Making Thinner Solar Cells Without Losing Light

What if solar cells could use less material without sacrificing their ability to capture sunlight?

Making the light-absorbing layer of a solar cell thinner reduces the amount of raw materials needed and, potentially, make manufacturing faster, cheaper, and more scalable. However, with less material to absorb sunlight, light passes through the light-absorbing layer without contributing to electricity generation.

The research carried out by INL researchers Enzo Ribeiro, André Violas, António Oliveira, Bárbara Sieira, Xavier Pinheiro, Paulo Fernandes, Pedro Salomé and Jennifer Teixeira, demonstrates a new nanofabricated solar cell architecture to overcome such challenge in ultrathin solar cells. By adding a nanoscale structure to the rear of the cell, they found a way to increase the amount of light that can be captured.

Salomé group, in collaboration with Uppsala University and the University of Luxembourg, first used computer simulations to optimise the design of the nanostructures. Then, these structures were fabricated using nanoimprint lithography. The researchers worked with ultrathin solar cells based on (Ag,Cu)(In,Ga)Se2 (ACIGS). ACIGS is a semiconductor that absorbs sunlight and converts that energy into electrical current. It is particularly interesting for thin-film photovoltaics, because the light-absorbing layer can be much thinner than the silicon wafers used in conventional solar panels opening the door to several low-weight and flexible applications.

Their approach uses a periodic array of nanoscale silicon oxide pillars at the rear contact of the cell, which scatter incoming light, increasing its optical path through the absorber, and giving it more opportunities to be absorbed. The nanostructures were particularly effective at improving light absorption in the infrared part of the solar spectrum, where ultrathin cells typically struggle to absorb enough light. By helping light travel through the absorber for longer, the structures allowed the ultrathin device to achieve an optical performance comparable to that of a conventional solar cell with a much thicker, 2-micrometre absorber.

The work, published in Laser and Photonics Reviews, was carried out, and supported by the EU-funded project Hi-BITS, FCT – Fundação para a Ciência e Tecnologia, and the R2UTechnologies – modular systems project under the NextGenerationEU program through the PRR plan. The results demonstrate how nanoscale light management can help overcome a fundamental limitation of ultrathin solar cells, opening possibilities for material-efficient photovoltaic technologies.