Removal Mechanism and Defect Characterization for Glass Side Laser Scribing of CdTe/CdS Multilayer in Solar Cells

Abstract

Laser scribing is an important manufacturing process used to reduce photocurrent and resistance losses and increase solar cell efficiency through the formation of serial interconnections in largearea solar cells. Highquality scribing is crucial since the main impediment to largescale adoption of solar power is its highproduction cost (priceperwatt) compared to competing energy sources such as wind and fossil fuels. In recent years, the use of glassside laser scribing processes has led to increased scribe quality and solar cell efficiencies; however, defects introduced during the process such as thermal effect, microcracks, film delamination, and removal uncleanliness keep the modules from reaching their theoretical efficiencies. Moreover, limited numerical work has been performed in predicting thinfilm laser removal processes. In this study, a nanosecond (ns) laser with a wavelength at 532 nm is employed for pattern 2 (P2) scribing on CdTe (cadmium telluride) based thinfilm solar cells. The film removal mechanism and defects caused by laserinduced microexplosion process are studied. The relationship between those defects, removal geometry, laser fluences, and scribing speeds are also investigated. Thermal and mechanical numerical models are developed to analyze the laserinduced spatiotemporal temperature and pressure responsible for film removal. The simulation can wellpredict the film removal geometries, transparent conducting oxide (TCO) layer thermal damage, generation of microcracks, film delamination, and residual materials. The characterization of removal qualities will enable the process optimization and design required to enhance solar module efficiency.