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F15.1.1

Flexible, Monolithically Integrated Cu(In,Ga)Se2 Thin-Film Solar Modules Dirk Herrmann, Friedrich Kessler, Ulf Klemm, Robert Kniese, Theresa Magorian Friedlmeier, Stefanie Spiering, Wolfram Witte, and Michael Powalla Zentrum fuer Sonnenenergie- und Wasserstoff-Forschung Baden-Wuerttemberg (ZSW) Industriestrasse 6, D-70565 Stuttgart, Germany ABSTRACT CIGS (Cu(In,Ga)Se2) thin-film solar modules on glass substrates are currently on the verge of commercialization. Entirely new application areas could be accessed with CIGS modules fabricated on thin and flexible non-glass substrates. Additionally, the roll-to-roll manufacturing of such flexible CIGS modules promises to be a low-cost production method. Different external Na supply methods and a vacuum-deposited buffer were investigated in this contribution, a sample of the challenges we face when modifying the standard, industrial CIGS module production process to the particular requirements of flexible substrates. Both metal foil substrates and polymer films are considered. Our excellent best results of above 14 % for single cells on titanium, more than 11% on polyimide, and around 7 % for modules on both substrates indicate our progress in developing flexible CIGS.

INTRODUCTION Low materials and energy consumption, low total weight, and high flexibility are inherent features of CIGS thin-film solar cells, but their full competitive potential can only be achieved if they are embedded between protective films instead of thick glass plates. Furthermore, features like monolithic cell integration and cost-effective roll-to-roll manufacturing will enable CIGS to compete with the much more established Si technology. The road to success, however, is not straightforward and many obstacles must be overcome. Nearly all challenges we have to meet are more or less related to the non-glass and flexible substrates. High small-area efficiencies in the range of η = 17 % could be demonstrated by independent laboratories on metallic substrates applying the so-called 3-stage CIGS co-evaporation process [1,2,3]. In contrast, our main research focuses on single- or double-stage in-line deposition methods for flexible CIGS devices which are compatible with industrial requirements [4]. Record efficiencies only play a minor role if the applied deposition methods cannot be up-scaled.

EXPERIMENTAL DETAILS Flexible CIGS solar cells and monolithically integrated modules were produced using flexible substrates of polyimide (PI) films with a thickness of 50 µm and titanium (Ti) foils with a thickness of 25 µm. A Na-containing soda-lime glass of 3 mm thickness was used as a reference. In order to use our in-line equipment designed for the preparation of cells and modules on glass, all flexible substrates were fixed in a metallic frame throughout all processes. The frames are considered as an intermediate step in the process of developing roll-to-roll processing techniques.

F15.1.2

The device structure includes a 0.6-µm-thick Mo back contact (DC sputtered) sometimes preceded by either an