J.S. Colton, Ferritin nanocrystals for solar energy harvesting
Ferritin-based nanocrystals
for solar energy harvesting
Dr. John S. Colton
Stephen Erickson, Cameron Olson, Jacob Embley
Physics Department, Brigham Young University
Dr. Richard Watt
Trevor Smith
Chemistry Department, Brigham Young University
Funding: Utah Office of Energy Dev., BYU Physics Dept
Ref: Erickson et al., Nanotechn. 26, 015703 (2015)
APS March Meeting, Mar 4, 2015
J.S. Colton, Ferritin nanocrystals for solar energy harvesting
This work:
Stereogram
of ferritin
Co(O)OH,
Mn(O)OH,
Ti(O)OH
8 nm
8 nm
Bandgaps via optical absorption
Spectrometer
Xenon
Arc Lamp
Iris
Lens
Sample in
cuvette
Photodiode
Chopper
Computer steps through
wavelength of spectrometer
and records data from lock-in
Ref
Signal
Lock-in Amplifier
J.S. Colton, Ferritin nanocrystals for solar energy harvesting
Previous work on ferrihydrite, Fe(O)OH
Indirect gap
Direct transition
Defect State
Band gap
Eg = 1.92 – 2.24 eV,
depending on size
Higher
transition
direct = 2.92 – 3.12 eV,
depending on size
J.S. Colton, Ferritin nanocrystals for solar energy harvesting
Recent band gap results
Co(O)OH
Mn(O)OH
Solar cells:
Direct transition
Increase efficiency via
multiple absorbers
Ti(O)OH
Eg
1.60-1.65 eV
1.93-2.15 eV
Total range: Eg from 1.60 – 2.29 eV
2.19-2.29 eV
J.S. Colton, Ferritin nanocrystals for solar energy harvesting
Efficiency calcs: Shockley-Queisser model
n-type
p-type
CB
EF
VB
Photo-current
Recombination current
 depends on operating voltage
Arrows: direction of electrons
J.S. Colton, Ferritin nanocrystals for solar energy harvesting
Shockley-Queisser Results, 1961
• Eg = 1.1 eV (silicon)  eff. = 29%
• Best Eg = 1.34 eV  eff. = 33.7%, “SQ limit”
Too much
unabsorbed
(Using actual solar spectrum
rather than SQ’s 6000K
blackbody model of the sun)
From Wikipedia, “Shockley–Queisser_limit”
Lose too much
to phonons
J.S. Colton, Ferritin nanocrystals for solar energy harvesting
A Review of the Equations
Solar spectrum
constant with V
concentration factor
Blackbody spectrum
exponential with V
maximum
power
I
V
Then compare Pmax to total solar energy
to define the efficiency
J.S. Colton, Ferritin nanocrystals for solar energy harvesting
Extension to multiple layers, “i” = “ith layer”
(top layer: i=1)
Not zero, because photons are
absorbed by upper layers
Radiative recombination
from layer just above
Radiative recombination
from layer just below
Irecomb, i
General method of: De Vos, J Phys D (1980)
Maximize P w.r.t. all of the Vi’s
(coupled nonlinear eqns)
Then compare Pmax to total solar
energy to define the efficiency
J.S. Colton, Ferritin nanocrystals for solar energy harvesting
Maximizing Power, Independent Cells
Black line: solar spectrum
eff = 38%, w/o 1.1 eV layer
eff = 51%, with 1.1 eV layer
J.S. Colton, Ferritin nanocrystals for solar energy harvesting
Maximizing Power, Current Matched
eff = 42%, with 1.1 eV layer
Vtot = 5.5 V
J.S. Colton, Ferritin nanocrystals for solar energy harvesting
Can we get the electrons out of the ferritin?
Gold nanoparticle formation
hv
AuIII
Au0
Au
e-
Metal Oxide
eCitrate
Citrateox
J.S. Colton, Ferritin nanocrystals for solar energy harvesting
Ti(O)OH and Gold Nanoparticles
Ti(O)OH
nanoparticle core
Protein
shell
Gold nanoparticles
attached to surface
20 nm
TEM image
J.S. Colton, Ferritin nanocrystals for solar energy harvesting
Conclusions
• We’ve got a variety of ferritin-based nanoparticles
• Multiple band gaps  Large theoretical efficiencies
• Maybe we can make an efficient solar cell
• Future work: other materials, redox potentials, etc.
J.S. Colton, Ferritin nanocrystals for solar energy harvesting
J.S. Colton, Ferritin nanocrystals for solar energy harvesting
Why is ferritin interesting?
•
•
•
•
•
Native ferrihydrite mineral
Template for nanocrystals
Self healing against photocorrosion
Photo-oxidation catalyst
Can be arranged in ordered 2D and 3D arrays
This work:
Co(O)OH
Mn(O)OH
Ti(O)OH
J.S. Colton, Ferritin nanocrystals for solar energy harvesting
Nanocrystal synthesis: Fe-, Co-, Mn- and Ti(O)OH
F
e
F
e
Fe(O)OH
J.S. Colton, Ferritin nanocrystals for solar energy harvesting
Nanocrystal synthesis: Fe-, Co-, Mn- and Ti(O)OH
Mn2+
+ O2
Fe2+ +
O2
M(O)OH
Co2+ + H2O2
J.S. Colton, Ferritin nanocrystals for solar energy harvesting
Typical Raw Data
Blank, solution
Control
with no
ferritin
With ferritin
J.S. Colton, Ferritin nanocrystals for solar energy harvesting
Data Analysis
Absorption coefficient:
Direct gap
Indirect gap
We arrive at the band gap by plotting α2 and α1/2 versus
photon energy then extrapolating a linear fit to the x-axis20
J.S. Colton, Ferritin nanocrystals for solar energy harvesting
Absorption to measure band gaps
(1967)
(1955)
•
Figures from Yu and Cardona, Fundamentals of Semiconductors (2010)
J.S. Colton, Ferritin nanocrystals for solar energy harvesting
Solar cells
Example: quantum dot solar cell
Our goal: increase efficiencies via multiple absorbers
J.S. Colton, Ferritin nanocrystals for solar energy harvesting
New Mn-Oxide Synthesis Method
J.S. Colton, Ferritin nanocrystals for solar energy harvesting
Typical Raw Data
Blank, solution
Control
with no
ferritin
With ferritin
J.S. Colton, Ferritin nanocrystals for solar energy harvesting
QDSC band
diagram
Image: Jordan Katz
https://www.ocf.berk
eley.edu/~jordank/J
ordan_Katz/Researc
h.html
J.S. Colton, Ferritin nanocrystals for solar energy harvesting
Numerically solving the system
• Coupled nonlinear equations
• Initial guess via solving the uncoupled layers
• Try different materials; also some optimization for
particle size