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A B S T R A C THybrid interfaces are attracting increasing interest forphotovoltaic applications due to their low cost of productioncompared to traditional silicon-based systems and easyprocessability. This is the case of polymer/metal oxide systems.In particular, hybrid P3HT/ZnO can be consideredas a possible alternative to organic solar cells because, byreplacing the organic electron acceptor with the inorganicmetal oxide it is, in principle, possible to improve the stabilityas well as the durability of the system.In this thesis, by means of a combination of large scalemolecular dynamics simulations and ab initio methods, westudy at the atomic scale the interface between the polymerP3HT and the ZnO crystalline surface.We investigate the structure and morphology of the polymerat the interface at low and room temperature, we characterizein detail the polymer disorder close to the ZnOsurface and we discuss the implications of this disorderon transport properties. Furthermore, we investigate thepossible presence of residual molecules of solvent at the interfaceafter the synthesis process, that can affect the propertiesof the interface.A novel strategy to improve the polymer/metal oxide interfaceis proposed and investigated. Specifically, we studythe deposition and assembling of zinc phthalocyanine moleculeson ZnO and we investigate the modification of the P3HT/ZnOinterface, induced by the use of a ZnPc optically activemolecular interlayer. The structure and morphology of theZnO/ZnPc/P3HT system, studied by molecular dynamicssimulations, are used as starting point for DFT calculations.We discuss the electronic and optical properties ofthis ternary system reporting indications of an improvementin hybrid photovoltaic devices due to the hinderingof the charge recombination and a better exploitation ofthe solar spectrum.This kind of architecture, theoretically designed by amultiscale predictive modeling in the present thesis, is anv
example of a novel class of systems whose performancesare currently under experimental investigation.S O M M A R I OAttualmente le interfacce ibride richiamano un notevoleinteresse per applicazioni fotovoltaiche grazie al loro minorecosto di produzione rispetto alla tradizionale tecnologiaa base-silicio e alla loro facilità di produzione. Questoè il caso dei sistemi polimero/metalossido. In particolare,l’interfaccia ibrida P3HT/ZnO può a tutti gli effetti essereconsiderata come una possibile alternativa alle celle solariorganiche, poiché permette di utilizzare il componente inorganicoal posto dell’accettore di elettroni organico, migliorandola stabilità e la durata del sistema.In questo lavoro studiamo alla scala atomica l’interfacciatra il polimero P3HT e la superficie cristallina di ZnO, utilizzandouna combinazione di simulazioni di dinamica molecolaree metodi da principi primi.Studieremo la morfologia e la struttura del polimero all’interfacciaa bassa temperatura e a temperatura ambiente, e caratterizzeremoin dettaglio il disordine del polimero vicinoalla superficie. Le implicazioni di tale disordine sulle proprietàdi trasporto del polimero verranno discusse, cosìcome la possibile presenza all’interfaccia, dopo la sintesi,di molecole residue di solvente, che possono avere un ruolonelle proprietà dell’interfaccia.Una nuova strategia atta a migliorare le prestazioni dell’interfacciapolimero/metalossido verrà proposta e investigata. Nellospecifico, studieremo la deposizione e l’aggregazione dizinco ftalocianine sullo ZnO e investigheremo le modificazioniall’interfaccia con il P3HT indotte dall’uso di untale layer molecolare otticamente attivo. Le informazionisulla struttura e morfologia del sistema ZnO/ZnPc/P3HT,ottenute tramite la dinamica moleculare, verranno utilizzatecome punto di partenza per calcoli DFT. In particolare,discuteremo le proprietà elettroniche e ottiche di questosistema ternario, e vedremo come la presenza di tale interlayerpuò risultare utile nel migliorare le interfacce ibridefotovoltaiche poiché può ostacolare la ricombinazione trale cariche ed è in grado di sfruttare meglio lo spettro solare.vi
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 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 52 and 53: 3.3 adhesion of a single p3ht molec
Page 54 and 55: 3.4 p3ht/zno interface 35surface (t
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3.5 p3ht/zno interface: low deposit
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3.6 p3ht/zno interface: high deposi
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3.7 effective model for the transpo
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3.8 conclusions 47As for the low te
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T E R N A RY Z N O / Z N P C / P 3
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4.1 self assembling of znpcs on zno
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4.2 polymer interaction with znpcs
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4.3 electronic and optical properti
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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
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5.2 solvent thf interaction with zn
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5.3 conclusions 69γ L/L ∼ 0.112
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C O N C L U S I O N SIn this thesis
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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
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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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