Date of Award
Doctor of Philosophy (PhD)
With significant global growth and aspirations to have a healthy and comfortable lifestyle that promote productivity, the demand for energy will continue to increase. However, there is a need to address the energy-environment nexus. Energy production methodologies have to address challenges of emissions impacting climate change and other health effects. Furthermore, fossil fuels that are dominant today are bound to be limited in the distant future, as the rate of consumption exceeds the slower geological rate of formation of such sources. Thus, one must begin the transition to more renewable forms of energy production. Sunlight is by far the most abundant and cleaner source of energy available in nature. However, the lack of affordable and efficient solar energy conversion systems (photovoltaics and photo-electrochemical) makes it challenging to take full advantage of the freely available sunlight. An important aspect of building low-cost, efficient, and durable systems is designing novel materials with the right chemistry for sunlight harvesting and long-term stability. In this regard, it is very crucial to develop new techniques and tools to enable control over the material characteristics and fabricate efficient and stable solar energy conversion systems, which will eventually reduce the overall cost of solar energy conversion.
The dissertation demonstrates a novel aerosol-based technique (electrohydrodynamic atomization or electrospray) to synthesize light absorbing materials and thin films from droplets by precisely controlling the solvent evaporation from the droplet. The thesis is divided into two parts for synthesis and engineering of two different types of materials: (1) natural photosynthetic light-harvesting complexes for biohybrid photo-electrochemical cells and (2) synthetic inorganic-organic perovskite (CH3NH3PbI3) for photovoltaic cells.
The first part discusses on modifying the naturally occurring photosynthetic thylakoid membrane, which contains the light-harvesting protein complexes, Photosystem (PS) I and II, to convert sunlight into fuels. These light-harvesting complexes are very efficient in harvesting sunlight in nature to make food for themselves. Therefore, we can use them to capture and convert sunlight in artificial devices. Traditional techniques isolate PSI and PSII and then combine them with linkers, artificial electron donors, or mediators to enable electron transfer in the cell. However, this process decreases the light harvesting efficiency and makes fabrication more complex. Here, we utilize the thylakoid membrane directly (without isolating PSI and PSII) and re-engineer the photosynthetic circuit using the electrospray, discarding unwanted matter and then re-assembling the membrane. In this way, we can harvest sunlight efficiently without needing a linker or an electron donor/mediator.
The second part focuses on the fabrication of perovskite (CH3NH3PbI3) solar cells (PSCs), which are highly efficient and easy and cheap to fabricate. However, humid conditions both interfere with the fabrication of stable and efficient cells and degrade their performance rapidly. Therefore, a novel strategy to fabricate stable perovskite film using electrospray under ambient humidity (30-50% RH) is developed by controlling the rate of solvent evaporation from the droplet and forming an in-situ smooth perovskite layer on the substrate. The formation mechanism of perovskite film and its stability is further investigated by in-situ grazing incidence wide angle X-ray scattering (GIWAXS) at synchrotron X-ray facility, Argonne National Laboratory. The perovskite layer formed by this technique is moisture-resistant than the film fabricated by the conventional techniques, and the solar cells retain 70% of the initial efficiency on an average, after 5.5 months without encapsulation.
Finally yet importantly, the dissertation also includes the synthesis of metal oxides and carbon-based materials (crumpled graphene oxide and ZnO1-x/Carbon composite hollow spheres) with unique properties for solar energy applications. In summary, the dissertation provides an understanding of materials synthesis and engineering using aerosolized droplets, and demonstrate that the development of new light absorbing materials, when guided by a mechanistic understanding of their formation, could lead to efficient utilization of freely available sunlight.
Pratim Biswas, Robert E. Blankenship, Rajan Chakrabarty, Su Huang,
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