Improved performance on multi-crystalline silicon solar cells by optimizing aluminum back surface field process

Abstract

Traditional aluminum back surface field (Al-BSF) multi-crystalline silicon (mc-Si) solar cells have been favored by the market for a long time due to their low cost. However, the Al-BSF formed after Al screen printing and firing restrict the doping profile and the passivation effect. Here we report a scheme to produce the Al-BSF in advance (before phosphorus diffusion) by using the additional preparation processes consisting of three successive steps, namely Al screen printing, annealing and Al removing. The Al removing process helps optimize the depth of Al-BSF, while the annealing process and the subsequent diffusion process helps improve the doping profiles. As a result, the passivation performance of such improved Al-BSF is greatly improved in terms of electrochemical capacitance voltage measurements (ECV) and minority carrier lifetime characterizations. Also the average conversion efficiency for such mc-Si cells with improved Al-BSF reaches 18.73%, which is 0.27% higher than that of the same batch of traditional Al-BSF solar cells. This approach represents an efficient method for further improving mc-Si solar cells.