Optimization of Rear Side Al Fire-Through Contacts for AlOx-SiNx Rear Passivated Bifacial Cz p-PERC cells

While standard monofacial p-type passivated emitter and rear cells (PERC) require laser contact opening (LCO) of the rear side (RS) passivation layers, bifacial (bifi) PERC allow for application of RS Al fire-through contact (FTC) fingers that etch through the RS passivation layers during the contact firing step [1] with the help of the added glass frit. Hence the bifi PERC process chain can be skipped by the relatively demanding laser step, making the further growth of bifi PERC in market share [2] more promising. So far, successful RS passivation layer etching and subsequent back surface field (BSF) formation have been achieved with FTC for various RS passivation types [1, 3, 4]. However, for AlOX/SiNX passivation - the PERC RS passivation type with the highest market share [2] - BSF formation has not been successful yet. Combined with generally higher contact area for FTC, the missing BSF leads to higher recombination, compared to the non-FTC (NFTC) bifi PERC approach. Therefore the aim of this work is to reduce the recombination of FTC to the level of NFTC and thus optimizing Al-FTC bifi p-type PERC with RS AlOX/SiNX passivation.