Front metal and diffusion optimization for selective emitter

Abstract

A complex optimization is required to reach the full poten tial 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 con sideration of Rsheet (sheet resistance) of the field and con tact regions as a function of diffusion recipe, metal Rcontact (contact resistance) as a function metal paste, and Remitter (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 0/0. To quantify the impact of Rcontact, an advanced formulation metal paste with reduced Rcontact was compared to an industry bench mark. The final parameter varied is the finger spacing, varied from 1.6 -2.1 mm. Testing reveals there are mar ginal gains from increasing the diffusion RSheet , field above 100 % due to reduced front surface field below the metal contacts causing reduced Voc. More substantial gains were realized by from an advanced metal paste formula tion which reduces Rcontact. Finally the concept that re duced finger spacing can be used to reduce Remitter com ponent 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 optimiza tion yield a mean efficiency of 19.2%, +0.2%abs gain over the control.

Front-side Ag contacts enabling superior recombination and fine-line performance

“…A final conductor line width reduction of approximately 10 μm is measured. According to previous calculations, a 10 μm line width reduction is expected to give a 0.3 mA / cm 2 increase in Jsc [3]. No additional fingers were added to the design, so this reduced width enabled a laydown reduction of 10 -20 mg.…”