A team of researchers from the Institute for Science and Technology Hokuriku (JAIST), and JSR Corporation, a company specializing in the production of rubbers and plastics, has succeeded for the first time ever, to make a photovoltaic cell with thin layers of amorphous silicon from liquid silicon.
Cells thin-film amorphous silicon represent a cheaper alternative to crystalline silicon cells that dominate the market (90% modules sold), but whose production cost is higher. However, their conversion efficiency is much lower (7% to 9% in industrial cons 15% to 20% for crystalline silicon cells). They are currently manufactured by chemical vapor deposition assisted by plasma (method for depositing thin films from a gas). The development of a production method by coating would reduce production costs and thus increase interest in technology.
With this in mind that the team of JAIST and JSR headed by Professor Tatsuya Shimoda, worked to develop a mode of production from liquid silicon. To do this, she first developed a “silicon ink”, by dissolving the polysilane (SiH 2 chain) in a special solvent. She then developed a coating technique that allows to form regular layers and flawless polysilane on a substrate. The heating of these layers is used to extract hydrogen and obtain solid layers of amorphous silicon.
By this technique, the team managed to produce three inks silicon, a pure silicon, boron doped another and a third doped with phosphorus. The successive use of these three inks helped produce a photovoltaic cell with thin film silicon pin type, ie consisting of a positively doped layer (p), a layer of pure silicon (i – intrinsic) and a negatively doped layer (n).
The conversion efficiency of this cell is still low (0.51%). However, researchers believe they can improve performance by increasing the thickness of the intrinsic layer (currently 120 nm against 250 nm for a cell fabricated by chemical vapor deposition).