Current Conduction Mechanism of Front-Side Contact of N-Type Crystalline Si Solar Cells With Ag/Al Pastes

Recently, n-type crystalline Si (c-Si) cells with front-side (FS) metallization Ag/Al paste have attracted considerable attention. However, a clear understanding of current conduction mechanism is still lacking. We report here the results of our microstructural investigation of the interfacial contact region using electron microscopy techniques. In optimally fired cells, we did not find any Al-Si eutectic layer on the emitter surface that would support a regrowth mechanism as found during the back surface field formation process commonly practiced to create the full plane Al back contact of p-type industrial solar cells. The presence of SiN x antireflection coating has possibly altered significantly the chemistry between Si and Al. The observed microstructures suggest that the current conduction is predominantly tunneling through ultrathin interfacial glass, assisted by the presence of nano-Ag colloids. We believe this mechanism is similar to the current conduction model we have proposed previously for FS Ag-contact of p-type c-Si solar cells with Ag paste.