High-Efficiency, Scalable Solar Cells of Earth-Abundant Materials

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3.40/22.71

• Summary of 10/23/2012
• Sergio Castellanos
• Mechanical Engineering Department
• Massachusetts Institute of Technology, Cambridge,
  MA (USA)

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Stress-Strain
s

• Constitutive Relations
• Strength A
• Ductility B
• Toughness C

e
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Inelastic Processes

• Plasticity
• Phase Transformation

• Fracture

Potential Energy (V)
Potential Energy (V)
Non-Periodic
Periodic
Cleavage Opening
Slip Displacement
V0
Total Metal-Metal Coordination remains constant
One-off dissipation mechanism
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Inelastic Processes in Metals

• Easier to follow the path of plasticity
  (sustainable dissipation)
• Fracture toughness Resistance against crack
  propagation

Material KIC-Max MPa/m0.5
Cu 107
Ag 105
Fe 150
Ni 150
W 150
SiC 5.1
B-Si3N4 10
TiC 3
MgO 2.8
NaCl 0.19
Metallic Ionic Covalent
S. Ogata and J. Li Toughness scale from first
principles J. Appl. Phys. 106, 113534 (2009)
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Inelastic Processes in Metals

• Easier to follow the path of plasticity
  (sustainable dissipation)
• Fracture toughness Resistance against crack
  propagation

BBulk Modulus GShear Modulus OCell Volume

• KIC function of
• Bonding energy
• Ideal strength
• Bandgap
• Ionicity

S. Ogata and J. Li Toughness scale from first
principles J. Appl. Phys. 106, (2009) 113534
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Flow in the presence of Diffusion Creep
Input
Output

s
e
e(t-to)
so
eo
to
t
t
to

• Different stages on Creep
• Progression towards steady state flow (s.s.
  dislocation density gen.)
• Static recovery counterbalances new dislocation
  generation
• Terminal failure (e.g. necking in tension test)

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Deformation-Mechanism Map
Frost, Harold Jefferson, and M. F. Ashby.
"Deformation-mechanism maps The plasticity and
creep of metals and ceramics. Pergamon Press,
Oxford, UK (1982).
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Deformation-Mechanism Map
Limit on Ideal Shear Strength
Low T plasticity by dislocation glide and
twinning Limited by Discrete
obstacles Lattice Friction
Displacive
Power Law by Glide / Glide Climb Limited
by Glide processes Lattice-Diffusion
controlled climb Core-Diffusion controlled
climb Breakdown Harper-Dorn Dynamic
Recristallization
Mixed
Diffusional
Diffusional Flow Limited by Lattice-Diffusion
(Nabarro-Herring) GB Diffusion
(Coble) Interface-reaction controlled
Frost, Harold Jefferson, and M. F. Ashby.
"Deformation-mechanism maps The plasticity and
creep of metals and ceramics. Pergamon Press,
Oxford, UK (1982).
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Coble (Surface)
Nabarro-Herring (Lattice)
, Low T
, High T
DsurfacegtgtDbulk
Dsurface comparable Dbulk
1 Image from http//en.wikipedia.org/wiki/Frank_
Nabarro 2 Image from http//news.stanford.edu/ne
ws/2009/july27/herring-physics-obit-073109.html 3
Brown, L.M. Frank Reginald Nunes Nabarro MBE
Biographical Memoirs of Fellows of the Royal
Society (2009)
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Hall-Petch Smaller is Stronger
Copper
M.A. Meyers et al. Mechanical Properties of
nanocrystalline materials Progress in Materials
Science 51 (2006), 427-556
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Surface Dislocation Nucleation

• Nucleation Stress value computed
• Transition predicted from collective dislocation
  dynamics to signle dislocation nucleation
• Geomtry Long Range Elastic Interaction
  (Corner/Image)

T. Zhu et al. Temperature and Strain-Rate
Dependence of Surface Dislocation Nucleation PRL
100, (2008) 025502
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Ultra-Strength Materials

• This implies that properties (thermal
  conductivity, transmittance, etc) can be modified
  while in the elastic regime.

DoE (Taguchi)
2
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Elastic-Strain Engineering
E
M G K M
Synthesize
Strain and Measure Force
Measure Strain
Numerical Prediction

• Graphene
• Carbon Nanotubes
• Bulk Nanocrystals

• AFM

• Synchrotron
• In-situ TEM

• DFT

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Cool (or Hot?) Application Photovoltaics
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Challenges - Thermalization Losses -
Non-Absorption Losses
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1 Image http//en.wikibooks.org/wiki/Microtechn
ology/Semiconductors 2 Ji Feng et al.
Strain-Engineered Artificial Atom as a
Broad-Spectrum Solar Energy Funnel Nature (2012)
Accepted