The comparison of MWT solar cell fbrication by two novel and stable approaches

This study focuses on two novel approaches (co-firing and non-cofiring) for metal wrap through (MWT) solar cell fabrication and compares their electric properties using DuPont MWT specialized paste. The co-firing process involves 3 printing steps followed by co-firing of metallization contacts. The non-cofiring process involves sequential processing steps: first printing and firing of rear aluminum and front Ag finger; thereafter via and rear busbar printing and IR drying at 400°C. The best cell efficiency of 17.0% was demonstrated in this work based on 200 μm thick multi-crystalline silicon having an area of 125×125 mm2. On average, MWT cells showed 0.3~0.4% efficiency gain compared to conventional cells, due to 2% higher short circuit current (Isc). Although the shunting resistance of conventional solar cells is still slightly better than the two MWT approaches, results indicate that both MWT cells maintained good shunt performance and did not negatively impact fill factor (F.F.). The depth of vias is only 200 μm so that the contribution of via paste on Rs was concluded to be negligible compared to other dominating resistances. The electrical characteristics demonstrated in this work indicate that both MWT approaches proposed are reliable and industrially feasible.