3. 2 CdTe, CIS and Related Ternary and Quaternary Thin Film Solar Cells
Laser Processing, Thin Film Solar Cell, Transparent Conductive Oxides, Femtosecond Laser Pulses
Summary / Abstract:
Few micrometer wide scribes of almost rectangular cross section have been prepared by femtosecond laser processing of two different transparent conductive oxide (TCO) layers: (i) ~ 600 nm thick indium-doped tin oxide (ITO) layers, and (ii) ~ 1000 nm thick aluminum-doped zinc oxide (AZO) layers on soda-lime float glass sheets of ~ 3 mm thickness. Using 300 fs laser pulses at a wavelength of 1030 nm irradiated through the glass, selective liftoff of the TCO layers is achieved at fluences more than an order of magnitude lower than by nanosecond laser processing. Detailed structural and electrical characterization of the produced trenches shows that ultrafast laser-induced generation of high carrier density at the interface initiates a non-thermal ablation process, leaving the glass as well as the adjacent TCO without any noticeable (thermal) modification; the desired electrical isolation across the scribe is obtained already with trenches of about 5 μm width. This non-thermal ablation mechanism, with the necessary strong absorption being created by the leading edge of the fs pulse itself, can be generalized to specifically address almost any (semi-)conducting layer when suitable laser parameters are being used. Therefore, fs laser processing appears to be a fast and versatile tool for many scribing processes in thin-film photovoltaics, offering the potential to reduce the total width of the scribe region to below 50 μm.