Front metal and diffusion optimization for selective emitter

A complex optimization is required to reach the full potential of the selective emitter (SE) architecture. The focus of this report will be the front metal contact and phosphorous emitter diffusion strength. This optimization requires consideration of R_sheet (sheet resistance) of the field and contact regions as a function of diffusion recipe, metal R_contact (contact resistance) as a function metal paste, and R_emitter (emitter resistance) as a function of finger spacing. To cover the Rsheet,field range of interest, the field diffusion strength was varied from 60 - 100 Ω/□. To quantify the impact of R_contact, an advanced formulation metal paste with reduced R_contact was compared to an industry benchmark. The final parameter varied is the finger spacing, varied from 1.6 - 2.1 mm. Testing reveals there are marginal gains from increasing the diffusion R_{sheet, field} above 100 Ω/□ due to reduced front surface field below the metal contacts causing reduced Voc. More substantial gains were realized by from an advanced metal paste formulation which reduces R_contact. Finally the concept that reduced finger spacing can be used to reduce R_emitter component is pushed until it falls into printability limitations due to the need for progressively thinner fingers. The net result from diffusion strength, paste, and finger spacing optimization yield a mean efficiency of 19.2%, +0.2%_abs gain over the control.