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Design and Synthesis of Organic Dyes for Solar Energy Conversion and Storage

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2017, Doctor of Philosophy, Ohio State University, Chemistry.
Solar energy is undoubtedly the most abundant source of renewable energy. Thus far, solar cell technologies have been limited from wide spread use due to their high material and fabrication costs. Dye sensitized solar cells (DSSCs) are an attractive type of solar cell that is cheap, easily fabricated and highly tunable. A tandem DSSC combines the highly studied and efficient dye sensitized photoanode with the rarely studied dye sensitized photocathode. Although this Tandem design can increase the theoretical maximum efficiency of DSSCs, it is limited by the slowest photocurrent producing electrode which is currently the p-type DSSC. Also, DSSCs can be modified into solar driven water splitting dye sensitized photoelectrochemical cells (DSPECs). DSPECs are similar to DSSCs and have all the same advantages of cost, fabrication and tunability, but offer more practicality. Rather than just converting light to electricity, a DSPEC uses the energy of light to split H2O into its molecular components O2 and H2 which can be stored and used later as a fuel source. DSPECs can likewise be fabricated into tandem DSPECs where the proton reduction and oxygen evolution half reactions of solar driven water splitting can be divided between the p-type and n-type DSPECs respectively. This tandem DSPEC design increases the maximum possible efficiency similar to that of a tandem DSSC. Though tandem DSPECs can offer even more promise in simultaneous solar energy conversion and storage, they face similar and additional issues of tandem DSSCs. Tandem DSPECs have been limited by photocurrent mismatch between the slow photocathode and the photoanode similar to the tandem DSSC. Additionally, photocurrent decay under long-term operation, especially in low/high pH aqueous media is another major concern for DSPECs. This work focuses on organic dye design to boast the photocurrents and stability of p-type photocathodes for both DSSC and DSPEC applications. An introduction is presented in Chapter 1 that describes the basic working principles and operation of DSSCs. A summary of the relevant literature is presented for each component of the p-type DSSC. Then the scope and goals of this dissertation are discussed. Chapter 2 introduces a novel “double acceptor” dye design principle when the core structure of a triphenylamine (TPA) donor is used in donor-p-acceptor dyes for either application in n-type or p-type DSSCs. A series of novel double acceptor dyes (BH2, BH4, BH6) are synthesized and fully characterized. The double accepter dye design doubles the molar extinction coefficient of the dye when compared to the single acceptor version. This enhanced light absorption doubles the photocurrent of the p-type DSSC. Chapter 3 exploits the unique highly hydrophobic and large light absorption properties of the BH4 dye to answer the stability and wettability issues faced in solar driven water splitting applications. The unprecedented stability of the BH4 dye on NiO allowed the first use of low pH electrolytes to be used in p-type water splitting DSPECs. The ability to use acidic electrolytes likewise allowed the use of an acidically soluble and active earth abundant [Mo3S4]4+ homogeneous catalyst for the first time. Chapter 4 further utilizes the aqueous stability of the BH series dyes for aqueous based DSSCs. Utilizing water as the electrolyte solvent makes the already cost effective tandem DSSCs even more economical and environmentally friendly. The BH2 dye was used to fabricate entirely aqueous p-type DSSCs using the iodide/triiodide redox for the first time. The BH2 dye displayed aqueous p-type DSSC photocurrents greater than most non-aqueous p-type DSSCs and were stable for up to 4 months with no sign of photocathode degradation. Furthermore, aqueous tandem DSSC were fabricated with a completely aqueous electrolyte with all earth abundant materials with no use of any precious metals. Chapter 5 introduces a new dye (KC2) designed specifically for aqueous based dye sensitized electrodes. From what was learned in Chapters 2 – 4, there exists a dilemma between aqueous dye stability and wettability in the form of hydrophobicity. A novel layered amphiphilic structure is proposed to balance both the aqueous stability and wettability of dye sensitized films. The new amphiphilic KC2 dye was synthesized and fully characterized. It was compared to its purely hydrophobic analog (BH2) in all aspects including electrochemical, photo-physical and device performance properties. The KC2 dye doubles the aqueous wettability of sensitized NiO films and displays excellent stability identical to that of the hydrophobic BH2 dye. Finally from what was discovered from the KC2 dye, a new amphiphilic structure is proposed for further exploration. Chapter 6 summarizes the common experimental procedures and details used throughout the dissertation. More specific procedures relevant to each chapter are discussed in each corresponding chapter introduction.
Yiying Wu (Advisor)
Patrick Woodward (Committee Member)
Joshua Goldberger (Committee Member)
225 p.

Recommended Citations

Citations

  • Click, K. A. (2017). Design and Synthesis of Organic Dyes for Solar Energy Conversion and Storage [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1492448144094887

    APA Style (7th edition)

  • Click, Kevin. Design and Synthesis of Organic Dyes for Solar Energy Conversion and Storage. 2017. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1492448144094887.

    MLA Style (8th edition)

  • Click, Kevin. "Design and Synthesis of Organic Dyes for Solar Energy Conversion and Storage." Doctoral dissertation, Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1492448144094887

    Chicago Manual of Style (17th edition)