Ultrasonic Spraying Deposition of Perovskite Functional Layer

Perovskite solar cells: Ideal for depositing perovskite absorber layers, electron transport layers, and hole transport layers, their high uniformity is crucial for efficiency and stability.

Application and core value of ultrasonic spraying machine in the deposition of perovskite functional layer
Perovskite materials have become core candidate materials for the next generation of photovoltaic, optoelectronic detection, and other devices due to their high light absorption coefficient, excellent carrier mobility, and solution processability. The performance and stability of such devices are highly dependent on the deposition quality of the three functional layers: the light absorbing layer, the electron transport layer, and the hole transport layer. As an efficient solution deposition device, ultrasonic spraying machine has become a key tool for the preparation of these three functional layers due to its unique process advantages. The high uniformity thin film achieved by it is the core prerequisite for ensuring the efficient operation and long-term stability of the device.

Process advantages of ultrasonic spraying machine: solving traditional deposition problems
In the preparation of perovskite functional layers, traditional solution deposition processes (such as spin coating), although easy to operate, have limitations that are difficult to overcome. On the one hand, during the spin coating process, a large amount of precursor solution is thrown out due to centrifugal force, and the material utilization rate is usually less than 30%, which increases costs and causes environmental pollution; On the other hand, spin coating on large-area substrates is prone to “edge effects”, where the thickness of the thin film at the edge of the substrate is significantly thinner than in the central area, and the uniformity deviation often exceeds 15%, which cannot meet the performance consistency requirements of large-scale devices.

The ultrasonic spraying machine has solved these problems through a completely new process logic. The core principle is to use high-frequency ultrasonic vibration (usually above 20kHz) to atomize the precursor solution of the functional layer into tiny droplets with a diameter of only 2-10 microns. These droplets are uniformly sprayed onto the preheated substrate surface under low-pressure airflow, and then quickly dried and crystallized to form a thin film. Throughout the process, the material utilization rate can be increased to over 80%, and by accurately controlling the movement trajectory of the spray head, atomization pressure, and substrate temperature, edge effects can be effectively avoided. Even on large-area substrates, the thickness deviation of the film can be controlled within ± 5%, laying the foundation for the uniformity of the functional layer.

Functional layer deposition: precise adaptation scenarios for ultrasonic spraying machines
Ultrasonic spraying machine is not a simple “universal equipment”, but a device that optimizes process parameters to achieve targeted high-quality deposition based on the characteristics of different functional layers. The uniformity of each type of functional layer is directly related to the core performance of the device.

1. Perovskite absorber layer: uniformity determines the efficiency of photo generated charge carriers
The absorbing layer is the “core region” of perovskite devices that captures photons and generates photo generated charge carriers. Its film thickness and composition uniformity directly determine the light absorption efficiency and charge carrier generation efficiency. If the absorbing layer is locally too thick, carriers will experience increased recombination losses due to longer paths and higher collision probabilities during their transport to the electrode; If the local thickness is too thin, there will be a problem of photons penetrating the thin film without being fully absorbed, both of which will significantly reduce the photoelectric conversion efficiency of the device.

The ultrasonic spraying machine can achieve uniformity in the deposition of the absorbing layer through triple parameter control: firstly, adjusting the atomization pressure to control the consistency of droplet size and avoid local accumulation caused by large droplets; The second is to set a uniform movement path for the spraying head to ensure that the same amount of liquid droplet coverage is obtained at every part of the substrate; The third is to match the concentration of precursor solution with the substrate temperature, control the crystallization rate, and avoid uneven composition caused by rapid local crystallization. Through this combination control, the ultrasonic spraying machine can prepare an absorbing layer with uniform thickness and complete crystallization, ensuring that photons are uniformly absorbed throughout the entire substrate range and maximizing the efficiency of carrier generation.

2. Electronic transport layer: Uniformity reduces the risk of leakage current
The electron transport layer is located between the absorber layer and the negative electrode, and its core function is to “rapidly pump” the electrons generated by the absorber layer and block the migration of holes to the negative electrode. The density and uniformity of its thin film directly affect the leakage current and charge separation efficiency of the device. The electron transport layer (such as metal oxide layer) prepared by traditional processes is prone to pinholes or local thickness deviations due to droplet aggregation, which can become “charge recombination channels” – holes and electrons recombine before reaching the electrode, resulting in severe leakage current and a decrease in device fill factor (a key indicator of charge collection efficiency).

Ultrasonic spraying machine decomposes metal oxide solution into ultrafine droplets through high-frequency atomization in electronic transport layer deposition. These droplets can naturally fill small gaps on the substrate surface and form a continuous, pinhole free dense film; At the same time, by monitoring the film thickness in different areas of the substrate in real-time and dynamically adjusting the dwell time of the spray head, the thickness of the transport layer is ensured to be consistent throughout the entire area. This uniformity not only blocks the charge recombination channel, but also reduces the electron transmission impedance, allowing electrons to be transmitted to the negative electrode without loss, significantly improving the charge separation efficiency of the device.

3. Hole transport layer: Uniformity ensures the integrity of charge extraction
The hole transport layer and the electron transport layer complement each other in function, located between the absorbing layer and the positive electrode, responsible for extracting and transporting holes, and their uniformity is also the “key puzzle” of device performance. If there are local defects (such as thin areas or cracks) in the hole transport layer, the holes will be blocked in their path during transport, unable to reach the positive electrode and recombine with electrons, resulting in carrier loss; However, excessively thick areas will increase hole transport impedance and reduce transport speed.

Ultrasonic spraying machine can achieve uniformity in the deposition of hole transport layer by optimizing the drying process: after the atomized droplets are sprayed onto the substrate, the substrate will be precisely heated to a specific temperature, causing the solvent to slowly evaporate and avoiding uneven film shrinkage caused by rapid drying; At the same time, the spray head adopts a “cross path” design to ensure that each area is uniformly covered by droplets multiple times, forming a transport layer with consistent thickness and good interface contact. This uniformity not only reduces hole transport losses, but also optimizes the interface contact between the absorbing layer and the positive electrode, further improving the overall photoelectric conversion efficiency of the device.

The core value of high uniformity: dual guarantee of efficiency and stability
For perovskite devices, the high uniformity achieved by ultrasonic spraying machines is not a “process detail”, but a “core element” that determines the upper limit of device performance and service life. Its value is reflected in two dimensions: efficiency and stability.

In terms of efficiency, a uniform functional layer can minimize carrier loss to the greatest extent possible. The uniformity of the absorbing layer ensures that photons are fully absorbed, avoiding “insufficient absorption” or “excessive recombination”; The uniformity of the electron hole transport layer opens up charge transport channels, avoiding charge recombination caused by defects. The synergistic effect of the three can improve the photoelectric conversion efficiency of the device to over 90% of the optimal level in the laboratory, and effectively avoid the problem of “small area efficiency and large area failure” in large-area devices, ensuring consistent performance in large-scale production.

In terms of stability, uniformity is the “first line of defense” against external erosion. Uneven thin films can generate local stress due to differences in thermal expansion coefficients over long-term use – the degree of thermal shrinkage between thick and thin regions is different, which can easily lead to film cracking or detachment from the substrate, forming “channels” for water vapor and oxygen permeation. After external water vapor and oxygen enter the interior of the device, they will react chemically with the perovskite material, causing its components to degrade, and the device performance may deteriorate by more than 50% within a few months. The high uniformity thin film prepared by ultrasonic spraying mechanism has a more stable structure, uniform stress distribution, and can effectively block the invasion of water vapor and oxygen, extending the service life of the device from several months to several years, clearing key obstacles for the industrial application of perovskite devices.

Technical iteration direction: from “uniform” to “more precise”
With the development of perovskite technology towards higher efficiency and longer lifespan, the process accuracy of ultrasonic spraying machines is also continuously upgrading. In the future, by integrating AI parameter optimization algorithms, a closed-loop control of “real-time monitoring automatic adjustment” can be achieved, further controlling the film thickness deviation within ± 2%; At the same time, the development of new atomization units will achieve precise control of droplet size and adapt to more complex functional layer components (such as mixed cationic perovskites). In addition, the ultrasonic spraying machine will be combined with processes such as vacuum evaporation and laser annealing to form a “multi process collaborative” preparation system, further improving the quality of functional layers and device performance.

Overall, the application of ultrasonic spraying machines in the deposition of perovskite functional layers not only solves the pain points of traditional processes, but also provides dual guarantees for device efficiency and stability through high uniformity. In the process of industrialization of perovskite technology, ultrasonic spraying machines will become one of the core equipment, promoting the new generation of optoelectronic devices from the laboratory to practical applications.

About Cheersonic

Cheersonic is the leading developer and manufacturer of ultrasonic coating systems for applying precise, thin film coatings to protect, strengthen or smooth surfaces on parts and components for the microelectronics/electronics, alternative energy, medical and industrial markets, including specialized glass applications in construction and automotive.

Our coating solutions are environmentally-friendly, efficient and highly reliable, and enable dramatic reductions in overspray, savings in raw material, water and energy usage and provide improved process repeatability, transfer efficiency, high uniformity and reduced emissions.

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