Laser ablation of thin SiN _x layer coated on silicon wafer—evaluation of process performance for PERC solar cell application

Abstract

In fabricating passivated emitter and rear contact (PERC) solar cells, creating small openings on the SiNx-coated silicon substrate to establish metal contacts necessitates using a nanosecond pulsed green laser for ablation. However, the thermal nature of laser ablation poses a challenge. Excessive nitrogen diffusion from SiNx into the silicon substrate can compromise the electrical performance of solar cells. Therefore, this study aims to comprehensively understand how laser parameters impact the electrical properties of such solar cells. PERC solar cell precursors were initially crafted by ablating the SiNx layer at four laser fluences, each corresponding to different regimes: solid, liquid, vapor, and phase explosion. Subsequently, various optical, chemical, and electrical characterizations were conducted on the solar cell precursors. Complete PERC solar cells were also fabricated to measure quantum efficiency (QE). In the solid regime, SiNx removal is precise, with minimal thermal damage, resulting in a nitrogen concentration of approximately 0.15\%. Photoluminescence count and carrier lifetime are notably higher by 21\% in the solid regime compared to the explosive regime. The QE measurement at 984 nm quantitatively assesses rear-side recombination losses. Notably, 26\% of the area exhibits a 56\% QE in the solid state, while this figure drops to around 22\% in the explosive state. This decline can be attributed to increased thermal damage in the explosive regime, which augments recombination centers and diminishes the solar cell performance. PERC solar cells ablated in the solid regime showcase lower subsurface damage, superior electrical characteristics, and higher performance than those ablated in the explosive regime.