Fabrication of superhydrophillic and graded index antireflective double layer coating for solar photovoltaics module using aerosol impact deposition assembly

In the study presented, a double layer graded refractive indices silicon dioxide nano-porous coating was deposited on glass substrates to reduce the optical losses in solar photovoltaics using the technique referred as Aerosol Impact Deposition Assembly (AIDA). The proposed system consists of the gaseous precursors namely Silane, Oxygen and Helium that ionize in the plasma reaction chamber of AIDA to form silica nanoparticles. The nanoparticles size and shape can be controlled by the flow rates of each precursor gas, pressure difference in reaction and deposition chamber, and the proportion of helium gas. The assembly accelerates the silica nanoparticles towards deposition chamber with high impact speed using a small slit nozzle where they are coated on a glass/silicon substrate placed on a moving stage. Using this technique, thin film silica nanoparticle double layer was coated and characterized using Transmission electron microscope (TEM), Scanning Electron Microscope and Atomic Force Microscope to determine the particle shape, size, and morphology respectively. The average nanoparticle size determined from TEM image was 12.5 nm while the porosity of the top and bottom thin films was 60% and 42%, respectively. The UV-Spectroscopy results showed that reflection losses were decreased from 9% to 2% in a broad range of solar spectrum i.e., wavelength 300-1200 nm. In addition, due to high porosity and sufficient roughness, the coated thin film showed excellent self-cleaning and antifogging properties with water contact angle less than 5^o. Moreover, short current density of the cell was increased by 1.4 mA/cm², from 39.1 mA/cm² to 40.5 mA/cm², which shows enhancement in the electrical performance of the solar cell.