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.
Transcript of "Nano solar cells"
Nano solar cells 1
Contents• Introduction• Solar cells• Solar product availability• Thin film materials• Cadmium Telluride solar cells• CIGS solar cells• CIGS manufacturing process• Nanosolar• Conclusion 2
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 3
Photovoltaic Solar CellsGenerate 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 4
Current Technology: Photovoltaic CellsShort 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. 5
…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 6
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. 7
• 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. 8
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 9
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) 11
Sources of energy loss Thermalization of excess energyEfficiency limits CB Below band gap photons not absorbed VB 12
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 13
Comparison of materialsTechnology 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 14
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) 15
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 cellsSearch for other abundant materials… 16
CIGS solar cellsCIGS - 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 17
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 18
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. 19
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 22
PV Solutions for Urban Solarcells Future of Nano solar Applications 23