1. 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. Colton Stephen Erickson, Cameron Olson, Jacob Embley Physics Department, Brigham Young University Dr. Richard Watt Trevor Smith Chemistry Department, Brigham Young University Ref: Erickson et al., Nanotechn. 26, 015703 (2015) Funding: Utah Office of Energy Dev., BYU Physics Dept

2. J.S. Colton, Ferritin nanocrystals for solar energy harvesting Stereogram of ferritin 8 nm This work: Co(O)OH, Mn(O)OH, Ti(O)OH

3. Bandgaps via optical absorption Xenon Arc Lamp Spectrometer Iris Lens Chopper Sample in cuvette Photodiode RefSignal Lock-in Amplifier Computer steps through wavelength of spectrometer and records data from lock-in

4. J.S. Colton, Ferritin nanocrystals for solar energy harvesting Indirect gapDirect transition Defect State Band gap Higher transition E g = 1.92 – 2.24 eV, depending on size direct = 2.92 – 3.12 eV, depending on size Previous work on ferrihydrite, Fe(O)OH

5. J.S. Colton, Ferritin nanocrystals for solar energy harvesting Recent band gap results Co(O)OH Mn(O)OHTi(O)OH EgEg Direct transition Total range: E g from 1.60 – 2.29 eV 2.19-2.29 eV 1.60-1.65 eV 1.93-2.15 eV Solar cells: Increase efficiency via multiple absorbers

6. J.S. Colton, Ferritin nanocrystals for solar energy harvesting Efficiency calcs: Shockley-Queisser model EFEF EFEF CB VB n-typep-type Photo-current Recombination current  depends on operating voltage Arrows: direction of electrons

7. J.S. Colton, Ferritin nanocrystals for solar energy harvesting Shockley-Queisser Results, 1961 E g = 1.1 eV (silicon)  eff. = 29% Best E g = 1.34 eV  eff. = 33.7%, “SQ limit” From Wikipedia, “Shockley–Queisser_limit” (Using actual solar spectrum rather than SQ’s 6000K blackbody model of the sun) Lose too much to phonons Too much unabsorbed

8. J.S. Colton, Ferritin nanocrystals for solar energy harvesting A Review of the Equations Then compare P max to total solar energy to define the efficiency I V exponential with V maximum power Blackbody spectrum constant with V concentration factor Solar spectrum

9. J.S. Colton, Ferritin nanocrystals for solar energy harvesting Extension to multiple layers, “i” = “i th layer” Then compare P max to total solar energy to define the efficiency Maximize P w.r.t. all of the V i ’s (coupled nonlinear eqns) Not zero, because photons are absorbed by upper layers Radiative recombination from layer just above Radiative recombination from layer just below I recomb, i (top layer: i=1) General method of: De Vos, J Phys D (1980)

10. J.S. Colton, Ferritin nanocrystals for solar energy harvesting Maximizing Power, Independent Cells eff = 38%, w/o 1.1 eV layer eff = 51%, with 1.1 eV layer Black line: solar spectrum

11. J.S. Colton, Ferritin nanocrystals for solar energy harvesting Maximizing Power, Current Matched eff = 42%, with 1.1 eV layer V tot = 5.5 V

12. J.S. Colton, Ferritin nanocrystals for solar energy harvesting e-e- e-e- Au hv Citrate Citrate ox Au III Au 0 e-e- Metal Oxide Can we get the electrons out of the ferritin? Gold nanoparticle formation

13. 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

14. 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.

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

16. 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

17. J.S. Colton, Ferritin nanocrystals for solar energy harvesting Fe(O)OH FeFe FeFe Nanocrystal synthesis: Fe-, Co-, Mn- and Ti(O)OH

18. J.S. Colton, Ferritin nanocrystals for solar energy harvesting M(O)OH Co 2+ + H 2 O 2 Fe 2+ + O 2 Mn 2+ + O 2 Nanocrystal synthesis: Fe-, Co-, Mn- and Ti(O)OH

19. J.S. Colton, Ferritin nanocrystals for solar energy harvesting Typical Raw Data Control With ferritin Blank, solution with no ferritin

20. J.S. Colton, Ferritin nanocrystals for solar energy harvesting Data Analysis 20 We arrive at the band gap by plotting α 2 and α 1/2 versus photon energy then extrapolating a linear fit to the x-axis Absorption coefficient: Direct gap Indirect gap

21. J.S. Colton, Ferritin nanocrystals for solar energy harvesting Absorption to measure band gaps Figures from Yu and Cardona, Fundamentals of Semiconductors (2010) (1967) (1955)

22. J.S. Colton, Ferritin nanocrystals for solar energy harvesting Solar cells Our goal: increase efficiencies via multiple absorbers Example: quantum dot solar cell

23. J.S. Colton, Ferritin nanocrystals for solar energy harvesting New Mn-Oxide Synthesis Method

24. J.S. Colton, Ferritin nanocrystals for solar energy harvesting Typical Raw Data Control With ferritin Blank, solution with no ferritin

25. 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

26. 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