Back-Contact Modules: Cheaper and Better Performance

The development of solar cells and modules continues at a rapid pace. Yield must be increased and production costs must go down. ECN conducted a test with a back-contact module, and will present the results at the European PV Solar Energy Conference.

“As opposed to a conventional solar panel, the contacts of a back-contact module are interconnected at the back of the cell, both positive and negative,” said Ian Bennett, a senior researcher at ECN. “The advantage is that shade is not a problem and that cells are packed more closely together. The technology is also well suited to thinner cells.”

The back-contact module has been around for a decade now and will be further developed at a modular level. Despite the many advantages, the costs of the development of the module are an obstacle to its practical application.

“Particularly the use of copper components adds to the costs of the module,” Bennett added. “This is why ECN conducts tests aimed at reducing costs.”

The test focuses on three strategies.

“We applied aluminum as a substitute for copper, reduced the distance between the conductive foil and the cell, and increased the number of vias,” Bennett noted. “The results were surprising. We used more than 20% less silver on the cell and simultaneously improved the yield by 20%.”

In order to keep the costs low, ECN investigated ways of optimizing the cell and the module.

“The additional vias make the distance to the outlets shorter and reduce the resistance,” Bennett said. “Due to the fact that we use more than twice as many contact points on a cell, you would expect us to need more glue. Yet by placing the cells closer to the conductive foil, the layer of glue needed becomes thinner.”

The results of the test with the mini-module matched ECN’s earlier calculations.

”We are currently working on a 60-cell module with cells that have 36 vias<” Bennett reported. “This module should have an output of 300 watt. In parallel, we are developing an ‘interdigitated back-contact cell’ and ‘back-contact heterojunction cells.’ We want to demonstrate that our module technology is future-proof. The next step is to develop cells with thinner wafers. This also helps bring down solar panel production costs. Current wafers have a thickness of 180 microns. We want to use wafers with a thickness well below 100 microns. We are continuously working on improvement.”