Processing Techniques for Monolithic Interconnection of Solar Cells at Wafer Level

Monolithic interconnected modules are large-area high-voltage photovoltaic devices that are realized through solar cell segments that are series-connected via interconnection trenches during wafer processing. This paper investigates different processing techniques, giving detailed information about each processing sequence. In the first approach, a wet chemical etching procedure and photo-defined polyimide as dielectric film is used, leading to minimal trench width of 86 mu m. Furthermore, we examine the applicability of advanced processing techniques. An alternative dry-etching process using reactive ion etching in inductively coupled plasma is investigated. With this technique, smooth and near-vertical sidewalls could be achieved, whereas the undercuts in etching profile, which are inevitable when using wet chemical etching, could be avoided. Moreover, an accurate processing technique for plasma-enhanced chemical vapor deposited SiNx as a dielectric film for electrical isolation is presented. This allowed sufficient isolation to be achieved, as well as enabling precise structuring. With these advanced processing techniques, trench widths of 57 mu m were realized, resulting in a reduction of area losses due to interconnection from 9% to below 6%.