1. Advanced Photovoltaics
Including New Materials and Approaches; GRID Applications
By Zachary Koop, with motivation from Dr. Stan Burns

2. Outline Silicon and Solar New Developments in PV
Grid Integration and Micro-Grids
Sources
5 Key Points

3. Silicon Materials as Solar Devices
Si is a semiconductor (bandgap ~ 1.1eV)
Si is the second most abundant resource on Earth, 27.7% of Earth’s crust
Our economy is adept at processing Si (think “Silicon Valley”).
Si is not the most efficient material for absorbing the Sun’s light.
The theoretical maximum efficiency of Si solar cells is 30%.
Education at Jlab.org

4. Solar Cells: The Basic Structure
Incident photons excite electrons beyond the bandgap caused by the pn-junction.
Electrons captured by metal contact, and then complete a circuit, powering a load.
The electron are returned to their lowest possible state.
*Traditional silicon absorb a relatively small portion of the solar spectrum.
NREL
NREL

5. Monocrystalline, Polycrystalline, Amorphous
Most Efficient (23%), Most Expensive
Efficiency is ~ 15%
Least Efficient (<10%), Least Expensive
Wikimedia Commons, public domain

6. High-Concentration III-V Multijunction Solar Cells
Layering multiple semiconductor materials to generate more current from Sun’s photons of various wavelengths.
Popular materials: Gallium-Indium-Arsenide, Gallium-Indium-Phosphide
Law of diminishing returns
NREL
NREL
NREL

7. Hydride Vapor-Phase Epitaxy (HVPE) Manufacturing
Low-cost, ultra-high efficiency.
Addresses two major costs of III-V solar devices, epitaxial growth and single-crystalline substrates used for growth (seed).
Targets production tandem cells with goal achieving of >30% efficiency.
Essentially, takes what used to be a series production process and makes it parallel.
The idea is to drive down the marginal cost of production using new manufacturing technologies.
National Renewable Energy Lab

8. Electro-Absorption Modulators and the Quantum Confined Stark Effect
Two promising traits:
Would allow the absorption spectra of a solar cell to be shifted.
By introduces new nanopaticle material, can achieve additional absorption peaks.
Koop, Gansen, King, Bailey
Koop, Gansen, King, Bailey

9. Pictures of actual nano-particle layers using Atomic Force Microscopy.
Koop, Gansen, King, Bailey

10. Organic Dye-Sensitized Photovoltaics: “Gratzel Cell”
Quasi-Semiconductor that is cheaper to manufacture.
Efficiencies theorized to reach 15%.
Relatively new, won the 2010 Millennium Technology Prize (aka Nobel Prize)
‘gcell.com’
National Renewable Energy Lab
National Renewable Energy Lab

11. How it works: “Photoelectrochemical System”
Incident photons excite electrons in the TiO2 dye-sensitized layer.
Transparent Conducting Oxide Glass Substrate
Titanium Dioxide
Dye-Sensitized Titanium Dioxide
Triiodide Electrolyte
(Graphite) Carbonized Layer e- Ec Ev
Koop, Elliott

12. How it works: “Photoelectrochemical System”
Incident photons excite electrons in the TiO2 dye-sensitized layer.
e- absorbed into TiO2 layer and transported to the TCO layer.
Transparent Conducting Oxide Glass Substrate
Titanium Dioxide
Dye-Sensitized Titanium Dioxide
Triiodide Electrolyte
(Graphite) Carbonized Layer e- Ec Ev
Koop, Elliott

13. How it works: “Photoelectrochemical System”
Incident photons excite electrons in the TiO2 dye-sensitized layer.
e- absorbed into TiO2 layer and transported to the TCO layer.
e- transported to opposite electrode generating a current.
Current
Transparent Conducting Oxide Glass Substrate
Titanium Dioxide
Dye-Sensitized Titanium Dioxide
Triiodide Electrolyte
(Graphite) Carbonized Layer
Koop, Elliott

14. How it works: “Photoelectrochemical System”
Incident photons excite electrons in the TiO2 dye-sensitized layer.
e- absorbed into TiO2 layer and transported to the TCO layer.
e- transported to opposite electrode generating a current.
e- are transported back to TiO2 sensitized-dye layer through iodide layer.
Current
Transparent Conducting Oxide Glass Substrate
Titanium Dioxide
Dye-Sensitized Titanium Dioxide
Triiodide Electrolyte
(Graphite) Carbonized Layer
Koop, Elliott

15. Grid-Integration: Solar Energy Grid Integration System
American Grid was developed technology a century ago.
Used to be as simple as supply and demand.
Consumption was predictable, production was static.
Today, consumption is still predictable, but production is dynamic.
Use software to optimize to generation/load balance.
Develop forms of energy storage.
Wikipedia

16. Derivation from Modern Survival Blog, see Appendix
Derivation from Modern Survival Blog, see Appendix. Uses data from US Census Report.

17. Microgrids
Allow energy to exist where no expansive energy grid pre-exists.
Underdeveloped parts of the world.
Decentralizes power generation.
Complex, unsophisticated, and expensive.
National Renewable Energy Lab

19. Summation of Sources Education.jlab.org www.rsc.org www.nrel.gov
Koop, Gansen, King, Bailey Research on ZnMgO EAM’s
Koop, Elliott Research on Organic Gratzel Cells
ModernSurvivalBlog.com w/ data from US Census Report
Commons.wikimedia.com: public domain pictures available for educational usage

20. 5 Key Points
The maximum efficiency for traditional Si solar cells is projected to be ~30
Si is a popular solar material because it is non-toxic, has a variable bandgap (semiconductor), abundant, and is a traditional material.
A majority of solar research is aimed at “fine tuning” solar technology.
Organic non-semiconductor solar cells (“Gratzel cells”) are a promising new technology with efficiencies approaching 15%.
The United States grid cannot sustain the future projection of renewables (solar energy) without radical innovations to technologies such as energy storage.