by Debra Vogler, senior technical editor, Photovoltaics World
July 8, 2009 – Mallinckrodt Baker announced two new solar cell surface modifier products, the PV-162 and PV-200, that will enhance solar cell efficiency by up to 0.7% absolute, increasing cell energy output for both inline and batch solar cell manufacturing processes.
The new processes enable efficiency enhancing benefits of post-emitter surface modification for both in line and batch c-Si solar cell manufacturing, according to John Harris, global marketing manager, photovoltaics materials, at Mallinckrodt Baker. “Previously, our PV-160 product was applicable only to inline processing,” he told PV World, “but these two new products have opened up another part of the c-Si market — batch processing, a large segment of the market that we couldn’t address before (Figure 1).”
Figure 1. Schematic overview of the solar cell manufacturing process. (Source: Mallinckrodt Baker)
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The products work to increase cell efficiency by reducing the amount of recombination sites at or near the surface of the emitter. “By doing this, we are either (depending on the solar cell product) increasing the fill factor, increasing the open circuit voltage, or increasing the short circuit current or some combination of these three,” explained Harris. He noted that the PV-162 increases all three attributes; the PV-200 only increases the open circuit voltage and short circuit current.
PV-162 is a second-generation post-emitter surface modification product that remains compatible with current manufacturing equipment used with the PV-160 chemistry. It is a 100% water-soluble formulation requiring no intermediate rinse.
PV-200 solar cell surface modifier extends the efficiency enhancing benefits of post-emitter surface modification to batch processes that use phosphorus oxychloride (POCl3 or POCL) doping technology. Additionally, its tunable etch enables optimization of the manufacturing process. Its low bath temperature (20-40°C) reduces energy expenditures while providing extended bath life, reducing overall cost-of-ownership.
Figure 2 shows the removal of phosphosilicate glass (PSG) remnants by emitter optimization technology. “PSG is formed during the doping process when the wafers are fed through an in line furnace to drive phosphorus atoms into the crystal lattice,” Harris told PV World. “PSG has to be removed prior to the next step (ARC) and an HF bath is usually used to do this.” He noted that the SEM shows a simple HF dip that leaves PSG residue, which creates recombination sites in the emitter and lowers cell efficiency. “Our emitter optimization removes this residue and creates a more optimal emitter, reducing recombination sites in the emitter and improving cell efficiency.” — D.V.
Figure 2. SEM micrographs showing the removal of PSG remnants by emitter optimization technology. Bar is 60μm (Source: Mallinckrodt Baker)