Insights into 2D Hybrid Perovskite Crystal Growth Using RIR-MAPLE

Two-dimensional (2D) perovskite passivation layers on three-dimensional (3D) perovskite active regions (2D/3D) have significant potential to enhance the performance and stability of perovskite solar cells. However, most 2D/3D heterostructures are prepared using quasi-2D perovskites by solution processing. Previously, a 2D(n=1)/3D heterostructure was successfully deposited using resonant infrared matrix-assisted pulsed laser evaporation (RIR-MAPLE),¹ a versatile technique for the deposition of hybrid organic-inorganic perovskites (HOIPs).^2-4 Nonetheless, obtaining a uniform and thin 2D passivation layer remains a critical challenge. This study investigates the crystal growth of 2D phenethylammonium lead iodide (PEA₂PbI₄) hybrid perovskites using RIR-MAPLE for application to thin 2D (n=1) passivation layers. To better understand growth mechanisms and identify approaches for controlled film growth, early film formation, and nucleation processes were studied by varying the deposition time from 1 to 30 minutes. Materials characterization included X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), photoluminescence spectroscopy (PL), and ultraviolet-visible absorbance spectroscopy (UV-Vis) to analyze the 2D perovskite growth. While these techniques provided valuable insights into the crystal structure, surface morphology, and optical properties of (PEA₂PbI₄) thin films, they lacked the sensitivity to fully capture the nucleation process and early crystal evolution. To overcome this limitation, fluorescence lifetime imaging microscopy (FLIM) analysis was completed, and three distinct lifetime constants were obtained by a fitting model. The shortest lifetime constant τ₁-0.3 ns is attributed to 2D (PEA₂PbI₄) crystals, while lifetime τ₂-1.5 ns and τ₃-9 ns are associated with precursor materials and surface defects, respectively. FLIM insights, such as the contribution percentage of the different lifetimes, as well as spatial images of the fluoresence lifetimes and intensities for each deposition provide a deeper understanding of RIR-MAPLE-deposited (PEA₂PbI₄) films. These insights are essential to optimize grain size, reduce surface roughness, and advance high-quality thin 2D passivation layers to improve the stability of perovskite solar cells.
References:
1. Wright, N. E., et al., 2020 Virtual MRS Spring/Fall Meeting, Virtual, December 2020
2. Wright, N. E., et al., Chemistry of Materials 34 (7), 3109, 2022
3. Phillips, N. E., et al., Duke University, 2023
4. Barraza, E., et al., Journal of Applied Physics 128 (10), 2020