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Wire Array Photovoltaics


Turner-Evans, Daniel B. (2013) Wire Array Photovoltaics. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/8E75-WH21.


Over the past five years, the cost of solar panels has dropped drastically and, in concert, the number of installed modules has risen exponentially. However, solar electricity is still more than twice as expensive as electricity from a natural gas plant. Fortunately, wire array solar cells have emerged as a promising technology for further lowering the cost of solar.

Si wire array solar cells are formed with a unique, low cost growth method and use 100 times less material than conventional Si cells. The wires can be embedded in a transparent, flexible polymer to create a free-standing array that can be rolled up for easy installation in a variety of form factors. Furthermore, by incorporating multijunctions into the wire morphology, higher efficiencies can be achieved while taking advantage of the unique defect relaxation pathways afforded by the 3D wire geometry.

The work in this thesis shepherded Si wires from undoped arrays to flexible, functional large area devices and laid the groundwork for multijunction wire array cells. Fabrication techniques were developed to turn intrinsic Si wires into full p-n junctions and the wires were passivated with a-Si:H and a-SiNx:H. Single wire devices yielded open circuit voltages of 600 mV and efficiencies of 9%. The arrays were then embedded in a polymer and contacted with a transparent, flexible, Ni nanoparticle and Ag nanowire top contact. The contact connected >99% of the wires in parallel and yielded flexible, substrate free solar cells featuring hundreds of thousands of wires.

Building on the success of the Si wire arrays, GaP was epitaxially grown on the material to create heterostructures for photoelectrochemistry. These cells were limited by low absorption in the GaP due to its indirect bandgap, and poor current collection due to a diffusion length of only 80 nm. However, GaAsP on SiGe offers a superior combination of materials, and wire architectures based on these semiconductors were investigated for multijunction arrays. These devices offer potential efficiencies of 34%, as demonstrated through an analytical model and optoelectronic simulations. SiGe and Ge wires were fabricated via chemical-vapor deposition and reactive ion etching. GaAs was then grown on these substrates at the National Renewable Energy Lab and yielded ns lifetime components, as required for achieving high efficiency devices.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Solar, photovoltaic, nanowire, microwire, heterostructure, chemical vapor deposition, vapor-liquid-solid, optoelectronic modeling
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Applied Physics
Awards:Graduate Deans’ Award for Outstanding Community Service, 2013.
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Atwater, Harry Albert
Thesis Committee:
  • Atwater, Harry Albert (chair)
  • Schwab, Keith C.
  • Lewis, Nathan Saul
  • Painter, Oskar J.
Defense Date:23 May 2013
Non-Caltech Author Email:daniel.turner.evans (AT)
Funding AgencyGrant Number
National Science Foundation fellowship2009063998
Department of EnergyDE-EE0005311
DARPAUCSD funding source# 10296067, Army prime agreement number W911NF-09-2-0011
British PetroleumUNSPECIFIED
National Science FoundationASU funding source# 12-729, and NSF prime award# EEC-1041895
Record Number:CaltechTHESIS:05292013-225612828
Persistent URL:
Related URLs:
URLURL TypeDescription
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:7769
Deposited By: Daniel Turner-Evans
Deposited On:06 Jun 2013 22:07
Last Modified:08 Nov 2023 00:12

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