High Contrast Nanophotonics for Scalable Photovoltaics and Solar Fuels

Citation

Bauser, Haley Coddington (2022) High Contrast Nanophotonics for Scalable Photovoltaics and Solar Fuels. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/2xqd-c773. https://resolver.caltech.edu/CaltechTHESIS:05242022-235412996

Abstract

Anthropogenic climate change is a massive threat to our planet’s stability and habitability. Carbon dioxide makes up the majority of the greenhouse gas emissions leading to rising global temperatures. In order to reduce the global temperature, it is imperative to reduce dependency on fossil fuels by mass adaptation of renewable energy with net-zero carbon emissions. In this work, we present designs to convert incident solar energy to power through scalable nanophotonic systems.

We first introduce a tandem luminescent solar concentrator (LSC). LSCs are of interest due to their ability to concentrate both direct and diffuse light expanding the regions in which LSCs can be deployed. The tandem LSC uses a novel architecture in which InGaP micro-cells lie co-planar and optically coupled to the waveguide as opposed to the traditional edge-lined LSC. The waveguide consists of highly efficient CdSe/CdS quantum dots with emissions tuned to the band edge of the InGaP cells. This LSC is then coupled to a Si sub-cell allowing the tandem LSC to effectively convert a greater portion of the incident solar spectrum. We fabricate and perform outdoor testing on the first co-planar tandem LSC demonstrating a path to high efficiency LSCs.

We then introduce two methods to more efficiently trap light within the LSC. The first is a high contrast grating spectrally selective reflector. By using a high contrast grating, we can achieve high reflectivity with a single layer of high index materially patterned at a sub-wavelength scale on a low index substrate. While we explore both AlSb and a-SiC:H as grating materials, we pursue a-SiC:H and fabricate such a spectrally selective reflector with over 94% reflectivity at 642 nm. We then move to eliminate the need for spectrally selective filters by using photonic crystal waveguides to trap quantum dot emission within the LSC. We present two designs in which over 90% of emission remains trapped in the photonic crystal waveguide and is therefore able to travel to the photovoltaic material. We demonstrate how such a design can be used for LSCs in terrestrial and space solar power applications.

Lastly, we expand on the photonic crystal waveguide and introduce a thermal concentrator for production of scalable solar fuels. The thermal concentrator absorbs incident sunlight and traps the generated heat within the photonic crystal. This elevates the temperature within the thermal concentrator creating conditions under which catalytic reactions producing solar fuels can occur. We design a thermal concentrator that can heat up to 507.3 Kelvin under 1 sun illumination and 729.4 Kelvin under 3 sun illumination.

Thesis Files