Towards In Situ Terahertz Spectroelectrochemistry [electronic resource].

9780438970502

Ann Arbor : ProQuest Dissertations & Theses, 2018.

1 online resource (211 p.)

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Terahertz (THz) spectroscopy has been used to probe a large variety of materials and processes. THz radiation is attenuated in proportion to the material's conductivity, which makes THz spectroscopy particularly suitable for probing the photo-induced response of semiconductor materials. By incorporating an ultrafast photoexcitation pulse, THz pulses can act as a non-contact electrical probe with sub-picosecond temporal resolution. Due to rising interest in photoelectrochemical devices, many have used optical-pump THz-probe (OPTP) and time-resolved THz spectroscopy (TRTS) to study materials used in photoelectrochemical devices, such as the mesoporous semiconductor films found in water splitting dye-sensitized photoelectrochemical cells (WS-DSPECs) and dye-sensitized solar cells (DSSCs). While a significant amount of information about charge carrier dynamics and photoconductivity has been elucidated through OPTP and TRTS studies of these active materials alone, few have attempted to study these properties under operating conditions. In situ THz spectroscopy probes the material of interest under operating conditions and the need to compare THz data of an isolated material with electrochemical data of the material in a different environment is avoided. However, in situ THz spectroscopy had been precluded by the use of conductive films for electrodes in photoelectrochemical devices. This is because conductive films are highly reflective to THz radiation, resulting in an insufficient amount of THz transmission through the cell for these measurements. THz-transparent electrodes were constructed using photolithography and etching to pattern fluorine-doped tin oxide (FTO) films into a wire-grid configuration. The electrodes, transparent to both optical and THz radiation, allowed for the construction of THz-transparent DSSCs. THz-transparent DSSCs were constructed and in situ OPTP experiments were performed on a sensitized TiO2 film under operating conditions. OPTP traces as a function of applied bias and illumination revealed a dependence of electron injection amplitude and trapping rate on the TiO2 Fermi level. In the DSSC, the counter electrode is held at a fixed potential therefore enabling it to act as a quasi-reference. Because of this aspect, changes in applied bias could be attributed to changes in the metal oxide Fermi level. In other types of photoelectrochemical cells, the counter electrode cannot act as a quasi-reference and a reference electrode must be used. Therefore, in order to do in situ THz spectroscopy of materials within these other types of electrochemical cells, such as a WS-DSPEC, a THz-transparent three-electrode electrochemical cell is required. A THz-transparent three-electrode electrochemical cell (THz cell) was designed and fabricated. Its capabilities and limitations were explored via THz spectroelectrochemical measurements of a SnO2 film. The transmitted THz amplitude and current were simultaneously measured during cyclic voltammetry measurements. A sharp decrease in transmitted THz amplitude was observed when SnO2 conduction band states were potentiostatically filled with electrons. No change in THz transmission was observed when SnO2 trap states were filled, highlighting the ability of THz radiation to distinguish between trapped and mobile electrons. The THz cell exhibited a large uncompensated resistance characteristic of thin layer electrochemical cells. A simple method for quantifying and correcting the uncompensated resistance is also presented.

Dissertations & Theses @ Yale University.

Books / Online / Dissertations & Theses

English

August 21, 2019

Thesis (Ph.D.)--Yale University, 2018.

Yale University.