Perovskite solar cells have attracted attention as next-generation photovoltaic technology due to their high power conversion efficiency, light weight, and potential for low-cost manufacturing. In particular, the vacuum deposition process is well suited to large-area fabrication and allows precise control of thin-film thickness and composition, making it highly advantageous for commercialization.

However, perovskite films produced by vacuum deposition have been reported to generate more non-radiative recombination from surface defects than solution-processed films. This reduces solar cell efficiency and causes long-term stability degradation, which has been a major barrier to commercialization.

A new solution capable of overcoming these technical challenges has been presented by Professor Seok-In Na and Research Professor Seong-nam Kwon's team (Graduate School of Flexible Pinted Electronics) at JBNU. The team reported the development of a 'Bilayer Passivation' technique that simultaneously improves the efficiency and stability of vacuum-deposition-based perovskite solar cells.

This research was carried out with Ph.D. candidate Mohammadhossein Kohan as the first author and Sang-Heon Lee and Jaswinder Singh as co-authors. It was published in the international materials science journal Advanced Functional Materials (IF = 19.9).

The team proposed an 'Anchor-and-Seal' strategy to stepwise control defects on the perovskite film surface. First, ethylenediammonium iodide (EDAI2) was introduced to serve as an 'anchor' that strongly binds to surface defects. Then 4-methoxy-phenethylammonium iodide (4MeO-PEAI) was applied to act as a 'seal' that fills residual defects and microscopic voids. The complementary action of the two materials suppresses defects more effectively than conventional single-layer passivation methods.

Computational modeling and various advanced analyses also elucidated the operating mechanism of this structure. At interfaces with the bilayer passivation, defect density was greatly reduced, non-radiative recombination was suppressed, and charge extraction and energy-level alignment were simultaneously improved. This reduced photocurrent and voltage losses, leading to overall device performance enhancement.

Clear improvements were confirmed in actual device performance. The solar cell developed by the team achieved a peak power conversion efficiency of 20.59% and retained 94% of its initial performance after 1,000 hours of storage in a nitrogen atmosphere. Under continuous light exposure, it maintained 90% of its initial efficiency after 200 hours of operation, showing excellent stability.

Large-area applicability was also demonstrated. A 2.4 cm² perovskite minimodule reached an efficiency of 18.46%, confirming that the technology can be scaled beyond laboratory demonstrations to practical manufacturing processes. Because vacuum deposition favors uniform film formation and large-area production, this research is expected to provide an important foundation for technology development toward commercialization of perovskite solar cells.

Professor Seok-In Na said, 'Although vacuum deposition is one of the most promising approaches for commercializing solar cells, surface defect control remains a key challenge. This study is an important achievement that demonstrates how a rationally designed bilayer passivation strategy can overcome these limitations and simultaneously improve performance.'

Meanwhile, this research was supported by the National Research Foundation of Korea (NRF) and Korea Electric Power Corporation (KEPCO).