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

Abstract

Recently, n-type crystalline Si (c-Si) cells with frontside (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.

Influence of the boron emitter profile on V OC and J SC losses in fully ion implanted n-type PERT solar cells

“…To summarize the discussion of the J 0e,met values, we found so far no striking evidence for an additional recombination path besides the metal/Si interface recombination. This is in agreement with recent findings from Liang et al that no Si–Al alloy formation was observed in structural investigations of Ag/Al screen‐printed contacts. The rather moderate J 0e,met values are reflected in the rather moderate V OC losses.…”

Emitter recombination current densities of boron emitters with silver/aluminum pastes

“…They assume a deep metal penetration into the silicon to simulate the increased surface recombination. On the other hand, Liang et al [13] recently reported that they found no evidence of aluminum diffusion from the Ag/Al paste into the silicon. The remaining hypothesis (ii) to (iv) are to be proven and further experiments on these hypothesis are ongoing.…”

Role of aluminum in silver paste contact to boron-doped silicon emitters

“…Different conduction models may also need to be considered. 25 For example, nanoAg colloids in the interfacial glass layer would also contribute to low contact resistivity. 12 But here we limit our studies in the fritless paste contacting with the boron-doped Si emitters.…”