Korean researchers achieve 24.6% efficiency in solar cell using dual-molecule passivation

Korean researchers have succeeded in simultaneously filling the microscopic gaps that degrade next-generation solar cell performance using two different types of molecules. The breakthrough is expected to accelerate the commercialization of high-efficiency flexible solar cells for use in building windows, automobile sunroofs and other applications by improving both power conversion efficiency and long-term stability.

A research team led by Hong Seong-jun of the Solar Energy Research Laboratory at the Korea Institute of Energy Research announced Thursday it had jointly developed a "dual-molecule passivation" technology with teams led by Park Young-seok, a professor at Ulsan National Institute of Science and Technology (UNIST), and Lee Kyung-gu, a professor at Gunsan University. The technology simultaneously boosts the efficiency and stability of inverted perovskite solar cells.

Perovskite solar cells are widely regarded as a next-generation photovoltaic technology to succeed silicon solar cells, owing to their light weight and simple manufacturing process. The inverted structure — in which the electrode arrangement is reversed from the conventional design — is particularly well-suited for producing large-area and flexible solar cells because it allows for low-temperature processing.

The key challenge lies in microscopic defects that form at grain boundaries and on the surface during the fabrication of perovskite thin films. These defects cause energy loss as electrons and holes move through the material, reducing both power conversion efficiency and long-term stability.

Conventional passivation techniques coat the surface with a thin molecular layer to reduce defects, but most approaches rely on a single type of molecule, making it difficult to simultaneously address the distinct defects found deep within grain boundaries and on the surface.

Instead of a single molecule, the team applied two organic molecules with different binding properties — PDAI and 4TF — in sequence. The smaller PDAI fills the microscopic gaps between grain boundaries to stabilize charge transport pathways, while 4TF bonds with unstable lead atoms remaining on the surface to eliminate additional defects. The approach is akin to using two differently shaped building blocks to fill two different kinds of gaps at the same time.

The solar cell treated with dual-molecule passivation achieved a power conversion efficiency of 24.6 percent — more than 3 percentage points above the 21.21 percent recorded without any surface treatment, and also surpassing the 23.17 percent achieved with PDAI alone. The team confirmed that applying the two molecules sequentially produces complementary effects in defect elimination and surface stabilization that neither molecule achieves on its own.

"This achievement is a core foundational technology that will accelerate the commercialization of high-efficiency flexible solar cells for use in building windows, automobile sunroofs and portable devices," Hong said. "We will apply it to a lineup of high-performance next-generation solar cell products to strengthen our technological competitiveness in the eco-friendly renewable energy market."

The findings were published in the international journal ACS Applied Materials & Interfaces.