Room-Temperature Epitaxy of α-CH3NH3PbI3 Halide Perovskite by Pulsed Laser Deposition

Nanoscience Physical Chemistry Chemistry Materials Science Inorganic Non-Metallic Materials Materials Chemistry
halide perovskite epitaxial growth pulsed laser deposition room temperature lattice matching

Academic Background

Metal Halide Perovskites (MHPs) have garnered significant attention in the field of photovoltaics due to their unique optoelectronic properties. In recent years, these materials have also been widely investigated for applications in light-emitting diodes, lasers, photodetectors, and spintronics. Despite notable progress in solution-processed perovskite thin films, research on the epitaxial growth of vapor-phase-deposited perovskite films remains limited. Epitaxial growth, a technique capable of producing single-crystal thin films, is crucial for understanding the fundamental physical properties of materials and developing high-performance devices. This study aims to achieve the epitaxial growth of α-CH3NH3PbI3 (methylammonium lead iodide perovskite) at room temperature using Pulsed Laser Deposition (PLD) and to investigate its optoelectronic properties.

Source of the Paper

This paper, titled “Room-temperature epitaxy of α-CH3NH3PbI3 halide perovskite by pulsed laser deposition,” was authored by Junia S. Solomon, Tatiana Soto-Montero, Yorick A. Birkhölzer, and others from the University of Twente in the Netherlands. It was published in the April 2025 issue of Nature Synthesis.

Research Process

1. Pulsed Laser Deposition (PLD) Film Fabrication

The research team first prepared α-CH3NH3PbI3 thin films at room temperature using PLD. PLD is a physical vapor deposition technique that allows precise control over film thickness and composition. In the experiment, a non-stoichiometric target (pbi2:mai = 1:8) was used to ensure the film’s stoichiometry. The target material was mixed in a ball mill for 48 hours and then pressed into a disc. During deposition, the laser energy density was maintained at 0.32 J/cm², with a deposition rate of approximately 0.7 nm/min. The films were grown on KCl (potassium chloride) substrates, which have lattice parameters closely matching those of α-CH3NH3PbI3, with a lattice mismatch ranging from -0.6% to 0.16%.

2. Structural Characterization

To verify the success of epitaxial growth, the research team employed various structural characterization techniques, including X-ray diffraction (XRD), electron backscatter diffraction (EBSD), and atomic force microscopy (AFM). Reciprocal Space Mapping (RSM) and Pole Figures (PFs) from XRD confirmed the strain relationship between the film and the substrate and demonstrated the stabilization of the cubic phase of α-CH3NH3PbI3 at room temperature. EBSD data further confirmed the single-oriented growth of the film, with all grains aligned along the [001] direction.

3. Optoelectronic Property Testing

The research team investigated the optoelectronic properties of the films using photoluminescence (PL) spectroscopy and optical-pump terahertz-probe (OPTP) spectroscopy. PL spectra revealed a bandgap of 1.66 eV for the 15 nm-thick film, which remained stable for 300 days. As the film thickness increased, the bandgap exhibited a slight red shift, indicating a gradual reduction in substrate-induced strain. Additionally, the team used first-principles density functional theory (DFT) calculations to predict the effect of strain on bandgap tuning.

Key Findings

1. Successful Epitaxial Growth

Through combined analysis of XRD and EBSD, the research team confirmed the epitaxial growth of α-CH3NH3PbI3 on KCl substrates. The cubic phase of the film was stabilized at room temperature, and the strain gradually diminished with increasing film thickness. AFM images revealed that the film consisted of columnar grains, with grain size increasing with thickness.

2. Excellent Optoelectronic Properties

PL spectra showed a bandgap of 1.66 eV for the 15 nm-thick film, which remained stable for 300 days. As the film thickness increased, the bandgap exhibited a slight red shift, indicating a reduction in substrate-induced strain. Furthermore, DFT calculations predicted significant bandgap tunability through epitaxial strain, demonstrating the potential for strain engineering in bandgap modulation.

3. Improved Charge Carrier Mobility

Using OPTP spectroscopy, the research team measured the charge carrier mobility of the films. The 15 nm-thick film exhibited a mobility of 4.2 cm²/V·s, while the 70 nm-thick film showed an increased mobility of 8.7 cm²/V·s. This result indicates that as the film thickness increases, the grain size grows, leading to enhanced charge carrier mobility.

Conclusion

This study successfully achieved the epitaxial growth of α-CH3NH3PbI3 at room temperature using PLD and demonstrated its excellent optoelectronic properties. The findings suggest that by selecting appropriate substrates and controlling film thickness, precise control over the phase stability and optoelectronic properties of perovskite materials can be achieved. This research provides new insights for the development of high-performance perovskite devices and offers important experimental evidence for understanding the fundamental physical properties of perovskite materials.

Research Highlights

  1. Room-Temperature Epitaxial Growth: For the first time, epitaxial growth of α-CH3NH3PbI3 was achieved at room temperature using PLD, overcoming the high-temperature limitations of traditional vapor-phase deposition techniques.
  2. Excellent Phase Stability: XRD and EBSD confirmed the stabilization of the cubic phase of α-CH3NH3PbI3 at room temperature, with the bandgap remaining stable for 300 days.
  3. Strain-Induced Bandgap Tuning: DFT calculations predicted significant bandgap modulation through epitaxial strain, providing theoretical support for the development of novel optoelectronic materials.
  4. Improved Charge Carrier Mobility: As film thickness increased, charge carrier mobility significantly improved, indicating that device performance can be optimized by controlling film thickness.

Research Significance

This study not only provides a new technical pathway for the epitaxial growth of perovskite materials but also offers important experimental and theoretical insights into the effects of strain on the phase stability and optoelectronic properties of perovskites. The findings are expected to advance the application of perovskite materials in photovoltaics, light-emitting diodes, photodetectors, and other fields, offering new strategies for developing high-performance optoelectronic devices.