Fabrication of contact holes by rear side laser ablation of polyimide foils for CIGS solar modules

Laser technology is of increasing interest for the improvement of photovoltaic generators also for mass production. Copper–indium–gallium–diselenide (CIGS) thin film solar cells on flexible polyimide (PI) foil have great potential for specific applications requiring mechanical flexibility. To reduce the dead area of solar modules especially that of the serial interconnection shingling of the solar cells is one encouraging approach. The former developed back side opening process is utilized for via preparation to realize the serial interconnection at the rear side of the solar cells. Arrays of square vias that were fabricated into the polyimide foil by UV laser ablation were filled with a silver-based conductive adhesive for realizing the electrical and mechanical interconnection. Contact resistance of the silver-based adhesive to the solar cell back contact of less than 0.2 Ω mm2 has been measured. Shingled CIGS modules with a size of 100 cm2 having an open circuit voltage of 2.3 V and a short circuit current of more than 500 mA demonstrate the great potential of this interconnection approach for flexible electronic applications.