Development of a phosphorus spray diffusion system for low-cost silicon solar cells

Phosphoric acid was used an n-type doping source to make an emitter for silicon solar cells. This paper reports on a cold spray method to coat phosphoric acid on the silicon wafer without any additional complicated and corrosive heating system. The key spray parameters such as belt speed, flow rate of the carrier gas, and concentration of phosphoric acid are optimized to get uniform and reproducible sheet resistance for the emitter. The diffusion process has been studied by firing silicon wafers that are spray-coated with phosphoric acid. screen printed solar cells have been fabricated using the emitter formed by the spray coating. The effects of the emitter on cell performance have been investigated and compared with those of the conventional POCl3-diffused emitter. screen printed/spray- diffused cells give impressive cell efficiencies of similar to 16.6% on 1 Omega cm float zone wafers, which is nearly equal to those of POCl3 emitter cells (similar to 16.9% ). Compared with the POCl3 emitter cell, the spray-diffused cells show slightly lower quantum efficiency at the short-wavelength response and slightly higher emitter saturation current density (similar to 3.59 x 10(-13) A/cm(2)) compared with (2.73 x 10(-13) A/cm(2)). Further optimization can eliminate this small difference in efficiency.