High-efficiency n-type silicon solar cells: Advances in PassDop technology and NiCu plating on boron emitter
An approach for n-type passivated emitter and rear locally diffused (PERL) solar cells is presented that combines the PassDop technology with Ni- and Cu-plated front contacts. As a step toward an eased industrial implementation, a new PassDop layer-based on a-SiNx:P is presented and compared with the original layer based on a-SiCx:P. We show that the PassDop concept can be used as a rear-side approach for these solar cells that reach energy-conversion efficiencies up to 23.5% on a small-area (2 x 2 cm(2)) when using the layer based on a-SiCx:P, and 22.8% when using the layer based on a-SiNx:P. By applying the same technology on a larger scale, we achieved efficiencies that exceed 22% on 143.2 cm(2). We show that Ni-plating on boron emitters allows for excellent contact properties. With laser contact opening in conjunction with Ni-and Cu-plating, similar results for photolithographic opening (TiPdAg seed layer and Ag-plating) can be reached. Combining these technologies, cells are presented using PassDop as the rear-side approach and Ni-plating to contact the boron emitter with first results to achieve up to 21% cell efficiency on 148.6 cm(2).