30μm fine-line printing for solar cells

The width of screen printed lines can be decided by the emulsion opening of a screen mask of screen printing, but actually the printed width is very much affected by the roughness of a substrate and the rheology of the paste used. Finger lines of solar cells should be as narrow as possible to increase sunlight usage efficiency. Hence the printed condition to realize fine lines should be optimized by adjusting the mesh counts of the screen mask used and the rheology of the paste depending on the texture size of wafers. Screen print has to print on a flat surface of a substrate, but the screen print in solar cells is required to print on a rough surface like a textured surface, which causes widening printed lines due to the bleeding of paste leaking out through the gap between the flat emulsion surface of the screen and the textured surface of a silicon wafer. The effect of texture size on printed line width is studied by changing etching condition for texturing to make a large texture (roughly 8μm) and a small texture (roughly 3μm) on mono-crystalline wafers. And, the proper adjustment on screen printing conditions are accomplished to realize 30μm lines on the small textured wafer with normal silver paste by using screen mask of ultra-fine mesh.