Selective Femtosecond Laser Lift-off Process for Scribing in Thin-film Photovoltaics

A selective femtosecond laser lift-off process initiated by ultrafast non-thermal ablation of an ultrathin layer at the interface of two materials has been explored with regard to its applicability in thin film photovoltaics. It is demonstrated that the technique allows preparing fully functional, i.e., electrically isolating, scribes of less than 20 mu m groove width, leaving both groove bottom and laterally adjacent material without any indication of thermal damage or structural modification. The latter has been shown even for the textured interfaces of aluminium-doped zinc oxide (AZO) and silicon thin films. Laser wavelengths of 1030 nm and 515 nm were used for AZO and a-Si ablation, respectively. With this choice, sufficiently wide process windows of laser fluence could be identified for all three typical scribes usually denoted as P1, P2 and P3 for patterning of front contact, absorber and back contact. This shows that the femtosecond laser is a promising tool to reduce the total width of the scribe areas in thin film solar modules to less than 50 mu m. An additional benefit is the negligible thermal damage of the layers during scribing.