Increased wafer yield for solar cells in top and bottom regions of cast multicrystalline silicon

We present lifetime measurement and solar cell results of wafers cut out of the top and bottom region of a cast multicrystalline silicon block. Lifetime profiles of vertically cut wafers demonstrate the effect of two different emitter diffusion processes in the top and bottom region. The solar cell results on adjacent wafers show relatively high values especially for the top of the ingot. By processing solar cells on horizontally cut wafers we investigated the dependence of the cell parameters of the height in the top and bottom of the ingot. In the bottom region a process with a phosphorus-aluminium-codiffusion yields the best results. In the top a modified process with longer time on high temperature increases the cell efficiency further. In comparison with a normal phoshorus-diffusion process, an increased yield of up to 50 wafers per brick is possible by using adjusted processes.