Finland-based optical solutions company ICS Intelligent Control Systems Ltd announced a power improvement of about 3.8% achieved in heterojunction (HJT) solar modules when combined with its patented Solar Energy Optics (SEO) light redirecting film during a test at Fraunhofer Institute for Solar Energy Systems (Fraunhofer ISE).

The emerging HJT solar cell technology can achieve higher efficiencies than traditional c-Si cells and even cells processed with PERC techniques. But the power loss issue in the edge area of HJT cells has long been an obstacle to unlocking the optimal efficiency of these cells. By applying ICS' SEO film to the inside of the HJT module front glass, light is redirected from the less efficient edges into the more efficient regions of the cells.

During the test at Fraunhofer ISE, four M6 half-cut HJT solar cells with 1.7 mm cell and 2 mm string gaps were assembled into modules with two different SEO film configurations, overlapping the cell edges by 0.5 mm and 1 mm, respectively. The solar cells in the test were utilized in their original state without any additional customization or sorting.

The results showed a significant improvement in both maximum power and fill factor. An absolute increase in module efficiency by 0.66 % to 0.75 % was achieved, corresponding to 3.3 % and 3.8 % relative improvement.

The improved performance is a result of the combination of an increased solar cell efficiency by minimizing edge recombination losses and an improved utilization of light from inactive module areas.

According to ICS, detailed optical simulation models of the solar modules and the SEO film have been constructed and validated with experimental data. The results show that applying SEO film to a 120 or 144-cell module, with 2 mm cell gaps and a white backsheet, can provide an efficiency boost of 2.6 % relative improvement, or two power classes. As an improvement on transparent bifacial modules or alternative to the gapless solution currently applied by some module manufacturers, the efficiency gains can exceed 3.5%.

"These new results demonstrate that overlapping the edges of heterojunction solar cells with SEO film has the potential to be game changer for high efficiency PV modules," said Dr. Andrea Pfreundt, product manager at ICS.

"We are providing a manufacturable solution with added Wp costs well below the regular module cost for both residential and utility formats," said Kari Rinko, CTO of ICS.