Nano solar cells utilize tiny nanorods or nanoparticles to convert sunlight into electricity in a thin, inexpensive layer. These dye-sensitized or "nano" solar cells consist of a thin layer of nanorods dispersed in a polymer that can be easily mass produced. While efficiency is still low, nano solar cells have potential for low-cost electricity generation due to inexpensive manufacturing using solution-based coating or printing techniques.
2. Contents
• Introduction
• Solar cells
• Solar product availability
• Thin film materials
• Cadmium Telluride solar cells
• CIGS solar cells
• CIGS manufacturing process
• Nanosolar
• Conclusion
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3. What is a Solar Cell
• A device that converts solar energy directly to electricity by the photovoltaic
effect
– It supplies voltage and current to a
resistive load (light, battery, motor)
– It supplies DC power
• Solar Module or Solar Panel
– Solar Module: Solar cells are wired in series
– Solar Panel: Solar Modules are assembled together and placed into a frame
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4. Photovoltaic Solar Cells
Generate electricity directly from sunlight
2 Main types:
Single-crystal silicon (traditional)
Silicon-based solar
• Widespread cell
• Expensive to manufacture
Dye-sensitized (“nano”)
• Newer, less proven
• Inexpensive to manufacture
• Flexible
Dye-sensitized
solar cell
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5. Current Technology: Photovoltaic Cells
Short Version: Light in, electricity out.
• If the energy of the incident photons equals or exceeds the band gap energy of the
material, then the valence electrons will get excited, and enter the conduction band.
• They are susceptible to an electric field and form electricity.
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6. …But Not All Energy is Converted…
• Like chloroplasts in plants, solar cells can only absorb specific wavelengths of
light.
• In both, light that isn‟t absorbed is either transmitted through or reflected back.
• Whether a certain wavelength of lights gets absorbed depends on its energy.
Chlorophyll molecules absorb
blue and red light, but reflect
green light
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7. Nanotechnology To The Rescue
• Chemists at the University of California, Berkeley, have designed a „plastic‟
solar cell which utilizes tiny nanorods to convert light into electricity
• These solar cells consist of a layer of tiny nanorods only 200 nanometers thick,
dispersed within a polymer.
• So far these cells can produce only 0.7 volts, so they are only appropriate for
low-power devices.
• These cells could be mass produced because the nanorod layers could simply
be applied in separate coats.
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8. • Nanorods behave as wires because when they absorb light of a specific wavelength
they generate electrons.
• These electrons flow through the nanorods until they reach the aluminum electrode
where they are combined to form a current and are used as electricity.
This type of cell is cheaper to manufacture than conventional ones for two main reasons.
• Plastic cells are not made from silicon, which can be very expensive.
• Manufacturing these cells does not require expensive equipment like
conventional silicon based solar cells.
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9. How a Dye-Sensitized Cell Works
• Light with high enough energy excites electrons in dye molecules.
• Excited electrons infused into semiconducting TiO2, transported out of cell
• Positive “holes” left in dye molecules
• Separation of excited electrons and “holes” creates a voltage
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11. Thin film solar cells
• Made by depositing one or more thin layers (thin film)
of photovoltaic material on a substrate.
• A thin film of semiconductor is deposited by low cost methods
• Less material is required
• Cells can be flexible and integrated directly into roofing material.
• Categorized based on the material used
– Amorphous silicon (a-Si) and other thin-film silicon (TF-Si)
– Cadmium telluride (CdTe)
– Copper indium gallium selenide (CIS or CIGS)
– Dye-sensitized solar cell (DSC)
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12. Sources of energy loss
Thermalization of excess
energy
Efficiency limits CB
Below band gap photons
not absorbed
VB
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13. Advantages of thin films
• Efficient and high performing materials
– Direct bandgap semiconductors
– Better energy output –kWh/KW
– CIGS record at 20%+ conversion efficiency
• Significantly reduced costs
– Less material usage
– Not affected by silicon supply shortages
– Potential for improving costs throughout value chain
• Advanced manufacturing techniques
– Fewer processing steps
– Monolithic integration of circuits
– Automation
• Better aesthetics
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14. Comparison of materials
Technology Maximum Advantages Disadvantages
Demonstrate
d Efficiency
for small cells
a-Si 12.2% Mature Low efficiency
manufacturing High equipment costs
technology
CdTe 16.5% Low-cost Medium efficiency
manufacturing Rigid glass substrate
CIGS 19.9% High efficiency Film uniformity challenge
Glass or flexible on large substrates
substrates
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15. Cadmium Telluride (CdTe) Solar Cells
glass
CdS/CdTe
• Direct bandgap, Eg=1.45eV
• High efficiency (Record:16.5%;
Industry: 11%)
• High module production speed
• Long term stability (20 years)
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16. Disadvantages of Cadmium Telluride
• Cadmium is toxic
• Tellurium is a limited reserve
– First Solar used half of the world‟s annual production of Te in
2009
– The cost of Te could go up a lot before affecting the price of solar
cells
Search for other abundant materials…
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17. CIGS solar cells
CIGS - Copper Indium Gallium (di)Selenide
• The material is a solid solution of copper indium selenide (1.0 eV)
and copper gallium selenide (1.7 eV )
• Because the material strongly absorbs sunlight, a much thinner film is required
than of other semiconductor materials. The CIGS absorber is deposited on a
glass backing, along with electrodes to collect current
• CIGS solar cells has efficiencies greater than 20% as compared to 10% for
silicon based solar cell
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18. CIGS solar cells
Shell Solar, CA
Global Solar Energy, AZ
Energy Photovoltaics, NJ
ISET, CA
ITN/ES, CO
NanoSolar Inc., CA
DayStar Technologies, NY/CA
MiaSole, CA
HelioVolt, Tx
Solyndra, CA
SoloPower, CA
Wurth Solar, CIS Solartechnik and
Solarion, Germany
Solibro, Sweden
CISEL, France
Showa Shell and Honda, Japan
Mosar Baer and Rays Expert, India
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19. CIGS manufacturing process
• The most common vacuum-based process co-
sputters CIG, then anneals the resulting film
with a selenide vapor to form the final CIGS
structure.
• NanoSolar uses a non-vacuum-based process
that mixes the materials into a liquid then
deposits nano-particles of the precursor
materials on the substrate and then sinters it.
• SoloPower uses electroplating to apply the
CIGS layer.
• Another technique is to dissolve the material
into a liquid, apply it to a surface and bake it.
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22. Future of Nano solar cells
• There is huge demand for use of renewable resources due to its low
carbon footprint with solar energy is leading the race as a viable
alternative for fossil fuels
• Low efficiency and expensive silicon wafers, makes nano solar cells
the future of solar panels
• Along with silicon and CIGS, other materials are being studied which
produce higher efficiencies and at a low cost
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23. PV Solutions for Urban Solarcells
Future of Nano solar Applications
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Silicon wafers are 150 µm thick, the wafers demand multiple processing steps before they can be integrated into a module. On the contrary, thin-film solar cells utilize only a 1-4 µm-thick layer of semiconducting material to produce electricity, thus requiring less processing and fewer materials.
World record efficiency = 20.0 %.Many companies are evaporating, printing, sputtering and electro-depositing it.Handling a 4-element compound is tough.
Sputering: Atoms are ejected from a solid due to bombardment of energetic particlesSintering: Creating objects from powders
TCO - transparent conductive oxideIn chemistry, a precursor is a compound that participates in the chemical reaction that produces another compound.