Nanosecond Pulsed Laser Patterning of Interdigitated Back Contact Heterojunction Silicon Solar Cells

Abstract

Careful control of the laser patterning for the fabrication of an interdigitated back contact heterojunction (IBC-HJ) solar cell is needed to avoid laser-induced defects and heat-induced crystallization, which can produce higher carrier recombination and lower power conversion efficiency. The results of nanosecond laser patterning of an IBC-HJ test structure are reported, and it was shown that optimized laser ablation conditions using a sacrificial layer eliminates laser-induced damage of the underlying passivation layer. A rigorous set of characterizations, comprising of minority carrier lifetime, spatially resolved μ-photoluminescence, optical microscopy, ellipsometry, Essential Macleod program simulations, scanning electron microscopy, line-mapping energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy, were undertaken to provide a deeper understanding of the nanosecond laser processing under a wide range of laser fluence. The evolving changes in surface morphologies of top sacrificial a-Si and SiNx and the use of color chart simulation for ablation-depth analysis were investigated. The μ-photoluminescence, carrier lifetime, and crystallinity in the passivation layer were evaluated. The trend in the change in the surface chemical constituency was determined in terms of Si/N ratio. Finally, the minimum laser fluence for the IBC-HJ test structure was determined and a negligible change in the implied open-circuit voltage was demonstrated.