Modelling picosecond and nanosecond laser ablation for prediction of induced damage on textured SiNx/Si surfaces of Si solar cells

Abstract

AbstractThis study investigated the laser‐induced damage arising from 266 and 532 nm laser ablation of SiNx films on alkaline textured Si surfaces with nanosecond and picosecond pulse durations using a combination of optical‐thermal simulations and measurements of carrier recombination current density. Simulations predict that the melting depth is limited to within 150 nm of the SiNx/Si surface after 266 nm ps laser irradiation due to the greater absorption in both the SiNx and Si resulting in more direct ablation, while temperatures exceeding the melting temperature of Si are predicted to extend up to 1000 nm into the Si substrate with 532 nm ps pulses leading primarily to spallation. Ablation of the SiNx by 266 nm ps irradiation is predicted to be more homogeneous on smaller sized pyramids due to the increased absorption of double‐bounce reflected light on the pyramid faces. This finding has implications for applications requiring uniform ablation of dielectrics on textured Si surfaces. Ablation of SiNx by the longer wavelength 532 nm ps pulses also increases carrier recombination compared to that incurred with 266 nm ps pulses due to the increased melting depth. Longer ns pulses result in less steep temperature gradients and, for 266 nm pulses, an increased melting depth compared to ps pulses. Consequently, shorter ps UV pulses are preferred for SiNx ablation on Si surfaces due to their reduced laser damage penetration, whereas the less steep temperature gradients resulting from ns 532 nm pulses are beneficial for laser doping to form selective emitters.