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1.1 hybrid interfaces for photovoltaics 5ciently thick to absorb all the incident light [22]. By loweringthe band gap of the organic material it is possible toharvest a greater part of the sunlight increasing, in principle,the photocurrent. To this aim, in these last years the scientificcommunity began to investigate organic solar cellscomposed by a new type of low band gap organic polymers,such as the poly-thienothiophene-benzodithiophene(PTB) that have the same sequence of alternating thieno[3,4-b] thiophene (TT) and benzodithiophene (BDT) monomerunits attached with different side groups [23]. In particularPTB7 in combination with the PC 71 BM fullerene hadproduced efficiencies as high as 8% [24].The record efficiency for the organic solar cells (12%) iscurrently held by a type of multi-junction solar cell (tandemcell), that provide an effective way to harvest a broaderspectrum of solar radiation by combining several p-n junctionstuned to a different wavelength of light [25]. In Figure1.3 are reported the conversion efficiency for the differentkind of solar cells, and it can be observed the considerableSharp improvement obtained by the organic photovoltaic(OPV) in the last ten years.Conversion Efficiency (%)1985 1990 1995 2000 2005 2010 201514Amorphous Si single layerUnited Solar EPFL Heliatek/IAPP/UU12NIMSUnited SolarSharpMitsub.HeliatekUCLA10Mitsub.EPFLMitsubishi HeliatekDye sensitized Heliatek/IAPP8KonarkaSolarmerSolarex6EPFLPlextronics Heliatek/IAPPKonarka Konarka4Princeton UCertifiedSmall area "hero" OPV2U LinzSharp>1cm 2 OPVU Cambridge0KodakUCSB1985 1990 1995 2000 2005 2010 2015Year(c) K. Leo14121086420Figure 1.3.: Organic photovoltaic efficiencies from 1986 to 2013 (figurefrom [1]).As for the lifetime of the organic solar cells, the principalproblem is related to the degradation of active layer andelectrode materials due to water and oxygen. Even withthe most accurate protection there are several degradation
6 introductionprocesses that need to be eliminated to ensure stability [22,26].A possible and widely studied alternative to the organicsolar cells are the hybrid organic-inorganic systems, composedby an organic conductive polymer and a cheap andenvironmental friendly inorganic semiconductor, such as ametal oxide. These systems are of great interest since theycombine the peculiar properties of the two kinds of materialsinvolved at a relatively low cost of production. Inparticular, they allow to join the tailorable properties andthe flexibility of the organic polymers with the thermal andmechanical stability and the good transport properties ofthe inorganic materials [27].In hybrid solar cells the role of the acceptor is played bythe inorganic material, such as TiO 2 or ZnO, while the conductivepolymer (tipically the P3HT) has the role of electrondonor. Such systems are promising for their technologicalimpact though, until now, the highest achieved efficiencyfor a ZnO/P3HT binary system is as low as 2% [28](see Figure 1.4). This result is not comparable with that obtainedby fully organic devices and a clear motivation forthis poor behavior is still missing.Figure 1.4.: Efficiency of hybrid solar cells composed by P3HT andTiO 2 or ZnO.However, not all hybrid technologies have poor efficiencies.The most competitive hybrid systems are represented
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: 4 introductionorder in such a compl
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 52 and 53: 3.3 adhesion of a single p3ht molec
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
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4.4 conclusions 59ties. The absorpt
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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 84 and 85:
Page 86 and 87:
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
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A.1 molecular dynamics 75a.1.2The t
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A.2 the force field 77Finally, τ t
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A.2 the force field 79Waals interac
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A.3 methods 81tional Theory (DFT) l
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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,
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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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colophonThis document was typeset u
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