Fabrication and light management of microscale solar cells

Photovoltaic (PV) technology holds great promises to become one of the renewable alternatives that can eventually replace the depleting fossil fuel reserves. Challenges, however, remain in various disciplines to achieve a performance-to-cost ratio that can stay economically competitive against traditional energy sources. This dissertation highlights efforts that tackle such challenges from different perspectives, using lightweight microscale semiconductor membranes with unconventional form factors. We start with the fabrication of second-generation silicon solar microcells, with enhanced processing robustness and energy conversion efficiency by utilizing a thermally grown SiO2 material, which serves as both an etching/doping mask and a passivation/anti-reflection layer. Combined with a backside-reflector and a polymer waveguide, these ribbon-like miniature semiconductor membranes demonstrate performance merits that are comparable to commercial silicon solar cells, albeit with significantly less active material consumption. The inherent low optical absorption of these ultrathin devices can be effectively improved by either creating nanocone structures on the device surface that elongate the photon propagation path within the cell, or converting the polymer waveguide to a luminescent solar concentrator (LSC) with luminophores that actively down-converts incident sunlight and redirects it to the embedded microcells. Strategies explored in this work to improve the performance of such LSC devices include the use of core-shell quantum dots with tunable bandgaps and minimum reabsorption losses, the design of a luminescence-trapping photonic mirror with photon recycling effects and the assembly of a multilayer construct with expanded spectral coverage. The low-cost microcell concept can be extended from Si to III-V PV materials, which have much higher efficiency due to their direct bandgap structure and the ability to form multi-junction architectures that minimize both absorption and carrier thermalization losses. Their high material cost due to the epitaxy growth process is usually compensated by use of concentrating optics, which then leads to performance constraints that include the optical losses from the geometric lenses and the inability to capture diffuse solar radiation. In the last section of this work, novel nanoporous optical materials and hybrid module architectures are created for a commercial concentration photovoltaics (CPV) module that employs triple-junction III-V microcells, with significantly reduced Fresnel losses and added capability of utilizing diffuse sunlight.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Chemistry

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2017

Author dc:creator

• Yao, Yuan

Contributors dc:contributor

• Nuzzo, Ralph G.
• Gewirth, Andrew A.
• Braun, Paul V.
• Vura-Weis, Josh

• Microscale solar cells
• Photovoltaics
• Light Management

Statement dc:rights

• Copyright 2016 Yuan Yao

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/95480

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/95480