Progress in shingle interconnection based on electrically conductive adhesives at Fraunhofer ISE

Shingling is an alternative method to conventional wire soldering for the interconnection of solar cells in PV modules. In this article the production sequence from host cells to shingled modules is explained. The efficiency changes along the process chain are analyzed theoretically and by experiment. The I-V characterization of the host cells overestimates the efficiency of the later separated shingles, which are measured from front side busbar to back side busbar, because of the finger resistance effect. Additionally, edge recombination further reduces the efficiency, but half of this loss can be avoided by edge passivation (passivated edge technology, PET). The efficiency losses from shingle to module are domi-nated by geometrical factors, particularly the efficient use of space in the glass. In an experiment with small-scale modules the ECA amount was reduced to below 3 mg per shingle without affecting the initial performance and stability in thermal cycling (400 cycles). However, to hold down the shingles during ECA curing was found to be important for joint reliability. In a further experiment, 700 commercially available, monocrystalline, monofacial PERC host cells were separated into 156.75 mm×31.35 mm shingles by laser scribe and mechanical cleave and integrated in ten full-size shingled PV modules. The finger resistance effect after separation on efficiency was (-0.3±0.1) %abs and edge recombination led to an additional loss of (-0.8±0.1) %abs. The so-obtained (20.5±0.2) % efficient shingles were automatically connected to 31-shingle strings using a teamtechnik TT1600ECA stringer. The resulting modules had a full-area efficiency of (17.7±0.1) %. Ac-cording to a SmartCalc.Module simulation, the non-optimal use of glass alone results in an efficiency loss of -2.5 %abs. One module with 432 shingles reached a power of 412 Wp and 19.6 % efficiency demonstrating a greatly improved packing density. Finally, the modules were exposed to thermal cycling 200, damp heat 1000 h, mechanical load 5400 Pa, humidity freeze 10 cycles and hot spot tests, which were all passed without significant degradation.