Enabling thin wafers for today's high efficiency silicon solar cells

摘要

Reducing consumption of silicon through the use of thin wafers promises to significantly reduce the cost for photovoltaic electricity. To enable thinner wafer usage, the mechanical and electrical properties of the cell must be preserved and ultimately improved upon. Today's optimized solar cell structure applies aluminum to the back side of the silicon wafer to create back surface field or BSF that improves overall cell efficiency. Because silicon and aluminum have different thermal expansion coefficients, a bow is created in the wafer during the high temperature firing process. Tradeoffs in efficiency, breakage and yield have slowed the industries natural migration to thinner wafers. While new cell structures show the promise of overcoming these challenges, these new structures are more complex and may not be readily available to existing cell lines. This paper reports on the optimization of a simple low-temperature process that has successfully removed the bow without degrading cell electrical or mechanical performance and does not require significant materials optimization efforts. We have achieved equivalent cell efficiencies and mechanical properties after bow removal for silicon solar cells below 180μm, 160μm, etc. The performance of this simple process will be presented in this paper.