Monocrystalline photovoltaic cells

Monocrystalline cells are photovoltaic solar cells made from monocrystalline silicon, a high-purity semiconductor material. They are characterized by their uniform color, often black or dark blue, and their flat surface. These cells are manufactured by cutting thin wafers from a single-crystal silicon ingot. Thanks to their ordered crystalline structure and purity, they offer higher energy efficiency than polycrystalline cells, typically between 18 and 22%. They are also more expensive to produce, due to the complex manufacturing process and material waste.

Structure of a monocrystalline photovoltaic cell

The composition of a monocrystalline solar cell follows a logical structure to enable conversion of sunlight into electricity. Here are the main layers and components of a monocrystalline cell:

Here’s the structure of a monocrystalline photovoltaic cell from front to back:

  1. Anti-reflective coating : A thin layer that reduces reflection of sunlight and increases light absorption by the cell. Anti-reflective coatings are usually composed of silicon oxide or silicon nitride.
  2. Front contact grids : Thin conductive strips, usually made of silver, that collect electrons generated by the cell and transport them to the busbars. Contact grids are designed to minimize sunlight loss while ensuring good electrical conductivity.
  3. Emitter layer (P zone): A thin layer of silicon wafers doped with P-type impurities (such as boron), creating a zone of positive charge near the cell surface.
  4. PN junction : The region where the emitter layer (P zone) meets the base layer (N zone), creating an electric field that separates the positive and negative charges generated by the absorption of sunlight.
  5. Base layer (N zone): The majority of the cell is made up of monocrystalline silicon wafers doped with N-type impurities (such as phosphorus), creating a zone of negative charge.
  6. Back contacts : A conductive layer, usually made of aluminum, covers the back of the cell, collecting electrons and transporting them to the busbars or interconnector ribbons. For cells with passivated rear contacts (PERC), there is also a passivating layer between the base layer and the rear contacts, improving the cell’s efficiency.
  7. Busbars : Wider conductive strips that connect the front contact grids and rear contacts to the interconnector ribbons, enabling the electricity generated by the cell to be transferred to the other cells in the solar panel.

Comparing cell types

Heterojunction cells combine the advantages of monocrystalline and thin-film cells, offering even higher efficiency and better temperature tolerance. Thin-film cells are less efficient than monocrystalline cells, but are flexible, lightweight and less temperature-sensitive, making them ideal for specific applications. Multi-junction cells offer exceptional efficiency thanks to their ability to absorb different wavelengths of light, but they are expensive and mainly used in high-output applications such as aerospace.

Technical innovations

The technologies of bifacial panels, cut cells (half cells), PERC cells (Passivated Emitter and Rear Cell) and Tiling Ribbon Technology can be combined with monocrystalline solar cells to improve their performance and efficiency. Here are the main advantages of these technologies when applied to monocrystalline cells:

  1. Bifacial panels enable monocrystalline cells to capture sunlight on both their front and rear faces, increasing overall energy production and improving energy efficiency.
  2. Half-cell technology cuts monocrystalline cells in half to reduce internal resistance and shading losses, improving overall panel efficiency and shade tolerance.
  3. PERC cells add a passivating layer to the back of the monocrystalline cell, reflecting unabsorbed photons back into the cell for another chance at absorption. This improves overall efficiency and energy production.
  4. Tiling Ribbon Technology uses flat, seamless conductive ribbons to connect monocrystalline cells together. It reduces efficiency losses due to soldering and increases the active surface area of the cells, enabling higher efficiency and improved aesthetics.