Industrial bifacial n‐type silicon solar cells applying a boron co‐diffused rear emitter and an aluminum rear finger grid. Issue 11 (13th July 2016) - Dullweber, Thorsten
Abstract : The solar industry is introducing p‐type monofacial passivated emitter and rear cells (PERC) into mass production. However, the efficiency of p‐type PERC cells is subject to light‐induced degradation (LID). In this paper, we introduce a novel solar cell design which we name BiCoRE as abbreviation of "bifacial co‐diffused rear emitter." The BiCoRE cell process is very similar to the high volume proven PERC process sequence, but uses LID stable n‐type wafers. A boron silicate glass (BSG) silicon nitride (SiN z ) stack at the rear side of the BiCoRE cells acts as protection layer against texturing and POCl3 diffusion, as boron dopant source during the POCl3 co‐diffusion as well as passivation layer. The rear contacts are formed by laser contact opening (LCO) and screen printing of an Al finger grid similar to the recently introduced PERC+ solar cells. The Al finger grid enables bifaciality and results in up to 8.5 μm deep aluminum back surface fields (Al‐BSFs) and up to 21.1% conversion efficiency obtained with n‐type reference solar cells. The multifunctional BSG/SiN z stack demonstrates up to 20.6% conversion efficiency with BiCoRE solar cells. When illuminated from the rear side, the BiCoRE cells exhibit conversion efficiencies up to 16.1% which corresponds to a bifaciality of 78%.