The investigation on the front surface field of aluminum rear emitter N-type silicon solar cells

Abstract

N-type solar cells with aluminum rear emitter provide high power conversion efficiency and overcome light induced degradation. Meanwhile, since the processes are realized on the existing P-type cells, the fabrication cost gets lower for N-type solar cells. Front surface field (FSF) is an important part in this structure. The functions of FSF are similar to that of Al back surface field in P-type cells. FSF enhances carrier collection ability, increases the cells’ open-circuit voltage, as well as increases the efficiency. In this paper, the FSF profiles were investigated. The appropriate surface concentration was around 4×1020cm−3, meanwhile the depth should be kept between 0.25μm and 0.3μm from the experiment. A too low concentration cannot provide a strong field effect passivation, while a too high concentration will introduce much more recombination centers. A thin FSF layer increased the resistance, while a thick FSF layer made the short-circuit current decrease, because of the degradation of photoelectric response at the short wavelength. Thermal oxidation was introduced in the process. The FSF profiles were also studied. The minority lifetime and efficiency were enhanced after oxidation. The surface concentration of FSF should be adjusted to around 3×1019cm−3. The best cell efficiency has reached to 19.93%, tested by 18th Institute of China Electronics Group Corporation.