Researchers have developed an interface coating material that could accelerate the mass production and commercialization of the "perovskite-silicon tandem solar cell," which is drawing attention as a next-generation solar cell. The breakthrough makes it possible to stably produce ultra-high-efficiency tandem cells exceeding 31% in ordinary atmospheric conditions without expensive specialized equipment, signaling a green light for securing leadership in the global solar market.
The Ulsan National Institute of Science and Technology (UNIST) said Wednesday that a research team led by Sang-il Seok, distinguished professor in the Department of Energy and Chemical Engineering, and Professor Choi Kyoung-jin of the Department of Materials Science and Engineering, jointly developed a cell interface coating material using a three-component substance with a research team from KAUST in Saudi Arabia. The findings were published June 1 in Nature Photonics, a leading international journal in the field of optics.
The perovskite-silicon tandem solar cell is an ultra-high-efficiency device that stacks two cells on top of each other to overcome the efficiency limits of single silicon cells. The upper perovskite absorbs short-wavelength light while the lower silicon absorbs long-wavelength light, dividing the absorption, earning it the nickname "dream solar cell."
Until now, making high-efficiency tandem cells required evenly coating the "self-assembled monolayer (SAM)," the key layer that transfers charge. However, SAM is highly vulnerable to moisture in the air, causing a chronic problem of attaching unevenly to the electrode surface or easily peeling off in subsequent processes. For this reason, manufacturing was only possible inside expensive specialized equipment (glove boxes) that completely block moisture and oxygen, posing a major obstacle to scaling up surface area and reducing production costs.
The research team completely solved this problem by designing a three-component material (TSN) that combines the existing SAM material (Me-4PACz) with "GDMA," which serves a solidification and cross-linking role, and "AG," a material for binding passivation. GDMA firmly fixes the molecules to the substrate through a mild heat treatment process to prevent them from washing away, while AG effectively reduces lead-ion defects at the interface, blocking the loss of electric particles (charge).
The tandem solar cell using this new material achieved an ultra-high efficiency of 31.72% (certified efficiency of 31.36%) despite being manufactured in ordinary atmospheric conditions with humidity present. This is the highest efficiency among tandem solar cells made in open air worldwide. In addition, in a specialized process under a nitrogen atmosphere, it showed an overwhelming efficiency of as much as 32.60%.
Durability, an essential condition for commercialization, was also greatly improved. After being left for 600 hours in a high-temperature atmospheric environment of 85 degrees without separate protective packaging, it maintained more than 92% of its initial performance, and even when exposed to strong light similar to actual sunlight for 1,000 consecutive hours, it kept high efficiency of more than 90%. In addition, the thin film was formed uniformly even on a large 7×7 cm² substrate, dramatically lowering the defect rate and demonstrating process reproducibility.
"This research aligns with the development of 'ultra-gap, ultra-high-efficiency multi-junction solar cells,' which is the goal of the government's 'K-Moonshot Project,'" Professor Choi said. "We expect it to greatly contribute to the commercialization of next-generation solar power."
"To commercialize high-efficiency tandem solar cells, we must solve not only performance but also reproducibility in actual processes and production costs together," Professor Seok said. "Since this research showed that uniform interface thin films and high reproducibility can be secured even in ordinary atmosphere with moisture present, it will serve as the technical foundation needed to expand into large-area manufacturing processes."
Meanwhile, the research was carried out with full support from Hyundai Motor, the National Research Foundation of Korea (NRF) under the Ministry of Science and ICT, and the Korea Institute of Energy Technology Evaluation and Planning (KETEP) under the Ministry of Climate, Energy and Environment. UNIST researcher Kim Gwi-su, KAUST researcher Adi Prasetio, and UNIST researcher Noh Young-im participated as co-first authors, while UNIST distinguished professor Sang-il Seok, Professor Choi Kyoung-jin, and KAUST Professor Stefaan De Wolf participated as co-corresponding authors. Researchers from the Chinese University of Hong Kong, Shenzhen campus, and Germany's Jülich Research Center also took part.
