Design and development of front and back contact solar cells with selective poly-Si passivating contact on the front and local Al contact on the rear

Abstract

We present 22.5% efficient large area (M2), n-type rear junction biPoly™ solar cells featuring selective poly-Si based passivation on the front and full area poly-Si on the rear side. The metal contacts to the selective poly-Si fingers on the front are formed by screen-printing fire-through Ag paste. Two different approaches are compared for the contact formation on the rear side – using fire-through silver-aluminium paste are and non-fire – through Al paste. Prior to the screen-printing the Al paste, laser is used to pattern the local contact openings (LCO) wherein the Al paste alloys with the c-Si substrate during high temperature firing forming contacts. The impact of the LCO pitch, Si content in Al paste and the firing temperature is studied by meticulously designed experiments. We further develop a 3 dimensional model of the biPoly™ solar cells and try to explain the trends observed in the experimental results.