REDUCTION OF THE FILM THICKNESS IN PHOTOVOLTAIC SOLAR CELLS FABRICATION

Abstract

Photovoltaic solar cells are an attractive option to electric energy generation, but is still expensive if compared with traditional sources. One way to reduce the cost of solar cells is to use a thinner coating thickness. In the slot coating process, lower flow rates results in lower film thickness. However, there are physical and operational limits related with the method. One of them is the low-flow limit. This phenomena is observed at low film thickness, the downstream meniscus invades the gap between downstream slot die lip and the substrate creating a permanent and undesirable defect in the substrate. This work presents the numerical simulation of the slot coating process of Newtonian fluids, with the volume of fluid technique in order to determine the low-flow limit. The solution domain of the 2D governing equations is restricted to the downstream section of the slot coating die. It is verified that the minimal wet coating thickness increase with the capillary number, which means that thinner films will be obtained at lower substrate velocity. Further on the discussion about operational limits, highlighting the low flow limit, it is included a bibliographic revision about the oil production, photovoltaic solar cells and coating methods. Keywords: Two-phase flow, Low-flow limit, Slot coating, Volume of Fluid.