Solar Cell Materials
Solar cells, also known as photovoltaic (PV) cells, are devices that convert sunlight directly into electricity. Various materials and fabrication methods are used to create these cells, with silicon being the most widely used material due to its abundance and suitability for photovoltaic applications.
More than 80% of solar cells currently produced are crystalline silicon solar cells.
Nearly all of the other 20% are developed as amorphous silicon solar cells.
Silicon-Based Solar Cells
- Monocrystalline Silicon: High efficiency, made from a single crystal structure, but more expensive to produce.
- Multi-crystalline or Polycrystalline Silicon: Made by casting molten silicon, cheaper but less efficient due to crystal imperfections.
- Amorphous Silicon: A type of thin-film solar cell, created by depositing silicon on substrates like glass or plastic. It is less efficient but cheaper and versatile in application.
Thin-Film Solar Cells
Thin-film solar cells use very thin layers of semiconductor materials, which makes them lightweight and flexible. These cells can be used in various applications, such as:
- Rooftop Solar Shingles
- Roof Tiles
- Building Facades
- Glazing for Skylights or Atria
Materials: Include amorphous silicon, copper indium Diselenide (CuInSe2), cadmium telluride (CdTe), and gallium arsenide.
Emerging Technologies
Research in photovoltaic technology is exploring new materials and structures to improve efficiency and reduce costs. Some of these emerging technologies include:
- Dye-Sensitized Solar Cells (DSC): Use organic or inorganic semiconductors, offering low-cost fabrication options.
- Third-Generation Solar Cells: Research is ongoing in multi-junction devices and quantum-dot absorbers, which promise higher efficiencies and new applications.
Factors Influencing Solar Cell Material Choice
- Absorption Coefficient: Determines how well the material absorbs light.
- Bandgap Energy: The energy difference between the valence band and the conduction band in a semiconductor material, crucial for solar cell efficiency.
Factors Limiting the Efficiency of the Cell
- Wavelength of solar spectrum: Cell response to only a portion of wavelength available in the solar spectrum. Photon with wavelength > 1.1 μm does not have sufficient energy to create electron–hole pair in silicon cell.
- Temperature: Normal operating temperature of silicon cells can reach 60°C in peak sunlight and these temperature decreases the efficiency of the cells.
- Mounting of the cells: Solar cells need to be mounted on something that can help remove heat, like an aluminium plate. If they aren’t properly mounted, they might overheat and work less efficiently.
- Arrangement and maintenance of solar cell: The negative side of the cells usually faces the sun and has antireflection coatings. These coatings should be protected from dust, bird dropping, by a clear plastic or glass cover. Accumulated dust on the cover will reduce the output power by about 10%.
- Position of the cell: The cell or panel should be positioned either facing south in the north of equator or facing north in the south of equator for maximum power output and fixed panel applications.