🔬 materials science

Synthesis of organic-inorganic perovskite and all-inorganic lead-free double perovskite nanocrystals by femtosecond laser pulses

This paper presents a novel, ligand-free femtosecond laser ablation method performed in ambient air to synthesize high-purity, tunable organic-inorganic and lead-free inorganic perovskite nanocrystals, offering a scalable alternative to conventional chemical synthesis for next-generation optoelectronic applications.

Original authors: Volodymyr Vasylkovskyi, Andrey Evlyukhin, Elena Schlein, Mykola Slipchenko, Roman Kiyan, Kestutis Kurselis, Vladimir Dyakonov, Boris Chichkov

Published 2026-02-26

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CC BY 4.0

Original authors: Volodymyr Vasylkovskyi, Andrey Evlyukhin, Elena Schlein, Mykola Slipchenko, Roman Kiyan, Kestutis Kurselis, Vladimir Dyakonov, Boris Chichkov

Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine you have a giant, perfect Lego castle made of special, glowing bricks. These bricks are called perovskites, and they are the "superstars" of modern electronics because they are amazing at catching light and turning it into electricity (like in solar panels) or turning electricity into light (like in super-bright screens).

However, there's a problem. To use these bricks in tiny devices, you need to break the giant castle down into tiny, individual Lego pieces (nanocrystals). Usually, scientists do this by mixing chemicals in a bathtub of gooey liquids and using sticky "glue" (called ligands) to keep the tiny pieces from sticking back together. But this glue is messy; it gets in the way of electricity, and the chemicals can be toxic or unstable.

This paper introduces a brand new, super-clean way to break the castle down: using a super-fast laser.

Here is the story of what they did, explained simply:

1. The "Magic Laser" vs. The "Chemical Bathtub"

Instead of using a chemical bathtub, the scientists used a femtosecond laser. Think of this laser as a incredibly precise, super-fast pair of scissors that can cut things so quickly that it doesn't even have time to get hot.

The Old Way: Like trying to chop a carrot with a dull knife while it's soaking in soup. You get mush, and you have to wash off the soup later.
The New Way: Like using a laser scalpel in a dry room. It slices the giant crystal into tiny dust particles instantly, without any soup or sticky glue.

2. Two Different Types of Bricks

The team tested this laser on two different types of "castles":

Type A (The Hybrid): These are made of a mix of organic stuff (like a plastic Lego) and metal. They are colorful and glow brightly but are a bit fragile, like a house of cards.
Type B (The All-Inorganic): These are made entirely of metal and salt, with no plastic parts. They are tougher, like a stone fortress, and are safer because they don't contain lead (a toxic metal).

3. What Happened When They Zapped Them?

When they fired the laser at the giant crystals in the air (no water or chemicals needed), something cool happened:

The Hybrid Bricks (Type A): The laser chopped them into tiny cubes, about the size of a grain of sand (but much smaller, around 100 nanometers). Because they were so small, they started glowing in different colors than the big crystal. It's like how a big sheet of blue glass looks different from a tiny blue bead; the size changes the color.
The Stone Bricks (Type B): These broke into even tinier, rounder pebbles (about 10 nanometers). They were so small that they looked like tiny marbles rather than cubes.

4. Why Is This a Big Deal?

No Sticky Glue: Because they didn't use chemicals, the surface of these tiny particles is perfectly clean. Imagine a highway where the cars (electricity) can zoom at full speed without hitting any speed bumps (sticky glue). This makes the devices much more efficient.
Pure and Simple: They didn't need a lab full of toxic solvents. They just did it in the air. It's like baking a cake without needing a mixer or a bowl—just a laser and a crystal.
Tunable Colors: By changing how hard they hit the crystal with the laser, they could control the size of the pieces, which let them tune the color of light the pieces emit.

The Bottom Line

The scientists found a way to turn giant, glowing crystals into tiny, super-pure, glue-free dust using a laser. This is like discovering a new way to make "digital glitter" that is cleaner, faster, and more powerful than anything we've made before. This could lead to better solar panels, brighter phone screens, and new types of medical sensors in the future.

1. Problem Statement

Perovskite nanocrystals (NCs) are promising for next-generation optoelectronic devices (solar cells, LEDs, sensors) due to their exceptional optical and electronic properties. However, conventional bottom-up chemical synthesis methods (e.g., hot-injection, ligand-assisted reprecipitation) rely heavily on organic capping ligands (such as oleic acid or oleylamine) to stabilize particles and prevent aggregation.

Limitations of Ligands: These organic ligands hinder charge transport across the NC surface, limit device performance, and are prone to degradation under UV irradiation or prolonged storage.
Limitations of Other Top-Down Methods: Techniques like ball milling often fail to achieve sub-100 nm sizes and can introduce impurities.
The Gap: There is a lack of systematic, ligand-free synthesis methods that can produce high-purity perovskite NCs without solvent-induced transformations or thermal degradation, particularly for comparing hybrid organic-inorganic and lead-free inorganic double perovskites.

2. Methodology

The authors employed Femtosecond Pulsed Laser Ablation (PLA) as a top-down, "green" synthesis approach.

Setup: A femtosecond laser system (343 nm wavelength, 250 fs pulse duration, 100 kHz repetition rate) was focused onto bulk single-crystal targets.
Environment: The process was conducted in ambient air without any additional liquid or gas media. This avoids solvent-induced chemical transformations (e.g., those seen in toluene or chloroform) and ensures high purity.
Targets: Two distinct classes of perovskites were used as targets:
1. Hybrid Organic-Inorganic: Methylammonium lead halides ( $MAPbX_3$ , where $X = Cl, Br, I$).
2. All-Inorganic Lead-Free Double Perovskites: Cesium silver bismuth halides ( $Cs_2AgBiX_6$ , where $X = Cl, Br$).
Process: Laser pulses were scanned over the crystal surface using a combination of a translation stage and a fast scanner to induce ablation and generate nanopowders.
Characterization: The resulting NCs were analyzed using Transmission Electron Microscopy (TEM), X-ray Diffraction (XRD), UV-Vis absorption spectroscopy, and Photoluminescence (PL) spectroscopy.

3. Key Contributions

First Direct Comparison: This study provides the first systematic comparison of ligand-free NCs derived from both hybrid ( $MAPbX_3$ ) and fully inorganic lead-free ( $Cs_2AgBiX_6$ ) perovskites using femtosecond PLA.
Ligand-Free Synthesis: Demonstrated a scalable, eco-friendly method to produce high-purity NCs without organic stabilizers, addressing the charge transport limitations of chemically synthesized NCs.
Composition-Dependent Dynamics: Elucidated how perovskite composition (halide type, cation nature, and single vs. double structure) influences the ablation process, resulting NC morphology, size, and optical properties.
Structural Preservation: Confirmed that femtosecond pulses minimize thermal diffusion, preserving the crystallinity of sensitive multicomponent crystals that might otherwise degrade under thermal stress.

4. Key Results

A. Structural and Morphological Properties

$MAPbX_3$ (Hybrid):
- Morphology: Predominantly cubic-shaped NCs, likely resulting from laser-induced cleavage along crystal planes.
- Size: Larger average sizes, ranging from ~60 nm to 107 nm (e.g., $MAPbCl_3 \approx 107$ nm).
- Stability: $MAPbI_3$ showed signs of partial degradation (formation of yellow $PbI_2$ ) in air due to moisture sensitivity, necessitating storage in nonpolar solvents.
$Cs_2AgBiX_6$ (Lead-Free Double):
- Morphology: Predominantly rounded/spherical NCs with fewer flat edges.
- Size: Significantly smaller, with average sizes of ~11–16 nm (e.g., $Cs_2AgBiCl_6 \approx 11.4$ nm). This indicates a higher fragmentation rate, possibly due to the defect-prone nature of the double perovskite lattice.
- Stability: Enhanced stability in ambient conditions compared to hybrid perovskites due to the absence of degradable organic cations.
Crystallinity: Both TEM (lattice fringes, FFT patterns) and XRD confirmed that the synthesized NCs retained high crystallinity with no secondary phases detected.

B. Optical Properties

Quantum Confinement: Both classes exhibited size-dependent blue shifts in photoluminescence (PL) compared to their bulk counterparts, confirming quantum confinement effects.
- $MAPbX_3$ : Pronounced blue shifts of 17–40 nm (e.g., $MAPbBr_3$ shifted from 573 nm to 530 nm).
- $Cs_2AgBiX_6$ : A blue shift of 30 nm observed for $Cs_2AgBiBr_6$ . Interestingly, $Cs_2AgBiCl_6$ showed a slight red shift, attributed to overlapping peaks.
Emission Characteristics:
- Hybrid NCs: Showed sharp emission peaks (FWHM 17–61 nm).
- Double Perovskite NCs: Exhibited broad emission peaks (FWHM 125–240 nm). This broadening is attributed to defect states, electron-phonon coupling, or self-trapped excitons, consistent with the indirect bandgap and defect-tolerant nature of double perovskites.

C. Ablation Parameters

Optimal laser pulse energies varied by material stability and absorption:
- $MAPbCl_3$ : 1.7 $\mu$ J (highest energy required despite kinetic instability, likely due to absorption properties).
- $MAPbBr_3$ : 0.76 $\mu$ J.
- $MAPbI_3$ : 0.53 $\mu$ J.
- $Cs_2AgBiX_6$ : 0.76 $\mu$ J.

5. Significance

Device Performance: The production of ligand-free surfaces removes insulating barriers, potentially enhancing charge transport efficiency for applications in electrochemical sensing, catalysis, and photovoltaics.
Scalability and Purity: The method is scalable, avoids toxic solvents, and produces high-purity materials without post-synthesis purification steps.
Material Design: The study establishes a framework for tuning optical properties (via size control) and selecting materials based on stability requirements (hybrid for high luminescence, lead-free double perovskites for stability and toxicity reduction).
Future Applications: This approach opens new avenues for developing perovskite-based quantum devices, LEDs, and sensors where surface chemistry and purity are critical.