Ellipsometry study of dielectric function and thermal degradation of 2D L₂PbI₄ (L = PEA: C₈H₁₂N⁺, BA:C₄H₁₂N⁺) perovskite thin films

Zeyuan Lv , Yuxuan Su , Fuyang Cao

Optics Express +

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November 11, 2025

View abstract on PubMed

Summary

Two-dimensional Ruddlesden-Popper perovskites improve solar cell stability. (PEA)2PbI4 shows better thermal stability than (BA)2PbI4 due to its crystal structure and fewer defects.

Area Of Science

Materials Science
Solid-State Physics
Photovoltaics

Background

Two-dimensional (2D) Ruddlesden-Popper (RP) perovskites offer enhanced stability for perovskite solar cells (PSCs) compared to their 3D counterparts.
Limited research exists on the thermal degradation mechanisms of 2D perovskite thin films, hindering further development.

Purpose Of The Study

To systematically characterize the thermal degradation of (PEA)2PbI4 and (BA)2PbI4 thin films.
To investigate the relationship between the dielectric function, structural properties, and thermal stability of these 2D perovskites.
To identify factors contributing to the enhanced thermal stability of specific 2D perovskite compositions.

Main Methods

X-ray diffraction (XRD) for structural analysis.
Scanning electron microscopy (SEM) for morphological characterization.
Photoluminescence (PL) spectroscopy and spectroscopic ellipsometry to probe optical and electronic properties.
Analysis of the dynamic evolution of the dielectric function.

Main Results

The optical band gaps for (PEA)2PbI4 and (BA)2PbI4 were determined to be 2.42 ± 0.002 eV and 2.43 ± 0.002 eV, respectively.
(PEA)2PbI4 demonstrated superior thermal stability compared to (BA)2PbI4.
Enhanced stability in (PEA)2PbI4 is linked to a lower density of defect states and a rigid aromatic ring spacer cation.

Conclusions

The rigid aromatic ring spacer in (PEA)2PbI4 stabilizes the crystal structure through CH···π interactions, enhancing thermal resilience.
Understanding the dielectric function and thermal degradation pathways is crucial for optimizing 2D/3D perovskite solar cells.
This study provides insights into designing more thermally stable 2D perovskite materials for advanced photovoltaic applications.