Picosecond laser processing of ITO and AZO thin films: the impact of substrate material and multi-pulse incubation on ablation thresholds

Ultrashort-pulse laser processing enables selective layer removal in multilayer photovoltaic structures with precision and quality. Single-pulse ablation thresholds (1060 nm, 150 ps) were 1.15 J/cm² for ITO/glass and 0.14 J/cm² for ITO/PET. Photothermal mechanisms dominated the ablation on ITO/glass, whereas for ITO/PET, a stress-assisted thermomechanical mechanism was involved in the removal process. The charge-transporting AZO coating exhibited a single-layer ablation threshold of 0.21 J/cm² on ITO/glass, whereas the ablation threshold for an AZO/ITO stack was 0.71 J/cm². Compared to ITO alone, the notably lower single-pulse threshold for the AZO/ITO stack indicates that thin film removal mechanisms are influenced by interactions at the films' interface rather than photon absorption alone. Similar incubation coefficients of ITO on glass and PET (0.93-0.94) suggest comparable pulse-to-pulse damage accumulation for ITO, coincident with dielectric incubation behaviour and regardless of the substrates. The study further showed that under 600 kHz processing with a 93.3% pulse overlap ratio, ITO could be entirely removed without substrate damage using the ablation threshold fluences. The methodology, demonstrated with industrially relevant coating of ITO and AZO, provides a valuable toolset to support the expanding portfolio of materials used in photovoltaic devices.