periodic-non periodic conditions. The case (i) hasthe advantage of avoiding free surfaces, but it can introduceartifacts in the polymer assembling since it imposesthe same periodicity for both the polymer and the ZnO
Page 1 and 2: Università degli Studi di Cagliari
Page 4: A C K N O W L E D G M E N T SI woul
Page 7 and 8: example of a novel class of systems
Page 10 and 11: C O N T E N T S1 introduction 11.1
Page 12 and 13: L I S T O F F I G U R E SFigure 1.1
Page 14 and 15: List of FiguresxiiiFigure 2.15 Init
Page 16 and 17: List of FiguresxvFigure 4.6Figure 4
Page 18: Figure 5.7Figure 5.8Figure A.1Figur
Page 21 and 22: 2 introduction1-3 eV) and the trans
Page 23 and 24: 4 introductionorder in such a compl
Page 25 and 26: 6 introductionprocesses that need t
Page 27 and 28: 8 introduction1.2 physical factors
Page 29 and 30: 10 introductionrecovered by the int
Page 31 and 32: 12 introductionA cheap and environm
Page 33 and 34: 14 introductiondensed phases [63, 7
Page 36 and 37: P 3 H T - P O LY ( 3 - H E X Y LT H
Page 38 and 39: 2.1 mechanism of assembling and mor
Page 40 and 41: 2.2 p3ht assembling and intermolecu
Page 42 and 43: 2.3 p3ht crystalline bulk phases 23
Page 44 and 45: 2.5 nanocrystalline p3ht 25Figure 2
Page 46 and 47: 2.5 nanocrystalline p3ht 27Table 2.
Page 48 and 49: 2.6 conclusions 29Figure 2.13.: Ini
Page 50 and 51: P O LY M E R / S E M I C O N D U C
Page 54 and 55: 3.4 p3ht/zno interface 35surface (t
Page 56 and 57: 3.5 p3ht/zno interface: low deposit
Page 58 and 59: 3.6 p3ht/zno interface: high deposi
Page 64 and 65: 3.7 effective model for the transpo
Page 66 and 67: 3.8 conclusions 47As for the low te
Page 68 and 69: T E R N A RY Z N O / Z N P C / P 3
Page 70 and 71: 4.1 self assembling of znpcs on zno
Page 72 and 73: 4.2 polymer interaction with znpcs
Page 74 and 75: 4.3 electronic and optical properti
Page 76 and 77: 4.3 electronic and optical properti
Page 78 and 79: 4.4 conclusions 59ties. The absorpt
Page 80 and 81: I N T E R A C T I O N B E T W E E N
Page 82 and 83: 5.2 solvent thf interaction with zn
Page 88 and 89: 5.3 conclusions 69γ L/L ∼ 0.112
Page 90 and 91: C O N C L U S I O N SIn this thesis
Page 92 and 93: M O L E C U L A R D Y N A M I C SAa
Page 94 and 95: A.1 molecular dynamics 75a.1.2The t
Page 96 and 97: A.2 the force field 77Finally, τ t
Page 98 and 99: A.2 the force field 79Waals interac
Page 100 and 101: A.3 methods 81tional Theory (DFT) l
Page 102 and 103:
B I B L I O G R A P H Y[1] http://w
Page 104 and 105:
ibliography 85[17] J. D. Servaites,
Page 106 and 107:
ibliography 87Zakeeruddin, and M. G
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ibliography 89Phys. Chem. Chem. Phy
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ibliography 91[65] D. J. Binks and
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ibliography 93cells,” Energy Envi
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ibliography 95[97] C. Ingrosso, A.
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ibliography 97298.15 k,” Journal
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ibliography 99charges. am1-bcc mode
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