In perovskite cell production, film uniformity plays a decisive role in cell performance and is a key factor in industry development. A perovskite film of uneven thickness with pinholes can greatly reduce the battery's photoelectric conversion efficiency, seriously affecting its stability and service life. As key equipment for preparing perovskite films, how coating equipment can overcome the uniformity challenge of the film has become the core issue for perovskite cells moving from the laboratory to large-scale industrialization.

Film uniformity: the cornerstone of perovskite cell performance

The uniformity of perovskite films affects battery performance in multiple ways. At the microscopic level, a uniform thin film ensures carriers transport smoothly and unobstructedly, effectively reducing the probability of recombination. When the film thickness deviation exceeds 5%, laboratory data shows cell efficiency drops by 3–5 percentage points and degradation accelerates by 2–3 times. From a macroscopic perspective, a uniform thickness distribution can prevent local current concentration and prevent the occurrence of hot spot effects. For large-area module production, film uniformity is a key factor determining product yield, directly related to the company's production costs and market competitiveness.

In actual production, film non-uniformity usually manifests as localized excessive thickness forming "nodules," pinholes causing "light-leaking areas," and abnormal edge thickness causing "burr effects." The occurrence of these defects is closely related to the performance of coating equipment, process parameter settings, and the characteristics of raw materials, requiring joint efforts between equipment manufacturers and battery producers to resolve them.

Core technology of coating equipment: breaking through uniformity bottlenecks

Precision flow control technology

The flow control accuracy of coating equipment directly affects the stability of film thickness. Currently, mainstream equipment uses high-precision metering pumps driven by servo motors, combined with electromagnetic flowmeters to build closed-loop control systems, achieving flow control accuracy within ±0.5%. By compensating in real time for flow deviations caused by changes in raw material viscosity, it ensures that the slurry output remains uniform and stable throughout the coating process, laying the foundation for producing uniform films.

Precise temperature control technology

The viscosity of perovskite slurry is extremely sensitive to temperature; for every 1°C fluctuation in temperature, viscosity can change by 5% to 8%. Advanced coating equipment is equipped with a multi-stage temperature control module that can keep the slurry channel temperature within a range of ±0.1°C. The integrated infrared temperature sensor inside the equipment can monitor the slurry temperature in real time and adjust the heating unit via PID algorithms to avoid adverse effects on slurry performance caused by ambient temperature changes or equipment overheating, ensuring consistency in film thickness.

High-precision gap adjustment technology

The gap accuracy between the coating head and the substrate must reach the micron level, which requires equipment to have ultra-high-precision gap adjustment capability. Using a piezoelectric ceramic-driven micro-displacement platform, it can achieve 0.1-micron gap adjustment, combined with real-time monitoring and feedback from the laser interferometer, ensuring the coating head remains parallel to the substrate across the entire width direction, thereby guaranteeing film uniformity over large areas.

Process and equipment collaboration: improving film quality

Slurry pretreatment process

High-quality slurry is the foundation for preparing uniform films. Coating equipment typically integrates online defoaming and filtration systems, using vacuum defoaming devices to remove tiny bubbles from slurries, then passing through a 1μm precision filter cartridge to filter out impurities, effectively reducing pinhole defects during coating. Research shows that pretreated slurry can reduce film pinhole rate by more than 70%.

Dynamic coating parameter optimization

Advanced coating equipment equipped with intelligent algorithms can automatically optimize coating parameters based on substrate speed and width. When the production line speed changes, the system automatically adjusts the matching relationship between flow rate, pressure, and coating clearance to maintain a stable surface density. At the same time, machine learning accumulates a process parameter library for different slurry formulas, enabling rapid debugging of new formulations and shortening the process development cycle by more than 50%.

Innovative technological breakthroughs: solving the problem of film uniformity

Molecular glue interface anchoring technology

The research team at the Dalian Institute of Chemical Physics, Chinese Academy of Sciences, introduced tetramethylammonium chloride (TMACL) into a colloidal solution of tin oxide precursors. Through the interaction of positive and negative charges, they "anchored" tin oxide particles, inhibiting their agglomeration and enhancing solution stability. Experiments show that this technology reduces the surface roughness of coated films by 32%, while effectively minimizing pinhole defects. Additionally, nitrogen atoms in TMACL molecules form chemical bonds with lead ions in perovskite, tightly bonding the electron transport layer and perovskite light-absorbing layer, reducing interface defect density by 40% and significantly improving charge extraction efficiency.

3D laminar flow wind field technology

The innovative team from Chinese enterprises and universities proposed a three-dimensional laminar flow wind field technology that has overcome the problem of large-area crystallization uniformity in perovskite films. This technology cleverly combines spin coating and vacuum flash steaming processes, allowing airflow to smoothly, evenly, and directionally sweep across the glass substrate, achieving drying and thus enabling more uniform crystallization of perovskite. Through computational fluid dynamics simulation optimization, the three-dimensional laminar flow wind field technology achieves precise control of perovskite film thickness, causing the fluctuation of perovskite film thickness over a 0.79 square meter area to be less than 3 microns. Compared to traditional processes, this technology reduces surface defects, optimizes crystalline morphology, and cuts residual solvents by 90%.

Colloid size control technology

The research team at the University of Electronic Science and Technology of China utilizes the anchoring effect of PZ additives on perovskite components, enhancing the stability of the colloidal electric bilayer (EDL) in perovskite solutions, avoiding the formation of large-size colloids (>1000 nm) and improving the uniformity of colloid size distribution in the solution. Real-time characterization shows that this method not only slows the crystal growth process but also ensures consistent crystallization rates between the upper and lower layers of perovskite films, helping to form large monoliths with "excellent uniformity," significantly improving the efficiency and stability of perovskite photovoltaic modules.

It is foreseeable that with continuous breakthroughs in core coating equipment technologies, the film uniformity issue of perovskite cells will gradually be resolved, creating favorable conditions for large-scale mass production in the industry and promoting perovskite batteries to play an increasingly important role in the global energy transition.