In the presented work, first principle studies on electronic structure, stability, and magnetic properties of metal chalcogenide, CrnTem clusters have been carried out within a density functional framework using generalized gradient functions to incorporate the exchange and correlation effects. The energetic and electronic stability was investigated, and it was found that they are not always correlated as seen in the cluster Cr6Te8 which has smaller gap between its HOMO (Highest Occupied Molecular Orbital) and LUMO (Lowest Unoccupied Molecular Orbital) and a high electron affinity of 3.39 eV indicating lower electronic stability whereas higher fragmentation energy indicating energetic stability. The high electron affinity shows that the stability of Cr6Te8 cluster can be enhanced by adding charge donating ligands including PEt3 to form stable Cr6Te8(PEt3)6 clusters as seen in experiments. The other cluster of interest was Cr4Te6 in which energetic stability was accompanied with electronic inertness marked by its large HOMO-LUMO gap, non-magnetic ground state and high fragmentation energy.

This thesis deals with development and synthesis of organic chromophores for dye sensitized solar cells. The chromophores are divided into three components; donor, linker and acceptor. The development of efficient organic chromophores for dye sensitized solar cells starts off with one new organic chromophore, D5. This chromophore consists of a triphenylamine moiety as an electron donor, a conjugated linker with a thiophene moiety and cyanoacrylic acid as an electron acceptor and anchoring group. Alternating the donor, linker or acceptor moieties independently, would give us the tool to tune the HOMO and LUMO energy levels of the chromophores. The following parts of this thesis regard this development strategy. The contributions to the HOMO and LUMO energy levels were investigated when alternating the linker moiety. Unexpected effects of the solar cell performances when increasing the linker length were revealed, however. In addition, the effect of an alternative acceptor group, rhodanine-3-acetic acid, in combination with different linker lengths was investigated. The HOMO and LUMO energy level tuning was once again successful. Electron recombination from the semiconductor to the electrolyte is probably the cause of the poor efficiencies obtained for this series of dyes. Finally, the development of functionalized triphenylamine based donors and the contributions from different substituents to the HOMO and LUMO energy levels and as insulating layers were investigated. This strategy has so far been the most successful in terms of reaching high efficiencies in the solar cell. A top overall efficiency of 7.79 % was achieved. / QC 20100716

Based on the solar cell¡¦s four characteristic parameter open-circuit voltage (Voc) makes the discussion.The study of the relation VOC¡¦s paper uses empirical formula. VOC¡¦s formula is ¡§VOC=(1/e)(¡UEDonorHOMO¡W-¡UEAcceptorLUMO¡W)-0.3V¡¨. We can know that VOC related to donor material¡¦s HOMO and acceptor material¡¦s LUMO, if we need a high VOC, it can change the structure of donor material to have higher HOMO value, as well as the acceptor material have lower LUMO value. Our active layer except poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-Butyric acid methyl ester (PCBM), the third material was blended to discuss their effect on the VOC. Two kind of different bromined-P3HT (Br-P3HT) were used 40% and 100% bromined-P3HT to blend in active layer. Their Three materials blended under the different weight percent and the basic device configurations in this study was ITO / PEDOT : PSS / P3HT : Br-P3HT : PCBM / Al , efficiency was measured under AM 1.5G 100mW/cm2 illumination. When blended Br-P3HT(100%) in the active layer, VOC increased from 0.6V to 0.68V and the surface roughness makes short-circuit current and fill factor, increased make lower power conversion efficiency. When blended Br-P3HT(40%) into the active layer, not only can increase VOC to 0.66V, but influence the short-circuit current and the fill factor. The power conversion efficiency changed from 2.20% to 2.46%.

Magister Scientiae - MSc / Solar energy generation arises as a result of direct conversion of sunlight into electricity a by solar cell; which is mainly made up of a semiconducting material incorporated into a system. It is emerging as one of the most reliable and cost efficient renewable energy sources. Within the solar field, organic bulk heterojunction photovoltaic cells have proved of being able to have a great impact in the future years; mainly due to the easy processability of the active layer and substrate, their cost effectiveness and above all, a good power conversion efficiency associated to the close 3-dimensional interpenetrating network that is generated from blending donor and acceptor semiconducting materials together in a bulk heterojunction active layer. In this research work, we therefore report on the study of a newly developed organic bulk heterojunction active layer based on a blend of a star-copolymer generation 1 poly(propylenethiophenoimine)-co-poly(ethylenedioxythiophene) (G1PPT-co-PEDOT) as donor material with N,N-diisopropylnaphthalene diimide (NDI) as acceptor material. Both materials were chemically synthesized. The synthesis of G1PPT-co-PEDOT started first by the functionalization of generation 1 poly(propyleneimine) tetramine, G1PPI into G1PPT by condensation reaction in the presence of 2-thiophene carboxaldehyde under Nitrogen gas followed by the copolymerization of G1PPT with ethylene dioxythiophene (EDOT) monomer in the presence of ammonium persulfate, (NH4)2S2O8 as oxidant. On the other hand, NDI was also synthesized via condensation reaction of 1,4,5,8-naphthalene tetracarboxylic dianhydride in the presence of two (2) equivalences of N,N-diisopropylamine at 110 oC overnight in DMF. Both materials were characterized using FT-IR, UV-Vis spectroscopy, Fluorescence spectroscopy, Voltammetry, HRSEM microscopy and XRD. Based on the cyclic voltammetry and UV-Vis results, we were able to calculate the HOMO, LUMO and band gap energy (Eg) values of both the donor and acceptor to be -4.03 eV, -6.287 eV and 2.25 eV for iii the donor G1PPT-co-PEDOT respectively and -4.302 eV, -7.572 eV and 3.27 eV for the acceptor respectively. From these results, the energy diagram for both donor and acceptor was drawn and it comes out that the separation between the HOMO of the donor and the LUMO of the acceptor ΔEg = 1.985 eV, the ideal value for a good donor-acceptor combination. Also the offset energy that is, the energy difference between the LUMO of the donor and the LUMO of the acceptor is 0.302 eV.

Department of Chemistry / As an alternative energy source, lithium ion batteries have become increasingly important with a wide range of applications in industry, and many international companies are investing in this big project. This study was aimed at the development of safer lithium-ion power sources by using new organic additives to overcome the possible safety problems. In this study, the conformations and energies of several synthesized boronates were investigated through computational study using density functional theory (DFT) with the Becke’s three-parameter hybrid method utilizing the Lee-Young-Parr correlation functional (B3LYP). After initial energy optimization using Møller-Plesset Perturbation theory (MP2), the conformational preferences and energetics in vacuo were investigated using DFT calculations and the 6-31G(d,p) basis set. Subsequently, cyclic voltammetry and electrochemical impedance spectroscopy were used to characterize the compounds in terms of their usefulness as electrolyte additives. At least two of these show excellent promise for use in lithium-ion batteries.

Aus der riesigen Vielfalt organischer Materialien sind gerade die Phthalocyanine dafür bekannt geworden, auf verschiedenen kristallinen Substraten geordnete Strukturen auszubilden. Außerdem dienen diese Moleküle als Modellsysteme für grundlegende Untersuchungen zur Einstellung elektronischer und struktureller Eigenschaften durch gezielten Einbau eines Metallatoms in den zentralen Hohlraum. Die Strukturen der Adsorptionsschichten von verschiedenen Metallphthalocyaninen, funktionalisierten Phthalocyaninen und Naphthalocyaninen auf der Basaldebene des Graphits werden verglichen, um die Adsorptionsstruktur der einzelnen Moleküle innerhalb der Adsorptionsschicht zu verstehen. Das erlaubt uns die Untersuchung der Molekül-Molekül- und Molekül-Substrat-Wechselwirkungen in Abhängigkeit von Molekularadsorption des zentralen Metallatoms, der Geometrie, einzelner funktionellen Gruppen oder ähnlichem am Molekül. Der Vergleich der Adsorptionsstrukturen von Phthalocyaninen wie PdPc und PtPc, welche d8-Metalle enthalten, dient dem Verständnis für den Effekt des Metallatoms, speziell bei großen Ordnungszahlen. Während beide Moleküle ähnliche Arten von Adsorptionsstrukturen ausbilden weist die PtPc-Adsorptionsschicht eine außergewöhnlich hohe thermische Stabilität auf. Das wurde auf die stark Molekül-Molekül-Wechselwirkung zurückgeführt, die durch die Metallatome in der Adsorptionsschicht vermittelt wird. Der Effekt langer molekularer ‚Flügel’ wird durch den Vergleich der Adsorptionsstrukturen ebener Naphthalocyanine mit denen von ebenen Metallphthalocyaninen demonstriert. Naphthalocyanine bilden viel lockerer gepackte Adsorptionsschichten als Phthalocyanine, was von der stärkeren sterischen Abstoßung zwischen den Wasserstoffatomen in benachbarten molekularen ‚Flügeln’ herrührt. Cyano-funktionalisierte metallfreie Phthalocyanine zeigen als Adsorptionsschicht eine poröse Netzwerkstruktur. Es konnte gezeigt werden, dass durch die Sondenspitze hervorgerufene Störungen dieser Struktur durch die elektrostatische Wechselwirkung zwischen den Molekülen in der Adsorptionsschicht bald weider ausheilen. Schließlich ist durch den Vergleich von Adsorptionsstrukturen ebener Naphthalocyanine und nichtebener Zinn-Naphthalocyanine auch der Geometrieeffekt untersucht worden. Abweichend von allen anderen untersuchten ebenen Molekülen haben Zinn-Naphthalocyanine eine Adsorptionstruktur, die der des Graphits ähnlich ist (hexagonal). Deshalb überwiegt in diesem Fall die Wechselwirkung zwischen Molekül und Substrat, und die Adsorptionsstruktur folgt der Geometrie des Graphitsubstates. Darüberhinaus sind mit der Tunnelspektroskopie in Abhängigkeit vom Abstand zwischen der Spitze und der Probe die elektronischen Eigenschaften der Molekül-Substrat-Grenzfläche für Naphthalocyanin und Zinn-Naphthalocyanin untersucht worden.

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<p>A systematic study of trends in band gap and lattice energies for bare zinc oxide nanoparticles were performed by means of quantum chemical density functional theory (DFT) calculations and density of states (DOS) calculations. The geometry of the optimized structures and the appearance of their frontier orbitals were also studied. The particles studied varied in sizes from (ZnO)₆ up to (ZnO)₁₉₂.The functionalization of bare and hydroxylated ZnO surfaces with MPTMS was studied with emphasis on the adsorption energies for adsorption to different surfaces and the effects on the band gap for such adsorptions.</p>

A systematic study of trends in band gap and lattice energies for bare zinc oxide nanoparticles were performed by means of quantum chemical density functional theory (DFT) calculations and density of states (DOS) calculations. The geometry of the optimized structures and the appearance of their frontier orbitals were also studied. The particles studied varied in sizes from (ZnO)6 up to (ZnO)192.The functionalization of bare and hydroxylated ZnO surfaces with MPTMS was studied with emphasis on the adsorption energies for adsorption to different surfaces and the effects on the band gap for such adsorptions.

This thesis gives a detailed description of the design and synthesis of new organic sensitizers for Dye sensitized Solar Cells (DSCs). It is divided in 7 chapters, where the first gives an introduction to the field of DSCs and the synthesis of organic sensitizers. Chapters 2 to 6 deal with the work of the author, starting with the first publication and the other following in chronological order. The thesis is completed with some concluding remarks (chapter 7). The DSC is a fairly new solar cell concept, also known as the Grätzel cell, after its inventor Michael Grätzel. It uses a dye (sensitizer) to capture the incident light. The dye is chemically connected to a porous layer of a wide band-gap semiconductor. The separation of light absorption and charge separation is different from the conventional Si-based solar cells. Therefore, it does not require the very high purity materials necessary for the Si-solar cells. This opens up the possibility of easier manufacturing for future large scale production. Since the groundbreaking work reported in 1991, the interest within the field has grown rapidly. Large companies have taken up their own research and new companies have started with their focus on the DSC. So far the highest solar energy to electricity conversion efficiencies have reached ~12%. The sensitizers in this thesis are based on triphenylamine or phenoxazine as the electron donating part in the molecule. A conjugated linker allows the electrons to flow from the donor to the acceptor, which will enable the electrons to inject into the semiconductor once they are excited. Changing the structure by introducing substituents, extending the conjugation and exchanging parts of the molecule, will influence the performance of the solar cell. By analyzing the performance, one can evaluate the importance of each component in the structure and thereby gain more insight into the complex nature of the dye sensitized solar cell. / QC 20110505