Investigation of Firing Conditions for Optimizing Aluminum-Doped p+-layer of Crystalline Silicon Solar Cells

Abstract

Screen printing technique followed by firing has commonly been used as metallization for both laboratory and industrial based solar cells. In the solar cell industry, the firing process is usually conducted in a belt furnace and needs to be optimized for fabricating high efficiency solar cells. The printed-Al layer on the silicon is rapidly heated at over 800°C which forms a layer of back surface field (BSF) between Si-Al interfaces. The BSF layer forms p-p + structure on the rear side of cells and lower rear surface recombination velocity (SRV). To have low SRV, deep p + layer and uniform junction formation are required. In this experiment, firing process was carried out by using conventional tube furnace with N₂ gas atmosphere to optimize V oc of laboratory cells. To measure the thickness of BSF layer, selective etching was conducted by using a solution composed of hydrogen fluoride, nitric acid and acetic acid. The V oc and pseudo efficiency were measured by Suns-V oc to compare cell properties with varied firing condition.