Co-diffused APCVD boron rear emitter with selectively etched-back FSF for industrial N-type Si solar cells

Abstract

The employment of a B-doped atmospheric pressure chemical vapor deposited (inline belt APCVD) borosilicate glass is an elegant technology for industrially realizing a p+ emitter. By drive-in of B and a subsequent POCl3 co-diffusion, p+ emitter and n+ front surface field (FSF) are established in a single process step. APCVD-SiOx is used to prevent the p+ emitter from being compensated during P diffusion. Its thickness needs to be adapted in order not to affect the p+ profile during POCl3 diffusion while keeping it removable. For rear junction solar cells, it is crucial to ensure low recombination activity at the front. Therefore, a selectively etched-back FSF is to be established in the solar cell. An adjusted etch-back solution increases n+ Rsheet successively and well controllably, accompanied by a drastic j0FSF reduction while simultaneously almost completely maintaining p+ Rsheet. A 43 /sq APCVD-AlOx passivated p+ emitter achieves j0E of only 52 fA/cm2. Total implied VOC of a pseudo solar cell structure attains up to 695 mV. The newly developed APCVD p+ emitter combined with the co-diffused and selectively etched-back FSF employed in an industrial n-type solar cell achieves 18.8% efficiency in a first experiment being still limited by a poor Ag/Al contact to the B-emitter.