CMPL SEMICON
National Institute of Physics
University of the Philippines - Diliman
Solar cells have an important coating that is composed of transparent conducting oxides (TCO) responsible for transporting the electrons in the solar cell module. For the TCO to be effective in its function it must have good conductivity and good transmission in the light spectrum in which the solar cell operates. The TCO layer must also be able to filter out ultraviolet (UV) light since it degrades the solar cell.
Fluorine-doped tin oxide (FTO) is one of the promising TCO thin film material for solar applications. FTO is an optically transparent and electrically conducting material usually deposited on glass. Moreover, FTO thin films are stable at high temperatures, resistant to strong acids and bases at room temperature, resistant to mechanical abrasion, and have very good adhesion to many substrates.
Nebulized spray pyrolysis is a simple and inexpensive technique for depositing FTO. Using a medical nebulizer, a solution prepared from stannous chloride (SnCl2• 2H20), ammonium fluoride (NH4F), and ethanol is sprayed onto preheated glass substrates. Thermal decomposition takes place in the heated substrate giving rise to a continuous film of FTO.
Transparent Conducting Oxides
One of the cheapest TCOs available is zinc oxide (ZnO) doped with aluminum (Al) due to the abundance of both these materials. The addition of aluminum serves to increase the amount of electrons that the TCO coating can transport. A solution of zinc acetate and AlCl3· 6H2O was prepared and then sprayed on silicon and glass substrates at high temperatures in a fabrication process called spray pyrolysis. The high temperatures evaporate the aqueous mixture and leaves behind a film of Al-doped ZnO.