Στην εργασία αυτή μελετάμε διάφορα πολυοξομεταλλικά οξείδια (POMs) τα οποία μπορούν να χρησιμοποιηθούν ως διεπιφανιακά υμένια για την βελτίωση της απόδοσης και των διάφορων χαρακτηριστικών των οργανικών φωτοβολταικών διατάξεων καθώς και ενα νέο πολυμερές (cbz-bt) το οποίο μπορεί να χρησιμοποιηθεί σαν αντικαταστάτης του P3HT για να παίξει τον ρόλο του δότη σε οργανικές φωτοβολταικές διατάξεις. / In the present thesis we studied some polyoxometallates(POMs) which can be used as interfacial films in order to improve the efficiency and other featurew of organic OPVs and we also studied a new polymer (cbz-bt) which can be used instead of P3HT,playing the role of donor in OPVs.

Organic-based electronic devices have received considerable attention because of their presumable advantages over traditional inorganic-based electronics, such as low cost, flexibility, and applicability for large area production. Because of the possible commercialization of electronic products based on organic conducting materials, it is important to develop a variety of organic semiconductors (OSCs) that are categorized as hole transporting (p-type), electron-transporting (n-type) or ambipolar transporting (both hole and electron). P-type OSCs have been the most thoroughly studied. N-type semiconductors are much less common and the charge carrier mobilities have lagged considerably behind their p-type counterparts. Fullerene-based materials are currently the most widely used n-type semiconductors in OPVs. The cage-like structure associated with buckminsterfullerene is made of fused six- and five-member rings. Acenaphthylene is a basic fragment of C60 and has shown potential as a valuable building block for n-type OSCs. To utilize this promising structure, the acenaphthylene unit has been incorporated into a variety of molecular structures to produce both small molecule and polymeric materials. We started with the study of fully unsaturated tetraquinane derivatives, which contain four linearly fused five-membered rings. The desired diacenaphthylpentalenes were synthesized via a palladium-catalyzed dimerization of 1-iodo-2-arylethynyl-acenaphthylenes. The compounds are benchtop and solution stable and behave as hole-transporting or ambipolar semiconductors in organic field effect transistors. The X-ray crystal structure demonstrates the importance the fused naphthalene units as they stabilize the pentalene core with an extended π-framework. The tetraquinane derivatives possess high optical gap materials owing to a forbidden HOMO to LUMO transition, yet have narrow electrochemical gaps and are reduced at small negative potentials giving lowest unoccupied molecular energy levels of -3.57 to -3.74 eV. In addition to the unsaturated tetraquinane derivatives, this thesis also includes work on the creation of macrocycles containing acenaphthylene or cyclopenta[cd]perylene units. The stabilized annulenes, with rigid and π-conjugated structures, have potential application as discotic liquid crystals and porous organic solid. 1H NMR and low resolution mass spectra gave solid proof that a target macrocycle was synthesized; however, the tedious work up and limited purification techniques did not enable large scale synthesis. The investigation of new donor-acceptor copolymers incorporating acenaphthylene or cyclopenta[cd]perylene units was also explored. Since the molecular scaffolds of the desired polymers have structural resemblance and electron affinities compared to bis-imide rylene dyes (NDI and PDI), the resulting materials have relavence for a varety of OSC based devicse. UV-Vis spectroscopy and cyclic voltammetry were utilized to probe the photoelectronic properties of these materials.

No description available.

Τα οργανικά φωτοβολταϊκά (OPV) είναι συσκευές που παρουσιάζουν μια ελκυστική λύση για εφαρμογές ηλιακής ενέργειας λόγω του χαμηλού κόστους παραγωγής τους, της μηχανικής ευκαμψίας και τη δυνατότητα παραγωγής συσκευών μεγάλης έκτασης και μικρού βάρους. Οι πιο αποδοτικοί δέκτες ηλεκτρονίων μέχρι σήμερα στα OPVs βασίζονται σε τροποποιημένα φουλερένια. Ωστόσο, χρειάζονται περαιτέρω βελτιώσεις προκειμένου να επιτευχθεί πιο αποτελεσματική μεταφορά των διαχωρισμένων φορέων στα αντίστοιχα ηλεκτρόδια. Προσπάθειες προς αυτή την κατεύθυνση έχουν γίνει, είτε επηρεάζοντας την αναμειξιμότητα μεταξύ του δότη και δέκτη είτε με την ανάπτυξη πιο αποτελεσματικών δοτών ή δεκτών ηλεκτρονίων. Νέα υβριδικά υλικά με βάση το φουλλερένιο έχουν χρησιμοποιηθεί για να επηρεάσουν τις ημιαγώγιμες ιδιότητες των πολυμερών. Δεδομένου ότι οι πολυκινολίνες αποτελούν μια από τις πλέον υποσχόμενες κατηγορίες πολυμερών μεταφοράς φορτίου (οπής ή ηλεκτρονίου) για εφαρμογή σε διάφορες οπτοηλεκτρονικές εφαρμογές, ο συνδυασμός τους με C60 αναμένεται να παράσχει μια λύση για την ενίσχυση των οπτικών, μορφολογικών και ηλεκτρονικών τους ιδιοτήτων. Πρόσφατη έρευνα έχει δείξει ότι η τροποποίηση των πολυκινολινών ώστε να έχουν χαμηλότρες τιμές LUMO θα ενισχύσει τις ιδιότητες τους ως δέκτες ηλεκτρονίων. Στην εργασία αυτή μελετήθηκαν οι ηλεκτρονικές ιδιότητες διαφόρων υλικών που αντιστοιχούν στα διαδοχικά στάδια σύνθεση ενός νέου υβριδικού συμπολυμερικού δέκτη μέσω των φασματοσκοπιών φωτοηλεκτρονίων από ακτίνες-Χ και ακτινοβολία UV (XPS/UPS). Το τελικό υβριδικό πολυμερές που μελετήθηκε είναι η πολυ-πενταφθόροφενυλοκινολίνη η οποία υβριδίστηκε με C60 (P5FQ-C60). Το μονομερές πενταφθόροφενυλοκινολίνη (Ph5FQ), το καθαρό C60 και το υβριδικό μονομερές Ph5FQ-C60 έχουν επίσης μελετηθεί. Επίσης μελετήθηκαν τα υβριδικά συμπολυμερή P3OT-co-P5FQ και P3OT-co-(P5FQ-Ν-C60) με αναλογία 1:10 για χρήση ως δέκτες ηλεκτρονίων με καλύτερη αναμειξιμότητα με τον δότη. Για την φασματοσκοπική έρευνα τα δείγματα αποτέθηκαν σε υποστρώματα Si με χρήση spin coating από διαλύματα τολουολίου, THF ή χλωροφορμίου. Οι μετρήσεις πραγματοποιήθηκαν σε θάλαμο ανάλυσης υπερυψηλού κενού (βασική πίεση 5x10-9 mbar). Από τις μετρήσεις XPS η κορυφή F1s των μη υβριδικών μορίων εμφανίστηκε σε ενέργεια σύνδεσης (BE) 688.3 eV, μια τιμή που αντιστοιχεί σε άτομα φθορίου με δεσμούς C-F. Η ίδια κορυφή μετατοπίζεται σε χαμηλότερες ενέργειες σύνδεσης σε όλα τα υβριδικά υλικά, υποδεικνύοντας την επίδραση των μορίων C60 στο ηλεκτρονιακό νέφος των φθορίων της κινολίνης. Από τα φάσματα UPS μετρήθηκε το υψηλότερο κατειλημμένο μοριακό τροχιακό (HOMO) σε σχέση με το επίπεδο Fermi καθώς και το κατώφλι υψηλών ενεργειών σύνδεσης (HBE) για κάθε υλικό. Από αυτά, υπολογίστηκε το έργο εξόδου τους, ενώ από το άθροισμα του έργου εξόδου και της ενέργειας σύνδεσης του ΗΟΜΟ υπολογίστηκαν οι Ενέργειες Ιονισμού (ΙΡ). Αυτή είναι μια χρήσιμη παράμετρος για τον χαρακτηρισμό των ημιαγώγιμων πολυμερών επειδή αντιστοιχεί στην απόσταση μεταξύ του ΗΟΜΟ και του επιπέδου κενού και σε συνδυασμό με το ενεργειακό χάσμα (Eg) μπορεί να υπολογιστεί η χαμηλότερο μη κατειλημμένο μοριακό τροχιακό (LUMO). Τα αποτελέσματα δείχνουν ότι οι ιδιότητες των ημιαγώγιμων πολυμερών ή μονομερών μπορούν αποτελεσματικά να επηρεαστούν με υβριδοποίηση με χρήση νανοδομών του άνθρακα, που σε αυτή την περίπτωση είναι το C60. / Organic photovoltaic (OPV) devices present an attractive solution for solar energy applications due to their inherently low material costs, mechanical flexibility, and the potential of scalability to large area, light weight, devices. The most efficient electron accepting materials used so far in OPVs are based on modified fullerenes. However, further improvement is needed in order to achieve more efficient transport of the separated charges to the respective electrodes. Attempts to this direction have been made either by influencing the miscibility between the donor and acceptor phases or by the development of more efficient electron donor or electron acceptor materials. New hybrid materials comprising of fullerene can been used to tune the semiconducting properties of polymers. Since polyquinolines are one of the most promising classes of electron-transporting and electron-accepting polymers for use in various optoelectronic applications their combination with C60 is expected to provide a route for the modulation of their optical, morphological as well as their electronic properties. Previous work has shown that the modification of polyquinolines towards lower LUMO values will increase their electron accepting properties. In this work the electronic properties of various materials that correspond to the sequential synthesis steps of a novel hybrid copolymeric acceptor are investigated by x-ray and UV photoelectron spectroscopies (XPS/UPS). The hybrid material under investigation is the newly synthesised poly-perfluorophenylquinoline(P5FQ-C60) hybridised with C60. The perfluorophenylquinoline monomer (P5FQ, Fig1a), C60 on its own and the hybrid P5FQ-C60 are also studied. The hybrid copolymers P3OT-co-P5FQ and P3OT-co- (P5FQ-N-C60) with a ratio of 1:10 are also studied for use as electron acceptors to confer better miscibility with the donor. For the spectroscopic investigation the samples were deposited on Si substrates by spin coating from toluene,THF or chloroform solutions. The measurements were carried out in an ultrahigh vacuum analysis chamber (base pressure 5x10-9 mbar) equipped with a hemispherical electron energy analyzer, a twin anode X-ray source for XPS and a discharge UV lamp for UPS. The XPS F1s photo-peak from the non hybrid samples appeared at binding energy (BE) 688.3 eV, a value that corresponds to fluorine atoms in C-F bonds. The same peak was shifted to lower binding energy in the case of all hybrid materials. Despite the fact that the F1s peak has a measurable signal, the C1s component corresponding to C-F bonds (BE=289.4 eV) appeared to be at noise level for all the materials under investigation. This is attributed to the fact that the photoionization cross section of C1s is about four times lower than that for F1s. From the UP spectra the Highest Occupied Molecular Orbital (HOMO) with respect to the Fermi Level and the high binding energy (HBE) cut off can be measured. From the latter the work function of the material is calculated, while the sum of the work function and the binding energy of HOMO correspond to the Ionization Potential (IP). This is a useful parameter for the characterization of semiconducting polymers because it corresponds to the distance between the HOMO and the vacuum level and in combination with band gap (Eg) values can be used for the calculation of the Electron Affinity or in other words the Lowest Unoccupied Molecular Orbital (LUMO) position. The results demonstrate that the semiconducting properties of polymeric or monomeric materials can be effectively tuned by hybridization with carbon based nanostructures, in this case C60.

<p>Recent trends in materials science have exploited noncovalent monolayer chemistries to modulate the physical properties of 2D materials, while minimally disrupting their intrinsic properties (such as conductivity and tensile strength). Highly ordered monolayers with pattern resolutions <10 nm over large scales are frequently necessary for device applications such as energy conversion or nanoscale electronics. Scanning probe microscopy is commonly employed to assess molecular ordering and orientation over nanoscopic areas of flat substrates such as highly oriented pyrolytic graphite, but routine preparation of high-quality substrates for device and other applications would require analyzing much larger areas of topographically rougher substrates such as graphene. In this work, we combine scanning electron microscopy with polarization modulated IR reflection adsorption spectroscopy to quantify the order of lying down monolayers of diynoic acids on few layer graphene and graphite substrates across areas of ~1 cm². We then utilize these highly ordered molecular films for templating assembly of di-peptide semiconductor precursors at the nanoscale, for applications in organic optoelectronic device fabrication.<br></p><p></p>

No description available.

Donor-acceptor copolymers have received a great deal of attention for application as organic semiconductors, in particular as the active layers in low-cost consumer electronics. The functional groups grafted to the polymer backbones generally dictate the molecular orbital energies of the final materials as well as aid in self-assembly. Additionally, the side chains attached to these functional groups not only dictate the solubility of the final materials, but also their morphological characteristics. The bulk of the research presented in this dissertation focuses on the synthesis and structure-property relationships of polymers containing novel acceptor motifs. Chapter 2 focuses on the synthesis of 1,2-disubstituted cyanoarene monomers as the acceptor motif for copolymerization with known donors. It was found that cyanation of both benzene and thiophene aromatic cores resulted in a decrease of the molecular orbital energy levels. Additionally, the small size of this functional group allowed favorable self-assembly and close π-stacking to occur relative to related acceptor cores carrying alkyl side chains as evidenced by UV-Vis and WAXD data. Chapter 3 describes the systematic variation of side chain branching length and position within a series of phthalimide-based polymers. Branching of the side chains on bithiophene donor units resulted in the expected increase in solubility for these materials. Furthermore, a correlation was found between the branching position, size, and the HOMO energy levels for the polymers. Additionally, it was demonstrated that branching the alkyl side chains in close proximity to polymer backbones does not disrupt conjugation in these systems. A novel acceptor motif based on the 1,3-indanedione unit is presented in Chapter 4. Despite the stronger electron withdrawing capability of this functional group relativeto phthalimide, it was found that polymers based on this unit have the same HOMO molecular orbital energy levels as those presented in Chapter 3. It was found, however, the presence of orthogonal side chains greatly enhanced the solubility of the final polymers. Additionally, UV-Vis and WAXD measurements revealed that thermal annealing had a profound effect on the ordering of these polymers. Despite the presence of orthogonal side chains, long range order and close π-stacking distances were still achieved with these materials. Finally, alkynyl “spacers” were used in Chapter 5 to separate the solubilizing alkyl side chains from the polymer backbones on bithiophene donor monomers. The alkynyl groups allowed for conjugated polymer backbones to be achieved as well as low HOMO energy levels. A correlation between the side chain size, π-stacking distances and HOMO-LUMO energy levels was measured in this polymer series.

Organic semiconductors functionalized nanostructures are becoming as promising materials for electronic device applications including organic photovoltaics (OPVs). Perylenediimide (PDI) derivatives have also been known as one of the best n-type organic semiconductors. PDI derivatives can form bulk materials, which are both photochemically and thermally stable and have been widely used in various optoelectronic devices. Due to the formation of high electron mobility of crystalline domains, they prefer to incorporate into a silsesquioxane network. Here, we describe the potential applicability of perylenediimide functionalized silsesquioxane nanoribbons (PDI-dimethyl nanoribbons) as an acceptor for optoelectronic devices. We have developed synthetic procedures to make the PDI-dimethyl nanoribbons by the substitution reaction and the modified Stöber method. The PDI-dimethylethoxy silane precursor was produced in high yield by substituting 3-aminopropyldimethylethoxysilane on perylene-3,4,9,10-tetracarboxylicdianhydride as side chains. The optically active PDI-dimethyl nanoribbons were then formed upon hydrolysis with the certain concentration of ammonium hydroxide as a base. These nanoribbons were characterized using transmission electron microscopy (TEM), elemental analysis, and polarized optical microscopy. The photophysical properties in solution phase were also studied. The synthesis procedure developed here will have a great promise in large-scale manufacturing. Different shapes of PDI-dimethyl nanostructures, such as nanorods, nanochains, and nanoparticles, were discovered while varying the base concentrations. Also the morphologies of these PDI nanostructures were studied using TEM. Future studies will focus on optimizing procedures of PDI-dimethyl nanostructures and exploring new derivatives like perylenediimide dimer functionalized silsesquioxane polymers.

Durable, cheap, and lightweight polymer based solar cells are needed, if simply to meet the demand for decentralized electrical power production in traditionally “off-grid” areas. Using a blend of Poly(3-hexylthiophene-2,5-diyl) (P3HT), Phenyl-C61-butyric acid methyl ester (PCBM), and the low band-gap polymer Poly[2,6-(4,4-bis-(2- ethylhexyl)-4H-cyclopenta [2,1-b;3,4-b′]dithiophene)-alt-4,7(2,1,3-benzothiadiazole)] (PCPDTBT), we have fabricated devices with a wide spectral response and 3% power conversion efficiency in AM 1.5 conditions; however, this thin film system exhibits only 0.43 optical density at 500 nm. To improve the performance of this polymer blend photovoltaic, we aim to increase absorption by adding CdSe(ZnS) core (shell) quantum dots. Four groups of devices are fabricated: a control group with an active polymer layer of 16 mg/mL P3HT, 16 mg/mL PCBM, and 4 mg/mL PCPDTBT; and three groups with dispersed quantum dots at 4 mg/ml, 1 mg/mL, and 0.25 mg/mL. The (CdSe)ZnS quantum dots are coated with octadecylamine ligands and have a peak absorbance at 560 nm and peak emission at 577 nm. The active layer was dissolved in chlorobenzene solvent and spun on glass substrates, patterned with indium tin oxide. The devices were then annealed for fifteen minutes at 110° C, 140° C, and 170° C. Current-voltage characteristic curves v and optical density data were taken before and after the anneal step. Finally, surface characterization was conducted with atomic force microscopy and electrostatic force microscopy. When compared to the control, the sensitized devices exhibited increased absorption and depressed electrical performance with increasing quantum dot loading. The surface morphology, both electrical and physical, showed deviation from the typical values and patterns shown by the control that increased with quantum dot loading. When the degrading electrical characteristics, increasing optical absorbance, and surface changes, are considered together, it becomes likely that the quantum dots interact in a significant manner with the morphology of the P3HT phase, which leads to an overall decrease in performance.