Thesis (Ph. D.)--University of Hong Kong, 2009. / Includes bibliographical references. Also available in print.

Thesis (M.Sc.). / Written for the Dept. of Chemistry. Title from title page of PDF (viewed 2009/09/07). Includes bibliographical references.

Thesis (Ph.D.) - University of St Andrews, June 2009. / Restricted until 1st June 2010.

Thesis (Ph. D.)--University of Washington, 2006. / Vita. Includes bibliographical references (leaves 256-264).

This thesis is dedicated to developing conjugated polymer and small-molecule donor materials for solution-processable organic solar cells. To begin with, a brief introduction of organic solar cells (OSCs) and an overview of donor materials development were presented in Chapter 1. In chapter 2, we used carbon-carbon triple bands as linkage of the TVT unit to develop a new building block, ATVTA. Small molecules S-03, S-04, and S-05 with ATVTA as building block showed broad absorption spectra and low-lying HOMO energy levels. S-01 with TVT unit and S-02 with AT2 as building block were also synthesized for clear comparison. OSCs devices based on S-01 and S-02 showed a Voc of 0.88 V and 0.89 V, respectively. The device based on S-03 exhibited a high Voc of 0.96 V, leading to a PCE of 2.19%. The devices based on S-04 and S-05 afforded a notable Voc over 1.0 V. The results demonstrate that ATVTA unit is a promising building block for extending π conjugation of the molecules without pulling up their HOMO energy levels. Chapter 3 focused on the development of 2D-conjugated small-molecule donor materials. The 2D-conjugated small molecule S-06 possesses excellent solution processability, broad absorption feature, respectable hole mobility and good film-forming morphology. The conjugated thiophene side chain not only effectively extends the absorption spectrum, but also lowers the HOMO energy level, which is desirable for obtaining high Voc. The BHJ OSCs based on S-06:PC70BM (1:0.5, w/w) afforded a high PCE of 4.0% and a notable FF of 0.63 without any special treatment needed. This preliminary work demonstrates that this kind of 2D-conjugated small molecules offer a good strategy to design new photovoltaic small molecule-based donor materials with high FF and Voc for high-efficiency OSCs. The consistently developed two 2D-conjugated small molecules S-07 and S-08 also possess low-lying HOMO energy levels. OSC device based on S-07:PC60BM (1:3, w/w) afforded a notable Voc of 0.96 V, with a PCE of 2.52%. BHJ devices based on S-08 will be fabricated and tested to investigate its photovoltaic properties in the near future. We developed a series of oligothiophenes with platinum(Ⅱ) as the building block in Chapter 4. These small metallated conjugated small molecules exhibited broad spectra and relatively low-lying HOMO energy levels in the range of –5.27 eV to –5.40 eV. Introducing platinum(Ⅱ) arylene ethynylenes as building block can be considered as an approach to obtain small-molecule donors with satisfactory absorption features and HOMO energy levels. Nevertheless, due to the low FF, the PCEs of these donor materials based devices are lower than 2%. Fine tuning the film morphologies of this kind of metallated small-molecule donor materials should be carried out to improve their photovoltaic performance. We addressed an efficient approach to improve the photovoltaic properties by side chain engineering in 2D-conjugated polymers in Chapter 5. Considering the fact that the Voc of PBDTTT based devices is less than 0.8 V, we introduced alkylthio substituent on the conjugated thiophene side chains of the 2D-conjugated copolymer to further improve the photovoltaic performance of the 2D-conjugated copolymers PBDTTTs. The weak electron-donating ability of the alkylthio side chains effectively down-shifted the HOMO energy level of PBDTT-S-TT by 0.11 eV in comparison to the corresponding polymer with alkyl substitution on the conjugated thiophene side chains. The PSC device based on PBDTT-S-TT showed an enhanced Voc of 0.84 V, which is among the highest one in the reported copolymers based on BDT and TT units, leading to an enhanced PCE of 8.42%. The results indicate that molecular modification by introducing alkylthio side chain will be a promising strategy to broaden the absorption, down-shift the HOMO energy level and increase the hole mobility of the low band gap 2D-conjugated polymers for further enhancing the photovoltaic performance of PSCs. PBDTT-O-TT-C and PBDTT-S-TT-C were developed to further study the conclusion. We found that OSC device based on PBDTT-S-TT-C with alkylthio side chain also demonstrated a high Voc of 0.89 V, with a PCE of 6.85% when processed with 3% DIO additive

Conjugated polymers and related molecular materials comprise a field of materials chemistry focused on the development of semiconducting organic plastics that find use in applications such as organic solar cells and organic light-emitting diodes. The optical and electronic properties of these molecules, such as absorption and emission of light, can be tuned through engineering at the molecular level. However, many of the current molecules of choice suffer from high-lying frontier orbitals, which results in a mismatch of energy levels to common components of electronic devices along with potential oxidative instability, constraining device performance in real environments. To rectify these issues, the electron-deficient thiazole heterocycle has been incorporated into fused-ring conjugated motifs of both organic and inorganic nature. The new thiazole materials all exhibited the expected stabilization of their frontier orbitals compared to the thiophene analogues. The absorption profiles of the thiazole materials are similar to the thiophene analogues, but with reduced molar absorptivity as a general trend, potentially limiting the efficiency of thiazole derived materials as components of photovoltaic devices. Through experimentation and development of multiple new classes of organic and inorganic thiazole materials, it was found that a larger proportion of thiazole content correlates to a larger decrease in molar absorptivity, but also a larger relative stabilization of the frontier orbitals. The limitations in molar absorptivity can thus be mitigated to an extent by increasing the molecule’s effective conjugation path through functionalization with additional conjugated units, but with the countereffect of less-stabilized frontier orbitals.

Single-walled carbon nanotubes (SWNTs), since their first discovery in early 1990s, have drawn enormous research attention owing to their extraordinary properties. These excellent optical, electrical, thermal and mechanical properties have enabled SWNTs to make profound impacts in the field of nanotechnology, which includes nanoscale nanoelectronics, chemo-/biosensors, photovoltaics, drug delivery, and advanced nanocomposite materials. However, the as-produced SWNT samples contain a mixture of metallic and semiconducting SWNTs, amorphous carbon, and metal catalyst particles. Also, due to π-π stacking and van der Waals forces, pristine SWNTs tend to form bundles, making them insoluble in most of organic solvents. The poor processibility and purity hinder the direct use of as-produced SWNTs as the material for fabrication of SWNT-based devices. Therefore, the post-synthesis purification is highly required. Conjugated polymers have proven to be efficient SWNT dispersants, but after solution processing, conjugated polymers adhered to the sidewall of SWNTs can not be easily removed and thus negatively affect the performance of the resulting SWNT-based electronic devices. Therefore, polymers that can dissociate from the surface of SWNTs after solution processing is highly desirable. Apart from the introduction to several other efficient purification methods of SWNTs, Chapter 1 also gives a brief review on reversible functionalization of SWNTs by polymers. The work reported in the literature categorized by the different external stimuli used to reverse the polymer-SWNT association. Chapter 2 describes the design and synthesis of a vinylogous tetrathiafulvalene (TTFV)-based conjugated polymer, which is responsive to pH changes and thus realized reversible functionalization of SWNTs. Chapter 3 describes the design and synthesis of dithiafulvenyl-grafted phenylene ethynylene polymers, which can reversibly interact with SWNTs by changing solvents. Chapter 4 describes the design and synthesis of dithiafulvene (DTF)-based electron-rich conjugated polymers, which can selectively bind with semiconducting SWNTs. In addition, Chapter 5 describes the use of SEC to achieve high-resolution separation, and isolation of surfactant-free metallic and semiconducting SWNTs. This allowed us to study the competition behavior when different ratios of metallic and semiconducting nanotubes are used as the starting material for polymer dispersions. Finally, Chapter 6 describes a side project that involves covalent functionalization of GO using Piers-Rubinsztajn reaction. The functionalized GO is loaded into silicone elastomer to reduce the air permeability and enhance the mechanical strength of the resulting silicone elastomer. / Thesis / Doctor of Philosophy (PhD)

Thesis (Ph. D.)--State University of New York at Binghamton, Department of Chemistry, 2006. / Includes bibliographical references.

published_or_final_version / Physics / Doctoral / Doctor of Philosophy

Electrochemical and electrogenerated chemiluminescence properties of the BODIPY (boron dipyrromethene) dyes are presented. Some specific features of the BODIPY dyes are obtained and described in the current dissertation. Separation of around 1.0-1.2 V is noticed between two oxidation and reduction waves for one center which is very different from 0.5 V seen for the polycyclic hydrocarbons. Cathodic and anodic stability is shown to depend upon absence or presence of certain degree of substitution. Different ways of electrochemical dimerization are explored and compared with the chemical dimerization. Photophysical and electrochemical properties of monomer, chemically synthesized dimer, trimer and polymer are described and the characteristic features determined. / text