Investigation of unusual shunting behavior due to phototransistor effect in n-type aluminum-alloyed rear junction solar cells

N-type silicon wafers have been found to offer numerous advantages over p-type silicon wafers, such that they are becoming more widely used for manufacturing high-efficiency commercial solar cells. This paper focuses on work done on n-type cell structures with a screen-printed aluminum-alloyed rear junction, laser-doped selective emitter and light-induced plated front contacts to suit large-scale commercial production. However, with such a cell structure we report unusual linear shunting behavior that is only present under illumination but disappears under dark conditions. It was shown that such a phenomenon can be represented by a phototransistor model. In fact, such shunting effects are found to have detrimental impacts on the cell short-circuit current density (Jsc) and fill factor (FF), which limits the efficiency of cells in this work to 12%.