UNDERSTANDING THE ROLE OF GLASS FRIT IN THE FRONT AG PASTE FOR HIGH SHEET RESISTANCE EMITTERS

摘要

One of the most difficult and challenging tasks in achieving high-efficiency screen-printed cells is toform high quality contacts to high sheet resistance emitters. The junction depth of high sheet resistance emitters isusually shallow, <0.3 μm and therefore, front silver paste and firing should not etch more than 0.1 μm of the siliconsurface to protect the junction. However, majority of the commercial front silver pastes available today cannot formgood ohmic contacts to high sheet resistance emitters without shunting the p-n junction or producing high idealityfactor. Since glass frit is responsible for Ag particles dissolution and silicon surface etching, we reduce the amount ofglass frit content in SOL9807A [1] by 20% (paste A), 30% (paste B), and 50% (paste C). We achieved good contactsto high sheet resistance emitters with average fill factors of 0.770, 0.769 and 0.767, respectively, for pastes A, B andC. The series resistance increases as the glass frit level decreases (paste A-1.083 Ω-cm~2, B-1.109-Ω-cm~2 and C-1.160-Ω-cm~2). Therefore, average efficiencies of 17.2%, 17.1% and 17.1%, respectively, were achieved for cellsproduced with pastes A, B and C. The ideality factor stays the same at ～1.01 as the glass level decreased, whichsuggests that the amount of glass frit in the front silver paste is critical for making excellent contacts to high sheetresistance emitters.