Application of screen printing by photovoltaic cell realization

The screen printing is used in the photovoltaic for the realization of solar cells´s contacts. The screen printing is divided on this one of the front side and that one of the back side. Ag paste is used as the filling for screen printing. The drying of the spread paste follows after the screen printing of the silicon wafer. The higher stability of the print and the elimination of humidity before the firing are the purpose of this drying. The firing is founded on Ag diffusion from the contact to the desired depth in the silicon wafer. The temperature of firing is oscillating from 600degC to 900degC by the common thick films layers. These temperatures are high enough to change the silicon under the contact. The optimal print of the front side is 60 mum wide and 10-15 mum high. It is necessary to control the print during the screen printing because it can occur to the print´s defects (irregular width, bad resolution,...). These defects can be caused by the damaged membrane of screen, by the unsuitable speed or the wrong angle of spreading paste by a spatula