Laser fabricated back-end interconnections on CIGS thin film solar cells using ultrashort pulsed laser radiation for BIPV applications

Thin-film solar technologies are very attractive due to their potential for low production costs. As in all thin- film technologies, high efficiency of small cells might be maintained with the transition to larger areas when for this purpose the areas are segmented and electrically connected in series with each other. This reduces the current load on the thin-films and the related ohmic losses. For CuIn1-xGaxSe2 (CIGS) thin film solar cells the industrial segmentation and interconnection is mostly based on mechanical scratching. Here the individual layers - front contact, absorber and back contact - are locally and slightly offset to each other removed right after their deposition. In order to meet architects' (for e.g. BIPV applications) requirements for the shape of the module, it is beneficial to allow for a geometry adaption of the modules after the layer stack deposition. This is supported by a so-called back-end interconnection, i.e. to perform the segmentation and interconnection after the deposition of the whole layer stack. The back-end interconnection is enabled by the combination of laser-based segmentation processes and printing techniques. Furthermore, compared to mechanical scratching, laser-based interconnection promises a possible reduction of segmentation related dead area losses. In this paper we present a laser-based selective structuring of patterns for a back-end interconnection on CIGS thin film solar cells. We apply an ultrashort pulsed laser with a wavelength of 1030 nm and investigate the impact of various process parameters. Before laser processing samples were stabilized under AM1.5 at 55 degrees C for 40 minutes to reduce metastabilities within CIGS thin film solar cells.