Perovskite Synthesis by Ultrasonication

Ultrasonically induced and intensified reactions offer a facile, precisely controllable and versatile synthesis method for the production of light-activated materials, which often cannot prepared by conventional techniques.
The ultrasonic crystallization and precipitation of perovskite crystals is a highly effective and economical technique, which allows to produce perovskite nanocrystals on industrial scale for mass production.

Ultrasonic Synthesis of Perovskite Nanocrystals

Organic–inorganic lead halide perovskites exhibit exceptional optoelectronic properties such as high light absorption, very long long carrier lifetime, carrier diffusion length, and high carrier mobility, which makes the perovskite compounds a superior functional material for high-performance applications in solar panels, LEDs, photodetectors, lasers, etc.
Ultrasonication is one of the physical methods for accelerating various organic reactions. The crystallization process is influenced and controlled by the ultrasonic treatment, resulting in the controllable size properties of the single‐crystalline perovskite nanoparticles.

TEM images for CH₃NH₃PbBr₃ QDs (a) with and (b) without ultrasonic treatment.

Case Studies of Ultrasonic Perovskite Synthesis

Research has conducted manifold types of ultrasonically assisted perovskite crystal growth. In general, perovskite crystals are prepared with the liquid growth method. In order to precipitate perovskite crystals, the solubility of the target samples is slowly and controlled reduced in a precursor solution. Ultrasonic precipitation of perovskite nano crystals is mainly based on an antisolvent quenching.

Ultrasonic Crystallization of Perovskite Nanocrystals

Jang et al. (2016) report the succesful ultrasonically assisted synthesis of lead halide perovskite nanocrystals. Using ultrasound, APbX₃ perovskite nanocrystals with a wide range of compositions, where A = CH₃NH₃, Cs, or HN=CHNH₃ (formamidinium), and X = Cl, Br, or I, were precipitated. Ultrasonication accelerates the dissolving process of the precursors (AX and PbX₂) in toluene, and the dissolution rate determines the growth rate of the nanocrystals. Subsequently, the research team fabricated high-sensitivity photodetectors by homogenously spin coating the uniform size nanocrystals on large-area silicon oxide substrates.

Particle size distributions of CH3NH3PbBr3 (a) with and (b) without the ultrasonic treatment.
Chen et al. 2017

Ultrasonic Asymetrical Crystallization of Perovskite

Peng et al. (2016) developed new growth method based on a cavitation-triggered asymmetrical crystallization (CTAC), which promotes heterogeneous nucleation by providing enough energy to overcome the nucleation barrier. Briefly, they introduced a very short ultrasonic pulses (≈ 1sec) to the solution when it reached a low supersaturation level with antisolvent vapor diffusion. The ultrasonic pulse is introduced at high supersaturation levels, where cavitation triggers excessive nucleation events and therefore the growth of a plethora of tiny crystals. Promisingly, MAPbBr₃ monocrystalline films grew on the surface of various substrates within several hours of the cyclic ultrasonication treatment.

Ultrasonic Synthesis of Perovskite Quantum Dots

Chen et al. (2017) present in their research work a efficient method to prepare perovskite quantum dots (QDs) under ultrasonic irradiation. Ultrasonication is used as a mechanical method in order to accelerate the precipitation of perovskite quantum dots. The crystallization process of the perovskite quantum dots is intensified and controlled by the ultrasonic treatment, resulting in the precisely tailored size of the nanocrystals. The analysis of the structure, particle size and morphology of the perovskite quantum dots showed that the ultrasonic crystallization gives a smaller particle sizes and a more uniform particle size distribution. Using the ultrasonic (= sonochemical) synthesis, it was also possible to produce perovskite quantum dots with different chemical compositions. Those different compositions in the perovskite crystals allowed to unable emission peaks and adsorption edges of CH₃NH₃PbX₃ (X = Cl, Br and I), which led to an extremely wide color gamut.

Ultrasonic Dispersion

Ultrasonication of nano particle suspensions and inks is a reliable technique to disperse them homogeneously before applying the nano-suspension on substrates such as grids or electrodes. (cf. Belchi et al. 2019; Pichler et al. 2018)
Ultrasonic dispersion easily handles high solid concentrations (e.g. pastes) and distributes nano-particles into single-dispersed particles so that a uniform suspension is produced. This assures that in the subsequent application, when the substrate is coated, no clumping such as agglomerates impairs the performance of the coating.

Ultrasonic dispersion prepares uniform nano-sized suspensions: green curve – before sonication / red curve after sonication

Ultrasonic Processors for Perovskite Precipitation

Hielscher Ultrasonics designs and manufactures high-performance ultrasonic systems for the sonochemical synthesis of high-quality perovskite crystals. As market leader and with long-time experience in ultrasonic processing, Hielscher Ultrasonics assists its customers from first feasibility test to process optimization to the final installation of industrial ultrasonic processors for large scale production. Offering the full portfolio from lab and bench-top ultrasonicators up to industrial ultrasonic processors, Hielscher can recommend you the ideal device for your nanocrystal process.
All Hielscher ultrasonicators are precisely controllable and can be tuned from very low to very high amplitudes. The amplitude is one of the main factors that influences the impact and destructiveness of sonication processes. Hielscher Ultrasonics’ ultrasonic processors deliver a very wide spectrum of amplitudes covering the range of very mild and soft to very intense and destructive applications. Choosing the right amplitude setting, booster and sonotrode allows to set the required ultrasonic impact for your specific process. Hielscher’s special flow cell reactor insert MPC48 – MultiPhaseCavitator (see pic. left) – allows to inject the second phase via 48 cannulas as a thin strain into the cavitational hot-spot, where high performance ultrasound waves disperse the two phases into a homogeneous mixture. The MultiPhaseCavitator is ideal to initiate crystal seeding points and to control the precipitation reaction of perovskite nanocrystals.
Hielscher industrial ultrasonic processors can deliver extraordinarily high amplitudes. Amplitudes of up to 200µm can be easily continuously run in 24/7 operation. For even higher amplitudes, customized ultrasonic sonotrodes are available. The robustness of Hielscher’s ultrasonic equipment allows for 24/7 operation at heavy duty and in demanding environments.
Our customers are satisfied by the outstanding robustness and reliability of Hielscher Ultrasonic’s systems. The installation in fields of heavy-duty application, demanding environments and 24/7 operation ensure efficient and economical processing. Ultrasonic process intensification reduces processing time and achieves better results, i.e. higher quality, higher yields, innovative products.
The table below gives you an indication of the approximate processing capacity of our ultrasonicators: