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Studies on Backside Al-Contact Formation in Si Solar Cells: Fundamental Mechanisms

  • Bhushan Sopori (a1), Vishal Mehta (a1), Przemyslaw Rupnowski (a1), Helio Moutinho (a1), Aziz Shaikh (a2), Chandra Khadilkar (a2), Murray Bennett (a3) and Dave Carlson (a3)...

Abstract

We have studied mechanisms of back-contact formation in screen-printed Si solar cells by a fire-through process. An optimum firing temperature profile leads to the formation of a P-Si/P+- Si/ Si-Al eutectic/agglomerated Al at the back contact of a Si solar cell. Variations in the interface properties were found to arise from Al-Si melt instabilities. Experiments were performed to study melt formation. We show that this process is strongly controlled by diffusion of Si into Al. During the ramp-up, a melt is initiated at the Si-Al interface, which subsequently expands into Al and Si. During the ramp-down, the melt freezes, which causes the doped region to grow epitaxially on Si, followed by solidification of the Si-Al eutectic. Any agglomerated (or sintered) Al particles are dispersed with Si. Implications on the performance of the cell are described.

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