The CCI Solar SURFs will be doing the following projects:
Gray/Winkler Labs
Eric Chang (Caltech)
My research project will focus on studying multi-step electron transfer through outer membrane protein A (OmpA), a membrane protein, mediated by tryptophan residues. We are modeling our process after the electron transport process found in Photosystem II in photosynthesis because nature already employs an efficient electron shuttling process. Cysteine mutations will be introduced into OmpA where they will be covalently attached to photosensitive species. We will also introduce tryptophan molecules throughout the protein to act as intermediates for the long range electron transfer. By employing a tryptophan mediated system, we hope to achieve multi-step electron transfer on the order of nanoseconds, a timescale supportive of life.
Sijia Dong (Hong Kong University)
This research project is on the computational study of electronic structures of various iridium corroles that may be potential catalysts of important reactions, such as oxidizing water to oxygen. As some iridium complexes are reported to have oxidation potentials that are highly tunable by varying the ligands, and corrole is discovered to be able to stabilize metal center of high oxidation states, the effect of oxidation states and axial ligands on the electronic structures of iridium corroles will be analyzed. Also, compounds having porphyrin instead of corrole will also be studied for comparison. Since Ir(III) and Ir(IV) corroles have already been reported in literature, the focus will be on complexes of higher oxidation states. Oxo ligand(s) on the axial position will be of great interest. Computational approach, which will be mainly DFT in this project, will be taken as it has the advantage of producing semi-quantitative picture of electronic structures in a cost-effective way, and hence may be able to direct future more time-consuming experiments.
Jacquie Malette (Cal State University - Los Angeles)
Global energy is an increasing concern with the depletion of nonrenewable fuels and the United States’s dependence on foreign fuel. A potentially strong consideration to the replacement of fossil fuel is hydrogen; through the reduction of water via photochemical or electrochemical processes. A requirement of the electro- and photochemical processes involves a catalyst due to prohibition of the activation energy of splitting water. An ideal catalyst involves cost efficiency, production from abundant materials, adheres to band gap requirements for a kinetically favorable process, suitable stoichiometric quantities acceptable to demand, and minimal interactions with contaminants that may result in unwanted side products. Previously, platinum complexes have been used, but platinum is an expensive compound. Another metal that can be used as a catalyst is cobalt. Cobalt and its complexes will be investigated as a suitable catalyst for efficient production of H2 in the reduction of water.
Carolyn Valdez (Caltech)
It is undeniable that we need to find an alternative, renewable source of fuel. Many are looking to use solar energy in the future, but unfortunately, we have no efficient way of storing this energy. In relation to the CCI’s quest for the development of a three-component solar water splitter and energy storage system, my project focuses on synthesizing an efficient and rapid two electron reduction catalyst to take water, in the form of protons, and make dihydrogen. Assuming a bimetallic pathway of a known cobalt catalyst, or the mechanism in which two catalysts must physically come together in solution to produce dihydrogen, the first target molecule was an m-xylene linker used to connect the two metals together. Connecting catalysts in this way will theoretically reduce the time constraint of diffusion, but still allow reactivity. To further study hydrogen evolution and test the mechanistic pathway, we are also exploring other ways to tether together two metals, including using a flexible alkyl chain and a more rigid dibenzofuran linker. The synthetic pathway consists of selectively forming diketones with varying side chains using a dihalide. These ligands are then converted to the corresponding glyoxime and allowed to coordinate with cobalt. The electrochemistry of the complexes, including the reduction potential, is studied using cyclic voltammetry and soon we hope to use rotating ring disk electrochemistry. We are also working to synthesize an analogous catalyst with an olefin tail that can be attached onto a silicon membrane of the theoretical water splitter using cross metathesis, thus bringing us closer to realizing our goal of a three-component solar system.
Lewis/Brunschwig Labs
Tina Ding (Caltech)
The goal of my research is to gain control over the barrier height of Silicon interface by attaching conductive polythiophene brushes. Modification of silicon surfaces gives chemical control of semiconductor/metal which is essential in efficient electronic devices and is applicable to solar cells. This barrier height control will allow the Silicon/polymer junction to be used as from ohmic to rectifying contact. In application to the three-component solar device, ohmic contact is desired for the contact between the Si rods and metal rods, and rectifying contact is desired on the Si rods to cause working voltage when exposed to sunlight. My research in tackling this goal is to attach polythiophene brushes with varying functional groups on the 3 and 4 position of thiophenes on the Silicon surface. The different functional groups of fluoroalkane, alkane, 2,5-dioxahexyl, and 1,3-dioxapentyl will be used, and will change the redox potential of the polymer. This should result in varying barrier height of the Si interface, which will be measured by JV measurements and Impedance spectroscopy. The procedure of attaching the polythiophene brush also involves a new synthetic method which we hope to confirm.
Jessie Ku (Caltech)
This project is focused on integrating catalysts onto the surface of photoelectrochemical cells to increase the efficiency of a photoelectrochemical energy system greatly affected by the properties between the semiconductor and liquid. Platinum is the best known catalyst for the hydrogen generation reaction, but its scarcity and high cost prohibit its use for a low cost solar energy generation system. We will look at a variety of metals that are abundant but also have good catalytic properties for the hydrogen generation reaction such as nickel and cobalt. We will also be looking at different electrochemical and electroless deposition techniques of metal nanoparticles on planar Si surfaces, and will characterize them using SEM and examine the achievable open circuit voltages with photoelectrochemical cyclic voltammetry. These results will be applied to structured silicon arrays, both VLS grown microrods and reactive ion etched pillars.
Xueliang Liu (Caltech)
My project will be on investigating the junction properties between silicon and various types of conductive polymers for solar cell application. Specifically, I will make contacts to n and p type silicon in the planar and the nanowire array structures using conductive polymers such as PEDOTPSS, polypyrrole, polyaniline and P3HT, spincoated or electrochemically polymerized in-situ. Various properties of the resulting polymer as thickness, optical absorption and work function will be characterized. The junction I-V and C-V characteristics will also be obtained. The photovoltaic properties will be measured to optimize the performance of the silicon-polymer solar cell based on the variety of materials and cell geometries.
Miguel Ortiz (Cal State Univ. - Los Angeles)
The area of research that I will be working on consists of the development of a visible-light stable absorbing material with suitable properties for water oxidation. The material being study at the moment is Tungsten(III) Oxide (WO3). The initial approach is to grow by anodization a mesoporous WO3 film on a tungsten sheet. The conditions to manipulate are the voltage, the concentration of NaF and the time of anodization. One of the specific aims of the research at the moment is to increase the thickness of the WO3.To increase the thickness of WO3 I will modify the conditions in which the oxidation is achieved. Then I will analyze the conditions to understand which are favorable. The conditions to be modified are the voltage, anodization time, and electrolyte where the anodization is conducted. The thickness of the WO3 is then measure with the help of a scanning electron microscope. The initial assumption is that increasing the anodization time and using organic electrolytes the thickness could be increased. I will consider the first part of the project to be completed once the thickness of the oxide layer reaches six microns.
Jeanne Peng (Caltech)
Buffer layers are essential to the function of some photovoltaics because they prevent undesirable interaction between the emitter and collector. ZnS has been studied and used as a competent buffer layer in high-efficiency Cu(In,Ga)Se2 photovoltaics (CIGS). Thin films of ZnS have will be grown on slides using a chemical bath deposition process (CBD) for incorporation into zinc phosphide (Zn3P2) thin film solar cells. The CBD process will be carried out in an aqueous solution of zinc sulfate with the sulfur sources thiourea or thioacetamide. Different complexing agents (ammonia, hydrazine, triethanolamine, acetic acid) will be compared as used in these procedures. The characteristics of the various films will be compared using absorbance, X-ray diffraction, and preliminary data from Zn3P2/ZnS/ZnO test solar cells.
Peters Lab (MIT)
Chantal Mustoe (Caltech)
My project is focused on the design and synthesis of modified glyoxime ligands for cobalt based hydrogen evolving catalysts. The development of a versatile synthetic method for glyoxime based macrocycles will allow a wide array of functional groups to be incorporated, allowing for the tuning of both sterics and electronics. I am particularly interested in appending functional groups which will allow these complexes to be attached directly to modified silicon surfaces, uniting two components of our proposed solar cell. I am also exploring other ligand modifications may also provide access to binuclear species, which will allow us to exploit cooperativity between two cobalt centers for effective H2 evolution.
