INL researchers boost efficiency of ultrathin solar cells

Ultrathin solar cells are a promising path for clean energy: they use far less material, can be manufactured faster, and even applied on flexible or curved surfaces, in comparison with conventional technologies. But there is a catch – when the absorber layer is too thin, the cells lose performance because they do not capture enough light and energy leaks out the back.

A research team at INL, led by research group leader Pedro Salomé, in collaboration with other research institutions, including Uppsala University, in Sweden, has now developed a clever nanostructured “mirror” that solves part of this problem. By embedding an ultra-thin patterned layer of gold and encapsulating it with aluminium oxide, the team created a rear contact that both reflects light back into the solar cell and mitigates energy losses at the back interface. “This works by providing interface passivation,” explained Pedro Salomé.

The innovation lies not only in the design, but also in the way it’s made. Using one-step nanoimprint lithography, the researchers avoided the costly, multi-step nanofabrication processes usually required for this type of architecture. Pedro Salomé adds “this paves the way for industrial scale-up”.

Tested on ultrathin ACIGS solar cells ((Ag,Cu)(In,Ga)Se₂), the new architecture improved power conversion efficiency by 1.5% absolute, mainly thanks to higher light absorption. The method worked best at lower fabrication temperatures (450 °C), making it more compatible with flexible substrates and helping avoid diffusion problems that often plague gold-based contacts.

When tested on ultrathin ACIGS ((Ag,Cu)(In,Ga)Se₂) solar cells, the new architecture improved the power conversion efficiency, mainly because the nanostructures improved light absorption inside the cell. The approach proved most effective at a lower fabrication temperature of 450 °C. This not only kept the architecture stable, preventing the diffusion issues that gold layers often cause, but also made the process more compatible with flexible substrates, opening the door to lightweight and versatile solar applications.

“This architecture gives us a powerful way to manage light and reduce interface recombination in ultrathin devices, while keeping fabrication practical,” says first-author André Violas, currently working as a Research Engineer at the Nanofabrications, Optoelectronics and Energy Applications | Salomé group. “It brings us closer to making lightweight, flexible solar cells efficient enough for real-world applications.” For researcher Jennifer Teixeira, “this paper is the outcome of our efforts in merging light management and interface passivation, and by being able to merge both, we are starting to create novel solar cell architectures”.

The work, published in Solar RRL, was carried out under the R2U Technologies project, part of the Portuguese Resilience and Recovery Plan through the NextGenerationEU fund, and four individual Fundação para a Ciência e Tecnologia (FCT) fellowships.

Text by Catarina Moura
Photography by Rui Andrade