Industrial bifacial n‐type silicon solar cells applying a boron co‐diffused rear emitter and an aluminum rear finger grid

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 POCl 3 diffusion, as boron dopant source during the POCl 3 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 PERCþ solar cells. The Al finger grid enables bifaciality and results in up to 8.5 mm 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%.

Bifacial p-Type PERC Solar Cell with Efficiency over 22% Using Laser Doped Selective Emitter

“…All the time, n-type bifacial cells were paid close attention to by many PV researchers all the time [24][25][26], and a higher efficiency of solar cell was obtained [27,28]. Currently n-type wafer is much more expensive than p-type wafer and n-type PERC cell process is very complex.…”

Present status and future perspectives of bifacial PERC+ solar cells and modules

“…3) Presently, industrial bifacial solar cell concepts are mainly applying n-type wafers such as passivated emitter and rear totally diffused (PERT) solar cells. [6][7][8][9] However, a challenge of these bifacial PERT cells is that they typically require screen-printed silver (Ag) finger grids on both wafer sides and hence consume a high amount of expensive Ag paste. Also, the n-PERT cells use single sided boron and phosphorus doping which requires additional or other process steps compared to p-type PERC cells and hence may increase manufacturing costs.…”