Shingled cell interconnection: A new generation of bifacial PV-modules

The idea to interconnect solar cells in a shingled manner like roof tiles dates back to the 1960's. However, the standard interconnection technology in the PV industry nowadays is still the front to back series interconnection using solder coated copper ribbons. Shingle interconnection offers very high packing densities of solar cells and increases the module's active area by eliminating busbars from the illuminated area. Direct interconnection of stripe-like solar cells by electrical conductive adhesives (ECA) replaces the front-to-back ribbon interconnection and therefore eliminates the interconnectors' ohmic losses. Stripe-like solar cells additionally reduce the overall ohmic losses of the solar cell string by lower cell currents. In this work we provide an overview of the scientific state of the art and a summary of the most important features for shingled cell interconnection. We compare two calculation approaches for the joint deformation due to thermal expansion of the module materials and identify the most relevant parameters. The results show that the thickness of the joint material typically ranging from ~ 20-100 µm is crucial to reduce the shear deformation and therefore enabling sufficient long-term stability. Other geometrical parameters like the overlap width or number of solar cells per string only show a small effect on shear strain for cell widths >20 mm. First experimental prototypes of shingled mini-modules of bifacial pSPEER solar cells using low temperature soldering (Sn42Bi58) show a total power loss of < 5 % after accelerated TC200 testing.