Approaches to flexible CIGS thin-film solar cells

Even though the “standard” CIGS module fabrication on glass substrates is not yet really established, several CIGS (Cu(In,Ga)Se2) newcomers directly start with the development of flexible devices. The reasons to do so are manifold and so are the methods. We will briefly introduce a few approaches—especially from European laboratories—to fabricate flexible CIGS-based modules and discuss their respective features. Mainly, however, the approaches on metal and polymer substrates at ZSW are presented. Functioning monolithically integrated modules on titanium were fabricated up to a substrate area of 20×30 cm. Also, mini-modules on 10×10-cm2 polyimide sheets could be realised. Important challenges were the electrical insulation of titanium or steel substrates. Suitable dielectric barriers are, for example, pinhole-free SiOx layers deposited by a special plasma-CVD method which can withstand both the CIGS process and the structuring procedures. Adequate patterning methods such as direct laser scribing and mask-free photolithography were successfully applied to interconnect more than 30 cells.