Plasma enhanced chemical vapor deposition (PECVD) is applied to deposit boron silicate glasses (BSG) acting as boron diffusion source during the fabrication of n‐type silicon solar cells. We characterize the resulting boron‐diffused emitter after boron drive‐in from PECVD BSG by measuring the sheet resistances Rsheet,B and saturation current densities J0,B. For process optimization, we vary the PECVD deposition parameters such as the gas flows of the precursor gases silane and diborane and the PECVD BSG layer thickness. We find an optimum gas flow ratio of SiH4/B2H6= 8% and layer thickness of 40 nm. After boron drive in from these PECVD BSG diffusion sources, a low J0,B values of 21 fA/cm2 is reached for Rsheet,B = 70 Ω/□. The optimized PECVD BSG layers together with a co‐diffusion process are implemented into the fabrication process of passivated emitter and rear totally diffused (PERT) back junction (BJ) cells on n‐type silicon. An independently confirmed energy conversion efficiency of 21.0% is achieved on 15.6 × 15.6 cm2 cell area with a simplified process flow. This is the highest efficiency reported for a co‐diffused n‐type PERT BJ cell using PECVD BSG as diffusion source. A loss analysis shows a small contribution of 0.13 mW/cm2 of the boron diffusion to the recombination loss proving the high quality of this diffusion source. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)

No abstract

No 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%.

No abstract