Characterization of direct- and back-scribing laser patterning of SnO2:F for a-Si:H PV module fabrication

In thin film photovoltaic modules, the different solar cells are interconnected monolithically during the production process, which gives a greater control over the size and output characteristics of the finished module. The interconnection is typically achieved through different laser scribing processes made at different production steps. In thin film modules built in the superstrate configuration, the first laser process is the patterning of the transparent front electrode. This paper presents results on the investigation of this first laser scribing process on fluorine-doped tin oxide deposited onto a glass substrate using nanosecond diode-pumped solid-state laser sources. Processes made with two different wavelengths (1064 nm and 355 nm) and executed from the film-side and from the substrate side are compared and evaluated. The quality of the scribes is assessed with confocal and scanning electron microscopy images. In addition, Raman microscopy is used to study the extension of the heat affected zones. While good quality scribes were obtained using both wavelengths and either film-side or substrate-side irradiation, only using 355 nm and substrate-side scribing yielded grooves with no observable heat affected zones. It also needed the lowest values of energy per ablated volume and allowed for the highest processing speeds. As such, substrate side ablation with 355 nm is proposed as the best ablation strategy.