Thesis (M.M.S.E.)--University of Delaware, 2008. / Principal faculty advisor: Valeria Gabriela Stoleru, Dept. of Materials Science & Engineering. Includes bibliographical references.

Thesis (M.S.)--Rochester Institute of Technology, 2008. / Typescript. Includes bibliographical references (p. 151-153).

Dissertation (Ph.D.)--University of Toledo, 2005. / Typescript. "As partial fulfillment of the requirements for the Doctor of Philosophy Degree in Engineering."

Thesis (Ph.D.) - University of St Andrews, October 2006.

Thesis (M.S.)--University of Toledo, 2008. / Typescript. "Submitted as partial fulfillment of the requirements for Master of Science in Physics." "A thesis entitled"--at head of title. Bibliography: leaves 129-133.

Dissertation (Ph.D.)--University of Toledo, 2008. / Typescript. "Submitted as partial fulfillment of the requirements for The Doctor of Philosophy Degree in Physics." Bibliography: leaves 96-101.

Thesis (M.S.)--Tennessee Technological University, 2009. / Title from title page screen (viewed on July 26, 2010). Includes bibliographical references.

Thesis (M.E.E.)--University of Delaware, 2006. / Principal faculty advisor: Steven S. Hegedus, Institute of Energy Conversion. Includes bibliographical references.

Philosophiae Doctor - PhD / Research in renewable energy has become a focal point as a solution to the energy crisis. One of renewable forms of energy is solar energy, with the main challenge in the development of the solar cells being the high cost. This has led to the exploration of the use of organic molecules to construct solar cells since it will lead to lowered costs of construction. The focus of this research is on the synthesis and characterisation of the polyaniline derivatives materials and zinc gallate for application in the construction of hybrid solar cells with [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) as an acceptor. The polyaniline (PANi) and doped polyaniline derivatives, polyaniline phenathrene sulfonic acid (PANi-PSA), poly[ortho-methyl aniline] phenanthrene sulfonc acid (POMA-PSA) poly[ortho-methyl aniline] anthracene sulfonc acid (POMA-ASA) were produced via chemical synthetic procedures. The zinc gallate (ZnGa2O4) was also produced using a chemical method. The vibrational and electronic spectra of the polymers and zinc gallate were interrogated independently and dependently. Electronic transitions due to charge defects (polarons and bipolarons) were observed for the polymers that are doped. The PANi was the one with the lowest band gap of 2.4 eV with the POMA-ASA having the widest bandgap of 3.0 eV. The XRD and TEM analysis of the polymers revealed characteristics that show that the PANi has the highest level of crystallinity and the POMA-ASA displayed the least level of crystallinity. The electronic data, XRD, TEM data led to the conclusion that the conductivity of the polymers is decreasing in the following sequence, PANi > PANi-PSA > POMA-PSA > POMA-ASA. The photoluminescence of the polymers alone and with the nanoparticles was investigated in solution and on an ITO coated glass substrate. Photoluminescence was observed for the polymers due to relaxation of the exciton and also from the formation of excimers. The relaxation due to the exciton was observed at higher energy levels, while the one that is as a result of the excimer formation was seen at lower energy levels. Enhancement of the peak due to the excimer was observed when the compound is mixed with the nanoparticles in solution. When the analysis was done on the ITO coated glass substrate, it was found that zinc gallate does not lead to quenching of the emission of the polymers; hence it can not be used as an acceptor in this particular system. The electrochemical behaviour of the polyaniline derivatives was investigated using cyclic voltammetry and electrochemical impedance spectroscopy. Interaction of the polymers with the PCBM (acceptor) was investigated using UV-visible absorption spectroscopy and photoluminescence spectroscopy. It was able to quench the photoluminescence of the polymers. Hence it was used as an acceptor in the construction of the photovoltaic cells. The polymers alone and with the nanoparticles were used in the formation of bulk heterojunction photovoltaic cells with PCBM as an acceptor. The photovoltaic behaviour was investigated and PANi was the one that displayed the highest efficiency.

This thesis presents the transport, material characterization, and device applications of photovoltaic polymers used in bulk heterojunction solar cells. These three areas were found to be well correlated. Materials properties affect charge transport behaviors. Charge transport behaviors affect organic photovoltaic (OPV) cell performances. Two typical PV polymers were selected for investigation. They were poly(3-hexylthiophene) (P3HT) and poly[N-9-hepta- decanyl-2,7- carbazole-alt-5,5-(4’,7’-di-2- thienyl-2’,1’,3’- benzothiadiazole)] (PCDTBT). Different charge transport measurement techniques were employed to study how charge carriers move in OPV materials including space-charge-limited current (SCLC) measurement, dark-injection space-charge-limited current (DI-SCLC) measurement, and admittance spectroscopy (AS). For hole transport measurement on P3HT, electron leakages were found in a presumed hole-only device structure resulting in ill-defined DI-SCLC and AS signals. After inserting a thin electron blocking and trapping (EBT) layer between the active layer and the Au cathode, the electron leakages can be significantly suppressed leading to well-defined transport measurement signals. Applying the EBT layer to the polymer:fullerene bulk heterojunction (BHJ) blends, the transport properties can also be studied. Charge transport measurements were carried out at different temperatures for Gaussian Disorder Model (GDM) analysis to extract energetic disorders σ and high-temperature limit mobilities μ_∞. For P3HT BHJ films, σ were found to be much smaller than PCDTBT BHJ films. Within the same polymer system, similar σ were extracted. σ can be correlated to the device parameters such as open-circuit voltage V_OC and fill factor FF. Large σ was found to limit both V_OC and FF. With the experience of transport measurement for PV materials gained, we focused on a common problem of batch-to-batch variations in device performance. Five batches of amorphous polymers PCDTBT were purchased from two vendors. From gel permeation chromatography, bimodal distributions of molecular weight were observed in all five batches of PCDTBT with different fraction of small molecular weight component. The corresponding charge carrier mobilities and device performances drop significantly with the small molecular weight component. From GDM, all five batches of polymers have similar σ. However, μ_∞ for each batch of PCDTBT appear to have significant differences. The differences originate from the variation of charge carrier hopping distances caused by different amounts of the small molecular weight component of PCDTBT. At last, ZnO prepared by low temperature annealing sol gel method was used as functional layers for OPV cells and charge transport measurements. Structural, elemental, energetic, optical, and electrical characterizations were performed to examine the ZnO. The results suggested that the ZnO should be suitable for organic device applications. The applications of the ZnO on inverted OPV cells and charge transport measurements were demonstrated.