The pure organic dye sensitized solar cells (DSSCs) were studied and a new organic dye of donor-π-2acceptors (D-π-2A configuration) was fabricated. This dye, denoted as B2, was investigated and applied in DSSCs. Density functional theory (DFT) was used to examine the electronic distribution of the frontier orbitals of the B2 dye. It was found that intramolecular charge transfer (ICT) between the donor moieties and acceptor moieties of the B2 dye may take place under photo irradiation. The LUMO, LUMO+1 and LUMO+2 of B2 are all distributed on the acceptor moieties and this is very helpful to enhance the intramolecular electron transfer from the donor moieties to the acceptor moieties, which will consequently promote the chance of electron injection into the semiconductor. DSSCs based on B2 demonstrated an power conversion efficiency of 3.62 %. This efficiency value is approximately half of the power conversion efficiency of DSSCs based on N719 (7.69 %) under the same conditions. Femtosecond transient absorption and nanosecond transient absorption (TA), and time-correlated single photon counting (TCSPC) technique were applied to examine the electron transfer processes occurring on the surface of B2/TiO2. B2 dye has life time of the excited states three orders in magnitude shorter than that of N719. The electron injection time from excited B2 to TiO2 is also three orders in magnitude shorter than that from excited N719 to TiO2. It was revealed that the delocalized electrons of π → π* transition for both the B2 dye and the N719 dye could be further guided into the semiconductor, while such injection processes may not happen for the localized electrons in π → π* transition of these dyes. The nanosecond transient absorption and transient emission spectroscopy of the ruthenium bipyridyl sensitizer N719 in different solvents were studied. Three kinds of ZnO nanoparticles were utilized to study the electron transfer process taking place on the interface of N719/ZnO with and without electrolyte by Time-Correlated Single Photon Counting (TCSPC) technique, TA and transient emission spectroscopy. Isopropanol was found to stabilize the singlet excited state of N719 and a related emission band centered at 460 nm was observed in nanosecond time scale. It was revealed that the electrolyte has a significant impact upon the electron transfer dynamics on the N719/ZnO interface. In the absence of electrolyte, the electron transfer process on the N719/ZnO interface is dependent upon the depth of defects in ZnO nanoparticles. Conversely, in the presence of electrolyte, the impact of ZnO defects upon the electron transfer process is eliminated and the effective electron injection happens from the excited states of N719 to ZnO, in spite of the ZnO particle sizes. The polymer based solar cells were studied and a polymer incorporated with a pyrenylcarbazole pendant was synthesized and applied in the functionalization of multi-wall carbon nanotubes (MWCNT) by noncovalent π-π interaction. The polymer/MWCNT hybrids were isolated and examined. The strong interaction between the polymer and MWCNT in a 1,1,2,2-tetrachloroethane (TCE) solution was investigated. The emission spectra demonstrated an effective quenching of emission from the polymer by the MWCNT. DFT calculations showed an electron delocalization phenomenon between the pyrene and carbazole moieties. The LUMO of the polymer is mainly located on the pyrene moiety while the LUMO+1 of the polymer is predominantly positioned on the carbazole moiety. The electronic transition of LUMO+1→LUMO results in intramolecular charge transfer (ICT) from the carbazole moieties to the pyrene moieties. Femtosecond TA determined the characteristic TA feature of the excited states, which are contributed from both the pyrene and carbazole moieties. The excited state lifetime of the polymer was calculated to be 659 ps and the photo excited electrons can inject into the MWCNT very fast on a time scale of 420 fs. / published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

Dye-sensitized solar cells (DSSCs) are photoelectrochemical cells that offer efficient and potentially economical alternative to conventional solar electricity production technologies. DSSCs belong to the third generation of solar cells and offer several advantages over the solid-state junction solar cells. They utilize materials, such as titanium dioxide that are inexpensive and abundant relative to those used in conventional solar cells. Moreover, DSSCs can be fabricated with simple and scalable manufacturing processes. Finally, in DSSCs, photon absorption and charge-carrier transport are undertaken by different materials, namely molecular dyes and wide band gap semiconductors, respectively. Unlike conventional solar cells, no compromise is necessary between decreasing the band gap for visible light absorption and increasing the band gap to resist photocorrosion. For successful commercialization, a photovoltaic system incorporating DSSCs must operate reliably under a wide range of solar irradiance and operating temperatures. This experimental study reports the fabrication and characterization of the performance of a DSSC as a function of irradiance and operating temperature. The prototyped DSSCs had (i) nanocrystalline titanium(IV) dioxide, TiO₂, photoanode, (ii) platinum thin film cathode, and (iii) acetonitrile based liquid electrolyte. The photoanodes were sensitized with N-749 dye. The current-voltage characteristics of the DSSCs were measured at operating temperatures from 5 to 50° C and under 500, 1000, and 1500 W m⁻² irradiance. The open circuit voltage, V[subscript oc], decreased linearly with increasing temperature and had positive, logarithmic relation with irradiance. At temperatures lower than 15° C and 1500 W m⁻² irradiance, short circuit current density, J[subscript sc], was limited by the diffusion of I₃ in the electrolyte and increased with increasing temperature. At temperatures lower than 15° C and lower irradiance, J[subscript sc] increased with increasing temperature due to electron density limited recombination of electrons injected into the TiO₂ conduction band. At higher temperatures, the recombination was dominant over diffusion and J[scubscript sc] decreased with increasing temperature. Moreover, J[subscript sc] increased linearly with increasing irradiance. The DSSC photoconversion efficiency did not vary appreciably at temperatures lower than 15° C but decreased with increasing temperature. Finally, the DSSC efficiency increased with increasing irradiance. There was no indication of significant coupling effect of irradiance and temperature on DSSC efficiency. This study reports for the first time the coupling between irradiance and thermal effects on the operation of DSSCs. The results reported in this study can be used in recovering kinetic and transport properties that can be used in modeling and optimization of DSSCs. / text

Dye-sensitized solar cells (DSSCs) present an interesting method for the conversion of sunlight into electricity. Unlike in other photovoltaic technologies, the difficult tasks of light absorption and charge transport are handled by two different materials in DSSCs. At the heart of the DSSC, molecular light absorbers (dyes) are responsible for converting light into current. In this thesis the design, synthesis and properties of new metal-free D-π-A dyes for dye-sensitized solar cells will be explored. The thesis is divided into six parts: Part one offers a general introduction to DSSCs, dye design and device characterization. Part two is an investigation of a series of donor substituted dyes where structural benefits are compared against electronic benefits. In part three a dye assembly consisting of a chromophore tethered to two electronically decoupled donors is described. The assembly, capable of intramolecular regeneration, is found to impede recombination. Part four explores a method for rapidly synthesizing new D-π-A dyes by dividing them into donor, linker and acceptor fragments that can be assembled in two simple steps. The method is applied to synthesize a series of linker varied dyes for cobalt based redox mediators that builds upon the experience from part two. Part five describes the synthesis of a bromoacrylic acid based dye and explores the photoisomerization of a few bromo- and cyanoacrylic acid based dyes. Finally, in part six the experiences from previous chapters are combined in the design and synthesis of a D-π-A dye bearing a new pyridinedicarboxylic acid acceptor and anchoring group. / <p>QC 20140509</p>

With an increasing demand for renewable energy sources, research efforts on different solar cell technologies are increasing rapidly. The dye-sensitized solar cell (DSC) is one such technology, taking advantage of light absorption in dye molecules. The liquid based DSC contains several interesting and important interfaces, crucial for the understanding and development of the solar cell performance. Examples of such interfaces include dye-semiconductor, electrode-electrolyte and solute-solvent interfaces. Ultimately, complete interfaces with all these components included are of particular interest. One major challenge is to understand the key functions of these systems at an atomic level and one way to achieve this is to use an element specific and surface sensitive tool, such as photoelectron spectroscopy (PES). This thesis describes the use and development of PES for studying interfaces in the DSC. The materials part of the thesis focuses on interfaces in DSCs studied with PES and the methodology development parts focus on methods to use PES for investigations of solvated heterogeneous interfaces of interest for photoelectrochemical systems such as the DSC. More specifically, beginning with standard vacuum techniques, dye molecules bound to a semiconductor surface have been studied in terms of energy level alignment, surface coverage and binding configuration. To increase the understanding of solvation phenomena present in the liquid DSC, liquid jet experiments have been performed in close combination with theoretical quantum calculations. As a step towards an in-situ method to measure a complete, functioning (in operando) solar cell, methodology development and measurements performed with higher sample pressures are described using new high pressure X-ray photoelectron spectroscopy techniques (HPXPS).

The scalable syntheses of functional, porous nanostructures with tunable three-dimensional morphologies is a significant challenge with potential applications in chemical, electrical, electrochemical, optical, photochemical, and biochemical devices. As a result, several bio-enabled and synthetic approaches are explored in this work (with an emphasis on peptide-enabled deposition) for the generation of aligned nanotubes of nanostructured titania for application as electrodes in dye-sensitized solar cells and biofuel cells. As part of this work, peptide-enabled deposition was used to deposit conformal titania coatings onto porous anodic alumina templates under ambient conditions and near-neutral pH to generate aligned, porous-wall titania nanotube arrays that can be integrated into dye-sensitized solar cells where the arrays displayed improved functional dye loading compared to sol-gel-derived nanotubes. A detailed comparison between synthetic and bioorganic polyamines with respect to titania film properties deposition rate provided valuable information for future titania coating experimental design given specific applications. The development of template-based approaches to single-wall titania nanotube arrays led to the development of a new synthetic method to create aligned, multi-walled titania nanotube arrays. Lastly, peptide-enabled deposition methods were extended beyond inorganic mineral and used for enzyme immobilization by cross-linking the peptide with the multicopper oxidase laccase. Peptide-laccase hybrid enzyme coatings improved both the amount of enzyme adsorbed onto carbon nanotube “buckypaper” and allowed the enzyme to retain more activity upon immobilization onto the surface.

Thesis (Ph. D.)--University of Washington, 2007. / Vita. Includes bibliographical references (leaves 159-168).

Thesis (Ph. D.)--Rutgers University, 2008. / "Graduate Program in Electrical and Computer Engineering." Includes bibliographical references (p. 118-122).

Organic field-effect transistors (OFET) have attracted considerable interests as a promising technology for the next-generation flexible electronics. Thioacenes have recently emerged as potential semiconducting materials for OFETs. On the other hand, Photovoltaic (PV) technology is regarded as a prospective alternative for green and renewable energy source. Recently, dye sensitized solar cells (DSSCs) have drawn intensive attention and showed great potential for practical application. Herein, the research in this thesis would include the synthesis and characterization of novel thioacene-based semiconductors for OFET and DSSC applications. To begin with, a general review on the current status of organic semiconductors for OFET and DSSC applications was presented in Chapter 1. In chapter 2, a series of novel benzodithieno[3,2-b]thiophene derivatives (BDTT-n) with different lateral alkyloxy groups were designed and synthesized. In addition, alkyloxy-substituted benzo[2,1-b:3,4-b’]bis-[1]benzothiophenes derivatives (BBBT-n) were also synthesized. The performances of OFETs based on BDTT-n and BBBT-n have been fully investigated. Among them, BDTT-4 based OFET exhibited the highest hole mobility of 1.74 cm 2 /(Vs) with a current on/off ratio above 10 7 without annealing. In chapter 3, a novel series of naphthodithiophene-based oligomers with D-A- D-A- D structure motif were designed and synthesized. All these oligomers have 2 been fully characterized by NMR and mass spectrometry. The hole mobility properties of these oligomers were determined in OFETs as fabricated by drop- coating technique. These oligomers exhibited typical p-type semiconducting behavior. A mobility of 1.6x10 -2 cm 2 /(Vs) was demonstrated by ENBT based OFET with a current on/off ratio in the range of 10 5-7 after annealing at 160ºC. Besides, in chapter 4, a novel [pi]-bridge, namely naphthodithienothiophene was developed and employed to explore photosensitizers for DSSC application. In this work, four novel photosensitizers with D-A-[pi]-A or D-[pi]-A structure motif were designed and synthesized in which the carbazole or triphenylamine derivative was used as a donating group and benzothiadiazole was applied as auxiliary accepting group. The performances of DSSCs based on these photosensitizers have been fully investigated. Among them, CB-NDTT- CA based device exhibited the highest power conversion efficiency (PCE) of 7.29%. Meanwhile, the interfacial properties of these photosensitizers anchored on TiO 2 have also been studied by ab-initio simulation and Gaussian calculations. In chapter 5, another novel series of photosensitizers with benzodithienothiophene as the [pi]-bridge would be presented, in which different donors, auxiliary acceptors, and structures were incorporated into the frameworks of D-[pi]-A motif to investigate the relationship between the structure and properties. The performances of DSSCs based on these photosensitizers have been fully investigated, and BD-5 based device exhibited the best power conversion efficiency (PCE) of 4.66%. Furthermore, it was demonstrated that molecular engineering was an efficient way to modulate the performance of the DSSCs in 3 which benzothiadiazole was used as an effective auxiliary accepting group in constructing photosensitizers with D-A-[pi]-A structure motif. The di-anchoring approach was also found to be a promising method to design photosensitizers with improved performance.

Emerging solar energy technology, including photovoltaics, solar fuels generation and solar thermal systems, is considered as one of the most potential renewable energy resources because of the tremendous and free radiant energy supply by our sun. Unlike burning of fossil fuels, carbon dioxide emission-free energy conversion process is definitely another key feature and attracting scientists to explore these research areas. Besides, this implies a giant business market to compete with traditional fossil fuel companies. Nevertheless, it is too early to realize commercial application since the technologies are in the early development stage and there is still much room to explore and improve. Simply speaking, energy conversion efficiency, robustness, environmental impacts and cost are the major factors the community should deeply concentrate on at this moment. This provides many research opportunities on the creation of novel molecular functional materials and investigates the relationship between the molecular design and functional properties, and they obviously take up significant roles in the technology evolution. The basic concepts and conspectuses regarding organic photovoltaics and light-driven hydrogen generation are collected in Chapter 1. In Chapter 2, a series of new thiophene-based small molecules is presented and the discussion is focused on its application in the bulk-heterojunction organic solar cells. Importantly, the structure-property relationship is elucidated by varying the terminal electron withdrawing group and elongating the central electron donating unit. The highest power conversion efficiency (η) of 2.6% is attained by the device with compound M3 as the active material with traditional device configuration (without any annealing process and additives addition) under AM 1.5G irradiation. In Chapter 3, a series of DπA organic dyes is introduced and the discussion concentrates on its application in the dye-sensitized solar cells. Briefly, a case study on alkyl chain effects is investigated while a new starburst triarylamine donor and uncommon selenophene-containing π-linker are studied separately. The highest power conversion efficiency (η) of 6.7% is achieved by D11 under AM 1.5G irradiation with a high open-circuit voltage of 0.825 V. In Chapter 4, three new platinum(II) diimine complexes are synthesized and they are utilized as photosensitizers with platinized titanium dioxide as catalyst site in the context of light-driven hydrogen generation. Comparison between platinum(II) diimine dithiolate complex and platinum(II) diimine bis(acetylide) complex is accomplished, and the importance of photosensitization using an organic chromophore with a desirable energy transfer consideration is accounted. Finally, Chapter 5 puts forward the concluding remarks and possible future works while Chapter 6 includes all the experimental details of the studied compounds presented in Chapter 24.

abstract: Natural photosynthesis dedicates specific proteins to achieve the modular division of the essential roles of solar energy harvesting, charge separation and carrier transport within natural photosynthesis. The modern understanding of the fundamental photochemistry by which natural photosynthesis operates is well advanced and solution state mimics of the key photochemical processes have been reported previously. All of the early events in natural photosynthesis responsible for the conversion of solar energy to electric potential energy occur within proteins and phospholipid membranes that act as scaffolds for arranging the active chromophores. Accordingly, for creating artificial photovoltaic (PV) systems, scaffolds are required to imbue structure to the systems. An approach to incorporating modular design into solid-state organic mimics of the natural system is presented together with how conductive scaffolds can be utilized in organic PV systems. To support the chromophore arrays present within this design and to extract separated charges from within the structure, linear pyrazine-containing molecular ribbons were chosen as candidates for forming conductive linear scaffolds that could be functionalized orthogonally to the linear axis. A series of donor-wire-acceptor (D-W-A) compounds employing porphyrins as the donors and a C60 fullerene adduct as the acceptors have been synthesized for studying the ability of the pyrazine-containing hetero-aromatic wires to mediate photoinduced electron transfer between the porphyrin donor and fullerene acceptor. Appropriate substitutions were made and the necessary model compounds useful for dissecting the complex photochemistry that the series is expected to display were also synthesized. A dye was synthesized using a pyrazine-containing heteroaromatic spacer that features two porphyrin chromophores. The dye dramatically outperforms the control dye featuring the same porphyrin and a simple benzoic acid linker. A novel, highly soluble 6+kDa extended phthalocyanine was also synthesized and exhibits absorption out to 900nm. The extensive functionalization of the extended phthalocyanine core with dodecyl groups enabled purification and characterization of an otherwise insoluble entity. Finally, in the interest of incorporating modular design into plastic solar cells, a series of porphyrin-containing monomers have been synthesized that are intended to form dyadic and triadic molecular-heterojunction polymers with dedicated hole and electron transport pathways during electrochemical polymerization. / Dissertation/Thesis / Ph.D. Chemistry 2013