Thesis (Ph. D.)--University of Missouri-Columbia, 2005. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file viewed on (November 13, 2006) Vita. Includes bibliographical references.

The Fourier transforms of the thermal two-time single-particle Green functions may be expressed as matrix elements of the resolvent of the Liouville operator, in an abstract Hilbert space. This abstract Hilbert space (the "superspace") contains elements f, g, etc. which are products of an odd number of fermion creation and/or annihilation operators. These operators may also be expressed as linear combinations of a set of stepping operators Φ = fig, where I is the projection operator for the vacuum in the ordinary Fock space. The Judd operators are stepping operators which step between many-particle states which usually differ in particle number. In the calculation of the single-particle Green function, only those single-particle Judd operators which step between states differing by one electron are relevant. The Judd operators obey a Lie algebra analogous to the angular momentum stepping operators L_±. The single-site and two-site Hubbard model for arvitrary electron density are solved exactly using the Judd operator formalism. The correlation functions are evaluated as functions of chemical potential, temperature and t/U, where t is the hopping energy and U is the intasite Coulomb energy. / Ph. D.

Thesis: B.S., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 1978 / Includes bibliographical references. / by Patricia E. Clark. / B.S. / B.S. Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Physics, 1979. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Includes bibliographical references. / by Robert B. Laughlin. / Ph.D.

Magister Scientiae - MSc / In this research, novel hybrid perovskite materials were synthesized, characterized and applied in photovoltaic cells (PVCs) to enhance the performance of PVCs. Mixed-organic-cations tin halide perovskites (MOCTPs) were successfully synthesized using sol-gel method. These MOCTPs include guanidinium dimethylammonium tin iodide ([GA][(CH3)2NH2]SnI3) and guanidinium ethylmmonium tin iodide ([GA][CH3CH2NH3]SnI3). The MOCTPs were studied in comparison to their single-organic-cation tin perovskites (SOCTPs), which include guanidinium tin iodide (GASnI3), ethylammonium tin iodide ([CH3CH2NH3]SnI3) and dimethylammonium tin iodide [(CH3)2NH2]SnI3. High Resolution Scanning Electron Microscopy (HR SEM) of the five perovskite materials showed good crystallinity and tetragonal and hexagonal cubic shapes, characteristic of perovskites. These shapes were also confirmed from High Resolution Transmission Electron Microscopy (HR TEM), and the internal structure of the perovskites gave similar zone axes (ZAs) with those obtained from X-ray Diffraction (XRD). XRD showed tetragonal lattice shape for these perovskite materials. Fourier Transform Infrared (FTIR) demonstrated similar functional groups for both the SOCTPs and MOCTPs. FTIR bands that were observed are; N-H, C-H sp3, C-H aldehyde, N-H bend, C-N sp3 and N-H wag. From the 13C Nuclear Magnetic Resonance (NMR) results, the carbon atom of guanidinium iodide precursor shifts from downfield to upfield position, e.g. from 110.57 ppm to 38.49 ppm in GASnI3 SOCTP. This confirms a shift upfield of the carbon atom in guanidinium iodide precursor as it bonded to Sn metal in the perovskite chemical structure. Similar behavior was also observed for the NMR spectra of [GA][CH3CH2NH3]SnI3 MOCTP, where C-2 and C-3 atoms of ethylammonium iodide precursor shifted upfield from 37.03 ppm to 15.69 ppm and 16.06 ppm to 14.39 ppm respectively.

Thin Film CdS/CdTe Solar cells have been an attrative alternative to silicon solar cells because of their low cost. Numerical Modeliong using using various tools pertinent only to solar cells have been employed to study the device properties. In this work a powerful device simulation tool MEDICI is used to develop a quantitative device model. The model is modified to accommodate a glass layer and an AM1.5 spectrum is used as the simlation of light source. Analysis of the response of solar cell J-V parameters like voc and Jsc to changes in acceptor concentration, CdTe thickness and changes in the work function of the back contact under intrinsic conditions were done. Trap levels were then added in the midgap regionof the device and the earlier variations were comprehensively studied to establish the trap parameters. Further this model was extended to perform the C-V analysis of the device. Finally two cases were analysed having their energy band profile as the baseline to fix their corresponding J-V responses. The anamolous behaviour of the J-V curves namely the rollover and crossover effects were noted in detail.

No description available.

Thesis (M.S.) -- Mississippi State University. Department of Physics and Astronomy. / Title from title screen. Includes bibliographical references.

Thesis (Ph.D.)--Mississippi State University. Department of Physics and Astronomy. / Title from title screen. Includes bibliographical references.

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.