HIGH EFFICIENCY ACHIEVED ON POCl3 EMITTER SI SOLAR CELLS WITH LOW SATURATION CURRENT DENSITY WHILE REDUCING AG CONSUMPTION BY 40-60

摘要

The market price of Ag has fluctuated 10X over the past 10 years and has impacted the manufacturing cost of Si solar cells and the price of Si PV. Reduction of Ag consumption can decrease this cost, however, such reduction may come at the expense of cell performance. In order to address the issue of Ag cost reduction while maintaining high cell efficiency, we tailored phosphorus emitter profiles via POCl_3 diffusion to create solar cell emitters displaying low saturation current density (J_(0e)), variable electrically active surface phosphorus concentration ([P_(surface)]), and variable sheet resistance with the aim of reducing Ag consumption. By optimizing emitter diffusion conditions, we were able to reduce screen-printed Ag paste consumption by 40 – 60% with no loss in cell performance. Using a screen-printable Ag conductor paste designed to contact low [P_(surface)] emitters, we compared the performance of cells with screen-printed Ag paste dry masses of 200, 120, and 80 mg. Using a tailored Low J_(0e) 55 Ω/sq emitter, high open circuit voltage (V_(OC)) and short circuit current (J_(SC)) are achieved to give average cell efficiencies of 18.64% and 18.73% for 120 mg and 80 mg Ag paste dry mass, respectively. This is compared to efficiencies of 18.52% and 18.21% for cell using industrial-type 65 Ω/sq emitter with 120 and 80 mg Ag paste dry mass, respectively. Based on US$32/Troy oz. Ag market price and 85% by weight thick film paste Ag metal content, Ag front side metallization cost of US￠2.11/W can be achieved by using 80 mg Ag paste dry mass. This is compared to US￠3.19/W (33% cost savings) and US￠5.44/W (60% cost savings) for use of 120 and 200 mg Ag paste dry mass, respectively, on industrial-type emitter.