Application of Coating Machines in the Fabrication of Functional Layers for Perovskite Solar Cells

As an emerging photovoltaic technology, the performance of perovskite solar cells is highly dependent on the uniformity and crystallization quality of functional layers (such as electron transport layer, perovskite absorbing layer, and hole transport layer). Functional layers are usually prepared by solution method, where the coating process is a key step, which directly affects the thickness, morphology and coverage of the film. By precisely controlling the coating parameters, the coating machine provides a reliable way to achieve the preparation of large-area, high-performance perovskite cells.

How the film coating machine works:

The coating machine mainly applies the solution evenly to the substrate surface, which is then dried or annealed to form a solid film. Common coating techniques include scraper coating, slit extrusion coating, and spin coating. The squeegee coating adjusts the thickness of the wet film by controlling the gap between the squeegee and the substrate and the moving speed. slit extrusion coating flows out through the slit nozzle by pumping the solution to form a uniform liquid film on the moving substrate; Spin-coating relies on the centrifugal force generated by high-speed rotation to expand the solution. These technologies have their own characteristics and are suitable for the preparation needs of different functional layers.

Several parameters in the coating process directly affect the final performance of the functional layer. Variables such as coating speed, solution concentration, substrate temperature, and ambient humidity need to be precisely controlled. For example, the relationship between coating speed and wet film thickness can be roughly described by the formula:h = k · (η·v/ρ·g)^1/2, among themhis the thickness of the wet film,ηis the viscosity of the solution,vfor the coating speed,ρis the density of the solution,gis the acceleration of gravity,kis a constant related to the coating method. By optimizing these parameters, film uniformity can be improved and defects can be reduced.

Application of coating machine in the preparation of various functional layers of perovskite batteries

At the electron transport layer (e.g. TiO₂、SnO₂In the preparation, the coating machine can achieve uniform coating of nanoparticle slurry, forming a dense and flat film. For perovskite absorbers, slit extrusion coating or scraper coating helps control the crystallization process, resulting in perovskite films with large grains and low pinhole density. In the preparation of hole transfer layers (e.g., Spiro-OMeTAD, PTAA), the applicator can precisely regulate the application of organic solutions to ensure uniform film coverage. The following table briefly compares the characteristics of different coating technologies in the preparation of functional layers:

In order to improve the efficiency and stability of perovskite cells, the coating process needs to be combined with post-processing steps such as annealing and gas phase assistance. For example, after coating a perovskite precursor solution, the crystal growth kinetics can be controlled by controlling the annealing temperature and time. At the same time, environmental control (e.g. humidity below a certain value) has a positive effect on reducing film defects. The challenge is to transition lab-optimized coating processes to large-area, continuous production and maintain consistent film performance.

The development and evaluation of coating processes can refer to relevant domestic and foreign standards, such as the International Electrotechnical Commission (IEC) standard series on photovoltaic device testing, as well as domestic guiding technical documents for film preparation. These standards provide a basis for coating parameter setting, film thickness measurement, and defect detection, helping to establish a repeatable preparation process.

As the core equipment for the preparation of functional layers of perovskite solar cells, the technological progress and process optimization of the coating machine are of positive significance for improving battery performance and promoting industrialization. By deeply understanding the coating mechanism and integrating process control, it is expected to achieve efficient preparation of high-quality functional layers and promote the sustainable development of perovskite photovoltaic technology.