Diffusion‐free high efficiency silicon solar cells

Abstract

Traditional POCl3 diffusion is performed in large diffusion furnaces heated to ~850 C and takes an hour long. This may be replaced by an implant and subsequent 90‐s rapid thermal annealing step (in a firing furnace) for the fabrication of p‐type passivated emitter rear contacted silicon solar cells. Implantation has long been deemed a technology too expensive for fabrication of silicon solar cells, but if coupled with innovative process flows as that which is mentioned in this paper, implantation has a fighting chance. An SiOx/SiNy rear side passivated p‐type wafer is implanted at the front with phosphorus. The implantation creates an inactive amorphous layer and a region of silicon full of interstitials and vacancies. The front side is then passivated using a plasma‐enhanced chemical vapor deposited SiNxHy. The wafer is placed in a firing furnace to achieve dopant activation. The hydrogen‐rich silicon nitride releases hydrogen that is diffused into the Si, the defect rich amorphous front side is immediately passivated by the readily available hydrogen; all the while, the amorphous silicon recrystallizes and dopants become electrically active. It is shown in this paper that the combination of this particular process flow leads to an efficient Si solar cell. Cell results on 160‐µm thick, 148.25‐cm2 Cz Si wafers with the use of the proposed traditional diffusion‐free process flow are up to 18.8% with a Voc of 638 mV, Jsc of 38.5 mA/cm2, and a fill factor of 76.6%. Copyright © 2012 John Wiley & Sons, Ltd.

Finite- vs. infinite-source emitters in silicon photovoltaics: Effect on transition metal gettering

“…The implant was activated by annealing at 850°C for 20 minutes. These implant parameters are typical for silicon solar cells [4,5]. After the implant activation, the wafers were cooled at 4°C/min to either i) 700°C and pulled out of the furnace to room temperature, or underwent a low temperature anneal (LTA) at ii) 700°C for 5.5 hours or iii) 620°C for 8 hours.…”

“…While this topic is thoroughly researched for phosphorus emitters operating under infinite-source diffusion, the topic of gettering with finite-source emitters is still in its infancy [1][2][3]. Finite-source emitters offer benefits, such as, better blue response and no phosphosilicate glass formation [3][4][5].…”

Impact of Iron Precipitation on Phosphorus-Implanted Silicon Solar Cells

“…Ion implantation offers numerous benefits over the traditional dopant in-diffusion, such as 1) higher blue response and lower surface recombination velocity with easy fine-tuning of the dopant profile [1], [2]; 2) possible reduction in processing steps through in-situ oxide passivation and the avoidance of phosphorus-silicate glass and laser edge isolation [1], [3]; 3) high run-to-run and wafer-to-wafer homogeneity thanks to precise spatial control of dopants [4], [5]; and 4) streamlined process into advanced solar cell architectures [3], [6], [7].…”