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Ferritin-based nanocrystals for solar energy harvesting

This research focuses on the synthesis and characterization of ferritin-based nanocrystals with multiple band gaps for efficient solar energy harvesting. The study explores the potential of these nanocrystals to increase the efficiency of solar cells through the use of multiple absorbers. The results suggest promising prospects for developing more efficient solar energy harvesting technologies.

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Ferritin-based nanocrystals for solar energy harvesting

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  1. 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

  2. Stereogram of ferritin This work: Co(O)OH, Mn(O)OH, Ti(O)OH 8 nm 8 nm

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

  4. Previous work on ferrihydrite, Fe(O)OH Indirect gap Direct transition Defect State Higher transition Band gap Eg = 1.92 – 2.24 eV, depending on size direct = 2.92 – 3.12 eV, depending on size

  5. Recent band gap results Mn(O)OH Ti(O)OH Co(O)OH Solar cells: Increase efficiency via multiple absorbers Direct transition Eg 2.19-2.29 eV 1.60-1.65 eV 1.93-2.15 eV Total range: Eg from 1.60 – 2.29 eV

  6. Efficiency calcs: Shockley-Queisser model n-type p-type CB EF EF VB Photo-current Recombination current  depends on operating voltage Arrows: direction of electrons

  7. 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) Lose too much to phonons From Wikipedia, “Shockley–Queisser_limit”

  8. A Review of the Equations maximum power I V Solar spectrum constant with V concentration factor Blackbody spectrum exponential with V Then compare Pmax to total solar energy to define the efficiency

  9. Extension to multiple layers, “i” = “ith layer” Irecomb, i (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 Maximize P w.r.t. all of the Vi’s (coupled nonlinear eqns) Then compare Pmax to total solar energy to define the efficiency General method of: De Vos, J Phys D (1980)

  10. Maximizing Power, Independent Cells Black line: solar spectrum eff = 38%, w/o 1.1 eV layer eff = 51%, with 1.1 eV layer

  11. Maximizing Power, Current Matched eff = 42%, with 1.1 eV layer Vtot = 5.5 V

  12. Can we get the electrons out of the ferritin?Gold nanoparticle formation hv AuIII Au Au0 e- Metal Oxide e- Citrateox Citrate

  13. Ti(O)OH and Gold Nanoparticles Ti(O)OH nanoparticle core Protein shell Gold nanoparticles attached to surface 20 nm TEM image

  14. 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. 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

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

  17. Nanocrystal synthesis: Fe-, Co-, Mn- and Ti(O)OH Co2+ + H2O2 Mn2+ + O2 Fe2+ + O2 M(O)OH

  18. Typical Raw Data Blank, solution with no ferritin Control With ferritin

  19. 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-axis 20

  20. Absorption to measure band gaps Figures from Yu and Cardona, Fundamentals of Semiconductors (2010) (1967) (1955)

  21. Solar cells Example: quantum dot solar cell Our goal: increase efficiencies via multiple absorbers

  22. New Mn-Oxide Synthesis Method

  23. Typical Raw Data Blank, solution with no ferritin Control With ferritin

  24. QDSC band diagram Image: Jordan Katz https://www.ocf.berkeley.edu/~jordank/Jordan_Katz/Research.html

  25. Numerically solving the system Coupled nonlinear equations Initial guess via solving the uncoupled layers Try different materials; also some optimization for particle size

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