18.3% Efficiency on High Ohmic Emitters without Selective Emitters

Abstract

Crystalline silicon solar cells with high ohmic emitters show higher efficiencies due to a better blue response. Unfortunately, the only way to contact them by screen printing is using the selective emitter technology. This study shows that contacting emitters with Rsh = 100Ω/sq can be achieved by standard screen printing technology without selective emitter processing thanks to the development of a new silver paste. Thus, no additional process steps are needed to selectively dope the emitter. We study the electrical properties of industrially processed c-Si solar cells, with two different screen printing silver pastes (Pastes A and B) and emitters with sheet resistances Rsh = 80Ω/sq, 100Ω/sq, and laser doped selective emitter with Rsh = 20Ω/sq on Rsh = 100Ω/sq. On the solar cells with 80Ω/sq emitter, paste B yields a low series resistance Rs = 0.72Ω cm2, thanks to its lower contact resistance ρc and its lower penetration into the space charge region, compared to paste A. The low series resistance leads to an efficiency gain Δη = 0.7%abs. We also obtain promising results on 100Ω/sq, as the contact resistance ρc ≤ 3.1 mΩcm2 leads to a maximum fill factor FF = 78.8%. The efficiency η = 18.3% of the 100Ω/sq emitter solar cells is then comparable to the one of the selective emitter cells. With paste B, we demonstrate that it is now possible to contact high ohmic emitters, without the use of a selective emitter structure.