Edge passivation improves shingled solar module performance

Researchers at Germany's Fraunhofer Institute for Solar Energy Systems (Fraunhofer ISE) tested the so-called passivated edge technology (PET) on shingled solar cells and found it can improve their pseudo-fill factor (pFF) without compromising their interconnection quality.

Shingled panels feature a busbar-free structure in which only a small proportion of cells are not exposed to sunlight. The cells are bonded with electrically conductive adhesive to form a shingled high-density string and the resulting strips are connected. The reduced number of busbars reduces shadowing losses.

The scientists explained the fill factor is a “questionable” parameter for comparing the performance of small-format shingle modules with and without edge passivation, as it is too sensitive to current mismatch. The pFF, by contrast, reflects saturation currents and parallel resistance and, according to the research team, can help quantify fill factor losses at the module level.

In the paper “Investigating the impact of edge passivation on shingle solar modules,” published in Solar Energy Materials and Solar Cells, the group said their work was mainly intended to investigate the implications of the so-called passivated edge technology (PET) on experimental data collected at the module level from prototype manufacturing.

The PET technology was developed by the Fraunhofer ISE itself and consists of passivating the cut edges of the shingles by depositing a dielectric layer after solar cell separation. The German institute filed a patent application back in 2018 and is offering a sampling of the technology for interested partners. Solaria was one of the first industry partners testing post-metallization PET on TOPCon shingle solar cells.

The Fraunhofer ISE researchers used Python software to conduct a series of simulations on six small-format modules containing 14 rectangular-shaped center shingles to assess if the pFF parameter is a “reasonable” quantity to assess the impact of the PET on shingle modules. “This is meant to be done on a proof-of-concept level, meaning that relative differences of pFF are considered more relevant than absolute values,” they explained.

The performance of the modules was also compared to that of reference panels without edge passivation. “On a proof-of-concept level, simulations of shingle strings with and without edge passivation show that pFF is a well-suited quantity to assess the edge recombination inside shingle solar modules, as it is widely unaffected by current mismatch effects,” the academics stated. “For ideal strings, pFF linearly correlates with the peak power.”

They also found that the modules designed with the PET approach offered a pFF that was around 0.5% higher than that of the reference panels. “This number is in accordance with the pFF increase found on shingle level, when considering median values,” they concluded. “At the same time, the PET process applied in this work did not involve a significant compromise in interconnection quality.”