Ultra-short laser patterning of thin-film CIGS solar cells through glass substrate

Abstract

A comparative analysis and a novel method involving a monolithic interconnection process (scribing) of creating thin film CIGS solar cells are presented based on experimental approaches and models. The boundaries of the delamination and ablation of molybdenum film in the P1 process of low-intensity picosecond (ps) laser irradiation through a substrate (substrate-side processing) are investigated. The observed ablation is explained in two steps based on the boundary formation observed and the deformation of the molybdenum layer resulting in the ablation of the delaminated layer. A novel idea of the P2 process through the substrate using a ps laser is then proposed and tested based on these explanations. The new P2 process can ablate nearly 2 microns of an absorber layer of a CIGS sample at a laser pulse energy of 5.3 μJ (with a 36 micron (1/e2) spot diameter) without signs of thermal effects while the conventional film-side processing for P2 requires 78 μJ and exhibits a typical laser induced heat-affected zone. Scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDS) observations show the advantages of the new process, which can prevent melting and other heat effects on the absorber and molybdenum layers.