N-type al-alloyed rear junction silicon solar cells with implanted front surface field

N-type wafer, which has high minority carrier lifetime and high tolerance of metal impurities, can provide the advantage such as no LID (Light Induced Degradation) for developing high efficiency solar cells. The ion implantation technology becomes an emerging method to be applied in photovoltaic (PV) industrial field. This technique was known as doping method to form the junction at room temperature. It has been proven to be superior to the conventional diffusion process, which requires high operating temperature and additional oneside isolation step. In this work, n⁺/n/p⁺ rear emitter cells are fabricated by using 2.2-2.8 ohm-cm 156 mm n-type CZ wafers. The front surface field (n⁺ layer) is implanted by phosphorus (P) species and rear junction (p⁺ layer) is formed by printed Al paste, which is eventually treated by rapid thermal process. The key improvements of reduction of the Auger recombination associated with selective front surface field (s-FSF), enlargement and planarization of rear surface for more uniform rear junction have been demonstrated. Furthermore, the optimization of thinner thermal-oxide layer is presented in order to reduce the optical losses at front surface field. Therefore, these approaches could improve 1 mA/cm² in J_sc and 3 mV in V_oc, resulting in higher cell efficiency of 0.44%. Accordingly, the champion cell efficiency, V_oc, J_sc and FF could be obtained as high as 18.89%, 643.1 mV, 37.15 mA/cm² and 79.06%, respectively.