Fast screen printing and curing process for silicon heterojunction solar cells
Within this work, we present industrially feasible and well-applicable methods to effectively lower the costs of silicon heterojunction (SHJ) solar cell processing by reducing cycle time of the screen printing and the subsequent thermal curing step using industrial process equipment. For six out of nine tested low-temperature silver pastes, process velocity in screen printing could be doubled compared to typical printing velocity, equaling a reduction of cycle time in this process step by 1 sec. Using a convection curing process supported by infrared radiation (IR) and an adapted process temperature, curing dwell time of SHJ solar cells can be substantially reduced from 10 min to 0.5 min, allowing for higher throughput and/or smaller machine dimensioning (footprint). Furthermore, an improved solar cell conversion efficiency by up to +0.1 %abs is demonstrated which is likely to be caused by the so-called light soaking effect. When applying an additional process step with IR at high illumination density, a further increase of cell efficiency by up to +0.3 %abs can be achieved. With regard to the soldered interconnection, the combination of a short and hot curing process and their diametrical effects on adhesion properties resulted in similar peel force values as for the reference process. Also, treatment of the SHJ solar cells with a laser-based IR light soaking process does not exhibit a significant effect on peel forces. In summary, our work shows that process times of the metallization for SHJ solar cells can be strongly reduced while maintaining cell performance and applicability for soldered interconnection.