Dispensing of etching paste and inkjetting of diffusion barrier for MWT solar cell processing

MWT (metal wrap through) solar cells address the target of reaching higher efficiencies, while only requiring two additional process steps compared with conventional solar cells. To further reduce the production costs of MWT solar cells one possibility is to reduce the breakage, which mainly occurs during the production from cell to module and is caused by laser grooves on the rear. These laser grooves isolate the n- from the p-contacts and almost run across the whole cell. For this purpose two alternative isolation methods have been developed; one is based on the etching paste SolarEtch® SiD, which etches a groove that replaces the laser groove; the other developed method is based on the diffusion barrier SolarResist TM. Apart from the advantage of less breakage the damaging impact of the laser on the crystalline structure of the wafer is avoided. The functionality of the developed methods has been verified on appropriate test structures. Furthermore the adaptability of the methods has been proved by processing functional MWT solar cells with pFF values of around 82%. At the same time the comparability with the laser groove has been shown by producing reference cells. The reliability was shown during repeated runs of MWT cell production.