Katz, Jordan E. (2008) Metal oxide-based photoelectrochemical cells for solar energy conversion. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechETD:etd-10192007-190231
In order to address the need for CO2-free energy, recent trends in global CO2 emissions and energy production are analyzed, and the photoelectrochemical properties of two types of metal oxide-based solar cells are presented.
The effects of potential-determining cations (Li+, H+) in the electrolyte of TiO2-based dye-sensitized solar cells, using Ru(H2L’)2(NCS)2, where H2L’ is 4,4’-dicarboxylic acid-2,2’bipyridine, as a sensitizer was investigated using current density vs potential (J-E), spectrochronocoulometric, and spectroscopic methods. Photoelectrochemical cells with lower concentrations of the cations Li+ and H+ had increased open-circuit voltages (Voc), and decreased short-circuit current densities (Jsc). Spectrochronocoulometric methods indicated that the energy of states in TiO2 shifted by approximately -1 V when in contact with electrolytes lacking small cations. Spectral response measurements indicated that the loss of photocurrent was accompanied by a nearly monotonic drop in the external quantum yield across all wavelengths.
Transient absorption spectroscopy was used to measure the kinetics of interfacial electron transfer of the same system. No dependence was observed on the ultrafast dynamics of electron injection on cations used in ClO4--based solutions. However, in solutions of TBA+ with I3-/I-, femtosecond, but not picosecond, dynamics were observed. In contrast, for solutions with Li+ and ClO4-, I- or I-/I3-, both femtosecond and picosecond dynamics were observed. Nanosecond-resolved spectroscopy results show that the absence of small cations did not affect the rate of recombination, while the regeneration rate of [RuIII(H2L’)2(NCS)2]+ was decreased. Results indicate that both the ground and excited state reduction potentials of the sensitizer shift as a function of small cations in solution, along with the energy of states in TiO2. The efficiency of electron injection is thus largely unchanged; rather a decrease in the regeneration rate accounts for the loss of Jsc.
Finally, a novel, high-throughput, combinatorial approach for the synthesis and screening of mixed-metal oxides for use as water-splitting photocatalysts was developed. The methodology relies on inkjet printing to form quantitative mixtures of aqueous metal oxide precursors. After pyrolysis, the photoelectrochemical properties of metal oxides can be fully characterized in an automated high-speed system, including measurement of the Voc and J-E curves.
|Item Type:||Thesis (Dissertation (Ph.D.))|
|Subject Keywords:||carbon dioxide emissions; combinatorial synthesis; dye-sensitized solar cell; inkjet printer; metal oxides; solar energy; spectrochronocoulometry; water splitting|
|Degree Grantor:||California Institute of Technology|
|Division:||Chemistry and Chemical Engineering|
|Thesis Availability:||Public (worldwide access)|
|Defense Date:||19 October 2007|
|Author Email:||jordan.e.katz (AT) gmail.com|
|Default Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Imported from ETD-db|
|Deposited On:||30 Nov 2007|
|Last Modified:||26 Dec 2012 03:06|
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