A core interface technology that enables perovskite-silicon tandem solar cells, dubbed "dream solar cells," to be produced at high efficiency even in ordinary air has been developed in Korea. The technology achieves world-leading efficiency without special equipment to block moisture and oxygen, drawing assessments that it has lowered the barrier to commercializing and mass-producing next-generation solar cells.
The Ulsan National Institute of Science and Technology (UNIST) said Tuesday that a joint research team led by Sang-il Seok, distinguished professor in the Department of Energy and Chemical Engineering, and Kyung-jin Choi, professor in the Department of Materials Science and Engineering, developed a ternary self-assembled molecular contact layer (TSN) together with a research team from King Abdullah University of Science and Technology (KAUST) in Saudi Arabia. The findings were published in Nature Photonics, an international journal in the field of optics and photonics, on the first of this month.
A perovskite-silicon tandem solar cell has a structure in which a perovskite solar cell is stacked on top of a silicon solar cell. The upper perovskite layer absorbs short-wavelength light while the lower silicon layer absorbs the remaining light, allowing higher efficiency than conventional silicon solar cells. For this reason, it is considered a next-generation solar technology in which major countries such as China are seeking to secure leadership.
The self-assembled monolayer (SAM) widely used in high-efficiency tandem cells is a thin contact layer that moves charges well, but it is vulnerable to moisture in the air. When moisture interferes with the bonding between the electrode surface and the molecular layer, the coating layer does not form evenly, and part of it becomes disrupted during the subsequent process of applying the perovskite solution. For this reason, equipment that blocks moisture and oxygen, such as a glove box, was previously required, acting as an obstacle to large-area, low-cost production.
The research team designed a ternary contact layer by adding GDMA and AG to Me-4PACz, an existing SAM material. GDMA helps the molecules spread evenly on the electrode and become firmly fixed after heat treatment. AG reduces defects at the interface in contact with the perovskite, suppressing the phenomenon in which charges generated by light disappear midway. As a result, the team was able to create a uniform interface film even in air and reduce charge loss.
The perovskite-silicon tandem solar cell using this material recorded an efficiency of 31.72% under ordinary air manufacturing conditions. This is the world's highest efficiency among tandem cells manufactured in air. The officially certified efficiency was also confirmed at 31.36%. In a nitrogen atmosphere, it achieved an efficiency of 32.60%.
Durability also improved. Even after being exposed to a high-temperature environment of 85 degrees Celsius for 600 hours without protective packaging, it maintained more than 92% of its initial performance, and even after being continuously exposed to strong light simulating actual sunlight for 1,000 hours, it kept more than 90% of its efficiency. The perovskite film also formed evenly on a 7×7㎠ large-area substrate, confirming the potential to expand to industrial large-area processes such as blade coating and slot-die coating in the future.
"To commercialize high-efficiency tandem solar cells, we must resolve not only performance but also reproducibility in actual processes and production costs," Seok said. "This research will serve as the technical foundation needed to expand into large-area manufacturing processes."
