BELT FURNACE VERSUS STANDARD TUBE FURNACE TO PRODUCE Al BSF

摘要

Aluminum is the most used material to produce back surface field (BSF) in solar cells and low cost or more efficient fabrication processes have been studied. The purpose of this paper is to compare n~+pp~+ solar cells with BSF obtained by Al diffused in belt and standard furnace. Aluminum was deposited by e-beam evaporation. Cells processed in standard furnace were fabricated in pilot production with optimized process. In order to compare the results, the process to perform the Al-BSF in the belt furnace was also optimized. In this process, the belt speed during aluminum diffusion and firing temperature of the metallization pastes were experimentally optimized considering the electric characteristics of the solar cells. The minority carrier lifetime was measured after thermal steps and diffusion length was obtained from LBIC measurements. We observed that solar cells processed in belt furnace present the average diffusion length 45% lower, but the uniformity of this parameter is higher. The efficiency of 15.2% was obtained when solar cells with Al-BSF were processed in the belt furnace and dry air. This result is similar to the efficiency of 15.4% measured in solar cells fabricated in the standard furnace using high purity gases.