Selective emitter formation process using single screen-printed phosphorus diffusion source

Abstract

Diffusion parameters including the ambient gas, temperature, and time for the phosphorus diffusion process were examined and optimized for selective emitter solar cell processing using a novel screen-printable phosphorus paste. The carrier lifetime of CZ p-type wafers were increased to up to 350μs from an initial lifetime of 195μs and up to 10-fold carrier lifetime improvements were observed for mc-Si p-type wafers. Selective emitter structures on CZ-Si p-type wafers were fabricated by a single screen-printed diffusion process using two simple steps: a single screen-printing of phosphorous paste and an optimized single diffusion process. Highly doped regions under the printed fingers and lowly doped regions between the fingers were realized by phosphorus atoms being diffused out of the printed paste via ambient gas. After optimization of the screen-printed selective emitter, this diffusion process was applied to industrial-type large-area monocrystalline solar cells. A conversion cell efficiency of 18.1% was realized with a fill factor of 79.2%.