20% Efficient screen-printed and aluminum-alloyed back-contact back-junction cells and interconnection scheme of point-shaped metalized cells

A back-contact back-junction silicon solar cell is presented that was exclusively structured and metalized by screen-printing technology. On n-type base material the emitter was formed by locally printed and alloyed aluminum structures in a co-firing process. By a varying emitter coverage on the rear the influence on the collection probability and thus the short-circuit current density is analyzed by light beam induced current (LBIC) measurements. Efficiencies of up to 20% were realized and independently confirmed by Fraunhofer ISE CalLab. Two-dimensional simulations of the cell structure are performed and agree well with the processed cell. Variations of several parameters show room for further efficiency increase. Furthermore a new module concept for back-contact cells is presented where the metallization on cell level is point-shaped. The lateral conductance of collected carriers is enabled on module level by a structured printed circuit board. On the contacts an adhesive agent is screen-printed in order to make the aluminum contacts solderable. Afterwards a soldering paste is screen-printed which connects the cell and the printed circuit board or foil during a reflow process. This concept overcomes the restriction in cell size of back-contact back-junction modules due to thick copper layer.