ULTRA-SHORT PULSE LASER ABLATION FOR HIGH-EFFICIENCY SILICON WAFER SOLAR CELLS

Abstract

Femtosecond (fs) lasers are capable of ablating dielectrics with negligible damage to the underlying silicon. This thesis investigated applications of fs laser ablation with aims to reduce processing time and cost for ablation-intensive solar cell architectures. Fundamental studies were carried out which revealed the presence of two distinct regimes (gentle and strong), and also led to improved analytical models for laser groove dimensions. Etch-back experiments showed that the gentle regime needed < 5 s of damage etching, making this process suitable for high-efficiency solar cell architectures, whereas the strong regime induced severe bulk damage. The fs laser process was then applied to front and rear dielectric ablation for Aluminium Local Back Surface Field (Al-LBSF) solar cells. The gentle regime led to efficiencies of up to 21%, whereas the strong regime led to degraded cell parameters. A loss analysis was carried out to identify the mechanisms causing cell degradation in the strong regime.