[Research Necessity]

Although halide perovskite solar cells have gathered attention as a next-generation photovoltaic technology and achieved rapid improvements in efficiency, they still face technical limitations regarding long-term stability and reproducibility. Especially, defects at the surface and interfaces induce non-radiative recombination, which critically affects the device's electrical performance and degradation. To address these issues, an interfacial passivation strategy based on a 2D/3D perovskite heterostructure is gaining prominence, with the key lying in the molecular structure control of high-functionality organic ligands.

 

[Research Content]

This study aimed to investigate how the spatial atomic arrangement (cis/trans configuration) of cyclohexyl-based ligands affects the formation of 2D Ruddlesden–Popper perovskite (RPP) layers and their interfacial passivation effects. For this purpose, two stereoisomers, cis- and trans-aminocyclohexanol hydrochloride (ACHACl), were compared to effectively suppress perovskite surface defects by leveraging the interaction of the –NH3+ and –OH functional groups. Specifically, it was experimentally demonstrated that cis-ACHACl, which possesses an asymmetric dipole moment, provides superior crystallinity, energy level alignment, and hole extraction selectivity.

 

[Originality]

The originality of this research lies in its experimental demonstration that even for ligands with the same chemical composition, differences in spatial atomic arrangement between stereoisomers can significantly impact the interfacial electronic structure and device performance. Notably, by introducing a non-aromatic cyclohexyl backbone instead of an aromatic ring, the study induced electron density localization in the –NH3+ functional group and enhanced hydrogen bonding strength, thereby achieving an interfacial stabilization effect. Furthermore, it proposed a strategy to comprehensively suppress perovskite surface defects by utilizing the dual functional groups (–OH and –NH3+). Through this structural and electronic property modulation, the crystallinity, alignment orientation, and energy level alignment of the 2D/3D interface were precisely controlled.

 

[Research Achievements / Expected Impact]

The results showed that introducing the cis-ACHACl ligand, with its asymmetric molecular arrangement, led to the uniform formation of a highly crystalline RPP layer on top of the 3D perovskite. This significantly improved the device's open-circuit voltage and fill factor through enhanced selective hole extraction. Consequently, a power conversion efficiency (PCE) of 23.46% was achieved, which is a 5.8% improvement over the untreated device. Moreover, the device demonstrated a 59% improvement in long-term stability during a 150-hour degradation test under maximum power point tracking (MPPT).

This study provides a quantitative experimental analysis of how the stereochemical design of interfacial ligands impacts device performance, suggesting a clear direction for the molecular design of organic ligands to develop high-efficiency, high-stability perovskite solar cells. The findings were published in the international journal Small in a paper titled “Spatial Atomic Arrangement of Cyclohexyl-Based Ligands for Enhanced Interface Passivation in 2D/3D Perovskite Solar Cells,” with Yonghoon Jung (an integrated MS/Ph.D. student in Professor Lee, Yun Seog’s research team) as the first author. The paper was also selected as a Front Cover feature.