Keming Ren1 Veysel Unsur1 Ahrar Chowdhury1 Tang Ye1 Abasifreke Ebong1

1, Chemistry, University North Carolina at Charlotte, Charlotte, North Carolina, United States

Fire through dielectric (FTD) contact is the dominant technology for contacting a commercial silicon solar cell because of its low-cost and high throughput attributes. During the FTD process, the glass frits in the Ag paste melt and etch the dielectric (anti-reflecting layer) first, to have Ag metal contact directly to the bulk Si. The redox reaction between the glass frits melting and dielectric etching leads to the formation of a recrystallized glass layer, which distributes within the Ag gridlines and bulk Si emitter surface, and silver nano-particles, which are mainly silver alloys (Ag2Te and PbTe) encapsulated in the glass layer. When without the Ag2Te and PbTe nano-particles/colloids, due to the existence of glass layer, silver gridlines rarely directly contact with the bulk silicon and electrons have to tunnel through the glass layer. However, in this work, Ag2Te and PbTe are semimetals which have very narrow bandgaps. The existence of Ag2Te and PbTe nano-particles/colloids in the glass layer can change the electrical property of the glass layer. Thus, the specific contact resistance of silver gridlines cannot be calculated based on simplified metal-semiconductor contacts. The possible electron transport on the silver/silicon interface includes: 1. through silver gridline contact directly with bulk silicon; 2. tunneling through an ultrathin glass layer; 3. through Ag2Te and PbTe nano-colloids assisted tunneling; 4. through multistep tunneling. This suggests that the contact resistivity in the presence of Ag2Te and PbTe nano-particles/colloids is independent of the inverse square root of emitter peak surface concentration. Lower contact resistances were measured in the presence of Ag2Te and PbTe nano-particles on the silicon emitter with relatively low peak surface concentration.