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Si Microwire-Array Solar Cells


Putnam, Morgan Charles (2010) Si Microwire-Array Solar Cells. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/JSVM-J029.


By allowing for the fabrication of flexible crystalline-Si (c-Si) solar cells that employ ~1/100th) the Si of a traditional wafer-based c-Si solar cell, while maintaining high photovoltaic efficiencies, vertically aligned arrays of c-Si microwires provide a novel photovoltaic geometry that has the potential to dramatically reduce the cost of solar electricity. In this thesis we report on 1) the growth of Si microwire arrays, 2) the chemical and electrical characterization of Si microwire arrays, and 3) the fabrication of Si microwire-array solar cells.

Using the vapor-liquid-solid (VLS) growth mechanism in combination with photolithographic patterning, vertically aligned arrays of Si microwires, with nominally identical heights and diameters, were fabricated over areas > 1 cm2. Chemical characterization of the Si wires was then performed using secondary ion mass spectrometry to measure the incorporation of the Au VLS-catalyst into the Si wire. The incorporation of the VLS-catalyst into the Si wires at its thermodynamic equilibrium concentration suggested that the use of Cu as a VLS-catalyst was less likely to limit the photovoltaic performance of Si microwire-array solar cells. Switching to the Cu-catalyzed growth of Si wires, in-situ doping with BCl3 was used to demonstrate control of the electrically active dopant concentration from 8 x 1015 to 4 x 1019 dopants cm-3. Scanning photocurrent measurements were then made to measure the minority-carrier diffusion length. The observation of 10 μm minority-carrier diffusion lengths indicated that solar cells with efficiencies of 17.5% should be possible. With the knowledge that highly efficient solar cells were possible, methods for the fabrication of a p-n junction and a transparent top contact in a solid-state solar cell were developed. This culminated in the demonstration of Si microwire-array solar cells with Air Mass 1.5 Global photovoltaic conversion efficiencies of up to η = 7.9%. Through improved device processing and the use of an amorphous Si passivation layer at the top contact, ~15% efficient solar cells should be possible.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Solar Cell, Wire Array, Si, Vapor-Liquid-Solid Growth, Microwires, Silicon
Degree Grantor:California Institute of Technology
Division:Chemistry and Chemical Engineering
Major Option:Chemical Engineering
Awards:Demetriades-Tsafka-Kokkalis Prize in Entrepreneurship or Related Fields, 2010.
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Atwater, Harry Albert
Thesis Committee:
  • Atwater, Harry Albert (chair)
  • Lewis, Nathan Saul
  • Flagan, Richard C.
  • Davis, Mark E.
Defense Date:19 May 2010
Non-Caltech Author Email:morganputnam (AT)
Record Number:CaltechTHESIS:06072010-170215356
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:5933
Deposited By: Morgan Putnam
Deposited On:08 Jan 2015 17:07
Last Modified:08 Nov 2023 00:12

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