Regioregular poly(3-alkylthiophenes) is a kind of conjugated polymers with HT-coupled structures . P3HT(head-to-tail) can be easy to access a low energy and low space obstacle coplanar conformation that leads to highly conjugated polymer , better conductivity and optical properties. In this research, we found out the different way of synthesis led to differences in properties such like regioregular, molecular weight. Above mentioned would influence spectrum of materials and device morphology. We chosen three kind of methods easily to synthesize from papers included FeCl3 Method, Grignard metathesis methods(Methylmagnesium bromide¡BTert-butylmagnesium chloride). We observed the different synthetic methods we used led to different reaction and color. After the analysis, there are not only differences between regioregular and molecular weight but molecular conformation. We also noted there were some residues that could not be completely removed by ion in the polymerization process. Absorption spectrum of film is shifted showed it has different degrees of phase separation. The literature tell us that the molecular weight greatly influences the device efficiency, because it changes the morphology and that affects the mobility and Regioregular. In this study, another field of research discusses the impact of ion. It was found after polymerization. The product not clean in the absorption spectrum of performance does not meet the solar cell requirements. After washing, it couldn¡¦t wash away the small amount of residue ion Fe, Mg, Ni, and it¡¦s about 1 ~ 3% in the total material. The experiment shows the various characteristics of different materials leads to change in device efficiency. Among them, the devices have the high molecular weight and good regioregular have the higher efficiency.

Conjugated polymers have attracted much interest as promising alternatives to inorganic semiconductors, due to their low-temperature, solution-based processability, which may provide for low-cost, large-area electronic device fabrication. However, commercialization of polymer-based electronic devices has been restricted owing to low device performance of solidified thin-films. In order to enhance charge transport of polymer semiconductor thin-films, the self-organization of organic polymer semiconductors into ordered supramolecular assemblies has been achieved by tuning a range of process parameters including film deposition method (spin vs. drop cast), solvent boiling point (low vs. high boiling point), polymer-dielectric interface treatment, and post-deposition processing (solvent vapor or thermal annealing). However, these strategies give rise to limitations for large-scale high-throughput processing due to associated pre- and/or post semiconductor deposition steps. Therefore, in this thesis, we identify alternative processing parameters (i.e., hydrogen bonds between good and poor solvents, UV irradiation to polymer precursor solutions, and combination of sonication and subsequent UV irradiation to polymer precursor solutions) which can contribute to enhancement in charge transport of a model polymer semiconductor, poly(3-hexylthiophene) (P3HT), eliminating the additional pre- and/or post-steps mentioned above. Further, we understand of how the processing parameters effect intra- and intermolecular interactions of the polymer chains, micro- through macroscopic morphologies, and charge transport characteristics of the resultant films.

The widespread adoption of hybrid organic-inorganic solar cells has been delayed by low performance. Improving performance requires a firm understanding of how to optimize both material composition and processing parameters. In this thesis, we examine processing parameters that include solution composition, annealing temperature, and the rates of spin casting and evaporative coating. We also find that the optimal weight ratio for the active layer of a ZnO:P3HT solar cell is 40 wt. % ZnO. / text

Conjugated polymer architecture and morphology are two of the key factors that determine corresponding opto-electronic device performance. It is well-known that conjugated polymers display a variety of conformations and exhibit aggregation in their materials and even for individual polymer chains. The intrinsic structural heterogeneity of conjugated polymers strongly complicates the active layer morphology and phase separation, which are crucial for photoinduced charge generation and transport in polymer based bulk heterojunction-organic photovoltaics device (BHJ-OPVs). Aiming to probe the molecular level correlations between conjugated polymer architecture, morphology and optoelectronic properties, single molecule spectroscopy (SMS) and single particle spectroscopy (SPS) were employed. The molecular level folding properties of conjugated polymers were studied and correlated to the chemical architecture and rigidness of the polymer backbones by means of SMS and single molecule polarization anisotropy imaging. First, a block copolymer consisting of poly(3-hexylthiophene) (P3HT) and (60)fullerene (C₆₀) was investigated due to its potential for forming active layers in OPV devices that exhibit long-term phase stability and efficient exciton dissociation into free charge carriers. It was demonstrated that the grafting of the C₆₀-containing block does not significantly affect the conformation of the backbone of the P3HT block. Next, a series of thiophene based polymers showing different macroscale crystallization behavior were investigated. The rigidness of the conjugated polymer backbones was found to be correlated with the chemical architecture of the molecules. However, even the polymers that show no folding in their respective crystals and are thus expected to be the most rigid, still exhibit folding at the single molecule level. From this work it is clear that besides chemical architecture, intermolecular interactions in the crystal structure also need to be considered. For conjugated polymer materials, in this dissertation specifically the blends of conjugated polymers with fullerenes as found in the active layer of OPVs, the investigation of the molecular level correlations between conjugated polymer architecture, morphology and optoelectronic properties can be prohibitively complex due to the presence of a large number of molecules. Furthermore, in the research presented herein, as well as in the literature, it has been clearly shown that the polymer molecules themselves exhibit severe heterogeneity in their properties (chain morphology, aggregation, optical and electronic properties). Therefore, in order to simplify the structure-property investigations concerning nanodomains in BHJ-OPVs, we developed P3HT/PC₆₀BM (PC₆₀BM: (6,6)-phenyl-C₆₁-butyric acid methyl ester) composite nanoparticles (NPs). The size of the nanoparticles corresponds with a few polymer and fullerene domains when considering a similarly sized volume in the active layer of OPVs. Single particle spectroscopy combined with this unique nanoparticle material system reveals variations in molecular conformation and aggregation of the conjugated polymer chains upon doping with different weight percentages of fullerene. These newly developed NPs were embedded in a hole-injection device to study the exciton-hole polaron interactions and the charge transfer processes at the interface between a hole-transporting layer and the NPs. Pronounced charge trapping was observed for donor-acceptor blend NPs due to the large amount of photogenerated free charge carriers. Besides fundamental studies on morphology-property relations for thiophene based conjugated polymers, fabrication of BHJ-OPVs based on P3HT and PC₆₀BM was also completed. Low band gap polymer PTB-7 (poly((4,8-bis((2-ethylhexyl)oxy)benzo (1,2-b:4,5-b')dithiophene-2,6-diyl)(3-fluoro-2-((2-ethylhexyl)carbonyl)thieno(3,4-b) thiophenediyl))) and a near-infrared (NIR) small dye molecule were incorporated into active layers of these P3HT/PC₆₀BM BHJ-OPVs to expand the photoresponse of the devices. The effects of doping the P3HT/PC₆₀BM BHJ-OPVs with PTB-7 and NIR dye on the device performance and film morphology were investigated. The doping of PTB-7 can efficiently extend the photoresponse of the resultant devices into the NIR regime and improve the device performance with respect to the reference (undoped) devices, demonstrating an elegant and pragmatic approach in improving light-harvesting efficiency in BHJ-OPVs.

The electrospinning technique is an attractive route for processing conjugated polymers (CPs) in a significant quantity for large-scale applications. However, the processing-structure-property relationship of the electrospinning process for CPs is not well understood. This dissertation provides a fundamental understanding regarding the structure development of CPs in electrospun fibers because of different processing conditions and relates that to fiber properties. Electrospinning was conducted for a mixture of polyethylene oxide (PEO) and poly(3-hexylthiophene) (P3HT) of three different molecular weights and two aging conditions: freshly prepared and 24 h aged spinning solutions. The aging of the spinning solution led to the self-assembly of P3HT chains, particularly with dominant H-aggregation for the higher molecular weight of P3HT. Those preexisting H-aggregates in the solution were retained and even increased in the fibers during electrospinning. Single fiber electrical conductivity, measured using a custom-built technique, has been found to increase with increasing molecular weight, particularly, a significant enhancement of that was observed for the fibers from the aged solution compared to the fibers obtained from the freshly prepared solution. Blending insulating polymers in CPs for electrospinning can hamper charge-carrier transfer, particularly when a large amount of insulating polymers is used for electrospinning. Thus, we adopted a coaxial electrospinning approach to avoid the blending of insulating components and to preserve the electrical properties of CPs. The coaxial fiber consisted of flexible polymers such as butyl rubber (BR), polymethylmethacrylate (PMMA), and PEO in the core and P3HT in the shell. BR in the core led to highly stretchable fibers. Further, P3HT in the shell facilitated the direct doping of the fiber without any post-treatment. The electrical conductivity of the doped fibers did not change significantly up to 400% strain and remained almost unchanged under cyclic loading, showing excellent mechanical reversibility. The general applicability of the spinning approach developed here has been demonstrated by successfully electrospinning donor-acceptor CP at the shell of the coaxial fibers. Our results provide new understandings linking the processing of CPs in fibers, the structural evolution of CPs in the fibers, and the corresponding electrical properties as a function of molecular weight, aging of solution, and mechanical loading.

<p>In this thesis, regioregularpoly( 3-hexylthiophene) (rr-P3HT) polymer was used as a light absorption and electron donating material, while the C60 fullerene and its derivative [6,6]-phenyl C61-butyric acid methyl ester (PCBM) were used as electron acceptor materials. The effect of solvent to control the degree of mixing of the polymer and fullerene components, as well as the domain size and charge transport properties of the blends were investigated in detail using P3HT:C60 films. The photo-physical, structural and electrical transport properties of the polymer blends were carried out according to their ratios. A distinctive photoluminescence (PL) quenching effect was observed indicating a photo-induced electron transfer. In this thesis, the effect of solvents on the crystallization and interchain interaction of P3HT and C60 fullerene films were studied using XRD, UV-vis, PL, Raman and FTIR spectroscopy. The polymer blends formed with non-aromatic solvents exhibited an improved crystallinity and polymer morphology than that formed with aromatic solvents. An improved ordering was demonstrated in the polymer films spin coated from non-aromatic solvents. This indicates that the limited solubility of rr P3HT in a marginal solvent such as non-aromatic solvents can offer a strategy to obtain highly ordered crystal structures and lead directly to optimal morphologies on the films.</p>

Label-free detection of DNA has been successfully demonstrated on field effect transistor (FET) based devices. Since conducting organic materials was discovered and have attracted more and more research efforts by their profound advantages, this work will focus on utilizing an organic field effect transistor (OFET) as DNA sensor. An OFET constructed with a transporting fluidic channel, WetOFET, forms a fluid-polymer (active layer) interface where the probe DNA can be introduced. DNA hybridization and non-hybridization after injecting target DNA and non-target DNA were monitored by transistor characteristics. The Hysteresis area of transfer curve increased after DNA hybridization which may be caused by the increasing electrostatic screening induced by the increasing negative charge from target DNA. The different morphology of coating surface could also influence the OFET response.

<p>Label-free detection of DNA has been successfully demonstrated on field effect transistor (FET) based devices. Since conducting organic materials was discovered and have attracted more and more research efforts by their profound advantages, this work will focus on utilizing an organic field effect transistor (OFET) as DNA sensor.</p><p>An OFET constructed with a transporting fluidic channel, WetOFET, forms a fluid-polymer (active layer) interface where the probe DNA can be introduced. DNA hybridization and non-hybridization after injecting target DNA and non-target DNA were monitored by transistor characteristics. The Hysteresis area of transfer curve increased after DNA hybridization which may be caused by the increasing electrostatic screening induced by the increasing negative charge from target DNA. The different morphology of coating surface could also influence the OFET response.</p>

<p>In this thesis, regioregularpoly( 3-hexylthiophene) (rr-P3HT) polymer was used as a light absorption and electron donating material, while the C60 fullerene and its derivative [6,6]-phenyl C61-butyric acid methyl ester (PCBM) were used as electron acceptor materials. The effect of solvent to control the degree of mixing of the polymer and fullerene components, as well as the domain size and charge transport properties of the blends were investigated in detail using P3HT:C60 films. The photo-physical, structural and electrical transport properties of the polymer blends were carried out according to their ratios. A distinctive photoluminescence (PL) quenching effect was observed indicating a photo-induced electron transfer. In this thesis, the effect of solvents on the crystallization and interchain interaction of P3HT and C60 fullerene films were studied using XRD, UV-vis, PL, Raman and FTIR spectroscopy. The polymer blends formed with non-aromatic solvents exhibited an improved crystallinity and polymer morphology than that formed with aromatic solvents. An improved ordering was demonstrated in the polymer films spin coated from non-aromatic solvents. This indicates that the limited solubility of rr P3HT in a marginal solvent such as non-aromatic solvents can offer a strategy to obtain highly ordered crystal structures and lead directly to optimal morphologies on the films.</p>

Philosophiae Doctor - PhD / In this thesis, regioregularpoly( 3-hexylthiophene) (rr-P3HT) polymer was used as a light absorption and electron donating material, while the C60 fullerene and its derivative [6,6]-phenyl C61-butyric acid methyl ester (PCBM) were used as electron acceptor materials. The effect of solvent to control the degree of mixing of the polymer and fullerene components, as well as the domain size and charge transport properties of the blends were investigated in detail using P3HT:C60 films. The photo-physical, structural and electrical transport properties of the polymer blends were carried out according to their ratios. A distinctive photoluminescence (PL) quenching effect was observed indicating a photo-induced electron transfer. In this thesis, the effect of solvents on the crystallization and interchain interaction of P3HT and C60 fullerene films were studied using XRD, UV-vis, PL, Raman and FTIR spectroscopy. The polymer blends formed with non-aromatic solvents exhibited an improved crystallinity and polymer morphology than that formed with aromatic solvents. An improved ordering was demonstrated in the polymer films spin coated from non-aromatic solvents. This indicates that the limited solubility of rr P3HT in a marginal solvent such as non-aromatic solvents can offer a strategy to obtain highly ordered crystal structures and lead directly to optimal morphologies on the films. / South Africa