J.S. Colton, Ferritin nanocrystals for solar energy harvesting Ferritin-based nanocrystals for solar energy harvesting APS March Meeting, Mar 4, 2015 Dr

J.S. Colton, Ferritin nanocrystals for solar energy harvesting

Ferritin-based nanocrystals for solar energy harvesting

APS March Meeting, Mar 4, 2015

Dr. John S. ColtonStephen Erickson, Cameron Olson, Jacob Embley

Physics Department, Brigham Young University

Dr. Richard WattTrevor Smith

Chemistry Department, Brigham Young University

Ref: Erickson et al., Nanotechn. 26, 015703 (2015)

Funding: Utah Office of Energy Dev., BYU Physics Dept


Stereogram of ferritin

8 nm 8 nm

This work: Co(O)OH, Mn(O)OH, Ti(O)OH

Bandgaps via optical absorption

Xenon Arc Lamp

Spectrometer

Iris Lens

Chopper

Sample in cuvette

Photodiode

Ref Signal

Lock-in AmplifierComputer steps through wavelength of spectrometer and records data from lock-in


Indirect gap Direct transition

Defect State

Band gapHigher transition

Eg = 1.92 – 2.24 eV,depending on size

direct = 2.92 – 3.12 eV,depending on size

Previous work on ferrihydrite, Fe(O)OH


Recent band gap results

Co(O)OH Mn(O)OH Ti(O)OH

Eg

Direct transition

Total range: Eg from 1.60 – 2.29 eV

2.19-2.29 eV1.60-1.65 eV

1.93-2.15 eV

Solar cells: Increase efficiency via multiple absorbers


Efficiency calcs: Shockley-Queisser model

EFEF

CB

VB

n-type p-type

Photo-current

Recombination current depends on operating voltage

Arrows: direction of electrons


Shockley-Queisser Results, 1961

• Eg = 1.1 eV (silicon) eff. = 29%

• Best Eg = 1.34 eV eff. = 33.7%, “SQ limit”

From Wikipedia, “Shockley–Queisser_limit”

(Using actual solar spectrumrather than SQ’s 6000K blackbody model of the sun)

Lose too much to phonons

Too much unabsorbed


A Review of the Equations

Then compare Pmax to total solar energyto define the efficiency

I

V

exponential with V

maximum power

Blackbody spectrum

constant with V

concentration factor

Solar spectrum


Extension to multiple layers, “i” = “ith layer”

Then compare Pmax to total solar energy to define the efficiency

Maximize P w.r.t. all of the Vi’s(coupled nonlinear eqns)

Not zero, because photons are absorbed by upper layers

Radiative recombination from layer just aboveRadiative recombination from layer just below

Irecomb, i

(top layer: i=1)

General method of: De Vos, J Phys D (1980)


Maximizing Power, Independent Cells

eff = 38%, w/o 1.1 eV layereff = 51%, with 1.1 eV layer

Black line: solar spectrum


Maximizing Power, Current Matched

eff = 42%, with 1.1 eV layerVtot = 5.5 V


e-

Au

hv

Citrate Citrateox

AuIII

Au0

e-

Metal Oxide

Can we get the electrons out of the ferritin?Gold nanoparticle formation


Ti(O)OH and Gold Nanoparticles

Ti(O)OH nanoparticle core

Proteinshell

Gold nanoparticlesattached to surface 20 nm

TEM image


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.



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


Fe(O)OHFe

Fe

Nanocrystal synthesis: Fe-, Co-, Mn- and Ti(O)OH


M(O)OH

Co2+ + H2O2Fe2+ + O2Mn2+ + O2

Nanocrystal synthesis: Fe-, Co-, Mn- and Ti(O)OH


Typical Raw Data

Control

With ferritin

Blank, solution with no ferritin


Data Analysis

20

We arrive at the band gap by plotting α2 and α1/2 versus photon energy then extrapolating a linear fit to the x-axis

Absorption coefficient:

Direct gap

Indirect gap


Absorption to measure band gaps

• Figures from Yu and Cardona, Fundamentals of Semiconductors (2010)

(1967)

(1955)


Solar cells

Our goal: increase efficiencies via multiple absorbers

Example: quantum dot solar cell


New Mn-Oxide Synthesis Method


Typical Raw Data

Control

With ferritin

Blank, solution with no ferritin


QDSC band diagram

Image: Jordan Katzhttps://www.ocf.berkeley.edu/~jordank/Jordan_Katz/Research.html


Numerically solving the system

• Coupled nonlinear equations• Initial guess via solving the uncoupled layers• Try different materials; also some optimization for

particle size

Documents

J.S. Colton, Ferritin nanocrystals for solar energy harvesting Ferritin-based nanocrystals for solar energy harvesting APS March Meeting, Mar 4, 2015 Dr