Abstract
Abstract An alternative process to the aluminium full back side is necessary to realize high efficiency solar cell on thin wafers. Even if metallization paste manufacturers deliver paste that minimize the wafer bowing to 1.5 mm for wafer lower than 200 μm, it is more and more critical to process wafers thinner than 150 μm with full aluminium back side. The objective of this work is to demonstrate on monocristalline silicon wafer that boron back surface field (BSF), diffused from BCl3 gas source or from oxide doped layer like Boron Silicon Glass (BSG), is as efficient as full back side aluminium BSF. In addition this work deal with integration of different passivation layer optimised to passivate high boron doped layer at the backside of a bifacial solar cell. The best efficiency obtained on monocristalline wafers shows an increase in efficiency of 0.9% absolute compare to our standard process with full aluminium back side. According to the process optimised for monocristalline wafers, the process was transferred on multicristalline wafer. Even if the gain in current, for bifacial solar cell, compared to standard process is confirmed, the high temperature process for boron diffusion, activate electrically lot of intra-grain defects and decrease the solar cell performance. A correlation between Light Beam Induced Current (LBIC) and electroluminescence highlight local shunt and explain why the solar cell performance with boron BSF diffused at the back side is impacted. An alternative solution is also proposed to reduce the thermal budget of boron diffusion and improve the solar cell efficiency.
Published Version
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