ROAD BLOCKS TO IMPLEMENTING A HIGH SHEET RESISTANCE EMITTER: FILL FACTOR ENTITLEMENT FROM FRONT GRID SCREEN DESIGN AND IMPROVING THE ASPECTRATIO

摘要

It is known that lowering the dopant level or surface phosphorus concentration of n-type emitters reduces recombination as a result of lower concentrations of inactive phosphorous, and improves quantum efficiency due to lower absorption in the blue region of the spectrum and possibly a narrowing of the dead layer. This is one route being taken by industry to raise cell efficiency. Focusing on Fill Factor loss mechanisms, as they relate to the front contact metallization, we model how the front screen design, and improvements to print quality impact efficiency. Without addressing print quality or screen design, we calculate a 1.5% loss in fill factor (77% → 75.9%) when the sheet resistance is changed from 55 Ω/□ to 85 Ω/□. By improving the print quality, via higher aspect ratios, the calculated FF goes from 75.9% → 76.1%. When the screen design is also optimized for the 85 Ω/□ emitter, the FF loss is further reduced (75.9% → 77.2%), and less shading adds 0.5% to JSC. In summary, when a cell's sheet resistance is increased form 55 to 85 Ω/□, implementing print improvements and a re-designed screen adds 2.3% to the relative efficiency.